PARKER, P.G.; University of Missouri — St. Louis: Recent Insights into Sexual Selection in Bird Mating Systems: What Bateman Couldn’t Have Known

Since tools of molecular genetics became readily available, our understanding of bird mating systems has undergone a revolution. The majority of passerine species investigated are socially monogamous, but have been shown to be genetically polygamous. Other avian taxa are more likely to be genetically monogamous than the short-lived songbirds. Theory predicts that males of long-lived species should abandon reproductive efforts under even very moderate rates of cuckoldry, while those in short-lived species should continue to provide care even when cuckoldry is high. Several data sets from natural populations of passerine birds suggest that the benefit to females of mating with multiple males results in a sexual selection gradient as steep for females as for males. However, the route to fitness benefits for multiple mating may differ between males and females. Fitness is enhanced directly through fertilization success with multiple matings in males, while female fitness may be enhanced directly through acquisition of nutrition or other resources from males, or indirectly through improvement of offspring quality, either by selection of genetically compatible males or superior males. But a steep sexual selection gradient for females can be difficult to interpret. If all females copulate with multiple partners who are equally likely to fertilize eggs, then females who produce more successful eggs for any reason will appear to have copulated with more males. Causation has yet to be established clearly for female avian sexual selection gradients. Costs and benefits of multiple matings will be reviewed in birds and insects, straying from birds to focus on a tenebrionid beetle in which female fecundity increases directly with number of spermatophores received and male survivorship declines with number of spermatophores produced.