Sexual conflict may play key role in speciation

A newly evolved sex chromosome in a fish contains genes that contribute to its diversification from other closely related species. The findings, published this week in the journal Nature, suggest that sex-chromosome changes may have a far greater role in speciation than was previously anticipated.

The Human Biology Division’s Drs. Katie Peichel and Jun Kitano, along with Joe Ross, a former graduate student in the Molecular and Cellular Biology program, and colleagues identified a new sex-chromosome system that is found in only one of two species of threespine stickleback fish that exist in the same habitat in the Sea of Japan.

Using genetic mapping, the scientists showed that the newly evolved X chromosome contains genes for male courtship behavior, whereas the ancestral X chromosome contains genes for both behavioral isolation and hybrid male sterility. These traits contribute to the reproductive barrier between the Japan Sea species and the ancestral form found in the Pacific Ocean.

Evolutionary biologists have long been puzzled by the fact that closely related species can have different sex chromosomes and have proposed that this might be driven by conflicts between the interests of males and females (sexual conflict).

“Our work provides some of the first empirical evidence supporting this theory,” Peichel said. “It further suggests that the rapid evolution of new sex chromosomes driven by sexual conflict can also play a key role in the formation of new species.

“We are also excited about this study because we were able to identify regions of the genome that contribute to differences in male mating behaviors between stickleback populations.”

Peichel said the findings lay the groundwork for her team’s long-term goal of identifying the actual genes that contribute to behavioral differences in natural populations like sticklebacks or humans.

The research was supported by the Uehara Memorial Foundation; the Ministry of Education, Culture, Sports, Science and Technology of Japan; the Research Institute for Humanity and Nature; an Akkeshi Town Grant-in-Aid for Scientific Research in the Lake Akkeshi-Bekanbeushi Wetland; a Burroughs Wellcome Fund Career Award; and the National Institutes of Health.

 [Adapted from a Nature news release.]