Temporally fluctuating selection on a personality trait in a wild rodent population

Lay Summary How is personality variation maintained in wild animal populations? To answer this question, we studied a population of Siberian chipmunks where some individuals tend to be bolder than others. When resources are scarce, bolder chipmunks reproduce better than shyer chipmunks, whereas the reverse is true when resources are plentiful. Because both types of personalities are advantageous in some circumstances, natural selection can maintain personality variation in this chipmunk population.Over the past decade, it has been recognized that in many animal species, individuals present consistent behavioral differences across time and/or contexts, thus defining personality traits. A general relationship seems to exist between personality and fitness in wild populations, which raises the question as to how variation in personality is maintained in the presence of selection. Fluctuating selection associated with a heterogeneous environment could contribute to maintaining personality variation, but its presence in wild populations has rarely been tested. In this 6-year study, we investigated the relationship between individual personality differences and 1 component of fitness, annual reproductive success (ARS), in a population of Siberian chipmunk Tamias sibiricus that experiences considerable annual variations in food availability. We estimated trappability-the propensity of chipmunks to enter traps-using capture-mark-recapture data, and we showed that it was repeatable over a 1-year interval. Genetic data were used to estimate parentage and thus ARS. Assuming that trappability is an indicator of boldness, we found that bolder chipmunks had higher ARS in years with low food availability, whereas lower ARS in years with high food availability. Temporally fluctuating selection therefore probably contributes to maintaining variation in boldness in the study population.