Inter- and Intra-individual Variation in Predator-related Behavioral Plasticity Expressed by Female Green Swordtails (<i>Xiphophorus hellerii</i>)

Phenotypic plasticity is the ability of a genotype to express different phenotypes, under different environmental conditions. Behavioral plasticity is a type of phenotypic plasticity in which a change in phenotype can rapidly occur. Though often studied at the level of the population, behavioral plasticity studies at the level of the individual could provide insight into how plasticity evolves and is maintained in a population. Further, individual differences in phenotypes (such as body size) may predict differences in the degree of plasticity expressed by individuals within a population. We used female green swordtails (Xiphophorus hellerii) to test the effects of body size at testing and age at maturation on the expression of predator-related behavioral plasticity in an intrasexual social context (i.e., two females). We found that all females, regardless of body size at testing or age at maturation, expressed predator-related plasticity in spatial positioning. Further, latermaturing females darted more from the monitor displaying a film stimulus than earliermaturing females, whether or not the filmed sequence included a predator. Finally, both body size at testing and age at maturation affected the degree of predator-related plasticity in the expression of an agonistic behavior: transverse display. In the presence of a predator, small, early-maturing females decreased the time spent transverse displaying, whereas small, late-maturing females increased the time spent transverse displaying. Large females expressed the opposite pattern. In the presence of a predator, large, early2 maturing females increased the time spent transverse displaying, whereas large, latematuring females decreased the time spent transverse displaying. This study shows that both body size at testing and age at maturation affect plasticity in at least one behavior in female green swordtails. In general, our results suggest that the degree and direction of plasticity expressed by an individual may be affected by complex interactions of its other traits . Thus, simple predictions concerning the effects of environment on plasticity expression may be misleading, and future studies should consider multiple factors when investigating individual differences in behavioral plasticity. INTRODUCTION The ability of one genotype to express different phenotypes under variable environmental conditions is referred to as phenotypic plasticity (West-Eberhard 1989; DeWitt et al. 1998). The evolution of such flexibility in fitness-related traits can provide individuals with the means to adaptively respond to environmental changes that occur within their lifetime. Behavioral plasticity is a type of phenotypic plasticity that allows organisms to make rapid behavioral responses to changes in their environment (Komers 1997;