Rarity of Males in Pea Aphids Results in Mutational Decay
Jennifer A. Brisson* and
Sergey V. Nuzhdin
When females can reproduce without males, do males become an
evolutionarily weaker sex whose genes experience mutational
decay? We addressed this hypothesis in aphids, whose reproduction
alternates between parthenogenetic and sexual forms: Over the
course of a year, there can be 10 to 20 generations of asexual
females but only a single, if any, generation with males. We
used microarray analyses to identify male-biased, asexual female-biased,
and neutral genes. Interspecific comparisons reveal accelerated
evolution of male-biased genes, and intraspecific polymorphisms
exhibit a significant excess of nonsynonymous coding variation
in male-biased genes. We conclude that the ability of females
to reproduce asexually without males reduces selection constraints
on male-based genes, resulting in their mutational decay.
Present address: University of Southern California, Los Angeles, CA 90089, USA.
* To whom correspondence should be addressed. E-mail: jabrisson{at}ucdavis.edu
