Abstract
Numerous studies have demonstrated that animals’ tolerance for risk when foraging can be affected by changes in metabolic state. Specifically, animals on a negative energy budget increase their preferences for risk, while animals on a positive energy budget are typically risk-averse. The malleability of these preferences may be evolutionarily advantageous, and important for maximizing chances of survival during brief periods of energetic stress. However, animals adapted to living in unpredictable conditions are unlikely to benefit from risk-seeking strategies, and instead are expected to reduce energetic demands while maintaining risk-aversion. We measured risk preferences in lemurs, a group of primates restricted to the island of Madagascar. Lemurs have evolved diverse anatomical and behavioral traits for survival in a harsh and unpredictable ecology, and these traits have been explained as forms of anatomical and behavioral risk reduction. We therefore predicted that lemurs would also be risk-averse in a behavioral task that offered subjects a choice between a small certain reward, and an uncertain but potentially large reward. In Experiment 1, the average rewards associated with the constant and variable options were equal and lemurs exhibited high levels of risk-aversion, replicating a phenomenon that has been demonstrated in dozens of taxa. In Experiment 2, we gradually increased the average value of the variable option relative to the constant option. Lemurs’ preferences tracked these changes and subjects became more risk-seeking as the risk premium increased. However, many subjects maintained high levels of risk-aversion even when the average payout of the variable option yielded double that of the constant option. These results are consistent with the notion that lemur cognition has evolved to minimize risk in an unpredictable island environment.
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Notes
One subject completed an extended version of this quantity discrimination that did not incorporate forced-choice trials.
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Acknowledgments
We thank the Duke Lemur Center and the many Duke University undergraduates who assisted with this research. We also thank Michael Platt, Benjamin Hayden, Sarah Heilbronner, Alexandra Rosati, and all members of the Brannon laboratory for their helpful discussion of these data. We thank Jeff Stevens and two anonymous reviewers for their helpful comments on previous versions of this manuscript. This work was supported by a National Science Foundation CAREER award (no. 0448250), National Institute of Child Health and Human Development Grant R01 (HD49912) and a John Merck Fund fellowship to E.M.B. This article is Duke Lemur Center publication # 1203.
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MacLean, E.L., Mandalaywala, T.M. & Brannon, E.M. Variance-sensitive choice in lemurs: constancy trumps quantity. Anim Cogn 15, 15–25 (2012). https://doi.org/10.1007/s10071-011-0425-2
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DOI: https://doi.org/10.1007/s10071-011-0425-2