Mate Choice - Speciation By Mate Choice

Speciation By Mate Choice

For many years it has been suggested that sexual isolation caused by differences in mating behaviors is a precursor for reproductive isolation (lack of gene flow), and consequently speciation, in nature. Mate choice behaviors are thought to be important forces that can result in speciation events because the strength of selection for attractive traits is often very strong. Speciation by this method occurs when a preference for some sexual trait shifts and produces a prezygotic barrier (preventing fertilization). These processes have been difficult to test until recently with advances in genetic modeling. Speciation by sexual selection is gaining popularity in the literature with increasing theoretical and empirical studies.

There is evidence of early speciation through mate preference in guppies. Guppies are located across several isolated streams in Trinidad and male color patterns differ geographically. Female guppies have no coloration but their preference for these color patterns also vary across locations. In a mate choice study, female guppies were shown to prefer males with color patterns that are typical of their home stream. This preference could result in reproductive isolation if two populations came into contact again.

The North American bird, black-throated blue warblers, is another example. Asymmetric recognition of local and nonlocal songs has been found between two populations of black-throated blue warblers in the United States, one in the northern United States (New Hampshire) and the other in the southern United States (North Carolina). Males in the northern population respond strongly to the local male songs but relatively weakly to the nonlocal songs of southern males. In contrast, southern males respond equally to both local and nonlocal songs. The fact that northern males exhibit differential recognition indicates that northern females tend not to mate with “heterospecific” males from the south; thus it is not necessary for the northern males to respond strongly to the song from a southern challenger. A barrier to gene flow exists from South to North as a result of the female choice, which can eventually lead to speciation.