Physiological Sex Predicts Hybrid Sterility Regardless of Genotype
John H. Malone* and
P. Michalak
Reproductive isolation between biological species is characterized by Haldane's rule, which states that the heterogametic sex (XY or ZW) suffers the most dysfunctional effects of hybridization. It has been hypothesized that, in addition to X-linked recessive genes, Haldane's rule also reflects the faster evolution of genes related to male reproduction (faster-male evolution). We used sex-reversed hybrid Xenopus to test faster-male evolution by examining the fertility of sex-reversed individuals with the genotype of the inverse phenotypic sex. Hybrid males are sterile and hybrid females are fertile irrespective of their genotypic sex. Gene expression profiles match these adult phenotypes, and our results demonstrate that faster-male evolution is the most likely mechanism producing hybrid male sterility.
Department of Biology, University of Texas at Arlington, Box 19498, Arlington, TX 76019, USA.
* Present address: Laboratory of Cellular and Developmental Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Department of Health and Human Services, Building 50, Room 3314, Bethesda, MD 20892, USA.
To whom correspondence should be addressed. E-mail: michalak{at}uta.edu
