Variable mode of estrus affects female decision for multiple mating

Investigating patterns of variation in mating strategies may shed light on their evolutionary importance as well as their impact on the strength and shape of sexual selection. Multimale mating (polyandry) and mate choice are intensely studied subjects in the area of sexual selection, but little is known about intraspecific patterns of variation that may respond to dynamic cost-benefit balances. In a laboratory study, we investigated the mating behavior of female bank voles (Myodes glareolus) with distinctly different time and energy budgets: They were either in cycling estrus (CE) or postpartum estrus (PPE) shortly after delivery. Postpartum mating is highly constrained by time and energy due to maternal commitments to the newborn litter. All females had a free and simultaneous choice among 4 males that differed in scent-marking frequency (indicator of dominance) and body mass. We show that females in CE engaged significantly more often in multimale mating than females in PPE. Additionally, PPE females mated with males that scent marked more, whereas CE females seemingly mated indiscriminately. We discuss our findings in light of time and energy budgets of females and also consider alternative explanations such as pup protection against infanticidal males or physiological constraints to estrus modes.