Vertebrate evolution generally proceeds at far less than a snail's pace, making study of the process in living animals difficult at best. One spectacular exception to this rule, however, is the three-spined stickleback fish. In the mere 15,000 years that have passed since it first appeared, the stickleback has undergone rapid speciation, evolving a large number of distinct forms, each adapted to a particular niche in the stream or lake it inhabits. It thus makes an ideal subject for researchers attempting to study the genetics underlying evolutionary change. In that regard, findings published today in the journal Nature represent an important advance. According to the report, a newly created genetic map of the fish enables investigators to link changes in, say, the fish's behavior or morphology to changes in its genome.

So far, the study authors have used the map to trace changes in the skeleton armor and feeding morphologies of fish from British Columbia's Priest Lake. Focusing on two stickleback species—one that dwells in the grassy shallows of the lake bottom and another that inhabits open water—the researchers found that different parts of the fish skeleton, even those that lie close to one another, are controlled by different chromosome regions. This, they say, provides a flexible genetic system for independent modification of the size and number of different feeding and armor structures.

The scientists' most important accomplishment, however, may be the development of the map itself. "We see this as our chance to find out how many genetic changes it takes to evolve new traits," team member David M. Kingsley of Stanford University remarks. "Using this method we can ask which genes or developmental pathways Nature uses to create a new species."