Hellbender Prey Preference Is Superseded by Native and Nonnative Prey Behavior
Long-term interactions often shape predator–prey relationships in the form of a co-evolutionary “arms race.” The arrival of nonnative species may disrupt these relationships by introducing novel behaviors that shift interactions in favor of one of the participants. Here we investigated the response of an imperiled native predator, the Eastern Hellbender (Cryptobranchus alleganiensis), to nonnative and native crayfish prey. Crayfish constitute an important prey item for hellbenders, and in the northern portion of its range where this research was conducted, the nonnative Rusty Crayfish (Orconectes rusticus) has become the dominant crayfish. The objective of this study was to determine prey choice and feeding success of hellbenders presented with native (Allegheny Crayfish; Orconectes obscurus) and nonnative (Rusty Crayfish) crayfish prey. We tested hellbender chemoreception in discriminating between the native and nonnative prey, analyzed behavioral interactions between hellbenders and crayfish during video-recorded trials, and assessed hellbender selectivity of crayfish during overnight feeding trials. Hellbenders were able to discriminate crayfish odor from controls, showed a preference for the scent of native crayfish over nonnative crayfish, and were more likely to strike at native crayfish than at nonnative crayfish; however, more nonnative crayfish were consumed during overnight feeding trials. This discrepancy apparently resulted from differences in avoidance behavior between the prey species; native crayfish engaged more in predator-avoidance tail-flip responses and climbing retreats than the nonnatives, who tended to “stand their ground.” Accordingly, during biotic invasions, food preferences of native predators may be superseded by antipredator prey behavior.Abstract
Rendering of the test arena used for Experiments 1–3 (not to scale). For Experiment 1, each of the three lanes received a randomly assigned treatment (control, parsley, fish analog). During Experiment 2, the center lane was blocked, and the outer lanes received water conditioned with native (Orconectes obscurus) or nonnative crayfish (O. rusticus). In Experiment 3, all three lanes were blocked off, restricting interactions to the downstream end of the arena. Blue arrows indicate the direction of water flow; water entered the arena at the upstream end exited the arena via openings in the downstream wall (not shown).
(A) Mean ± SE number of visits by treatment lane per trial (Experiment 1). Hellbenders made significantly more visits to lanes conditioned with fish analog compared to control and parsley-conditioned lanes, which were visited with similar frequency. (B) Mean ± SE proportion of aborted visits by treatment lane per trial (Experiment 1). Hellbenders were significantly less likely to abort visits to lanes conditioned with fish analog compared to control and parsley-conditioned lanes, which were aborted with similar frequency. Different letters above error bars represent significantly different means according to post hoc analysis (Tukey's HSD: P < 0.05).
(A) Mean ± SE number of lane visits by treatment per trial (Experiment 2). (B) Mean ± SE proportion of aborted lane visits by treatment per trial (Experiment 2).
Interaction plot displaying mean ± SE number of crayfish tail-flips by species per trial, as a function of hellbender snout contact (Experiment 3). Native crayfish significantly increased tail-flips in response to snout contact by hellbenders, whereas nonnative crayfish tail-flips remained equally low regardless of hellbender snout contact (P < 0.001).
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