Genetic control of premating-lsolating behavior: Kaneshiro's hypothesis and asymmetrical sexual selection in pocket gophers

We studied 112 individuals from a zone of hybridization between two species of pocket gophers, Geomys bursarius major and G. knoxjonesi. Each individual was examined and assigned to a genotypic class based on diploid number, mitochondrial DNA, ribosomal DNA, and three allozymic systems, all of which were fixed for alternative conditions in pure parental populations. F₁ and F₁-like individuals were found to possess only the mitochondrial DNA type of G. knoxjonesi, indicating that F₁. and "F₁-like" individuals are the result of unidirectional mating between G. knoxjonesi females and G. b. major males. We find these data compatible with the predictions of the Kaneshiro hypothesis that asymmetrical sexual isolation involves the preferential mating of females of the derived species with males of the species that have retained primitive character states.