No evidence of selection by predators on tadpole boldness

in Behaviour
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Animals typically exhibit adaptive behaviors that reduce their risk of predation. The term ‘boldness’ describes individual variation in the propensity to exhibit risk-reducing behavior and is the subject of much research attention. Predators should select against boldness, and this has been supported by empirical studies and behavioral ecology theory. We tested whether a standardized assay of three boldness-associated behaviors in wood frog (Lithobates sylvaticus) tadpoles predicted survival when faced with a predator. Tadpole behavior was assayed in an open field and then tadpoles were placed, in pairs, in an enclosure with a predator (newt or larval dragonfly). Survival did not depend on differences in measured boldness, and this result held when we accounted for interactions between different boldness behaviors and between behavior and size or predator identity. The absence of selection by predators against bolder tadpoles is counterintuitive and inconsistent with our understanding of the behavioral ecology of these animals. Two possible explanations are offered for this result. First, selection against boldness may be minimized by other phenotypic traits, such as escape ability. Alternatively, the potential lack of consistency between standardized boldness assays and natural encounters with predators may limit our capacity to study the evolution of boldness, cautioning against this approach. These results highlight the complexities of the relationships between behavioral traits and fitness and the challenges associated with their study.

No evidence of selection by predators on tadpole boldness

in Behaviour



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    Diagram of experimental setups for (a) assaying behavior in an open-field and (b) predator selection trials. Not to scale.

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    Distributions of behavioral scores for activity level in the (a) absence and (b) presence of predator cues, and (c) avoidance of predator cues. Activity levels represent the number of observations (out of 30) in which tadpoles were observed moving, while low numbers indicate avoidance of the predator cues.

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    Distribution of durations of predator selection trials used in the analyses. Trials were terminated when one tadpole was captured or eaten.

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    Relationships between survival of focal tadpoles in predation trials and relative differences in boldness-related behavior between the focal tadpole and the conspecific with which it was paired during a trial. Behaviors are (a) activity level in the presence of predator cues, (b) responsiveness (change in activity after adding predator cues) and (c) spatial avoidance of predator cues. Lines indicate 95% confidence intervals of predicted survival probability using logistic regressions with a single independent variable.


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