1982 (Chapter 8) OLIVER Fisiology of Ticks Tick Reproduction = Sperm Development and Cytogenetics

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C H A P T E R 8 
Tick Reproduction: Sperm Development and 
Cytogenetics 
J. H. OLIVER, Jr. 
Department of Biology, Georgia, Southern College, Statesboro, Georgia, USA 
C O N T E N T S 
8.1. Introduction 245 
8.2. Structure of the Male Genital System 246 
8.2.1. Testes 247 
8.2.2. Vasa Deferentia and Common Vas Deferens 248 
8.2.3. Ejaculatory Duct 248 
8.2.4. Accessory Genital Glands 248 
8.3. Development of Spermatozoa 249 
8.3.1. Spermatogenesis 250 
8.3.2. Spermiogenesis 252 
8.3.2.1. Precapacitation 252 
8.3.2.2. Capacitation 257 
8.3.2.3. Spermatid Transfer of Females—Mating Behaviour 260 
8.3.2.4. Spermatid Transfer to Females—Spermatophores 261 
8.4. Dynamics of Adult Testicular Growth, Spermatogenesis, Spermiogenesis, Sperm 
Transfer, and Capacitation 263 
8.4.1. Exogenous Factors 263 
8.4.2. Endogenous Factors 264 
8.4.3. Capacitation Factors 265 
8.5. Motility, Relocation, Storage, and Survival of Spermatozoa 266 
8.6. Syngamy 267 
8.7. Mating Capacity of Males 268 
8.8. Cytogenetics 269 
8.9. Conclusions 270 
Acknowledgements 271 
References 271 
8 .1 . I N T R O D U C T I O N 
Signif icant ly less is k n o w n a b o u t g a m e t o g e n e s i s in t h e m a l e a r t h r o p o d 
t h a n in t h e female , espec ia l ly t h e n o n s t r u c t u r a l a spec t s of g a m e t e fo rma t ion . 
I n t h e female it is c lea r t h a t egg m a t u r a t i o n , p a r t i c u l a r l y v i te l logenesis , is 
closely r e g u l a t e d b y h o r m o n a l s y s t e m s often a s soc ia t ed w i t h feeding. T h e 
wel l -def ined g o n o t r o p h i c a n d ov ipos i t iona l cycles a r e impres s ive . S p e r m 
p r o d u c t i o n is n o t a s s p e c t a c u l a r a n d easy to co r r e l a t e w i t h a d u l t feeding a n d 
P OT - I 245 
246 J. H. Oliver 
h o r m o n a l con t ro l s . N e v e r t h e l e s s , t h e fo rma t ion of s p e r m a t o z o a in a r t h r o p o d s 
is p r o b a b l y n o less c o m p l e x a p rocess t h a n fo rma t ion of eggs . F o r m a t i o n of 
s p e r m a t i d s a n d s p e r m a t o z o a is t h e resu l t of d i s c o n t i n u o u s d e v e l o p m e n t , a n d 
p r o d u c t i o n of these cells is u sua l ly d e l a y e d un t i l t he p e n u l t i m a t e o r a d u l t 
s t a d i u m is r e a c h e d . T h i s d i s c o n t i n u o u s d e v e l o p m e n t of m a l e g e r m i n a l cells 
a n d t h e co r r e l a t i on of the i r d i f ferent ia t ion w i t h s o m a t i c d e v e l o p m e n t , a r g u e 
s t rong ly for t h e ex i s t ence of r a t e - r e g u l a t i n g m e c h a n i s m s of t he s a m e o r d e r 
of c o m p l e x i t y as t hose invo lved w i t h egg p r o d u c t i o n . 
T h e c o m p l e x s e q u e n c e of d e v e l o p m e n t a l even t s e n d i n g in fully m a t u r e a n d 
c a p a c i t a t e d s p e r m a t o z o a in tick beg ins w i t h p r o d u c t i o n of p r i m a r y spe r -
m a t o g o n i a f rom g e r m i n a l s tem-ce l l s . T h e i n t e r v e n i n g s t ages a r e d e s c r i b e d 
in t h e fol lowing p a g e s a n d s o m e sugges t ions a b o u t r a t e - r e g u l a t i n g m e c h -
a n i s m s a n d / o r co r r e l a t i ons a r e offered. S o m e o u t s t a n d i n g p o i n t s to n o t e 
r e g a r d i n g p r o d u c t i o n of tick s p e r m i n c l u d e u n u s u a l l y l a rge s p e r m a t o c y t e s , 
f o rma t ion of c h r o m o s o m a l vesicles o r k a r y o m e r e s , p r e s e n c e of i n t r a c e l l u l a r 
b r i dges d u r i n g s p e r m a t o g e n e s i s a n d p a r t of spe rmiogenes i s , h a l t i n g of spe r -
m a t i d d e v e l o p m e n t in m a l e s a n d necess i ty of t r ans fe rence to females for final 
g r o w t h a n d d i f ferent ia t ion , u n u s u a l t y p e of s p e r m mot i l i ty , loca t ion of n u c l e u s 
a n d a c r o s o m e in pos t e r i o r p a r t of cells, a n d t h e c o m p a r a t i v e l y l a rge size of 
t ick s p e r m a t o z o a . 
S p a c e c o n s t r a i n t s of th is v o l u m e d o no t a l low a s e p a r a t e c h a p t e r d e v o t e d 
to t h e cy togene t i c s of t icks. S ince m o s t of t he cy togene t i c d a t a col lected o n 
t icks h a v e b e e n o b t a i n e d from m a l e g e r m i n a l cells, t h a t i n f o r m a t i o n is 
s u m m a r i z e d in th is c h a p t e r . T h e d a t a o n me io t i c c h r o m o s o m e s c o m e a l m o s t 
to ta l ly f rom s p e r m a t o c y t e s w h e r e a s i n fo rma t ion on mi to t i c fea tures w e r e 
g a t h e r e d f rom s p e r m a t o g o n i a , oogon ia , a n d e m b r y o n i c cells. E v e n t h o u g h 
on ly s l ight ly m o r e t h a n 100 species of t icks h a v e b e e n s t ud i ed cy togene t i ca l ly , 
a n d s o m e of these ve ry superf ic ia l ly , a r e m a r k a b l e a m o u n t of c h r o m o s o m a l 
d ive rs i ty h a s a l r e a d y b e e n d i scove red . A recen t rev iew (Ol ive r , 1977) a n d 
a n o t h e r p a p e r (Ol ive r , in p r e s s , Festschnft for M. J. D. White, C a m b r i d g e 
U n i v e r s i t y Press ) c a n b e c o n s u l t e d for a t h o r o u g h d i scuss ion of tick 
c h r o m o s o m e s . 
8.2. S T R U C T U R E O F T H E M A L E G E N I T A L SYSTEM 
T h e r e p r o d u c t i v e s y s t e m in a d u l t m a l e s cons is t s of p a i r e d t u b u l a r tes tes 
w h i c h m a y b e fused pos te r io r ly ( A r g a s i d a e ) , b r o a d l y j o i n e d ( m o s t Ixodes), 
or c o n n e c t e d on ly b y a n ex t r eme ly t h in filamentous s t r a n d of t i ssue ( M e t a -
s t r i a t a ) . A n t e r i o r l y t h e tes tes t a p e r i n to weak ly c o n v o l u t e d v a s a de fe ren t i a 
w h i c h j o i n an t e r i o r l y fo rming a s ingle d u c t ( c o m m o n vas deferens o r s e m i n a l 
vesicle) c o n n e c t i n g t h e v a s a defe ren t ia w i t h t h e e j acu la to ry d u c t . T h e l a rge 
m u l t i l o b e d accessory gen i t a l g l a n d is d o r s a d of a n d o p e n s i n t o t h e c o m m o n 
vas defe rens n e a r t h e j u n c t i o n of t he p a i r e d v a s a defe ren t ia (Fig . 8 .1 . ) . 
FIG. 8.1. Testes and accessory gland of Dermacentor showing terminal connection, central lumen, 
and areas of testes. (Redrawn from Oliver & Brinton, 1972.) 
8 .2 .1 . Testes 
T h e tes tes e x t e n d a l o n g b o t h s ides of t h e b o d y from t h e r e a r of t h e 
s y n g a n g l i o n to t h e p o s t e r i o r p a r t of t h e b o d y a n d c u r v e med ia l l y d o r s a d of 
t h e r ec t a l s ac . T h e tes tes in a d u l t s a r e cove red b y a th in connec t ive t i ssue 
m e m b r a n e a n d cons is t of g r o u p s of g e r m i n a l cells a r r a n g e d in cysts o r 
p a c k e t s . T h e s e s p e r m a t o c y s t s a r e b o u n d w i t h i n s ingle- layer wal l s of flat-
t e n e d ep i the l i a l cells a n d c o n n e c t i v e t i ssue a n d a r e a r r a n g e d r ad ia l ly a r o u n d 
a s m a l l l u m e n in e a c h tes t is . T h e l u m e n s e x t e n d the l eng th of t h e tes tes a n d 
a n t e r i o r l y a r e c o n t i n u o u s w i t h t h e l u m e n s of t he v a s a defe ren t ia (Fig . 8 .1 . ) . 
T h e l ong t u b u l a r tes tes m a y v a r y s l ight ly in a p p e a r a n c e even w i t h i n a 
s ingle species d e p e n d i n g on t h e n u t r i t i o n a l a n d r e p r o d u c t i v e s t a t e of t h e 
i n d i v i d u a l ( O l i v e r & B r i n t o n , 1972) . I t s eems likely t h a t th is m a y in p a r t 
exp l a in s o m e of t h e differences in tes tes d e p i c t e d in Ar gas vespertilionis, Ar gas 
boueti, Argas transgariepinus, a n d Argas brumpti ( R o s h d y , 1961, 1962, 1963, 
1966) . T e s t e s f rom unfed ticks a r e a l m o s t un i fo rmly n a r r o w a n d sma l l , b u t 
u p o n feeding t h e tes tes b e c o m e m u c h longe r a n d e n l a r g e d , especia l ly p o s -
ter ior ly (Fig . 8 .2 . ) . I n o lde r fed m a l e s t h e tes tes m a y a p p e a r still r ep le t e in 
FlG. 8.2. Testes and accessory glands of Dermacentor from A, unfed male; B, male attached for 
two days; C, male attached for five days. (Redrawn from Oliver & Brinton, 1972.) 
Tick Reproduction: Sperm Development 247 
248 J. H. Oliver 
p a r t s wh i l e o t h e r p a r t s a p p e a r to h a v e g rea t ly r e d u c e d cell p o p u l a t i o n s a n d 
a r e n a r r o w ; u sua l ly t he m o s t pos t e r io r p a r t s of t he tes tes a r e t h i n n e r t h a n 
the a n t e r i o r ha lves after t h e s p e r m a t i d s h a v e v a c a t e d t he a r e a a n d ce l lu la r 
d e b r i s r e m a i n s . T h e m o s t pos t e r io r p a r t s of testes of M e t a s t r i a t a species a n d 
the c o n n e c t i o n of t he d i s t a l e n d s in o t h e r t icks f requent ly c o n t a i n a yel low 
s u b s t a n c e . M o r e is sa id l a t e r in th is c h a p t e r r e g a r d i n g t h e d y n a m i c s of 
g r o w t h a n d c h a n g e of t h e tes tes in r e l a t ion to age a n d n u t r i t i o n a l s t a t e . 
8.2.2. Vasa Deferentia and Common Vas Deferens 
T h e a n t e r i o r e n d s of t h e tes tes c o n t i n u e fo rward as v a s a defe ren t ia w h i c h 
e x t e n d a n t e r o m e d i a l l y as coiled t u b e s . T h e size a n d s h a p e of t h e v a s a 
defe ren t ia v a r y f rom n a r r o w coiled t u b e s to e n l a r g e d s t r a i g h t s t r u c t u r e s 
d e p e n d i n g o n t h e r e p r o d u c t i v e s t a t e of t he i n d i v i d u a l . I n i m m a t u r e o r newly 
m a t u r e m a l e s t h e t u b e s a r e sma l l in c o m p a r i s o n to t he tes tes , b u t in o ld fed 
m a l e s t hey m a y a c t u a l l y b e l a rge r (swol len w i t h s p e r m a t i d s ) t h a n t h e tes tes . 
T h e v a s a de fe ren t i a fuse an t e r io r ly as t he c o m m o n vas deferens ( s emina l 
vesicle) w h i c h d o e s n o t differ h is to logica l ly f rom the v a s a defe ren t ia . I t h a s 
a n i n n e r ep i the l i a l l aye r of c u b o i d a l o r c o l u m n a r cells a n d is s u r r o u n d e d b y 
a connec t i ve t i ssue layer . 
8.2.3. Ejaculatory Duct 
T h i s d u c t c o n n e c t s w i t h t h e c o m m o n vas deferens a n d the accessory gen i t a l 
g l a n d a n d e x t e n d s a n t e r o v e n t r a l l y b e n e a t h t he s y n g a n g l i o n to t he e x t e r n a l 
gen i t a l o p e n i n g . I t is l ined dor sa l ly w i t h h a r d cut ic le a n d ven t r a l ly w i t h soft 
cu t ic le for a p p r o x i m a t e l y ha l f i ts l e n g t h in s o m e species . F r o m a b o u t t he 
m i d d l e of t h e d u c t pos te r io r ly to t h e c o m m o n vas deferens t h e c u t i c u l a r 
l in ing r e m a i n s soft b o t h do r sa l ly a n d ven t r a l l y (Ti l l , 1961). T h e e p i t h e l i u m 
cons is t s of flat to c u b o i d a l cells . 
8.2.4. Accessory Genital Glands 
Severa l t ypes of g l a n d u l a r t i ssue c o n t a i n i n g va r ious types of sec re to ry cells 
a r e o r g a n i z e d i n t o a l a rge m u l t i l o b e d " g l a n d " loca ted i m m e d i a t e l y p o s t e r i a d 
of t h e s y n g a n g l i o n a n d d o r s a d of t he c o m m o n vas deferens a n d e j acu la to ry 
d u c t . T h e n u m b e r s a n d sizes of t h e lobes v a r y w i t h i n t icks of different t a x a . 
A rev iew (Ba l a shov , 1972) s u m m a r i z e s t he w o r k of severa l a u t h o r s a n d m a y 
b e c o n s u l t e d for o r ig ina l references . I n a d d i t i o n w e ( M u r p h y & Ol ive r , 
u n p u b l i s h e d ; S m i t h & Ol ive r , u n p u b l i s h e d ; G o w a n & Ol ive r , u n p u b l i s h e d ) 
h a v e s t u d i e d th is g l a n d in Dermacentor variabilis, Argas radiatus a n d Antricola 
mexicanus, a n d Ixodes scapularis, respec t ive ly . H o m o l o g i e s of v a r i o u s lobes 
Tick Reproduction: Sperm Development 249 
a m o n g a r g a s i d s a n d ixod ids a r e difficult to d e t e r m i n e . N u t r i t i o n a l a n d 
r e p r o d u c t i v e s t ages affect lobe size, a s well as m o r p h o l o g i c a l a n d sec re to ry 
p r o p e r t i e s of cells , even w i t h a n i n d i v i d u a l . I n t e r e s t i ng ly , r e cen t cytological 
a n d h i s t o c h e m i c a l i nves t i ga t i ons of accesso ry g l a n d s h a v e i n d i c a t e d m a j o r 
weaknes se s in t h e cell c lassif icat ion s y s t e m of s p o n g y a n d g r a n u l a r types 
( R o b i n s o n & D a v i d s o n , 1913, 1914) , b u t these t e r m s a r e still found c o n v e n i e n t 
w h e n d i s c u s s i n g t h e accessory g l a n d . D e p e n d i n g o n n u t r i t i o n a l , m a t u r a t i o n a l , 
a n d r e p r o d u c t i v e s t a t e s , lobes o r p a r t s of t he s a m e lobe m a y b e c o m e g r a n u l a r 
o r s p o n g y . Ce l l s w h i c h a p p e a r m o r p h o l o g i c a l l y s imi l a r m a y , in fact, r e p r e s e n t 
severa l different s ec re to ry cell t ypes w h i c h c a n be i n t e r m i x e d or a r r a n g e d in 
sma l l g r o u p s . T h e s e cells sec re te m u c o p r o t e i n , m u c o p o l y s a c c h a r i d e , a n d 
o t h e r c o m p o u n d s . H i s t o c h e m i c a l s t a i n i n g r eac t i ons sugges t v a r i o u s funct ions 
of t h e g l a n d . T w o p r o m i n e n t func t ions a r e t h e p r o d u c t i o n of m a t e r i a l s t h a t 
form s p e r m a t o p h o r e s ( T a t c h e l l , 1962) a n d c o m p o u n d s r e spons ib l e for t h e 
in i t i a t ion of c a p a c i t a t i o n of s p e r m a t i d s ( S h e p h e r d & Ol ive r , u n p u b l i s h e d ) . 
T h e s e roles will b e d i s cus sed l a t e r in g r e a t e r de ta i l as well as s o m e sugges t ions 
of o t h e r poss ib le func t ions r e l a t e d to s p e r m re loca t ion in females a n d t r ig-
ge r i ng of ov ipos i t ion . 
8.3. D E V E L O P M E N T O F S P E R M A T O Z O A 
Severa l g r o w t h a n d d e v e l o p m e n t a l c h a n g e s o c c u r a m o n g t h e g e r m i n a l 
cells p r i o r to s p e r m p r o d u c t i o n . S p e r m a t o g o n i a u n d e r g o mi to t i c d iv is ions 
p r o d u c i n g severa l g e n e r a t i o n s of d a u g h t e r cells of w h i c h t h e las t g e n e r a t i o n 
p r o d u c e s p r i m a r y s p e r m a t o c y t e s . T h e l a t t e r d iv ide meio t ica l ly r e su l t i ng in 
s e c o n d a r y s p e r m a t o c y t e s a n d e a c h of these d iv ides e q u a t i o n a l l y to p r o d u c e 
t w o s p e r m a t i d s . F i n a l g r o w t h a n d d i f ferent ia t ion of s p e r m a t i d s to m a t u r e 
s p e r m is ca l led c a p a c i t a t i o n (O l ive r & B r i n t o n , 1973) a n d o c c u r s on ly after 
t ransfe r to females . F o r p u r p o s e s of d i scuss ion in th is c h a p t e r , t he t e r m 
s p e r m a t o g e n e s i s i n c l u d e s d e v e l o p m e n t f rom s p e r m a t o g o n i a to t h e r o u n d e d 
s p e r m a t i d s t a g e a n d s p e r m i o g e n e s i s refers to g r o w t h a n d di f ferent ia t ion of 
t h e r o u n d e d s p e r m a t i d to t h e fully m a t u r e , e longa t e , a n d nonf lage l la te 
s p e r m a t o z o o n found in t h e female t r ac t . 
R e m a r k a b l y , in t icks t h e g e r m i n a l cells a r e a r r a n g e d in t he reverse o r d e r 
u sua l ly f o u n d in m o s t t u b u l a r i n v e r t e b r a t e tes tes . T h o s e cells in t h e p o s t e r i o r 
p a r t ( a r e a 6)of t h e tes tes (Fig . 8.1) m a t u r e first a n d m a t u r a t i o n p r o c e e d s 
in a l i nea r fash ion t o w a r d t h e a n t e r i o r p a r t in a wave- l ike m a n n e r . T h i s 
pecu l i a r i t y in t h e s e q u e n c e of d e v e l o p m e n t c a u s e d severa l ea r l i e r a u t h o r s to 
incor rec t ly i n t e r p r e t s o m e of t he i r o b s e r v a t i o n s (Hel le r , 1858; C h r i s t o p h e r s , 
1906; R o b i n s o n & D a v i d s o n , 1914; Ste l la , 1938; O p p e r m a n n , 1935) . 
I n unfed a d u l t M e t a s t r i a t a , t h e test is c o n t a i n s s p e r m a t o g o n i a in t h e 
a n t e r i o r p a r t of a r e a 1 (Fig . 8 .1) . M o s t of t he r e m a i n d e r of t h e test is is 
c o m p o s e d of p r i m a r y s p e r m a t o c y t e s enc losed w i t h i n cys ts . A s is c o m m o n in 
250 J. H. Oliver 
a n i m a l s w i t h th is t ype of t e s t i cu la r a r c h i t e c t u r e , d e v e l o p m e n t of all cells 
w i t h i n a p a r t i c u l a r cyst is s y n c h r o n o u s . T h e s p e r m a t o c y s t a r r a n g e m e n t is 
a lso typ ica l of species of A r g a s i d a e a n d P r o s t r i a t a , b u t g e r m i n a l cell deve l -
o p m e n t in unfed a d u l t s is m o r e a d v a n c e d t h a n in M e t a s t r i a t a . I n d e e d , 
e l o n g a t e d s p e r m a t i d s m a y be p r e s e n t a t ecdysis in s o m e species of a r g a s i d s 
a n d Ixodes (O l ive r , 1974) . 
M o s t of t h e i m p o r t a n t p a p e r s r e g a r d i n g d e v e l o p m e n t of tick s p e r m t h a t 
w e r e p u b l i s h e d before 1974 a r e c i ted by B a l a s h o v (1972) a n d O l i v e r (1974) . 
S ince t h e n , h o w e v e r , severa l p a p e r s h a v e a p p e a r e d w h i c h c o n t r i b u t e to o u r 
u n d e r s t a n d i n g of s p e r m p r o d u c t i o n in t icks, especia l ly t h a t p a r t of deve l -
o p m e n t s t r ic t ly def ined as s p e r m i o g e n e s i s . 
8.3.1. Spermatogenesis 
After a n u m b e r of m i t o t i c s p e r m a t o g o n i a l d iv is ions h a v e s u p p l i e d t h e test is 
w i t h a full c o m p l e m e n t of encys t ed p r i m a r y s p e r m a t o c y t e s , s t imul i evoke 
g r o w t h a n d d e v e l o p m e n t of s o m e of t he s p e r m a t o c y t e s . T h e n u m b e r of 
p r i m a r y s p e r m a t o c y t e s in e a c h cyst d e p e n d s u p o n the n u m b e r of s p e r m a -
togon ia l d iv i s ions after e n c y s t m e n t a n d a p p e a r s to be species specific. 
Sixty-four p r i m a r y s p e r m a t o c y t e s p e r cyst o c c u r in Hyalomma anatolicum 
excavatum ( K h a l i l , 1970) w h e r e a s on ly 16 p e r cyst a r e p r e s e n t in Argas arboreus 
( K h a l i l , 1969) . I t is difficult to d i s t i ngu i sh cytological ly b e t w e e n s p e r m a t o -
g o n i a a n d y o u n g s p e r m a t o c y t e s . Cel l d i a m e t e r s a r e s imi la r ( a p p r o x i m a t e l y 
5 μηι in severa l species of ixod ids ) a n d nuc le i often a p p e a r s imi la r . Nuc l e i 
of s o m e y o u n g s p e r m a t o c y t e s , h o w e v e r , d e m o n s t r a t e c h r o m a t i n c l u m p s a n d 
t h r e a d s w i t h pos i t ive h e t e r o c h r o m a t i c c h r o m o m e r e s . G o r o s h c h e n k o (1960) 
referred to t h e fo rmer as p r o c h r o m o s o m e s a n d the l a t t e r as l e p t o t e n e c h r o -
m o s o m e s . O l d e r s p e r m a t o c y t e s possess nuc le i w i t h s l ight ly th icker c h r o m a t i n 
t h r e a d s w h i c h p r o b a b l y r e p r e s e n t p a c h y t e n e s tages . T y p i c a l l e p t o t e n e , zyg-
o t e n e , a n d p a c h y t e n e c h r o m o s o m e s a r e n o t c o m m o n in tick s p e r m a t o c y t e s , 
b u t t hese s t ages u n d o u b t e d l y o c c u r p r io r to o r d u r i n g the ear ly p a r t of t h e 
g r e a t g r o w t h p h a s e of t h e s p e r m a t o c y t e s . G o r o s h c h e n k o (1960) r e p o r t s t h a t 
s p e r m a t o c y t e s of Ornithodoros tholozani ( = 0. papillipes) a n d Argas persicus e n t e r 
d i p l o n e m m a p r i o r to t he g r e a t g r o w t h p h a s e . I t is u n c e r t a i n w h e t h e r this is 
t r u e for all t ick spec ies . I t is c e r t a in t h a t in m o s t species , if no t all , d i p l o n e m m a 
is t h e first r e c o g n i z a b l e me io t i c s t age a p p a r e n t a t t he e n d of t he g r e a t g r o w t h 
pe r iod . I t s eems likely t h a t c h r o m o s o m e s , after e n t e r i n g d i p l o n e m m a , lose 
the i r s t a inab i l i t y c o n c o m i t a n t l y w i t h t he g r e a t g r o w t h of t he c y t o p l a s m . 
A t t h e b e g i n n i n g of t he g r e a t g r o w t h p h a s e t he s p e r m a t o c y t e nuc le i s t a in 
faint ly a n d a r e l a rge in p r o p o r t i o n to t he sma l l a m o u n t of c y t o p l a s m . T h e 
l a t t e r s t a in s poor ly , a n d o rgane l l e s such as Golg i complexes (d i c tyosomes) 
Tick Reproduction: Sperm Development 251 
a n d m u l t i v e s i c u l a r bod ie s a r e a b s e n t ; m i t o c h o n d r i a a r e r a r e (Ol ive r & 
B r i n t o n , 1972) . T h e r e is a b a n d of c i s t e rnae a r o u n d the m a r g i n of t he 
c y t o p l a s m , a n d b r o a d in t e r ce l lu l a r c o n n e c t i o n s (br idges) exist a m o n g cells 
of e a c h cyst . T h e s e b r i dges r e m a i n un t i l j u s t p r i o r to s p e r m a t i d e longa t ion . 
G r o w t h of t h e p r i m a r y s p e r m a t o c y t e s c o n t i n u e s un t i l they b e c o m e five to six 
t imes t h e o r ig ina l d i a m e t e r . D u r i n g th is t i m e nucleol i a p p e a r a n d p a s s 
t h r o u g h a p e r i o d of i n t ense s t a i n i n g fol lowed b y lesser s t a in ing . T h e c y t o p l a s m 
inc reases a n d Golg i bod ie s , m u l t i v e s i c u l a r bod i e s , a n d a d i s t inc t b r a n c h i n g 
t u b u l e - s h a p e d e n d o p l a s m i c r e t i c u l u m b e c o m e a p p a r e n t . T h e l a rge inc rease 
in n u m b e r s of Go lg i bod ie s ( s o m e r ichly e n d o w e d w i t h m e m b r a n e whor l s ) 
a n d m i t o c h o n d r i a t h r o u g h o u t t h e c y t o p l a s m ind ica t e s i nc r ea sed phys io log ica l 
ac t iv i ty . 
As t h e p r i m a r y s p e r m a t o c y t e s r e a c h m a x i m u m d i a m e t e r , t he nucleol i s t a in 
poor ly to n o t a t al l , a n d long c h r o m o s o m a l b iva l en t s a t d i p l o n e m m a beg in 
to a p p e a r . F r o m d i p l o n e m m a o n w a r d t h r o u g h b o t h me io t i c d iv is ions t h e 
c h r o m o s o m e s t ages fo rm typ ica l conf igura t ions a n d a r e easi ly r ecogn izab le . 
E l e c t r o n m i c r o s c o p i c o b s e r v a t i o n s d u r i n g l a te p r o p h a s e a n d m e t a p h a s e I 
s h o w b i v a l e n t s enc losed b y a closely a p p r e s s e d d o u b l e m e m b r a n e w h i c h is 
t u b u l e - s h a p e d a n d a p p e a r s s imi l a r to t h e e n d o p l a s m i c r e t i c u l u m . 
A n a p h a s e I is t h e r e d u c t i o n a l a n d a n a p h a s e I I is t he e q u a t i o n a l d iv is ion . 
D u r i n g a n a p h a s e I t h e X - c h r o m o s o m e s o m e t i m e s m i g r a t e s p recoc ious ly o r 
m a y l ag b e h i n d t h e a u t o s o m e s . T h e c h r o m o s o m e s a t t e l o p h a s e I i nc rease in 
l e n g t h , b e c o m e t h i n n e r , c u r v e , a n d s t a in less in tense ly before b e c o m i n g ova l 
a n d f o r m i n g vesicle-l ike s t r u c t u r e s ( k a r y o m e r e s ) . A b o u t ha l f t h e c i rcumfer -
ence of e a c h vesicle s t a ins d a r k e r t h a n t h e r e m a i n i ng half, a n d even tua l l y 
t h e en t i r e vesic le , i n c l u d i n g t h e m a r g i n , is difficult to recognize . T h e n u c l e u s 
is n o t r e fo rmed before t h e s econd me io t i c d iv is ion . As p r o p h a s e I I beg ins t h e 
c h r o m a t i n in e a c h vesicle c o n d e n s e s i n to long , loosely coiled c h r o m o s o m e s . 
T h e s e c o n t r a c t a n d s t a in d a r k e r a t m e t a p h a s e I I . T h e d y a d s s e p a r a t e e q u a -
t iona l ly d u r i n g a n a p h a s e I I , a n d a t t e l o p h a s e I I e a c h c h r o m o s o m e a g a i n 
forms a vesicle-l ike b o d y . A d j a c e n t c h r o m o s o m a l vesicles usua l ly m e r g e 
t o g e t h e r a n d form l a r g e r vesicles w h i c h s o m e t i m e s a p p e a r l ike, b u t a r e no t , 
s e p a r a t e nuc le i . Al l vesicles of e a c h d a u g h t e r cell a r e i n c o r p o r a t e d in to o n e 
n u c l e u s a n d lose the i r i n d i v i d u a l s t a inab i l i t y as t h e cen t ra l ly loca ted n u c l e u s 
of t h e s p e r m a t i d a s s u m e s a d a r k l y s t a i n i n g a p p e a r a n c e . G o r o s h c h e n k o (1960) 
r e p o r t s t h a t s e c o n d a r y s p e r m a t o c y t e s a r e ha l f t h e v o l u m e of p r i m a r y sper -
m a t o c y t e s a n d t h a t s p e r m a t i d s a r e one - fou r th t h e v o l u m e in A. persicus a n d 
0. tholozani, b u t O l i v e r (1972) i n d i c a t e d t h a t in Dermacentor occidentalis r e d u c -
t ion in size a t e a c h s u c c e e d i n g d iv i s ion is p r e s e n t b u t less p r o n o u n c e d . T h e 
fo rmer a u t h o r ' s r esu l t s i n d i c a t e n o cell g r o w t h b e t w e e n d iv i s ions , w h e r e a s 
t he l a t t e r r e su l t s sugges t s o m e s l ight g r o w t h . Differences b e t w e e n resu l t s 
m i g h t b e d u e to differences in A r g a s i d a e a n d I x o d i d a e , b u t m i g h t a lso b e 
d u e to differences in t e c h n i q u e s a n d m e t h o d s of ana lys i s . 
252 J. H. Oliver 
8.3.2. Spermiogenes is 
S p e r m i o g e n e s i s is a c o m p l e x d e v e l o p m e n t a l a n d g r o w t h p h a s e in t h e 
p r o d u c t i o n of s p e r m a t o z o a t h a t involves c h a n g e s in t he r o u n d e d s p e r m a t i d 
to t he fully e l o n g a t e d a n d m a t u r e s p e r m a t o z o o n . T h e s e even t s l e a d i n g to t he 
p r o d u c t i o n of s p e r m a t o z o a c a n b e d i scussed as p r e c a p a c i t a t i o n d e v e l o p -
m e n t , c a p a c i t a t i o n , a n d final d e v e l o p m e n t . T h e p r e c a p a c i t a t i o n c h a n g e s 
beg in i m m e d i a t e l y u p o n p r o d u c t i o n of s p e r m a t i d s whi le they a r e still in t h e 
tes tes a n d c o n t i n u e a s t h e s p e r m a t i d s a r e m o v e d to t h e v a s a de fe ren t i a a n d 
c o m m o n v a s defe rens w h e r e they a r e s to red un t i l they a r e t r ans fe r r ed d u r i n g 
m a t i n g . C a p a c i t a t i o n beg ins in t h e s p e r m a t o p h o r e d u r i n g t rans fe r to t h e 
female a n d final m a t u r a t i o n occu r s in t h e gen i t a l t r a c t of t he female . T r e -
m e n d o u s phys io log ica l a n d m o r p h o g e n e t i c c h a n g e s o c c u r d u r i n g s p e r m i -
ogenes i s a n d , even t h o u g h severa l inves t iga t ions h a v e b e e n m a d e of v a r i o u s 
a spec t s of t he se c h a n g e s , m a n y g a p s in o u r u n d e r s t a n d i n g still exist . S o m e 
m a j o r c h a n g e s t h a t o c c u r i n c l u d e (1) r e loca t ion of n u c l e u s a n d s u b p l a s m a -
l e m m a l c i s t e r n a e to o p p o s i t e po les , (2) f o rma t ion of a l a rge c i s t e rna l cav i ty , 
i n v a g i n a t i o n of c y t o p l a s m i n t o it as t he s p e r m a t i d b e c o m e s a n e longa te t u b e , 
a n d (3) c a p a c i t a t i o n invo lv ing o p e n i n g of t he o p e r c u l u m (cap) a t t h e p o i n t e d 
e n d of t h e cell a l l owing evers ion of t h e i n n e r core . T h i s las t even t resu l t s in 
d o u b l i n g of t h e l e n g t h of t h e cell a n d mobi l i ty . 
83.2J. Precapacitation N e w l y fo rmed s p e r m a t i d s a r e r o u n d e d , c o n t a i n a few 
Golg i c o m p l e x e s a n d l a rge m u l t i v e s i c u l a r bod ie s , a n u m b e r of m i t o c h o n d r i a , 
a n d l a rge a m o u n t s of t u b u l e - s h a p e d e n d o p l a s m i c r e t i c u l u m . T h e n u c l e u s is 
l oca ted cen t r a l l y a n d the p e r i p h e r y of t h e cell r e m a i n s s u r r o u n d e d by c u p -
s h a p e d s u b p l a s m a l e m m a l c i s t e rnae (Fig. 8 .3 , D ) . As d e v e l o p m e n t c o n t i n u e s , 
t h e n u c l e u s a n d a d j a c e n t c y t o p l a s m m o v e t o w a r d o n e po le whi le t h e s u b -
p l a s m a l e m m a l c i s t e rnae l e n g t h e n , fuse, a n d form a s ingle l a rge c i s t e r n u m 
or cav i ty a t t h e o p p o s i t e po le (for de ta i l s of c i s t e rna l fusion, see Rege r , 1962) . 
O r i g i n of t h e s u b p l a s m a l e m m a l c i s t e rnae is u n c e r t a i n , a l t h o u g h the e n d o -
p l a s m i c r e t i c u l u m (Reger , 1961 , 1962) a n d Golg i c o m p l e x e s (Reger , 1974) 
h a v e b e e n sugges t ed as o r ig ins . L a c k of ev idence for sufficient e n d o p l a s m i c 
r e t i cu la a n d insufficient Golg i c o m p l e x e s in ve ry y o u n g p r i m a r y s p e r m a t o -
cytes (p r io r to t h e g r e a t g r o w t h s t a g e ) , b u t p r e s e n c e of s u b p l a s m a l e m m a l 
c i s t e rnae cas t s d o u b t o n t h e fo rmer s t r u c t u r e s as o r ig ina l sources . I t s eems 
m o r e likely t h a t t h e c i s t e rnae a r e de r ived from the p l a s m a m e m b r a n e 
( B r e u c k e r & H o r s t m a n n , 1972; O l i v e r & B r i n t o n , 1972; S u l e i m a n & B r o w n , 
1978). As t h e l a rge c i s t e rna l cav i ty is fo rmed , c y t o p l a s m i c processes e x t e n d 
in to it f rom t h e ins ide wal l a n d b e c o m e a g g r e g a t e d a t o n e e n d of t h e cav i ty . 
T h a t e n d is t h e p r e s u m p t i v e a n t e r i o r e n d of t h e i n n e r core w h i c h will 
even tua l l y d e v e l o p as t h e a n t e r i o r e n d of t he m a t u r e s p e r m a t o z o o n . 
P r io r to f o r m a t i o n of t h e l a rge c i s t e rna l cav i ty a n d m a j o r e l o n g a t i o n of t h e 
Tick Reproduction: Sperm Development 253 
F
lG
. 
8
.3
. 
D
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 o
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at
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. 
A
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sp
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; 
D
-N
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 i
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 m
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 N
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 f
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 f
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254 J. H. Oliver 
FlG. 8.4. Electron micrograph of young spermatid, a, developing acrosome; c, cisternae; n, 
nucleus. Scale = 0 . 5 μpiι. 
Tick Reproduction: Sperm Development 255 
s p e r m a t i d , a n d before t h e n u c l e u s r e a c h e s a p e r i p h e r a l loca t ion , a n a c r o s o m a l 
vesicle fo rms b e t w e e n t h e n u c l e u s a n d p l a s m a l e m m a (Reger , 1963; O l i v e r 
& B r i n t o n , u n p u b l i s h e d ) . As t h e n u c l e u s r e a c h e s t he p e r i p h e r y it b e c o m e s 
closely a p p l i e d to t h e d e v e l o p i n g a c r o s o m a l vesicle . T h e l a t t e r p r o b a b l y 
ar ises as a fusion of Golg i c o m p l e x vesicles (Reger , 1963). C e r t a i n l y m a n y 
vesicles a r e close to t h e a c r o s o m a l vesicle a n d s o m e a r e c o n t i n u o u s wi t h 
Golg i c o m p l e x e s . T h e a c r o s o m a l vesicle b e c o m e s n a r r o w a n d e longa tes 
c i r cumferen t i a l ly i m m e d i a t e l y b e n e a t h t h e p l a s m a l e m m a . A t th is t i m e elec-
t r o n d e n s e a c r o s o m a l m a t e r i a l a p p e a r s in t h e t w o e n d s of t h e vesicle , t h e n 
fills t h e vesicle w h i c h b e c o m e s p rogress ive ly d a r k e r s t a i n i n g a n d longer (Fig . 
8.4) . E v e n t u a l l y t h e a c r o s o m e comple t e ly fills t he vesicle a n d a p p e a r s as a 
FlG. 8.5. Proposed alternate developmental spermatid forms based on SEM observations of two 
species of Amblyomma and Dermacentor. Letters correspond with ones in Fig. 8.3. See text for full 
description. 
256 J. H. Oliver 
long d e n s e b o d y . D u r i n g th is t i m e t h e c h r o m a t i n a p p e a r s to b e dense ly 
s t a i n i n g a n d a g g r e g a t e s a r o u n d the p e r i p h e r y of t he i r r egu la r ly folded n u c l e a r 
m e m b r a n e (Fig . 8 .4) . T h e n u c l e u s un t i l n o w h a s r e m a i n e d in t he p e r i p h e r a l 
c y t o p l a s m in a t e r m i n a l loca t ion a t t h e b r o a d e n d of t he s p e r m a t i d (oppos i t e 
po le from t h e fusing c i s t e r n a e ) . W h i l e in th is pos i t ion , t he n u c l e u s beg ins to 
e l o n g a t e a n d f requen t ly ( b u t no t a lways ) a p p e a r s s o m e w h a t p o i n t e d o n its 
p e r i p h e r a l - m o s t s ide a n d s o m e t i m e s a p p e a r s to e x t e n d in to a cap- l ike o r 
finger-like p r o t r u s i o n ( p o i n t e d in s o m e s q u a s h a n d sec t ioned m a t e r i a l ) of t h e 
s p e r m a t i d a t its b r o a d e n d (Fig . 8 .5, G ) . 
T h e o c c u r r e n c e a n d role of t h e finger-like p r o t r u s i o n n e e d s i m m e d i a t e 
s t u d y . I t s p r e s e n c e is no t u sua l l y d i scussed in m o s t a c c o u n t s of s p e r m i o -
genes is . A few a u t h o r s , h o w e v e r , h a v e referred to a flag-like o r p e n n a n t - l i k e 
ex tens ion t h a t a p p e a r s a t a b o u t this s t age of d e v e l o p m e n t of t h e s p e r m a t i d . 
U n p u b l i s h e d s c a n n i n g e lec t ron mic roscop i c ( S E M ) o b s e r v a t i o n s (O l ive r & 
Cross ) on s p e r m i o g e n e s i s in Amblyomma hebraeum, howeve r , i n d i c a t e t h e p r e s -
ence of r a t h e r p r o m i n e n t finger-like ex tens ions o r p r o t r u s i o n s from e l o n g a t i n g 
s p e r m a t i d s . O n l y o n e ex tens ion p e r s p e r m a t i d is p r e s e n t a n d it first a p p e a r s 
as a s h o r t b r o a d i r r egu la r i t y of t h e s p e r m a t i d j u s t as t h e l a t t e r beg ins to 
e l o n g a t e (Fig . 8 .5 , F ) . As t h e s p e r m a t i d e longa tes so does t he ex tens ion a n d 
it soon a p p e a r s as a finger-like p rocess e x t e n d i n g pos te r io r ly f rom t h e sper -
m a t i d in s o m e p r e p a r a t i o n s . Ac tua l l y , S E M o b s e r v a t i o n s i n d i c a t e t h a t it is 
s u b t e r m i n a l a n d u sua l l y e x t e n d s a t a 45° to 90° ang l e from the long axis of 
t he s p e r m a t i d (Fig . 8 .5.) . T h e p ro jec t ion is no t seen in fully e l o n g a t e sper -
m a t i d s a n d p r e s u m a b l y is a b s o r b e d p r i o r to c o m p l e t e s p e r m a t i d e longa t ion . 
I t s ro le is u n k n o w n . I n d e e d , its p r e s e n c e in all species is o p e n to q u e s t i o n . 
A t p r e s e n t severa l e x p l a n a t i o n s m i g h t be a d v a n c e d as to w h y so p r o m i n e n t 
a s t r u c t u r e h a s rece ived so l i t t le a t t e n t i o n . F i rs t ly , p e r h a p s it does n o t o c c u r 
in s p e r m a t i d s of a l l t ick species . Second ly , it is n o t u n c o m m o n t h a t S E M 
s t u d y forces r e - e x a m i n a t i o n s a n d r e - i n t e r p r e t a t i o n s of s t r u c t u r e s n o t no t i ced 
o r m i s i n t e r p r e t e d w h e n u s i n g l igh t m i c r o s c o p y or t r a n s m i s s i o n e lec t ron 
m i c r o s c o p y . F ina l ly , t h e poss ib i l i ty exists t h a t m o r e t h a n o n e m o r p h o l o g i c a l 
t ype of t ick s p e r m a t o z o o n is fo rmed p e r i n d i v i d u a l , p e r h a p s in sma l l n u m b e r s 
a n d n o t in all spec ies . 
As t h e s p e r m a t i d e longa te s , dense ly s t a i n i n g m a t e r i a l a c c u m u l a t e s in t h e 
c y t o p l a s m a t t h e p o s t e r i o r ( " t o p " ) e n d of t h e c i s te rna l cavi ty . T h i s is t h e 
loca t ion w h e r e t h e i n n e r core will i n v a g i n a t e i n to t h e cav i ty (F ig . 8 .3 , K , L , 
M ) . M i t o c h o n d r i a t e n d to b e m o r e p r e v a l e n t in th is a r e a w h e r e i n v a g i n a t i o n 
will occu r , a n d n e a r t he n u c l e u s . M o r e o v e r , t he e n d o p l a s m i c r e t i c u l u m 
a p p e a r s m o r e ves i cu la r t h a n tubu le - l ike . U p o n i n v a g i n a t i o n m i t o c h o n d r i a 
a r e m o s t p r e v a l e n t in t h e a n t e r i o r t ip of t h e a d v a n c i n g i n n e r core ( i nne r co rd 
of Rege r , 1963) a n d m a i n t a i n th is loca t ion t h r o u g h o u t t he r e m a i n d e r of 
s p e r m a t i d d e v e l o p m e n t a n d s p e r m a t o z o a n life. A s g r o w t h of t h e i n n e r co re 
c o n t i n u e s , t h e n u c l e u s re loca tes to t he s ide of t he e l o n g a t i n g cell in t h e 
Tick Reproduction: Sperm Development 257 
p e r i p h e r a l c y t o p l a s m (ou t e r s h e a t h ) b e t w e e n t h e c i s t e rna l cav i ty a n d p l a s -
m a l e m m a a n d c h a n g e s f rom a b r o a d l y to a n a r r o w l y fusiform s h a p e (Fig . 
8 .3 , L , M , N ) . T h e i n n e r co re c o n t i n u e s its i n v a g i n a t i o n in to t he c i s t e rna l 
cav i ty un t i l it is en t i r e ly filled (Fig . 8 .3 , N ) . T h u s , t he i n n e r core b e c o m e s 
a t u b e w i t h i n a n o u t e r t u b e . T h e cell p rocesses o n t he surface of t h e i n n e r 
core a n d t h e i n n e r wa l l of t h e o u t e r s h e a t h (or t u b e ) a r e n o w in o p p o s i t i o n 
to e a c h o t h e r d u e to t h e wal l s of t h e cav i ty h a v i n g folded d o w n u p o n 
t hemse lves . As t h e l a t t e r o c c u r s t h e e l o n g a t e d fusiform n u c l e u s r e m a i n s in 
its p e r i p h e r a l pos i t ion , b u t n o w is l oca t ed n e a r e r t he p o i n t e d e n d of t h e 
a d v a n c e d s p e r m a t i d (Fig . 8 .3 , N ) . C o n c u r r e n t l y , t h e p r o x i m a l o n e - t h i r d of 
t h e i n v a g i n a t e d i n n e r co re n e a r e s t t h e p o i n t e d e n d of t he cell b r o a d e n s 
l a te ra l ly a n d folds u p o n itself in a t r a n s v e r s e fash ion w i t h r e spec t to t h e long 
axis of t h e cell (F ig . 8 .3 , N ) . T h e s p e r m a t i d is l ong a n d t u b u l a r a t th is s t age 
a n d u n d e r g o e s n o a d d i t i o n a l m o r p h o l o g i c a l d e v e l o p m e n t un less it leaves t h e 
m a l e . S p e r m a t i d s a r e s to red in t h e c o m m o n vas deferens ( s emina l vesicle) 
a n d v a s a de fe ren t i a a n d r a n g e in l e n g t h f rom 50 to 500 μ ιη d e p e n d i n g o n t h e 
spec ies . T h e y a r e u sua l l y t h r e e to five t imes longe r in a r g a s i d s t h a n ixod ids . 
T h e a n t e r i o r e n d is s l ight ly b r o a d e r t h a n t h e r e m a i n d e r of t h e cell a n d the 
a n t e r i o r t ip is t a p e r e d . T h e pos t e r i o r p a r t of t h e s p e r m a t i d ( p r o s p e r m i u m 
of s o m e a u t h o r s ) is of u n i f o r m d i a m e t e r a n d h a s a t r u n ca t e e n d w h i c h is 
c losed ( W ü e s t , et al., 1978) . T h e e x t e r n a l sur face is m o r e or less s m o o t h 
excep t for s o m e s l ight wr ink le s a n d c reases a l o n g the l eng th of t h e cell. A 
r i m of t w o pa ra l l e l r idges enc i rc les t h e s p e r m a t i d n e a r t he a n t e r i o r a p e x in 
A. hebraeum ( W ü e s t et al., 1978) , b u t it is n o t k n o w n w h e t h e r these o c c u r in 
o t h e r spec ies . T h e r e a r e def ini te a r e a s of w e a k n e s s in this r eg ion in m o s t 
spec ies , h o w e v e r , b e c a u s e th is is t h e p a r t of t h e o u t e r s h e a t h w h e r e t he i n n e r 
core e m e r g e s . O l i v e r a n d B r i n t o n (1972) n o t e in D. occidentalis, " a cap- l ike 
s t r u c t u r e is seen a t t h e p o i n t e d e n d " a n d i n d i c a t e t h a t th is is t h e a r e a t h a t 
r u p t u r e s a n d a l lows evers ion of t h e i n n e r core in n o r m a l l y d e v e l o p i n g sper -
m a t i d s after r e a c h i n g t h e female . T h e cap- l ike s t r u c t u r e w a s s u b s e q u e n t l y 
ca l led a n o p e r c u l u m ( B o r u t & F e l d m a n - M u h s a m , 1976) a n d c lear ly s h o w n 
n o t to b e forced off b y t he a d v a n c i n g i n n e r core in Ornithodoros delanoei, 
Ornithodoros gurneyi, a n d Haemaphysalis parva (= H. otophilia). 
8.3.2.2. Capacitation Phys io log ica l c h a n g e of s p e r m a t o z o a o c c u r r i n g b e t w e e n 
i n s e m i n a t i o n a n d fer t i l izat ion w a s t e r m e d c a p a c i t a t i o n in m a m m a l s (Aus t in , 
1951; C h a n g , 1951) . A l t h o u g h it h a s rece ived w i d e s p r e a d s t u d y in m a m m a l s , 
re la t ive ly few s tud i e s of c a p a c i t a t i o n h a v e b e e n r e p o r t e d in o t h e r t a x a . I t h a s 
b e e n found in frogs (Sh ivers & J a m e s , 1970) , h o w e v e r , a n d if o n e is n o t 
over ly res t r i c t ive in def in ing t h e b i o c h e m i c a l p r o p e r t i e s of c a p a c i t a t i o n , it 
s eems likely t h a t it is p r e s e n t in m a n y (if n o t m o s t ) t axa . T h e first u se of t he 
t e r m c a p a c i t a t i o n in a n i n v e r t e b r a t e species w a s d u r i n g the 3 rd I n t e r n a t i o n a l 
C o n g r e s s of A c a r o l o g y (O l ive r & B r i n t o n , 1973) a n d dea l t w i t h t he t ick D. 
occidentalis. P r i o r to th i s , severa l sc ient i s t s rea l ized t h a t g e r m i n a l cells of t icks 
258 J. H. Oliver 
w e r e no t fully m a t u r e in the m a l e a n d t h a t e longa t ion of " p r o s p e r m i a " 
( e longa ted s p e r m a t i d s ) o c c u r r e d u p o n t ransfer to females ( S a m s o n , 1909; 
Cas t ee l , 1917; O p p e r m a n n , 1935; a n d o t h e r s ) . T h e s e a u t h o r s w e r e no t fully 
a w a r e of all m o r p h o l o g i c a l a n d n o n m o r p h o l o g i c a l a spec t s of c h a n g e , h o w e v e r , 
a n d in fact even t o d a y m u c h in fo rma t ion r e m a i n s to be g a t h e r e d . I f a n 
e x p a n d e d def ini t ion of c a p a c i t a t i o n to i n c l u d e m o r p h o l o g i c a l a n d / o r p h y s i o -
logical c h a n g e s of s p e r m a t o z o a after t ransfer to t he female is a c c e p t e d , c lear ly 
s p e r m of m a n y a r t h r o p o d s u n d e r g o c a p a c i t a t i o n , i.e. s p e r m ac t i va t i on in 
b e d b u g s (Dav i s , 1965) , m o r p h o l o g i c a l c h a n g e s in s p e r m of t h e fly Sciara 
coprophila (Phi l l ips , 1966) , a n d o t h e r s . Biological c o n s e r v a t i s m or efficiency 
w o u l d s e e m to favour a n e v o l u t i o n a r y s t r a t egy w h e r e i n m a l e a n i m a l s possess 
u n c a p a c i t a t e d o r inac t ive s p e r m a t o z o a w h i c h a r e ac t i va t ed on ly w h e n con-
d i t ions a r e f avou rab l e for fer t i l izat ion. 
T h e las t p a r t of s p e r m i o g e n e s i s in t icks w h i c h w e refer to as c a p a c i t a t i o n 
(also ca l led spe rma te l eos i s ) on ly occu r s n a t u r a l l y in t he female . M o s t of o u r 
i n f o r m a t i o n o n c a p a c i t a t i o n of t ick s p e r m is of a m o r p h o l o g i c a l n a t u r e (Reger , 
1 9 6 1 , 1 9 6 2 , 1 9 6 3 , 1 9 7 4 ; W a g n e r - J e v e s e e n k o , 1958; R o t h s c h i l d , 1961; B r e u c k e r 
& H o r s t m a n n , 1968, 1972; O l i v e r & B r i n t o n 1972, 1973; B r i n t o n etal., 1974; 
B o r u t & F e l d m a n - M u h s a m , 1976; F e l d m a n - M u h s a m & Fi lshie , 1976; W ü e s t 
et al., 1978; S u l e i m a n & B r o w n , 1978) . T h e first s ign of c a p a c i t a t i o n of t h e 
s p e r m a t i d s is t h e o p e n i n g of t he cap- l ike t ip ( o p e r c u l u m ) a n d the e m e r g e n c e 
of t h e i n n e r core f rom t h e o p e n i n g (Fig . 8 .3 , N ) . As t he i n n e r core c o n t i n u e s 
to e l o n g a t e it a l so s p r e a d s s l ight ly l a te ra l ly a n d will b e c o m e the a n t e r i o r e n d 
of t h e m a t u r e s p e r m a t o z o o n . S i m u l t a n e o u s l y , t he o u t e r s h e a t h , " s l i d e s " 
b a c k w a r d ove r t h e i n n e r core , c a r r y i n g the n u c l e u s w i th it, a n d beg ins to 
i n v a g i n a t e a t t h e o p p o s i t e e n d . T h i s resu l t s in t he loca t ion of t he n u c l e u s 
a n d a c r o s o m e in t h e pos t e r io r p a r t of t he s p e r m a t o z o o n nex t to t he i n v a g i n a t e d 
a c r o s o m a l c a n a l (Fig . 8 .3 , P , Q ) . 
As t h e i n n e r core c o n t i n u e s to e m e r g e , t h e h e m i s p h e r i c a l a n t e r i o r t ip 
( h e a d ) c a n be seen w i t h S E M to c o n t a i n n u m e r o u s b u l b o u s e x p a n s i o n s 
( W ü e s t et al., 1978; O l i v e r & C r o s s , u n p u b l i s h e d ) o r a n e t w o r k of sma l l 
p ro jec t ions ( F e l d m a n - M u h s a m & Fi lsh ie , 1976). I t is s e p a r a t e d from the 
r e m a i n d e r of t h e s p e r m a t o z o o n by a n a r r o w col lar o r r idge . F r o m this a r e a 
pos te r io r ly , t h e surface is covered b y ce l lu la r p rocesses w h i c h a p p e a r as 
l o n g i t u d i n a l r idges t h a t e x t e n d a p p r o x i m a t e l y pa ra l l e l to e ach o the r . E a c h 
r idge c o n t i n u e s for a d i s t a n c e after w h i c h it t e r m i n a t e s a n d is usua l ly followed 
by a n o t h e r . T h e ce l lu la r p rocesses o r r idges a p p e a r s l ight ly s i n u o u s in s o m e 
reg ions . T h e p rocesses a r e a t t a c h e d only a t the i r a n t e r i o r e n d s by spec ia l ized 
c o n n e c t i o n s ("feet") in 0. gurneyi a n d 0. tholozani ( F e l d m a n - M u h s a m & 
Fi lsh ie , 1976) . 
Fu l ly c a p a c i t a t e d tick s p e r m a t o z o a a r e c l ava te o r p a d d l e - s h a p e d a t t h e 
a n t e r i o r e n d a n d t a p e r g r a d u a l l y i n t o long pos te r io r p o r t i o n s (Fig . 8 .3 , Q ) . 
T h e a n t e r i o r e n d is a b o u t twice t he w i d t h of t he pos t e r io r p a r t . T h e c l ava t e 
Tick Reproduction: Sperm Development 259 
a n t e r i o r p a r t flattens o u t a t t imes w h e r e a s t h e long pos t e r io r p a r t r e m a i n s 
cy l indr ica l . A t t h e p o s t e r i o r e n d t h e cell m e m b r a n e is i n v a g i n a t e d a n d forms 
a long i n t e r n a l c a n a l in 0. tholozani. I n A. hebraeum t h e a p e r t u r e l e a d i n g to 
t h e a c r o s o m a l c a n a l is sl i t- l ike. Fu l ly d i f ferent ia ted s p e r m a t o z o a r a n g e from 
150 to 1000 μpiι in l e n g t h d e p e n d i n g on the spec ies , a n d a r e a p p r o x i m a t e l y 
twice t h e l e n g t h of t h e longes t s t age r e a c h ed in t h e m a l e . A d d i t i o n a l l y , 
a r g a s i d s p e r m a r e m u c h longe r t h a n those of ixod ids . R o t h s c h i l d (1961) 
no tes t h a t t h e a v e r a g e s p e r m a t o z o o n , s u c h as t h a t of m a n or sea u r c h i n s , is 
a p p r o x i m a t e l y 60 μpiι long . 
T h e c o m p l i c a t e d m o r p h o l o g i c a l c h a n g e s r e su l t i ng in d o u b l i n g of l eng th 
of t ick s p e r m a t i d s d u r i n g c a p a c i t a t i o n a r e n o t t h e on ly s t r ik ing c h a n g e s 
n o t e d . T h e s p e r m a t o z o a b e c o m e mot i l e a n d d e v e l o p t h e ab i l i ty to p e n e t r a t e 
cells. A p p r o x i m a t e l y t h r e e (O l ive r & B r i n t o n , 1973; F e l d m a n - M u h s a m & 
Fi l sh ie , 1976) to five ( W ü e s t et al., 1978) types of s p e r m mot i l i ty exist 
d e p e n d i n g o n t h e m a n n e r in w h i c h m o v e m e n t s a r e classified. T h e five types 
i nc lude : (1) g l id ing o r t r a n s l a t o r y t y p e , (2) occas iona l r o t a t i o n s of t he s p e r m 
axis , (3) l a t e r a l b e n d i n g s of t h e tai l- l ike p a r t , (4) a ro l l ing u p a n d e x t e n d i n g 
m o t i o n of t h e h e m i s p h e r e a t t h e a n t e r i o r a p e x of t he cell ( the e x t e n d i n g 
m o t i o n is a c c o m p a n i e d b y a l o n g i t u d i n a l d e p r e s s i o n in t he c l ava te a n t e r i o r 
p a r t ) , a n d (5) w a v e s of cons t r i c t i on m o v i n g a l o n g t h e tai l- l ike pos te r io r . 
Ac tua l l y , t h e l a t t e r t y p e of mot i l i ty (waves of cons t r i c t ions ) m a y in p a r t 
p r o p e l t h e s p e r m a t o z o o n fo rward in a g l id ing fashion. I t s eems likely t h a t 
t h e cons t r i c t i ons a r e p r o d u c e d b y c o n t r a c t i o n of fibrils ( p r o b a b l y myofibr i ls) 
o r g a n i z e d a s b u n d l e s of filaments 0 . 1 -0 .2 μpiι b e n e a t h t h e cell m e m b r a n e 
( F e l d m a n - M u h s a m & Fi l sh ie , 1976) . E a c h fibril consis ts of 2 0 - 4 0 s e p a r a t e 
filaments a n d is o r i e n t e d pa ra l l e l w i t h t he long axis of t he cell. T h e fibrils 
beg in j u s t p o s t e r i o r to t h e h e a d a n d e x t e n d b a c k w a r d s to t he level of t h e 
n u c l e u s . T h e filaments a r e re la t ive ly s h o r t a n d n o n e of t h e m e x t e n d the 
en t i r e l e n g t h of t h e s p e r m a t o z o o n ( s p e r m i o p h o r e ) . A p p a r e n t l y in s o m e species 
(0. tholozani) t h e filaments a r e n o t a r r a n g e d in b u n d l e s , b u t r a t h e r in a layer . 
B r e u c k e r a n d H o r s t m a n n (1968) t h o u g h t t h e filaments w e r e mo rp h o l o g i ca l l y 
s imi l a r to myof ibr i l s , b u t d i d n o t t h ink they c a u s e d t h e m o t i o n of t h e 
s p e r m a t o z o a . T h e s e a u t h o r s a s s u m e t h a t t h e g l id ing m o v e m e n t is c o n n e c t e d 
w i t h t h e ce l lu la r p rocesses . F e l d m a n - M u h s a m a n d Fi lshie (1976) bel ieve 
t h a t t h e fibrils a n d p r o t r u d i n g ce l lu la r p rocesses a r e func t iona l ly r e l a t ed to 
o n e a n o t h e r a n d t h a t it is poss ib le t h a t t he p rocesses , a l o n g w i t h t he con-
s t r i c t ions , h a v e a func t ion in p r o d u c i n g t h e g l id ing m o v e m e n t s . W ü e s t et al. 
(1978) a g r e e t h a t t h e mot i l i ty of t h e s p e r m a t o z o o n m a y be in p a r t d u e to t he 
fibers b e n e a t h t h e ce l lu la r p rocesses a n d t h a t these fibers m a y r e p r e s e n t ac t in 
o r m y o s i n fibers. T h e s e a u t h o r s s h o w c lear ly by S E M the cons t r i c t ions o n 
t h e tai l - l ike p a r t of t h e s p e r m a t o z o a . T h e y a lso d e m o n s t r a t e d , v ia freeze-etch 
rep l i cas , a w a v y p a t t e r n of t h e ce l lu la r p rocesses a n d the u n d e r l y i n g m e m -
b r a n e . T h e s e w a v y p a t t e r n s m a y r e p r e s e n t u n d u l a t i o n s a s soc ia t ed w i t h s p e r m 
260 J. H. Oliver 
m o v e m e n t as sugges t ed b y R o t h s c h i l d (1961) . R o t h s c h i l d sugges t ed spe r -
m a t o z o a m o v e fo rward b y b e n d i n g w a v e s a l o n g s o m e of t h e surface r idges 
(ce l lu lar p roces ses ) . 
S o m e a u t h o r s c l a im t h e r e is a n o t h e r s t ep in c a p a c i t a t i o n of s p e r m a t o z o a 
in severa l a r g a s i d s i n c l u d i n g Ornithodoros a n d Argas species (Cas tee l , 1917; 
O p p e r m a n n , 1935; W a g n e r - J e v s e e n k o , 1958; K h a l i l , 1969; F e l d m a n -
M u h s a m & Fi l sh ie , 1976) . A p p a r e n t l y t h e i n v a g i n a t e d a c r o s o m a l c a n a l a t 
t he pos t e r io r e n d of t h e s p e r m a t o z o o n ever t s i n to a t h in p ro jec t ion p r i o r to 
oocy te p e n e t r a t i o n . T h e n u c l e a r r e loca t ion ins ide th is evers ion m i g h t exp la in 
h o w t h e s p e r m n u c l e u s r e a c h e s t he oocy te . T h e g r o w i n g oocy te is s e p a r a t e d 
f rom t h e o v a r i a n l u m e n b y t h e l u m e n a l e p i t h e l i u m a n d funicle cells. T h e 
l a t t e r s u r r o u n d a n a r r o w c h a n n e l l e a d i n g f rom t h e in te r io r o v a r i a n wal l to 
a m i c r o p y l e in t h e oocy te ' s c u t i c u l a r cove r ing ( B r i n t o n & Ol ive r , 1971a, b ) . 
T h i s m i c r o p y l e in D. andersoni exists on ly in re la t ive ly i m m a t u r e oocy tes , b u t 
r e m a i n s in yo lked-eggs for a p e r i o d of t i m e . A l t h o u g h b o t h t h e m i c r o p y l e 
a n d funicle cell c h a n n e l h a s a d i a m e t e r sma l l e r t h a n t h a t of t he w i d e p a r t 
of s p e r m a t o z o a , it still m a y serve as t h e r o u t e of e n t r y of t he m a l e p r o n u c l e u s . 
P e r h a p s t h e evers ion of t h e a c r o s o m a l c a n a l in these a r g a s i d s r e p r e s e n t s a 
n a t u r a l p rocess w h e r e b y the s p e r m n u c l e u s c a n be p ro jec ted t h r o u g h the 
n a r r o w funicle cel ls ' c h a n n e l a n d m i c r o p y l e . T h e r e seems to be i nc r ea s ing 
s u p p o r t for t h e h y p o t h e s i s t h a t on ly t h e n u c l e u s a n d no t t h e en t i r e spe r -
m a t o z o o n e n t e r s t h e egg (Ol ive r , 1974). Eve r s ion of t he a c r o s o m a l c a n a l h a s 
no t b e e n r e p o r t e d in s p e r m of ixod id species , howeve r , a n d t h u s it is u n c e r t a i n 
w h e t h e r t he evers ion o c c u r s in all species . 
8.3.2.3. Spermatid Transfer to Females—Mating Behaviour P r io r to c a p a c i t a t i o n 
s p e r m a t i d s m u s t b e t r ans fe r r ed to t h e females as n o t e d a b o v e . T h e in t e r e s t i ng 
m a n n e r in w h i c h th is is a c c o m p l i s h e d is d i scussed be low. 
M a t i n g a m o n g m o s t a r g a s i d s usua l ly occu r s in t he nes t s , b u r r o w s , d e n s , 
e tc . , of the i r hos t s . Ixodes species m a y m a t e in o r o u t of nes t s a n d o n or off 
hos t s , d e p e n d i n g o n t h e spec ies . T h e M e t a s t r i a t a h a r d ticks usua l ly c o p u l a t e 
o n t h e hos t s . U n t i l t en y e a r s a g o it w a s a m y s t e r y h o w the sexes found e a c h 
o t h e r . M a n y p e r s o n s t h o u g h t c o n t a c t w a s m a d e by c h a n c e , a l t h o u g h s o m e 
p e r s o n s s u s p e c t e d t h e r e w a s m o r e to it t h a n this ( L o u n s b u r y , 1899). D e m o n -
s t r a t i o n of a sex a t t r a c t a n t o r p h e r o m o n e a m o n g t icks w a s first d e m o n s t r a t e d 
in 1971 (Be rge r et al.) a n d s ince t h a t t i m e m a n y inves t iga t ions h a v eb e e n 
c o n d u c t e d o n t h e fasc ina t ing top ic of c h e m i c a l m e s s e n g e r s a m o n g t icks (see 
C h a p t e r 12 o n T i c k P h e r o m o n e M e c h a n i s m s ) . 
U p o n c o n t a c t b e t w e e n t h e sexes of r ep roduc t i ve ly m a t u r e i n d i v i d u a l s , a n 
in i t ia l s t i m u l a t o r y p h a s e occu r s p r i o r to s p e r m t ransfer . T h e m a l e pos i t ions 
h imse l f u n d e r t h e female so t h a t the i r v e n t e r s a r e a d j a c e n t a n d t h e n v a r i o u s 
p a r t s of t h e m a l e c a p i t u l u m a r e i n t r o d u c e d in to t he female gen i t a l a p e r t u r e . 
O n l y t h e che l i ce rae e n t e r t h e female a p e r t u r e in s o m e M e t a s t r i a t a species 
( F e l d m a n - M u h s a m & B o r u t , 1971; O l i v e r et al., 1974a) , t h e h y p o s t o m e a n d 
Tick Reproduction: Sperm Development 261 
che l i ce rae e n t e r in Ixodes species ( A r t h u r , 1962; M o o r h o u s e , 1966) a n d t h e 
h y p o s t o m e , che l i ce rae , a n d p a l p s a r e i n se r t ed in a r g a s i d species ( N u t t a l l 
& M e r r i m a n , 1911; R o b i n s o n , 1942a; F e l d m a n - M u h s a m , 1969; F e l d m a n -
M u h s a m & B o r u t , 1971) . After severa l m i n u t e s of t he ini t ia l s t i m u l a t o r y 
p h a s e , a s p e r m a t o p h o r e is fo rmed o u t s i d e of t h e m a l e gen i t a l o p e n i n g a n d 
s u b s e q u e n t l y t r ans fe r r ed to t h e female a p e r t u r e . T h e r e a r e different a c c o u n t s 
as to t h e exac t m e t h o d e m p l o y e d in a c c o m p l i s h i n g th i s , b u t t h e che l i ce rae 
a r e invo lved (see d i scuss ion in O l ive r , 1974) . Sa l iva secre ted by t h e m a l e 
i m m e d i a t e l y p r i o r to t r ans fe r of t h e s p e r m a t o p h o r e l ub r i ca t e s t he m a l e ' s 
m o u t h p a r t s a n d t h e v e n t e r s of b o t h sexes a n d p r e v e n t s i m p r o p e r a d h e s i o n 
of t h e s p e r m a t o p h o r e ( F e l d m a n - M u h s a m et al., 1970) . 
8.3.2.4. Spermatid Transfer to Females—Spermatophores O b s e r v a t i o n s h a v e b e e n 
r e p o r t e d o n s p e r m a t o p h o r e s of a t l eas t n i n e species of a r g a s i d s ( R o b i n s o n , 
1942a; T a t c h e l l , 1962; F e l d m a n - M u h s a m , 1967b, 1969; F e l d m a n - M u h s a m 
& B o r u t , 1978) a n d t w o species of ixod ids (Ol ive r et al., 1974a) a n d it a p p e a r s 
t h a t m o r e s imi la r i t i es t h a n differences exist b e t w e e n t h e two t a x a . M o r e is 
k n o w n of t h e de t a i l s c o n c e r n i n g s p e r m a t o p h o r e s of a r g a s i d s , n o t on ly b e c a u s e 
m o r e i nves t i ga t ions h a v e b e e n m a d e , b u t a l so b e c a u s e s p e r m a t o p h o r e s a r e 
eas ier to s t u d y in a r g a s i d s . T h e a r g a s i d h a b i t of m a t i n g off t h e hos t a l lows 
m a t i n g p a i r s to b e e x p e r i m e n t a l l y m a n i p u l a t e d a n d o b s e r v e d w i t h g r e a t e r 
p rec i s ion , a l t h o u g h t h e w h o l e p rocess of s p e r m a t o p h o r e fo rma t ion usua l ly 
r e q u i r e s less t h a n o n e m i n u t e . T h e r a p i d i t y of t h e p rocess a n d the loca t ion 
of t h e s p e r m a t o p h o r e b e t w e e n the v e n t e r s of t h e m a t i n g p a i r still i m p o s e s 
p r o b l e m s in t h e s t u d y of s p e r m a t o p h o r e fo rma t ion , a n d p r o b a b l y c a n b e 
b l a m e d for ea r l i e r i nco r r ec t conc lus ions t h a t t h e s p e r m a t o p h o r e s w e r e fo rmed 
ins ide t h e m a l e a n d e x t r u d e d as fully fo rmed ent i t ies ( N u t t a l l & M e r r i m a n , 
1911; W a g n e r - J e v s e e n k o , 1958; T a t c h e l l , 1962) . 
R e c e n t w o r k ( F e l d m a n - M u h s a m & B o r u t , 1978, in a r g a s i d s {Ornithodoros)) 
i n d i c a t e s t h a t t h e t h r e e m a i n s t ages of s p e r m a t o p h o r e fo rma t ion a r e c o m p o s e d 
of m a n y m o r e s m a l l e r s t ages a n d t h a t these s t ages i n c l u d e a c o n t i n u o u s series 
of p rocesses . Before r e l a t i ng t h e s e q u e n c e of f o rma t ion , howeve r , a d e s c r i p t i o n 
of t h e s t r u c t u r e is n e e d e d . T h e newly fo rmed s p e r m a t o p h o r e cons is t s of t w o 
c o n t a i n e r s , o n e ins ide t h e o t h e r . T h e o u t e r c o n t a i n e r is t h e e c t o s p e r m a t o -
p h o r e , a n d it c o n t a i n s t h e e n d o s p e r m a t o p h o r e . S p e r m a t i d s , s y m b i o t i c 
a lde rocys t s (yeas t - l ike o r g a n i s m s w h o s e role is d i scussed be low) a n d o t h e r 
m a t e r i a l s a r e l oca t ed in t h e s p a c e b e t w e e n these t w o c o n t a i n e r s ( F e l d m a n -
M u h s a m , 1974) . I n 0. savignyi t h e re la t ive ly th ick wal l of t he e c t o s p e r m a -
t o p h o r e is c o m p o s e d of t h r e e l aye r s . T h e o u t e r l aye r is 0 .5 -2 .2 μιτι th ick a n d 
is of a n ac id i c m u c o p o l y s a c c h a r i d e n a t u r e . T h e th icker ( 1 0 - 2 0 μηι) m i d d l e 
l ayer is p r o t e i n a n d t h e t h i n i n n e r l aye r (0.5 μηι) is of a m u c o p o l y s a c c h a r i d i c 
n a t u r e a n d PAS-pos i t i ve . L a r g e p r o t e i n g r a n u l e s ( 4 - 1 3 μpiι in d i a m e t e r ) a r e 
spa r se ly d i s t r i b u t e d on t h e sur face of t h e i n n e r layer . As i n d i c a t e d , t h e s p a c e 
b e t w e e n t h e wa l l of t h e e c t o s p e r m a t o p h o r e a n d t h e e n d o s p e r m a t o p h o r e a lso 
262 J. H. Oliver 
c o n t a i n s t h e dense ly p a c k e d s p e r m a t i d s in PAS-pos i t ive s e m i n a l fluid a n d 
ad l e rocys t s . 
T h e e n d o s p e r m a t o p h o r e is a b i l obed s t r u c t u r e w i t h a c u r v e d neck w h o s e 
d i s t a l e n d seals t h e o p e n i n g of t h e e c t o s p e r m a t o p h o r e . T h e wal l o r m e m b r a n e 
of t h e e n d o s p e r m a t o p h o r e is c o m p o s e d of two layers : t he th icker e x t e r n a l 
layer , w h i c h is p r o t e i n a c e o u s , a n d the t h i n n e r i n t e r n a l layer , w h i c h is of a 
m u c o p o l y s a c c h a r i d e n a t u r e . E a c h lobe of t he e n d o s p e r m a t o p h o r e is full of 
a n a m o r p h o u s p r o t e i n a c e o u s s u b s t a n c e . All l ayers of t h e wal ls a r e n o n c e l l u l a r 
a n d a r e e j acu l a t ed as v i scous s u b s t a n c e s before b e c o m i n g p l i ab le l aye rs . T h e 
th icker m i d d l e l aye r of t he e c t o s p e r m a t o p h o r e wal l b e c o m e s r ig id . 
T h e s e q u e n t i a l f o r m a t i o n of t h e s p e r m a t o p h o r e beg ins w h e n a sma l l d r o p l e t 
of ac id ic m u c o p o l y s a c c h a r i d e a p p e a r s f rom the gen i t a l a p e r t u r e . I n t o th is 
d r o p l e t , w h i c h will b e c o m e t h e o u t e r l ayer of t he wal l , is sec re ted a p r o t e i n 
d r o p l e t t h a t will fo rm t h e m i d d l e layer . T h i s second d r o p l e t en l a rges t he size 
of t h e first d r o p l e t a n d t u r n s it i n to a t r a n s p a r e n t p e a r - s h a p e d s h e a t h . 
C l u s t e r s of l a rge p r o t e i n g r a n u l e s , engulfed in a PAS-pos i t ive s u b s t a n c e 
a r e sec re ted in to t h e s h e a t h . T h i s s u b s t a n c e forms the th in i n n e r l aye r 
of t h e e c t o s p e r m a t o p h o r e , a n d t h e l a rge g r a n u l e s s p r e a d over t h e ins ide 
of th is l ayer . Q u i c k l y thereaf te r , t he s p e r m a t i d s a n d s e m i n a l fluid a r e 
e j acu la t ed , c a u s i ng t h e e c t o s p e r m a t o p h o r e to e n l a r g e s ignif icant ly. T h e n the 
s y m b i o t i c ad l e rocys t s , e m b e d d e d in a n adhes ive PAS-pos i t ive m a t e r i a l , a r e 
d e p o s i t e d . 
T h e las t ser ies of even t s involves t h e s e q u e n t i a l secre t ion of p a r t s of t h e 
e n d o s p e r m a t o p h o r e . F i r s t t h e b i lobed p a r t , followed by the t w o sacs con-
t a i n i n g p r o t e i n a c e o u s m a t e r i a l (one go ing to e a c h lobe) is p r o d u c e d . S im-
u l t a n e o u s l y t h e neck of t h e e n d o s p e r m a t o p h o r e is c o n t i n u o u s l y sec re ted a n d 
inc reases in l eng th . F ina l ly , t h e las t c o m p o n e n t to be d e p o s i t e d is t h e d i s ta l 
p a r t of t h e neck w h i c h c o n n e c t s t he e n d o s p e r m a t o p h o r e to t he o p e n i n g of 
t he e c t o s p e r m a t o p h o r e a n d p l u g s it. 
I t is n o t k n o w n w h a t ac t iva t e s t h e m a l e accessory gen i t a l g l a n d s to secre te 
t h e p r o d u c t s w h i c h s u b s e q u e n t l y form t h e s p e r m a t o p h o r e . P r e s u m a b l y s o m e 
sor t of n e r v o u s s t i m u l a t i o n beg ins t h e p rocess . W h a t e v e r t he t r igger m a y b e , 
o n c e it beg ins , t h e v a r i o u s accessory g l a n d cells c o n t i n u e to secre te t h e 
p r o d u c t s in p r o p e r s e q u e n c e a n d t i m i n g even if t h e female is r e m o v e d o r 
ea r l i e r sec re t ions a r e r e m o v e d f rom the m a l e gen i t a l a p e r t u r e . T h i s l a t t e r 
c h a r a c t e r i s t i c h a s m a d e it poss ib le to e x p e r i m e n t a l l y o b t a i n t he a b o v e 
i n fo rma t ion . 
E v e n t h o u g h less d a t a a r e ava i l ab l e c o n c e r n i n g s p e r m a t o p h o r e s of ixod ids , 
ex is t ing o b s e r v a t i o n s sugges t t h a t r a t h e r s imi l a r p rocesses o c c u r in b o t h 
famil ies . P e r h a p s t h e m a j o r m o r p h o l o g i c a l differences d i scovered t h u s far a r e 
t h a t t h e e n d o s p e r m a t o p h o r e is n o t b i lobed , b u t is s ingle in ixod ids , a n d 
c o n t a i n s t w o t u b e s p e r e n d o s p e r m a t o p h o r e (Ol ive r et al., 1974a) . S l ight 
differences in t h e s h a p e a n d size of e c t o s p e r m a t o p h o r e s exist a m o n g different 
Tick Reproduction: Sperm Development 263 
species of ixod ids a n d a r g a s i d s , a n d it is poss ib le t h a t de t a i l ed inves t iga t ions 
of s p e r m a t o p h o r e s m i g h t r evea l o t h e r differences. 
U p o n a t t a c h m e n t of t h e s p e r m a t o p h o r e to t h e female gen i t a l a p e r t u r e , t he 
e n d o s p e r m a t o p h o r e qu ick ly e v a g i n a t e s i n to t h e female t rac t ; whi le t h e ec to-
s p e r m a t o p h o r e r e m a i n s o u t s i d e , a n d t h e s p e r m a t i d s p a s s in to t he e n d o s p e r -
m a t o p h o r e . B o t h a c t i o n s r e q u i r e less t h a n t w o to t h r e e m i n u t e s . A p p a r e n t l y 
C O 2 is i nvo lved in t h e e v a g i n a t i o n a n d t ransfe r of s p e r m a t i d s to t he e n d o -
s p e r m a t o p h o r e s ( F e l d m a n - M u h s a m et al., 1973) . T h e e c t o s p e r m a t o p h o r e 
soon d r i e s a n d is lost . 
T h e s y m b i o t i c yeas t - l ike Adlerocystis m i c r o o r g a n i s m s found in t he sper -
m a t o p h o r e a r e t h o u g h t to b e p r e s e n t in all species of t icks ( F e l d m a n - M u h s a m , 
1974) . T h e y d e v e l o p in t h e pos t e r io r lobes of t he m a l e accessory gen i t a l g l a n d 
a n d , as a l r e a d y n o t e d , a r e t r ans fe r r ed t o g e t h e r w i t h t he s p e r m a t i d s to t h e 
s p e r m a t o p h o r e . T h e y a t t a c h to t h e s p e r m a t o z o a in s o m e species a n d d o n o t 
in o t h e r s . T h e y a t t a c h to s p e r m a t o z o a in n i n e of t h e 13 species of Ornithodoros 
t h a t h a v e b e e n s t u d i e d , b u t h a v e n o t b e e n seen to a t t a c h to s p e r m a t o z o a of 
a n y species of I x o d i d a e . T h e r e a p p e a r to b e severa l species of Adlerocystis a n d 
the i r d i s t r i b u t i o n in a w i d e va r i e ty of t ick species sugges t s a n a n c i e n t associ-
a t i on w i t h t icks . P r e s u m a b l y they a r e s y m b i o t i c , b u t the i r funct ion or role 
h a s n o t b e e n r e p o r t e d . 
8.4 . D Y N A M I C S O F A D U L T T E S T I C U L A R G R O W T H , 
S P E R M A T O G E N E S I S , S P E R M I O G E N E S I S , S P E R M TRANSFER, A N D 
C A P A C I T A T I O N 
8.4.1. Exogenous Factors 
T h e m a c r o - a n d m i c r o m o r p h o l o g i c a l s e q u e n c e of t e s t i cu la r d e v e l o p m e n t , 
s p e r m p r o d u c t i o n , a n d t ransfe r is r a t h e r well k n o w n , a l t h o u g h s o m e g a p s 
in o u r k n o w l e d g e h a v e b e e n n o t e d ea r l i e r in th is c h a p t e r a n d o t h e r s will b e 
p o i n t e d o u t be low. T h e phys io log ica l p rocesses invo lved in these even t s a r e 
poo r ly k n o w n . I t is c lea r t h a t a b lood m e a l is neces sa ry for e n l a r g e m e n t of 
tes tes a n d accesso ry g l a n d s a n d for s p e r m a t o g e n e s i s to o c c u r (Fig. 8 .2) . I n 
D. occidentalis ( M e t a s t r i a t a ) t he tes tes a n d accessory g l a n d s usua l ly r e a c h 
the i r m a x i m a l sizes after t h e t icks h a v e fed for a p p r o x i m a t e l y six d a y s (Ol ive r 
& B r i n t o n , 1972) . T h e s a m e app l i e s for D. variabilis ( H o m s h e r & S o n e n s h i n e , 
1972) a n d m o s t species of Dermacentor (Ol ive r , 1972) . I n fact, th is t i m i n g 
gene ra l ly app l i e s to m o s t species of M e t a s t r i a t a , excep t t h a t species of 
Boophilus m a t u r e t w o o r t h r e e d a y s ea r l i e r a n d s o m e Amblyomma species 
r e q u i r e t w o o r t h r e e d a y s l onge r ( t e m p e r a t u r e , hos t a n d o t h e r factors c a n 
a lso affect th is t i m i n g ) . T h e m i d d l e a n d d i s t a l p a r t s of t he tes tes ( a reas 3 -
6, F igs . 8.1 a n d 8.2) a r e l a rge r t h a n a r e a s 1 a n d 2 w h e n the tes tes a r e a t p e a k 
e n l a r g e m e n t . 
264 J. H. Oliver 
A m o n g t h e A r g a s i d a e a n d P r o s t r i a t a (Ixodes), t he t i m i n g of meios i s a n d 
spe rmiogenes i s is s imi l a r to t h a t in m o s t insec ts , i.e. o c c u r r i n g m a x i m a l l y 
d u r i n g t h e las t n y m p h a l s t a d i u m a n d y o u n g a d u l t pe r iod . I n these species 
it is t h e n y m p h a l b lood m e a l w h i c h s ignals t he b e g i n n i n g of meios is . A m o n g 
the M e t a s t r i a t a ( h a r d t icks excep t Ixodes), meios i s a n d s u b s e q u e n t deve l -
o p m e n t a l s t ages of s p e r m a t o z o a o c c u r on ly after t he a d u l t beg ins a b lood 
m e a l . T h e r e a r e a few excep t ions to th i s , b u t they a r e r a r e (Ol ive r , 1974) . 
R e q u i r e m e n t of a b lood m e a l for r e s u m p t i o n of ac t ive s p e r m a t o g e n e s i s in all 
t icks ra i ses t h e q u e s t i o n w h e t h e r t he p rocess is sw i t ched o n d i rec t ly o r 
ind i rec t ly b y feeding. O n e w o n d e r s w h e t h e r ac t iva t ion is d u e to s imp le 
n u t r i t i o n a l a d e q u a c y o r to a m o r e c o m p l e x a n d poss ib le h o r m o n a l s igna l . 
P r e s e n t i n fo rma t ion , a l t h o u g h ske tchy , sugges t s t h e l a t t e r a l t e r n a t i v e . Before 
d i s cus s ing s o m e of t h e ev idence for h o r m o n a l i n v o l v e m e n t , it s h o u l d b e n o t ed 
t h a t d e s p i t e t h e n a t u r e of t h e s t imul i c a u s i n g me io t i c d iv is ions a n d spe r -
miogenes i s , m a n y of t he s p e r m a t o c y t e s a n d s p e r m a t o g o n i a a r e n o t " s w i t c h e d 
o n " s u b s e q u e n t to feeding. M a n y of these cells in t he a n t e r i o r o n e - t h i r d to 
o n e - h a l f of t h e tes tes r e m a i n refract ive to d iv is ion a n d b e c o m e a c t i v a t e d a n d 
invo lved on ly after l a t e r feedings . T h e s e re la t ive ly i m m a t u r e g e r m i n a l cells 
a r e even found in those t icks w h i c h r e m a i n on the i r hos t s , w h e r e c o n t i n u e d 
feeding is poss ib le . A l t h o u g h food is ava i l ab l e , it is difficult to k n o w w h e t h e r 
these t icks c o n t i n u e to feed, a n d if t hey d o w h e t h e r cr i t ica l m i n i m u m a m o u n t s 
of b lood a r e i m b i b e d . D e t a i l e d inves t iga t ions of these p a r a m e t e r s , a l o n g w i t h 
the i r effects o n m a t i n g , n e e d to b e c o n d u c t e d on i n d i v i d u a l s p e c i m e n s . 
8.4.2. Endogenous Factors 
B e c a u s e of differences in t h e t i m e of me io t i c onse t a n d s p e r m a t i d e l o n g a t i o n 
b e t w e e n the A r g a s i d a e a n d P r o s t r i a t a , by c o m p a r i s o n to m o s t M e t a s t r i a t a , 
it is i m p o r t a n t to cons ide r ev idence for t he p r e s e n c e a n d role of h o r m o n e s 
in t he con t ro l of t ick s p e r m a t o g e n e s i s . T h e p r e c e d i n g b lood m e a l ( n y m p h a l 
a n d a d u l t , respec t ive ly , in t he t w o g r o u p i n g s ) m a y serve d i rec t ly o r ind i rec t ly 
to s t i m u l a t e t h e p r o d u c t i o n of necessa ry h o r m o n e s . N e u r o s e c r e t o r y cells a r e 
p r e s e n t in t he t ick s y n g a n g l i o n a n d c h a n g e s in the i r ac t iv i ty (Ioffe, 1964, 
1965; D h a n d a , 1967; O b e n c h a i n & Ol ive r , 1975) i n d i c a t e a poss ib le re la -
t i o n s h i p w i t h r e p r o d u c t i o n . R e c e n t ev idence ind ica t e s t he p r o b a b l e role of 
a n insect- l ike j u v e n i l e h o r m o n e ( J H ) , o r s imi l a r c o m p o u n d , in a d u l t female 
Ornithodoros parken a n d a r g u e s s t rong ly for a phys io log ica l role of J H in 
a c a r i n e r e p r o d u c t i o n ( P o u n d & Ol ive r , 1979). E v e n t h o u g h th is w o r k dea l s 
w i th oogenes i s a n d ov ipos i t ion , it s e e m s w o r t h c i t ing to d e m o n s t r a t e t h a t 
insect h o r m o n e s (or ve ry s imi l a r c o m p o u n d s ) func t ion in t ick r e p r o d u c t i o n . 
E c d y s t e r o n e is invo lved in t h e r e g u l a t i o n of g e r m i n a l cell d iv is ion in i m m a t u r e 
insec ts ( K a m b y s e l l i s & W i l l i a m s , 1971; D u m s e r & D a v e y , 1975) , b u t it 
gene ra l ly is n o t t h o u g h t to be p r e s e n t in a d u l t m a l e a r t h r o p o d s excep t for 
Tick Reproduction: Sperm Development 265 
s o m e t h a t c o n t i n u e to m o u l t ( C r u s t a c e a a n d t h y s a n u r a n insec t s ) . N e v e r t h e -
less, r e cen t p r e l i m i n a r y e x p e r i m e n t s ( D u m s e r & Ol ive r , u n p u b l i s h e d ) o n 
s p e r m a t o g e n e s i s in unfed D. variabilis sugges t t h a t in jected e c d y s t e r o n e s t i m u -
la tes syn thes i s of D N A in g e r m i n a l cells to a n e a r - m a x i m a l level c o m p a r e d 
to feeding m a l e s , a n d the r e s p o n s e of c u t i c u l a r t r a n s p l a n t s sugges t its p r e s e n c e 
in a d u l t m a l e s . A d d i t i o n a l e x p e r i m e n t s a r e n o w in p rog res s to o b v i a t e t he 
poss ib le w o u n d p h e n o m e n o n effect in t h e cu t ic le t r a n s p l a n t a t i o n e x p e r i m e n t 
a n d o t h e r a s says a r e b e i n g t e s ted . 
T h e o b s e r v e d d i s c o n t i n u o u s d e v e l o p m e n t of m a l e g e r m i n a l cells in t icks 
forces t h e q u e s t i o n of t h e d e t a i l e d n a t u r e of r a t e - r e g u l a t i o n . W h e r e a s mi to t i c 
a n d m e i o t i c b locks a p p e a r to o c c u r in t h e tes tes of unfed a d u l t M e t a s t r i a t a 
a n d unfed p e n u l t i m a t e n y m p h s of P r o s t r i a t a a n d A r g a s i d a e , q u a n t i t a t i v e 
a n d d e t a i l e d inves t iga t ions a r e l ack ing . A low r a t e of d iv i s ions , p a r t i c u l a r l y 
mi to t i c d iv i s ions , w o u l d go u n n o t i c e d un less m e t a p h a s e a c c u m u l a t i o n t ech-
n i q u e s ( such as co lch ic ine o r co l cemid t r e a t m e n t ) w e r e app l i ed . I t s eems 
ce r t a in , h o w e v e r , t h a t a cell d iv is ion r a t e - r e d u c t i o n m e c h a n i s m exis ts , if n o t 
a to ta l b lock o n t h e cell cycle . I t is u n k n o w n w h i c h p h a s e of t h e cell cycle 
t h e g e r m i n a l cells a r e in d u r i n g th is " b l o c k " . S ince m o s t cells s u s p e n d the i r 
d iv i s iona l ac t iv i ty p e r m a n e n t l y o r t e m p o r a r i l y in Gi ( D u m s e r , 1980; t h e 
p e r i o d of d i f ferent ia t ive cell func t ion fol lowing cytokines is) it is a s s u m e d t h a t 
t h e s p e r m a t o g o n i a l cells a r e in th is p h a s e . T h e s p e r m a t o c y t e s , h o w e v e r , 
a p p e a r to b e in t h e G 2 p h a s e w h i c h e x t e n d s " f rom t h e cessa t ion of D N A 
syn thes i s to t h e in i t i a t i on of c h r o m o s o m a l c o n d e n s a t i o n " (see D u m s e r , 1980, 
for d i scuss ion of cell cycle i n h i b i t i o n d u r i n g insec t g a m e t o g e n e s i s ) a n d exh ib i t 
a r e m a r k a b l e s y n c h r o n y . 
8.4.3. Capacitation Factors 
M o s t of t h e m o r p h o l o g i c a l a n d phys io log ica l c h a n g e s a s soc ia t ed w i t h t h e 
c a p a c i t a t i o n of t ick s p e r m o c c u r in t h e female gen i t a l t r ac t s , b u t in i t i a t ion 
of t h e p rocesses o c c u r s in s ide t h e s p e r m a t o p h o r e as it is b e i n g t r ans fe r r ed 
to t h e f emale . T h e r e is i n d i r e c t ev idence t h a t n o r m a l c a p a c i t a t i o n m a y r e q u i r e 
m o r e t h a n o n e s t i m u l u s a n d t h a t s e q u e n t i a l s t imu l i m a y be s u p p l i e d in t h e 
female (O l ive r , u n p u b l i s h e d ; S h e p h e r d , u n p u b l i s h e d ) . I t a p p e a r s t h a t 
in i t i a t ion of c a p a c i t a t i o n is d u e to m a l e accessory g l a n d sec re t ions w h i c h 
r e a c h t h e s p e r m a t i d s d u r i n g f o r m a t i o n of t he s p e r m a t o p h o r e . A d d i t i o n of 
w h o l e m a l e accessory g l a n d c o m p l e x e s , to s p e r m a t i d s r e m o v e d f rom the 
s e m i n a l vesicle of severa l a r g a s i d species a n d c u l t u r e d in vitro, s t i m u l a t e d t he 
o p e n i n g of o p e r c u l a of m a n y s p e r m a t i d s ( B o r u t & F e l d m a n - M u h s a m , 1976) . 
T h e o p e n i n g of o p e r c u l a is t h e first s ign of c a p a c i t a t i o n a n d a l lows con t i n -
u a t i o n of s p e r m a t i d m a t u r a t i o n . I f t h e s p e r m a t i d s a r e r e m o v e d from t h e fully 
fo rmed s p e r m a t o p h o r e , i n s t e a d of t h e s e m i n a l vesicle, a n d c u l t u r e d w i th 
accessory g l a n d in vitro, m a t u r a t i o n is fas ter a n d g r e a t e r n u m b e r s of spe r -
266 J. H. Oliver 
m a t i d s a r e invo lved . M a t u r a t i o n is fu r ther e n h a n c e d if the s p e r m a t i d s a r e 
col lected f rom t h e e n d o s p e r m a t o p h o r e after it h a s e v a g i n a t e d in to t he female 
r e p r o d