New models of sympatric speciation through sexual selection in animals

Abstract

The theory of sympatric speciation has gained support through both empirical evidence and theoretical analysis. Sexual selection has been empirically linked to sympatric speciation, and many models of sympatric speciation are based on non-random mating. This thesis presents an analysis of the model of sympatric speciation through sexual selection presented by Turner and Burrows (1995) in order to make predictions for the experimental analysis of modes of speciation.The introduction of a mutation in female preference does not guarantee the formation of sympatrically co-existent sibling species, but is dependent on a form of runaway process. Reduction in the genetic variation in male trait, either through fixation or through too few loci, is an obstacle to the formation of sympatric species. Increasing the strength of female preference or the effort females are prepared to make increases the strength of sexual selection and increases the likelihood of sympatric speciation. Population size affects the probability of sympatric speciation either through the excessive fixation of male trait loci in small populations, or through reducing the changes of individuals carrying mutations in female preference genes meeting and mating in larger populations.The Turner and Burrows (1995) model was found to be robust under a variety of genetic assumptions. A variation of the model, using dominance in male trait alleles and removing stabilising selection on male phenotype was less affected by fixation at the male courtship trait loci. Spatial distributions affected the probability of sympatric speciation when the dispersal of offspring is limited, creating localised concentrations of female preference types and the preferred male trait.Breeding experiments may be used to indicate whether this mode of speciation has operated in a particular instance.Fast, sympatric speciation was found to be more likely in clades with small population sizes, where females choose from a large number of males, if a moderate number of loci code for male courtship traits, and in taxa with a life history matching K-selected species rather than r-selected species.</p