Adaptively flexible polyandry

• Chance demography affects female multiple mating.
• Distributions of fitness under random mating determine adaptive significance of polyandry.
• No optimal mating rate exists for females.
• Polyandry often is correlated positively with higher offspring viability and lineage success.

Mating theory (Hubbell & Johnson 1987, American Naturalist, 130, 91–112; Gowaty & Hubbell 2009, Proceedings of the National Academy of Sciences, U.S.A., 106, 10017–10024) says that reproductive decisions of individuals are flexibly expressed and adaptive. It also makes the following five predictions about polyandry. (1) Demography determines within-population, between-female variation in mating rates. That is, (a) an individual's encounters with potential mates, (b) an individual's risk of death, (c) the number of potential mates in the population, (d) the distribution of fitness under random mating, and (e) for nonvirgins, the duration of any postcopulation period of nonreceptivity together determine within-population, between-female variation in mating rate. (2) When demography is dynamic, there is unlikely to be an optimal female mating rate. That is, when potential mates enter or leave the pool of potential mates or when decision makers face survival risks from conspecifics, predators, parasites or pathogens, females who adaptively adjust their reproductive decisions in real-time outcompete females whose behaviour is fixed. (3) Female multiple mating often increases production of adult offspring through enhanced offspring viability (indirect fitness) and between-generation lineage success. (4) Polyandry will increase female exposure to pathogens and thus decrease female survival (direct fitness cost) unless females use environmental or intrinsic resources or opportunities to reduce survival risks. (5) Under many circumstances, female remating may enhance female survival (direct fitness benefit). Future research attention will focus on how intrinsic, ecological and social opportunities/constraints affect the likelihood of polyandry and its fitness effects for particular females. Future researchers may also consider that polyandrous mating is sometimes sexually collaborative and cooperative, rather than always sexually antagonistic.