Cap 7
33 pág.

Cap 7


DisciplinaZoologia3.832 materiais32.548 seguidores
Pré-visualização17 páginas
distribution in turbulent 
water columns (Jonsson, 1989). Negative geotaxis 
may also enable these ciliates to move towards 
light, whose presence may be correlated with 
more abundant prey. Light may also enhance the 
digestion and growth rates of tintinnids , possibly 
by photooxidative breakdown of ingested food 
(Strom, 2001). In more stable aquatic habitats, 
where oxyclines become established, spirotrichs 
may distribute vertically both in the water column 
(Bernard & Fenchel, 1994; Fenchel et al., 1995) 
and in benthic microbial mats (Fenchel & Bernard, 
1996), seeking a preferred oxygen pressure. The 
 chemosensory behavior of benthic forms, such as 
Euplotes , has been interpreted as a form of the 
classical random walk , which enables populations 
to accumulate very quickly at point sources of 
attractants (Fenchel, 2004). 
 A behaviour unique to the tintinnid choreotrichs 
is the construction of the lorica in which the cell 
resides and which may have some selective advan-
tage for avoiding predation (Capriulo, Gold, & 
Okubo, 1982). The progeny of Favella constructs 
its hyaline lorica within 10 min of leaving the 
parental lorica (Laval-Peuto, 1977), while species 
with agglutinated loricae , like Tintinnopsis species, 
may take several hours to complete lorica construc-
tion (Gold, 1979). The materials agglutinated to the 
lorica secretory material may vary with the envi-
ronment in which the tintinnid is found and with 
the season (Bernatzky, Foissner, & Schubert, 1981; 
Gold, 1979). However, in field samples, there also 
appears to be some selectivity, both with respect 
to the size of the particles on the lorica relative to 
those in the environment and with respect to the 
quality of the particles (Gold & Morales, 1976; 
Rassoulzadegan, 1980). The basis of this selectiv-
ity is not understood, and cannot yet be duplicated 
in the laboratory (Gold, 1979). 
 Spirotrichs , like other ciliates, survive from days 
to weeks without food (Jackson & Berger, 1985b; 
Montagnes, 1996). If they are able to encyst , sur-
vival can be extended to years, and this is espe-
cially true of species found in soils and on mosses 
(Corliss & Esser, 1974). Both freshwater and 
marine choreo trichs and oligotrichs encyst ; tintin-
nids form their cyst within the lorica (Jonsson, 
1994; Müller & Wunsch, 1999; Paranjape, 1980; 
Reid & John, 1978). Encystment has been cor-
related with tidal rhythms (Fauré-Fremiet, 1948b; 
Jonsson, 1994), and reductions in prey density or 
increases in predator density (Müller & Wunsch, 
1999; Reid, 1987). Excystment may be stimulated 
by changes in temperature (Kim & Taniguchi, 
1995; Kim, Suzuki, & Taniguchi, 2002; Müller, 
2002; Paranjape), light (Kim & Taniguchi, 1995), 
algal exudates (Kamiyama, 1994), and soil extracts 
(Müller, Foissner, & Weisse, 2006). Cysts of plank-
tonic species settle through the water column 
during the productive season. These cysts may 
ultimately reach the sediments from which they are 
resuspended by turbulent events and turn over cur-
rents (Kim & Taniguchi, 1997; Müller & Wunsch, 
1999; Reid, 1987). Excystment may be facilitated 
by an expanding excystment vacuole (Rawlinson 
& Gates, 1985), often through a specialized region 
of the cyst wall, such as the papula in oligotrich 
and choreotrich cysts (Kim & Taniguchi, 1995; 
Kim et al., 2002; Müller & Wunsch, 1999; Reid, 
1987). The \u201ccystment cycle\u201d can be complex, vary 
seasonally, and is likely maintained in all cases by 
 natural selection of correctly phased individuals. 
This may be especially important for the mainte-
nance of the unusual tidal rhymicity of the cyst-
ment cycle in the tide-pool oligotrich Strombidium 
7.2 Life History and Ecology 155
156 7. Subphylum 2. INTRAMACRONUCLEATA: Class 1. SPIROTRICHEA
 oculatum (Jonsson; Montagnes, Wilson, Brooks, 
Lowe, & Campey, 2002).
 Oligotrich and tintinnid cysts are flask-shaped 
with a neck-like extension, which is sealed by 
a cap through which the ciliate exits the cyst 
(Jonsson, 1994; Kim et al., 2002; Müller and 
Wunsch, 1999; Reid, 1987; Reid & John, 1978). 
This characteristic cyst shape has lead Reid and 
John (1981) to suggest that tintinnids might be the 
enigmatic chitinozoa found in Proterozoic sedi-
ments, dating the fossil record of ciliates to well 
over 700 million years ago. Further, Reid and John 
(1983) argued that cyst morphology may be phy-
logenetically informative, noting that flask-shaped 
cysts are found in members of the now \u201cbasal\u201d 
Classes HETEROTRICHEA , SPIROTRICHEA , 
and ARMOPHOREA . 
 Hypotrichs and stichotrichs have been the main 
focus of ultrastructural descriptions of encystment
in spirotrichs . Walker and Maugel (1980) noted 
that resting cysts of hypotrichs and stichotrichs 
showed significant differences. Hypotrich cysts, 
termed non-kinetosome resorbing (NKR), are now 
characterized as retaining cilia and kinetosomes 
in the encysted cell (Foissner & Foissner, 1987; 
Walker & Maugel, 1980). Stichotrich cysts, termed 
 kinetosome-resorbing (KR), are now characterized 
as dedifferentiating cilia and kinetosomes in the 
mature cyst (Foissner & Foissner, 1987; Grimes, 
1973; Matsusaka, Nakamura, & Nagata, 1984; 
Walker & Maugel, 1980), a feature shared by at 
least the halteriid Meseres (Foissner, Müller, & 
Weisse, 2005a). Other studies have generally con-
firmed these features, indicating also that the NKR 
cyst wall typically has only three layers (Greco, 
Bussers, van Daele, & Goffinet, 1990; Walker & 
Maugel) while the KR cyst wall typically has four 
layers (Calvo & De Miguel, 1995/1996; Delgado, 
Calvo, & Torres, 1987; Gutiérrez, Torres, & Perez-
Silva, 1983; Walker, Maugel, & Goode, 1980). 
 Extrusomes provide the materials for the cyst wall 
components (Grim & Monganaro, 1985; Walker & 
Maugel, 1980; Walker et al., 1980). Cyst wall con-
situents include glycoproteins (Calvo & De Miguel, 
1995/1996; Matsusaka & Hongo, 1984) and chitin 
(Foissner et al., 2005a; Greco et al., 1990; Rosati, 
Verni, & Ricci, 1984). In the highly unusual sti-
chotrich Meseres , the surface of the resting cyst is 
coated by scale-like structures, called lepidosomes 
(Foissner, 2005b; Foissner et al., 2005a). 
 7.3 Somatic Structures 
 The great diversity of body shapes in spirotrichs is 
correlated both with the taxonomic diversity of the 
group and its seven subclasses and the tremendous 
diversity of habitats in which these groups are dis-
tributed. As with the heterotrichs (see Chapter 6 ), 
body shape generally correlates with benthic 
or planktonic habitat. Benthic forms, such as 
Phacodinium , hypotrichs , and stichotrichs , are typ-
ically dorsoventrally flattened and in most species 
dorsoventrally differentiated, with cilia forming 
large compound cirri scattered on the ventral sur-
face and widely spaced stiff bristles or dikinetids 
with more flexible cilia on the dorsal surface. 
Planktonic forms range from small spheroids to 
larger cone-shaped forms (Figs. 7.2\u20137.4). 
 The cell surface typically does not exhibit a con-
spicuous glycocalyx . In tintinnids and some stichot-
richs , at least, it is replaced by the perilemma , not 
a true cell membrane, which covers even the cilia 
(Foissner & Pichler, 2006; Laval-Peuto, 1975). The 
plasma membrane is typically not underlain by a 
well-developed layer of cortical alveoli . The hypot-
richs are an exception with their conspicuous silver-
line system (Valbonesi & Luporini, 1995; Wise,
1965), which reflects the extensive development of 
cortical alveoli containing novel \u201csupport\u201d protein 
called plateins (Böhm & Hausmann, 1981;Hausmann
& Kaiser, 1979; Kloetzel, 1991; Kloetzel, Hill, & 
Kosaka, 1992; Kloetzel et al., 2003). Cell form is 
likely maintained by cortical microtubules, either 
arising from kinetids or independently subtending 
a very fine epiplasmic layer (e.g., Fleury, 1991b; 
Grain,