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conjugation or selfing (Akada, 
1986; Kosaka, 1990; Machelon, 1986). This has 
the advantage of resetting the life cycle clock, but 
the disadvantage that it can only be a short term 
strategy as over several generations it leads to 
lethal inbreeding depression (Kosaka, 1982). 
 Another route to resetting the life cycle clock 
is autogamy , a process of self-fertilization under-
taken by a single cell. Some autogamous strains 
of Euplotes species are determined by a dominant 
allele at a single locus (Heckmann & Frankel, 
1968; Dini & Luporini, 1980). Although autogamy 
is an extreme form of inbreeding , heterozygosity 
is maintained for longer periods in these species 
because the meiotic products of non-sister nuclei 
form the zygotic nucleus or synkaryon (Dini et al.,
1999; Luporini & Dini, 1977). Nevertheless, auto-
gamous strains are less tolerant to stresses, for 
example, mercury toxicity, than non-autogamous or 
 outbreeding strains (Dini, 1981). Further, changes 
in body proportions of autogamous strains relative 
to non-autogamous strains may inhibit effective 
cell pairing (Gates, 1990). 
 Sibling or cryptic species are found among 
 spirotrichs (Valbonesi, Ortenzi, & Luporini, 1988; 
Valbonesi, Ortenzi, & Luporini, 1992) as they are 
among other groups of ciliates (Nanney & McCoy, 
1976; Sonneborn, 1957, 1975). Most genetic work 
on the species problem in spirotrichs has focused 
on Euplotes species where there are competing 
conclusions on whether one or another “species” 
of Euplotes is reproductively isolated. For exam-
ple, using mating tests , Valbonesi et al. (1988, 
1992) claimed that Euplotes crassus is not a sib-
ling species complex , but it is a species separate 
from Euplotes vannus . Caprette and Gates (1994) 
claimed that these two “species” were not repro-
ductively isolated. Nevertheless, they cautioned 
that until the extent of interbreeding is known in 
nature, results of laboratory experiments must be 
interpreted with caution. 
 Valbonesi et al. (1988) have also used characteristics 
of isoenzymes to distinguish E . crassus , E . vannus , and 
Euplotes minuta , all of which demonstrated discretely 
different patterns in five isoenzymes , differences that 
are as great as those used to separate species of the 
Tetrahymena and Paramecium sibling species com-
plexes (Nanney & McCoy, 1976; Sonneborn, 1975). 
 Isoenzyme differences clearly distinguish morpho-
logically different species of the hypotrich Euplotes
(Machelon & Demar, 1984; Schlegel, Kramer, & 
Hahn, 1988) and the stichotrich Stylonychia , even 
when isolated from separate continents (Ammermann 
et al., 1989). Schmidt, Ammermann, Schlegel, & 
Bernhard (2006a) have identified a single nucleotide 
difference in the SSUrRNA genes of Stylonychia 
lemnae from Eurasia and North America . This ten-
tatively suggests a biogeography , a conclusion that 
was also tentatively reached in a study of strains of 
the soil stichotrich Gonostomum affine from Europe , 
 Africa , and Asia (Foissner, Stoeck, Schmidt, & 
Berger, 2001). 
 More recently, random amplified polymorphic 
DNA or RAPD fingerprinting has been used to 
demonstrate genetic diversity within Euplotes 
aediculatus (Kusch et al., 2000) and Euplotes octo-
carinatus (Mollenbeck, 1999) and also between
 morphospecies of Euplotes (Chen, Song, & Warren, 
2000). The intraspecific analyses concluded that 
there was no geographic subdivision of species 
despite continental separation of some strains, con-
firming the results of isoenzyme studies on stichot-
richs (Ammermann et al., 1989). This indicates 
that conjugation must be frequent enough across 
intercontinental geographic distances to essentially 
maintain a single gene pool, even though it is 
rarely observed in natural populations (Lucchesi 
& Santangelo, 2004). The rarity of conjugation in 
Euplotes was supported by RAPD analysis of a 
population of Euplotes daidaleos in Germany : the 
 genetic diversity was very low, indicating a clonal 
population structure rarely undergoing conjugation 
(Kusch & Heckmann, 1996). 
 7.7 Other Features 
 As with heterotrichs (see Chapter 6 ), the widespread 
distribution of hypotrichs and stichotrichs coupled 
with the ease of culturing them has led to their use 
in monitoring environmental quality. Hypotrichs 
and stichotrichs can be found in extremely acidic 
environments (Packroff & Wöfl, 2000) although 
some oligotrichs may be quite sensitive (Pedersen 
& Hansen, 2003). They are also very abundant in 
the biofilms of water treatment facilities (Curds, 
1969; Martin-Cereceda, Serrano, & Guinea, 2001a; 
Perez-Uz et al., 1998), presumably playing a role 
by feeding upon bacteria in the biofilms (Lawrence 
& Snyder, 1998). Hypotrichs and stichotrichs have 
been used to bioassay copper, nickel, cadmium, 
and other organics (Albergoni et al., 2000; Madoni, 
2000; Piccinni, Irato, Cavallini, & Ammermann, 
1992; Stebbing, Soria, Burt, & Cleary, 1990). They 
showed broad variations in sensitivities to different 
toxicants: Euplotes species can be highly tolerant of 
nickel (Madoni, 2000) or highly sensitive to nickel 
(Madoni & Romeo, 2006) and to copper (Albergoni 
et al.); Halteria can be highly sensitive to cadmium 
(Madoni & Romeo). Resistance to heavy metals 
may be conferred on stichotrichs by the presence of 
unique metal-binding proteins, very different from 
 metallothioneins and chelatins isolated from other 
protozoa (Piccinni et al., 1992). 
 As noted above (see Life History ), spirotrichs 
can be important predators in microbial food webs , 
ingesting a variety of prey organisms from bac-
teria to other ciliates and metazoa . This can have 
important consequences for humans. For example, 
Tso and Taghon (1999) demonstrated that Euplotes
did not show selectivity for contaminant-degrad-
ing bacteria , which may have important implica-
tions for bioremediation initiatives . On the other 
hand, feeding by hypotrichs and stichotrichs might 
remove Cryptospori dium oocysts from wastewa-
ters , helping to decrease the incidence of water-
borne outbreaks of cryptosporidiosis (Stott, May, 
Matsushita, & Warren, 2001). 
7.7 Other Features 173