Predation by invertebrate predators on the colonial rotifer Sinantherina socialis

Abstract

Abstract. Colonies of the freshwater colonial rotifer Sinantherina socialis (Monogononta, Flosculariidae) have been shown to be unpalatable to a variety of small‐mouthed, zooplanktivorous fishes. To test whether invertebrate predators ingest the rotifer S. socialis, we conducted two types of experiments: (1) Microcosm experiments—in separate experiments, four invertebrate predators (i.e., dragonfly nymphs, damselfly nymphs, notonectids, and Hydra) were offered prey either singly or in combination. Prey were comprised of S. socialis; Epiphanes senta, a solitary, free‐swimming rotifer; and Daphnia magna, a microcrustacean. In each experiment, the percent of prey surviving after 12, 18, and 24 h was recorded. (2) Paired‐feeding experiments—in separate experiments, predators were offered prey in a pairwise fashion, in which members of D. magna were alternated with a rotifer, either S. socialis or E. senta. The results of the microcosm experiments showed that, after 24 h, 60–100% prey items of S. socialis survived the predators, but significantly fewer individuals of E. senta (6–89%) and D. magna (<25%) survived. When offered rotifers and individuals of D. magna simultaneously, predators tested consistently consumed more specimens of Daphnia. However, predators significantly reduced percent survival in E. senta but not in S. socialis. Predators, given a choice between the two rotifer species, all consumed significantly more specimens of E. senta than S. socialis after 24 h. In the paired‐feeding experiments, three of the four predators captured members of S. socialis, but these colonies were frequently released rather than ingested, although in some cases colony structure was seriously disrupted. Our results suggest that the unpalatable nature of members of S. socialis to certain fishes extends to several invertebrate predators, but the nature of the putative factor(s) responsible for this remains unknown.

Neuromuscular organization of the freshwater colonial rotifer, Sinantherina socialis, and its implications for understanding the evolution of coloniality in Rotifera

“…Behavioral defenses are generally tied to speciWc morphological features that enhance locomotion (e.g., paddles and arms that function in saltation in species of Polyarthra and Hexarthra; Gilbert 1987;Hochberg and Ablak Gurbuz 2008) or ward oV predators (e.g., setal abduction in species of Filinia; Williamson 1983;Hochberg and Ablak Gurbuz 2007). Some species may avoid predation by building tubes of cemented pellets (Fontaneto et al 2003) or jelly (reviewed in Wallace et al 2006), by secreting defensive compounds (Felix et al 1995;Walsh et al 2006), and/or forming colonies (Wallace 1987). Colony formation is generally uncommon among rotifers, but may have evolved as a form of defense against gape-limited predators (see Wallace 1987 for a review of coloniality in Rotifera).…”

Inducible defenses and rotifer food chain dynamics

“…Williamson's review of invertebrate predation on rotifers was updated by Brandl (2005) who discussed various factors determining predation rates, as well as the impact of freshwater copepods on rotifers. These and other works demonstrate numerous examples of defenses in rotifers including the following: (1) changes in morphology (e.g., spine development or elongation; reviewed in Gilbert, 1999); (2) behavioral response (e.g., vertical migration or escape reactions; Gilbert & Kirk, 1988); (3) life history changes (e.g., high maximum growth rate; Walz, 1995); and (4) chemical deterrents (Felix et al, 1995;Walsh et al, 2006). One of the first reports of inducible defenses in rotifers was the induction of spine formation in B. calyciflorus by Asplanchna (Gilbert, 1966;Gilbert, 1967).…”

Effects of predation by Hydra (Cnidaria) on cladocerans (Crustacea: Cladocera)

“…There are possibly several factors responsible for this. For example, prey species may have different strategies to avoid predation; these include changes in morphology, behavior, and life history variables (macháček, 1991;Walsh et al, 2006). For the prey used in this study, some strategies against predation, such as change in size and in various life history variables are already documented (Dodson, 1974;Burks et al, 2000).…”