The mating game: do opposites really attract?

When selecting a mate, females of many species face a complicated decision: choosing a very closely related mate will lead to inbreeding, while choosing a mate who is too genetically dissimilar risks breaking up beneficial gene complexes or local genetic adaptations. To ensure the best genetic quality of their offspring, the perfect compromise lies somewhere in between: an optimally genetically dissimilar partner. Empirical evidence demonstrating female preference for genetically dissimilar mates is proof of the adage 'opposites attract'. In stark contrast, Chandler & Zamudio (2008) show in this issue of Molecular Ecology that female spotted salamanders often choose males that are genetically more similar to themselves (although not if the males are small). Along with other recent work, these field studies highlight the broad spectrum of options available to females with respect to relatedness in their choice of mate that belies this rule of thumb.