Benefits of Polyandry: A Life History Perspective

Abstract

Bateman’s principle has been widely interpreted to imply that females gain no fitness benefits from polyandry (Bateman, 1948) and, therefore, should not be expected to mate multiply (here defined as mating with more than one male). Nevertheless, it is increasingly clear that females of many, if not most, taxa do copulate with multiple males (e.g. Birkhead and Wier, 1998). Moreover, polyandry is widespread despite considerable costs, including wasted time and energy, increased risk of predation and disease, potential damage caused by male seminal fluids and copulatory organs, and even death (Keller and Reeve, 1995; Eberhard, 1996). Despite these associated costs, females of diverse taxa not only accept several mates but also actively solicit multiple copulations in many instances (Birkhead and Moller, 1998). As evidence of diverse potential benefits associated with polyandry now accumulates, the assumption that females should not mate multiply because they cannot increase offspring numbers by doing so appears questionable. Importantly, since females have greater potential than males to influence the quality of their offspring, and investment in current reproduction has consequences for future reproductive attempts, they should be expected to optimise offspring numbers rather than maximise numbers produced in any given reproductive attempt (Roff, 1992; Stearns, 1992). Moreover, the relationship between female lifetime reproductive success and offspring numbers and/or size may not be as straightforward as is generally assumed (e.g. Madsen and Shine, 1998; Stockley and Macdonald, 1998). To suggest that females should not mate multiply simply because they cannot increase offspring numbers in a given reproductive attempt by doing so is therefore to confuse the currency of male and female fitness, and thereby to considerably under-estimate the complexity of female reproductive strategies.