The rarity of size-assortative mating in animals: assessing the evidence with anuran amphibians

Assortative mating in animals can have substantial evolutionary impact. Numerous reports also make it appear to be pervasive in occurrence. In assortative mating, defined here in behavioral terms, animals select their mates according to a particular shared trait such that mated individuals resemble each other phenotypically more than expected by chance. Body size is a widely studied assortment trait. This is especially relevant for anuran amphibians (frogs and toads), among whom reproductive advantages may accrue to large individuals of both sexes. Anurans also exhibit discrete forms of male mating behavior. Sedentary calling behavior of “sitters” allows for female choice whereas fighting for possession of mates by “scramblers” precludes female choice. Size-assortative mating in anurans, therefore, should be a property of sitters, not scramblers. I used meta-analysis to assess the occurrence of true size-assortative mating in relation to mating behaviour and other variables in 282 studi...