Cap 10
23 pág.

Cap 10

DisciplinaZoologia3.771 materiais31.632 seguidores
Pré-visualização11 páginas
the \u201cexconjugants\u201d (Kaczanowski, Radzikowski, 
Malejczyk, & Polakowski, 1980). Nevertheless, 
interaction of cells requires participation of the sur-
face glycocalyx as in other ciliates (Golembiewska 
& Radzikowski, 1980). Kaczanowski et al. (1980) 
speculated that the adaptive advantage of intrac-
lonal conjugation or inbreeding to Chilodonella
steini is that it is a rare ciliate and has a special 
feeding preference for living diatoms. Inbreeding 
species generally are adapted to narrow ecological 
niches (Nyberg, 1974). 
 The genetics of mating types in suctorians has 
been most thoroughly investigated in only one 
series of studies. Colgin-Bukovsan (1976) demon-
strated that Tokoprhya lemnarum has two mating 
types , one being homozygous and the other hetero-
zygous or hemizygous. Mating occurs between cells 
of complementary mating type . Although it occurs 
under all nutritive conditions, cells that are slightly 
starved showed peak reactivity (Colgin-Bukovsan, 
1979). This suctorian shows a typical clonal life 
cycle with immaturity, maturity, and senescence 
stages. The long periods of immaturity and maturity 
(i.e., at least 800 fissions) characterize this species 
as a typical outbreeder (Colgin-Bukovsan, 1979). 
The life span of individual Tokophrya is quite vari-
able, ranging from several days to over 1 month. 
However, individual lifespans are dramatically 
reduced as clones become senescent (Karakashian 
et al., 1984). Senescence is also accompanied by 
morphological abnormalities arising from incom-
plete budding (Batisse, 1994b). With so few stud-
ies, clearly much remains to be learned about 
sexual reproduction in this class. 
 10.7 Other Features 
 Cyrtophorians , especially chilodonellids , are con-
spicuous species in the biofilms in wastewater 
treatment facilities . Their presence has been used 
to assess efficiency of operation of these facilities 
where these ciliates were indicative of good water 
purification conditions, both within plants (Martin-
Cereceda, Serrano, & Guinea, 2001a) and in the 
natural environment (Bick, 1972; Foissner, 1988a). 
They do show high sensitivities to heavy metals , such 
as cadmium and copper , and this may negatively 
impact their role in treatment facilities (Madoni, 
Davoli, Gorbi, & Vescovi, 1995). However, this 
high sensitivity to copper has been exploited to our 
advantage as a preventative measure to reduce their 
incidence as fish ectoparasites in aquaculture facil-
ities (Horwath, Lang, & Tamas, 1978). Treatments 
with dilute sodium chloride and malachite green 
and formalin can also be effective (Hoffman, 1978; 
Lom, 1995; Rowland, Mifsud, Nixon, & Boyd, 
2006). Finally, Henebry and Ridgeway (1979) sug-
gested that the high prevalence of ectosymbiotic 
Tokophrya on planktonic microcrustaceans might be 
used as an indicator of eutrophic water conditions. 
10.7 Other Features 231