CONSPECIFIC SPERM PRECEDENCE IS AN EFFECTIVE BARRIER TO HYBRIDIZATIONBETWEEN CLOSELY-RELATED SPECIES

Conspecific sperm precedence is widespread in animals, appears to evol ve rapidly, and is thought to have the potential to prevent hybridizat ion between closely related species. However to date no study has test ed the isolating potential of such a barrier in mixed populations of t wo taxa under conditions in which other potential barriers to gene how are controlled for or are prevented from operating. We tested the iso lating potential of conspecific sperm precedence in the ground cricket s Allonemobius fasciatus and A. socius in population cage experiments in which the frequency of the two species was varied. Despite the obse rvation of abundant interspecific matings, the proportions of hybrid p rogeny were low and differed statistically from the proportions expect ed in the absence of conspecific sperm precedence. The results demonst rate that conspecific sperm precedence can severely limit gene flow be tween closely related species, even when one species is less abundant than the other.