The Response of a Piscivore (Micropterus salmoides) to a Venomous Prey Species (Noturus gyrinus)

Adaptive significance of venom glands in the tadpole madtom Noturus gyrinus (Siluriformes: Ictaluridae)

“…Naive bass were able to learn almost immediately (within a 1h session) to avoid a naturally occurring noxious prey source, a finding that has been paralleled in a previous study (Wright, 2011) utilizing M. salmoides as a model predator species (but on a non-native, aposematically colored prey species). In previous studies of predation on catfishes, much larger, experienced bass were used and showed limited ability to discriminate between potentially harmful and less well-defended prey, in one case requiring approximately 20 sessions with each prey item to establish an individual preference between intact and spineless prey catfish (Bosher et al, 2006), and in another (Emmett and Cochran, 2010) never showing a preference at all. These findings suggest that an initial negative experience with a relatively large and dangerous prey species is a powerful reinforcement that may become somewhat diminished in larger experienced prey, adding a previously unconsidered but potentially powerful ontogenetic component to the dangerous prey hypothesis.…”

“…To date, the only studies examining predator response to venomous fish species have been performed on catfishes (Bosher et al, 2006;Emmett and Cochran, 2010;Wright, 2011). The venom glands of catfishes are associated with sharp, bony spines that are found along the anterior margin of the dorsal and pectoral fins.…”

“…The presence of fin spines effectively increases the cross-sectional circumference of the catfish, offering intuitive protection from gape-limited predators by making the catfish too large to consume, or at least significantly increasing handling times, making catfishes a less energetically favorable prey choice. This scenario has been formally described as the 'dangerous prey hypothesis' (Forbes, 1989), and has gained empirical support from studies of zooplankton (Barnhisel, 1991;Kolar and Wahl, 1998), as well as being the focus of the studies of catfishes (for which the hypothesis was originally formulated) mentioned above (Bosher et al, 2006;Emmett and Cochran, 2010). While the possible benefits to dangerous individuals and prey species are clear, the way in which natural predator sensitization and choice is affected by differing levels of prey 'dangerousness' has yet to be examined.…”

“…While the catfish studies mentioned above (Bosher et al, 2006;Emmett and Cochran, 2010) did offer limited support for the dangerous prey hypothesis, neither separated the possible deterrent effects (and adaptive benefit) of the venoms produced by these species from those of the delivery apparatus itself. Bosher and colleagues confirmed that the presence of spines increased the difficulty of ingestion of Ictalurus punctatus (channel catfish) by a gape-limited predator Micropterus salmoides (largemouth bass), also noting decreased aggression in experienced predators and increased survivability in catfishes with their spines intact, all of which were taken to indicate apparent fitness benefits conferred by the presence of these structures (Bosher et al, 2006).…”

“…Their study, while clearly demonstrating deterrent effects, utilized a catfish species (I. punctatus) that possesses venom glands associated with its fin spines (Birkhead, 1967;Birkhead, 1972;Halstead, 1988;Wright, 2009), and therefore may have confused deterrence due to the presence of venom as an adaptive benefit of the spines themselves [although it should be noted that the catfish in Bosher et al's experiments (Bosher et al, 2006) were taken from an aquaculture population that had been released from predation pressure for many generations, and Birkhead (Birkhead, 1972) also indicated that the venom of I. punctatus may be relatively innocuous]. Emmett and Cochran (Emmett and Cochran, 2010) documented a similar effect on handling time in the tadpole madtom (Noturus gyrinus), although their comparisons were made with minnows rather than catfishes with modified phenotypes, leaving open the question of the relative contribution of the spines and venom glands to higher handling time. Furthermore, the increased survivorship and predator sensitization observed by Bosher and colleagues was not found in Emmett and Cochran's study.…”