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in lorica dimensions 
of tintinnids , correlated with the season (e.g., Gold 
& Morales, 1975) and water temperature (e.g., 
Boltovsky et al., 1995). Variation in community 
 lorica oral diameter has been correlated with the 
average size of available prey, suggesting some 
kind of trophic specialization of tintinnids on their 
prey (Middlebrook, Emerson, Roff, & Lynn, 1987; 
Verity). However, Dolan (2000) concluded that 
 trophic specialization , at least, is not the domi-
nant factor determining tintinnid diversity in the 
 Mediterranean Sea . Tintinnid diversity has been 
used to indicate different water masses in the North 
Pacific Ocean (Kato & Taniguchi, 1993). 
 Spirotrichs are considered to be upstream filter 
feeders that “select” particles primarily on the 
basis of the structural nature of the oral apparatus 
(Fenchel, 1980a, 1980b; Jonsson, 1986; Wilks & 
Sleigh, 1998). These theoretical predictions using 
various beads have been corroborated by feeding 
experiments on natural prey, which show a positive 
relation between size of the ciliate and the aver-
age size of the prey that it can efficiently ingest 
(Bernard & Rassoulzadegan, 1990; Kamiyama 
& Arima, 2001). Benthic or substrate-oriented 
 spirotrichs , like the hypotrich Euplotes and some 
substrate-oriented choreotrichs like Strobilidium , 
can likely survive on bacterivory in the wild 
(Lawrence & Snyder, 1998; Sime-Ngando, Demers, 
& Juniper, 1999). It is unlikely that pelagic oli-
gotrichs and choreotrichs will achieve maximal 
 growth rates by bacterivory since bacterial abun-
dances are often less than the critical concentration 
of 10 6 ml -1 necessary to support growth (Bernard & 
Rassoulzadegan; Fenchel, 1980c; Macek, Šimek, 
Pernthaler, Vyhnálek, & Psenner, 1996; Šimek, 
Macek, Pernthaler, Straškrabová, & Psenner, 
1996). Nevertheless, behavioral modification of 
the swimming pattern may enable some oligo-
trichs to exploit food patches of bacteria exceeding 
these minimum abundances (Fenchel & Jonsson, 
1988) and enable some tintinnids to remain in 
patches of dinoflagellate prey (Buskey & Stoecker, 
1989). Furthermore, chemosensory responses to 
prey particles may enable truly selective feed-
ing by some tintinnids and oligotrichs (Burkill, 
Mantoura, Llewellyn, & Owens, 1987; Stoecker, 
1988; Stoecker, Gallager, Langdon, & Davis, 1995; 
Taniguchi & Takeda, 1988; Verity, 1991). Selective 
food capture may also be enhanced by a lectin-type 
binding of prey to food-capturing cell membranes 
(Wilks & Sleigh, 2004). 
 The puzzle of average bacterial abundances being
too low to maintain the growth of planktonic spiro-
trichs has had at least three solutions. First, these 
ciliates may be omnivorous in nature. Second, 
they may browse on particles where bacterial 
abundances are higher. Third, these ciliates may 
have behavioral mechanisms that maintain them 
in small-scale patches (Tiselius, Jonsson, & Verity, 
1993; Montagnes, 1996). Patches of oligotrichs and 
 choreotrichs ranged from <13 m to <77 m in size in 
a tropical coast lagoon under non-turbulent condi-
tions (Bulit, Díaz-Avalos, Signoret, & Montagnes., 
2003). Turbulence will destroy this patch structure , 
and it may also reduce the feeding efficiency of 
these ciliates, by changing either the rate or 
pattern of their locomotion (Dolan, Sall, Metcalfe, 
& Gasser, 2003). 
 In recent years there has been considerable inter-
est in the feeding biology of oligotrichs and chore-
otrichs (Sanders & Wickham, 1993), particularly 
as they are dominant grazers in planktonic food 
webs. They can consume significant proportions 
of the primary production , up to 25% (Capriulo 
& Carpenter, 1983; Verity, 1985) and over 30% of 
the bacterial standing stock (Lavrentyev, McCarthy, 
Klarer, Jochem, & Gardner 2004; Rassoulzadegan, 
Laval-Peuto, & Sheldon, 1988; Sime-Ngando 
et al., 1999). Furthermore, their excretion of phos-
phorus and ammonia may fuel over 15% of the 
net primary production (Dolan, 1997; Stoecker, 
1984; Taylor, 1984; Verity). Field and laboratory 
studies have demonstrated that tintinnids con-
sume cyanobacteria , picoflagellates , chlorophytes , 
 prymnesiophytes , dinoflagellates , diatoms , euglen-
ophytes , prasinophytes , and raphidophytes (Aelion 
& Chisholm, 1985; Bernard & Rassoulzadegan, 
1993; Christaki, Jacquet, Dolan, Vaulot, & 
Rassoulzadegan, 1999; Dolan, 1991; Kamiyama 
& Arima, 2001; Rassoulzadegan & Etienne, 
1981; Stoecker, 1984; Verity; Verity & Villareal, 
1986). Toxic dinoflagellates , like Alexandrium , 
Gyrodinium , and Pfiesteria may increase tintinnid 
and oligotrich mortality, possibly due to secretion 
or ingestion of the toxins (Hansen, 1995; Hansen, 
Cembella, & Moestrup, 1992; Stoecker, Parrow, 
Burkholder, & Glasgow, 2002) as do thread-bear-
ing diatoms (Verity & Villareal). However, the 
toxic effect is at least species-specific as some 
 tintinnids and oligotrichs thrive on these toxic 
 dinoflagellates (Kamiyama, Suzuki, & Okumura, 
2006; Stoecker et al., 2002). Aloricate choreot-
richs , such as Strobilidium , Lohmanniella and 
Strombidinopsis , consume bacteria , prymnesio-
phytes , cryptophytes , dinoflagellates , chlorophytes , 
and prasinophytes (Burkill et al., 1987; Christaki, 
Dolan, Pelegri, & Rassoulzadegan, 1998; Jeong 
et al., 2004; Jonsson, 1986; Kamiyama & Matsuyama,
2005; Montagnes, 1996, 1999; Sime-Ngando et al., 
1999). Diatoms , kinetoplastids , and eustigmato-
phytes can be added to this list for aloricate oli-
gotrichs , such as Strombidium species (Bernard 
& Rassoulzadegan, 1990; Burkill et al., 1987; 
Christaki et al., 1998, 1999; Fenchel & Jonsson, 
1988; Jonsson; Montagnes, 1996; Ohman & 
Snyder, 1991). Tintinnids and oligotrichs generally 
consume food particles that are less than 20 µm in 
diameter (Rassoulzadegan, 1982; Rassoulzadegan 
et al., 1988). 
 Stichotrichs , like Halteria , Oxytricha , and Stylony-
chia , are probably omnivorous. They have been 
shown to feed on bacteria , diatoms , dinoflag-
ellates , chrysophytes , cryptophytes , and chloro-
phytes (Balczon & Pratt, 1996; Kaul & Sapra, 
1983; Skogstad, Granskog, & Klaveness, 1987). 
Oxytricha and Onychodromus can feed on other 
ciliates, including members of their own spe-
cies for which they may undergo a develop-
mental polymorphism to become cannibal giants 
(Foissner, Schlegel, & Prescott, 1987; Riggio, 
Ricci, Banchetti, & Seyfert, 1987; Wicklow, 1988). 
Euplotes species are the only hypotrichs that have 
recently been examined for feeding preferences . 
They can be omnivorous, ingesting bodonids and 
a variety of heterotrophic flagellates , in addition to 
those prey mentioned for stichotrichs , and includ-
ing other ciliates (Dolan & Coats, 1991a, 1991b; 
Gast & Horstmann, 1983; Lawrence & Snyder, 
1998; Premke & Arndt, 2000; Wilks & Sleigh,
1998). Dini and Nyberg (1999) have convincingly 
demonstrated that ecologically important differ-
ences in feeding responses among nine reproduc-
tively isolated groups of Euplotes are genetically
determined. They concluded that morphospecies 
inadequately represent the ecological diversity of 
 In addition to heterotrophy, some spirotrichs 
exhibit varying degrees of mixotrophy , either by 
sequestering chloroplasts from their prey or by 
harboring symbiotic Chlorella species (Sanders, 
1991). Retention of prey chloroplasts is common 
in oligotrichs , with a significant fraction of the 
species exhibiting this trait in some oligotrophic 
lakes (Macek, Callieri, Simek, & Vazquez, 2006), 
in the Mediterranean (Bernard & Rassoulzadegan, 
1994; Dolan & Pérez, 2000; Laval-Peuto & 
Rassoulzadegan, 1988), and in temperate oceans 
(Stoecker, Taniguchi, & Michaels, 1989). The 
 chloroplasts appear to originate from a variety 
of groups of chromophytic protists, many of the 
groups noted above that can serve as