Fourteen microsatellite loci were isolated from capybaras (Hydrochoerus hydrochaeris), which are large, diurnal social rodents that occur in the wet savannas of South America. Five of these loci were monomorphic. The remaining nine loci were polymorphic (two to seven alleles per locus), with observed levels of heterozygosity ranging from 0.063 to 0.800 (n = 17 animals). The latter loci provide a valuable tool for assessing patterns of parentage and kinship within capybara social groups.
The sexually dimorphic ornaments and songs of birds are generally thought to be the result of sexual selection. For some time, variation in dimorphism among taxa was attributed to differences in social mating patterns. However, extrapair mating provides an alternative mechanism for sexual selection in both monogamous and polygynous birds. In monogamous systems, extrapair mating typically increases variance in mating success and hence sexual selection. However, it is less clear how extrapair mating influences sexual selection in polygynous species. We measured sexual selection acting on 6 sexually dimorphic male traits in a polygynous songbird, the dickcissel (Spiza americana). We also examined patterns of association between social and extrapair mating success, between male traits and reproductive success within each mating context, and the contribution of each type of mating to overall reproductive success. Despite high variance in both mating success and male traits, we found no evidence for current sexual selection in dickcissels. Indeed, variance among males in dimorphic traits did not significantly contribute to male success in any mating context. These results add to an array of studies uncovering relatively weak sexual selection in polygynous species. It is possible that, in contrast to monogamous systems, extrapair paternity weakens sexual selection in polygynous systems. In addition, natural selection arising from high predation and interspecific brood parasitism, stochastic processes, or annual variation in selective pressures may also weaken sexual selection in this species.
The desert woodrat complex (Neotoma lepida group) is a set of four closely related species occupying the arid lands of western North America. We have developed 18 polymorphic microsatellite loci to analyse the population structure, mating patterns, and hybridization at points of contact between the contiguously allopatric species in the complex.
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