Quick-change artists: Male guppies pay no cost to repeatedly adjust their sexual strategies

Abstract

Sexually selected traits involved in mate acquisition and fertilization success are usually costly and males often plastically adjust their reproductive investment in response to social conditions. Phenotypic plasticity in male sexual traits is generally assumed to be adaptive, yet its costs are rarely investigated. Male guppies (Poecilia reticulata) adjust their ejaculate production and sexual behavior in response to perceived mating opportunities. In natural populations, mating opportunities can fluctuate continuously, and the iterated activation of plastic responses may impose a cost on males. To determine such costs, we experimentally manipulated male social environment by exposing males either to a constant number of females, or to weekly oscillations in female number. We measured traits linked to condition and reproductive success throughout male life. We found no significant difference in the expression of these traits nor in male lifespan between the 2 groups. Our results suggest that male guppies pay negligible costs for the iterated activation of plastic responses, possibly as a consequence of selection to minimize them.