The adaptive significance of polyandry: a meta-analysis

Polyandry is prevalent, but the optimal patterns of mating for females remain poorly understood despite their importance for our understanding of sexual selection. We therefore performed a meta-analysis on the female fitness consequences of mating with multiple males. Across 166 studies spanning 127 arthropod species, we found that mating with more males generally enhanced female fecundity and reduced female lifespan. The net fitness effects of polyandry, however, were small. Moreover, fecundity benefits were not clearly detectable when females mated with more than two males. Additionally, we found first, that studies assessing partial as opposed to lifetime fitness reported greater benefits of polyandry. Second, protocols involving selection bias, where females were afforded some control over mating rates, reported lower costs of polyandry compared to studies without selection bias. Third, polyandry was reported as less beneficial in experiments that involved continuous housing of females with males. Finally, polyandry was more beneficial in species that transfer nuptial gifts. We thus suggest that future polyandry studies aim to measure lifetime fitness while also mitigating selection bias and exposure of females to excessive harassment. Doing so will help us understand how sexual selection operates in both sexes.