Reproductive and Mating Success in the Small-Mouthed Salamander (Ambystoma texanum) Estimated via Microsatellite Parentage Analysis

Abstract

Bateman’s principles of sexual selection predict that the sex with “cheaper” gametes may maximize reproductive efforts by mating multiply and so display greater positive covariance between reproductive and mating success. We conducted a semi-controlled breeding experiment to genetically quantify sexual selection in adult Ambystoma texanum, a sexually monomorphic salamander with simple courtship behaviors. We used four polymorphic microsatellite loci to genotype 57 adults enclosed in a breeding wetland and compared their multilocus profiles to that of 862 embryos collected from the enclosure. The molecular data were used to assign parentage, investigate the mating system, and measure sexual selection intensity. Parentage analyses indicated 36% of dams and 93% of sires were genetically sampled via their gametes but physically unsampled, suggesting that a large number of breeders over-wintered within the enclosure and/or some females released into the enclosure were already inseminated. We used the genetic data to generate estimates of individual reproductive and mating success and we interpret these in light of salamander behavior and sexual selection theory. The incidence of multiple mating in females (86%) was considerably higher than in males (32%) and the standardized variance in mating success was significantly greater in females. The correlations between reproductive and mating success were significant and of similar magnitude between the sexes, indicating that both sexes increased reproductive success through increased mating success. This pattern may be a function of differential opportunities for mating success between the sexes.