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Why females fall for captivating males that apparently give them nothing but their genes and little else is a puzzling question for evolutionary biologists. Females typically incur more survival costs than males in rearing offspring, especially when they choose flashy mates. So why do they do it? Megan Head and colleagues now report in the freely-available online journal PLoS Biology, the results of simultaneously measuring both the costs and benefits of mating to female crickets and their offspring and provide new evidence that the costs that females pay for mating with attractive males are balanced by, and may even be outweighed by, the indirect benefits of spawning offspring with elevated fitness.
The authors paired females with either "attractive" or "unattractive" males (determining which males were attractive by running the equivalent of speed dating "tournaments") and measured the overall fitness consequences of the various unions. Although female crickets, they found, paid a higher survival price for mating with attractive males, these females produced both daughters that laid more eggs within a given time and sons that were more attractive. The benefit stems in large part, the authors argue, from siring "sexy" sons. Thus, by evaluating both the direct effects of mating on female lifetime fecundity and the indirect effects of offspring fitness, the authors determined the net consequences of a mating strategy.
With this approach, Head and colleagues bridge the gap between empirical studies of mate choice evolution, which rely largely on "rate-insensitive" measures (such as counting grandchildren), and theoretical studies, which typically use rate-sensitive measures. Despite some recent theoretical work with the opposite prediction, their results suggest that there may be selection for choosing costly mates and that generating a reliable analysis of the fitness consequences requires a long view: look at the reproductive success of mom's sons and daughters before judging her taste in mates.
Citation: Head M, Hunt J, Jennions M, Brooks R (2005) The indirect benefits of mating with attractive males outweigh the direct costs. PLoS Biol 3 (2): e33.
CONTACT:
Megan Head
The University of New South Wales
Anzac Parade
Sydney, Australia NSW 2052
61-2-9385-2124
megan.head@student.unsw.edu.au
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