Nothing brings two people closer together than sex, but for closely related species of fruit flies, it may be what keeps them apart. Researchers at the University of Chicago have recently discovered a gene that appears to play a crucial role in causing one species to split into two--and stay that way. The gene causes the male progeny of two recently separated species to be sterile--a condition known as hybrid male sterility.
"How speciation occurs is one of the central questions in evolutionary biology," says Chung-I Wu, Ph.D., chairman and professor of the department of ecology & evolution at the University of Chicago, and senior author of the paper in the November 20 issue of Science. "Geographic isolation and changes in the environment are only a part of what drives speciation. There are also changes at the genetic level that are driven by sexual selection. As a result, two newly formed species can't mix back into one."
Many species of insects and mammals exhibit male sterility in inter-species hybrids at the early stages of speciation. For example, the male progeny of the yak-cow cross are sterile. Male 'zonkeys,' the offspring of a zebra and a donkey, are also sterile. Wu speculated that hybrid male sterility must be an early indicator of speciation.
Chau-Ti Ting, a postdoctoral fellow in Wu's lab pinpointed a gene (there may be many) involved in producing sterility in hybrid males. It does this by evolving so rapidly that male offspring produced by two newly divergent or 'sibling' species are so different from their parents that they are unable to make sperm.
The gene Ting thinks contributes to hybrid male sterility is a homeobox
gene. Homeobox genes, usually involved in development and cell differentiation,
are some of the slowest evolving genes in all of nature. This means that they
are almost identical in organisms as diverse as worms and monkeys. But when Wu
looked at a certain homeobox gene in
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Contact: Sharon Parmet
sparmet@mcis.bsd.uchicago.edu
773-702-6241
University of Chicago
20-Nov-1998