Laura K. Reed and her advisor, Regents' Professor Therese Markow, made the discovery by observing breeding patterns of fruitflies that live among rotting cacti in western deserts. Whether the two closely related fruitfly populations, designated Drosophila mojavensis and Drosophila arizonae, represent one species or two is still debatable among biologists, testament to the Arizona researchers' assertion that they are in the early stages of diverging into separate species.
The seeds of speciation are sown when distinct factions of a species cease reproducing with one another. When the two groups can no longer interbreed, or prefer not to, they stop exchanging genes and eventually go their own evolutionary ways, forming separate species.
While the evolutionary record is brimming with examples of speciation events, Reed says, biologists haven't been able to put their finger on just what initiates the reproductive isolation. Several researchers have identified mutant forms of certain genes associated with the inability of fruitflies to hybridize with closely related species, but in all cases those genes were discovered long after the two species diverged. Those genetic changes could have caused the speciation or resulted from it, or they might even be incidental changes that occurred long after the species diverged. The difficulty, Reed explains, is that you have to catch the genetic schism while it's still brewing.
She and her advisor report that they have managed to do just that. In the wild, D. mojavensis and D. arizonae rarely if ever interbreed, even though their ranges overlap along a broad swath along the north