Evolution 2017: It Doesn’t Pay to Be Risky When Predators Are About

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Oriol Lapiedra opened up the penultimate day of Evolution by discussing his results of a recent field experiment in the Bahamas. In this project, Lapiedra and colleagues evaluated how inter-individual variation in behavior – specifically risk-taking – influenced survival. To do this, the research team took advantage of a well-understood model system in evolutionary ecology: brown anoles (Anolis sagrei) on islands with and without anole-predators (curly-tailed lizards; Leiocephalus carinatus) in the Bahamas. Male and female brown anoles were collected and subjected to a behavioural trial which measured the amount of time it took for a lizard to leave a refuge after being exposed to a predator. These observations were used to quantify each individual’s propensity to take risks. For example, those individuals that left their refuge shortly after seeing a predator were interpreted as being more ‘risky’ than more conservative individuals. Following these trials, each lizard was x-rayed to assess morphology and individually tagged, before being released onto one of 4 predator-free islands or 4 predator-present islands, all of which were currently void of anoles.

Lapiedra et al. started with a priori hypotheses that overall survival would be lower on those islands with predators, and those that did survive would be individuals considered less risky. After waiting 4 months, the research team returned to the Bahamas to collect all lizards from each island and see which individuals had survived. The authors report that, as expected, overall survival was lower on islands with predators, and that there was a significant relationship between behaviour and survival such that high risk-taking individuals had much lower survival when predators were present. This suggests that under those biotic conditions, natural selection operates against those riskier phenotypes. On closer inspection, this relationship was largely driven by a strong relationship in females, with no significant relationship existing between risk-taking behavior and survival of males.

Lapiedra et al. then contrasted these results by independently assessing how morphology was related to survival. The authors found that both risk-taking behavior and morphology influenced survival, however – and, important to this study – the relative effect of an individual’s risk-taking behaviour was much more influential on survival.

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