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.
* 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
