A MODEL OF SYMPATRIC SPECIATION BY SEXUAL SELECTION

Quantitative genetic models have indicated that sexual selection may lead to speciation in isolated populations or to exaggeration of differences in male traits along a dine. We argue that where female mate preference and opposing natural selection against conspicuous males have produced a stable equilibrium in male trait genotype, a reversed female mate preference may invade the population, initially assisted by reduced male mortality. The consequent linkage disequilibrium may lead to rapid sympatric speciation. Assuming a four-locus quantitative male trait and single-locus female preference rule and overlapping generations, we present a simulation model which indicates that reversal of female mate preference in a single individual can lead rapidly to full reproductive isolation in a small population. Speciation may be produced by the proposed mechanism in allopatry, parapatry or full sympatry. We suggest that differences in mating system and its genetic bases may account for some of the differences in speciation rates among lineages.