Convergent evolution - the explanation for different species evolving common solutions to the same problems, even though they have distinctly different ancestors - has been found to result from just a handful of genes.

Two separate U.S. studies looking at different characteristics of fruit flies, have found the changes in genetic pathways that caused differences between species. The work appears in today's issue of the journal.

The research involved a mixture of developmental genetics and evolutionary changes. By finding a link between the genetic pathway for changes in hair formation and pigmentation, the work suggests that just a few developmental changes may cause separate species to converge on a similar evolutionary solution.

Associate Professor David Stern from Princeton University and colleagues looked at different fruit fly species that had bald patches on their abdomens. The second study, by Dr Nicolas Gompel and Dr Sean Carroll from the University of Wisconsin, looked at the pigmentation of pattern on the abdomens of 13 different species of fruit fly.

Across species, changes in pigmentation and hair formation were sometimes, but not always linked. "Gompel and Carroll suggest that the two traits become uncoupled when they are under different selective pressures," writes Professor Michael Richardson from Leiden University in The Netherlands, in an accompanying commentary. "Each gene might represent a developmental 'hotspot' for evolution."

The Princeton group found that three of the lineages had independently evolved bald patches. The link between them was a gene called 'shavenbaby', which was absent in these regions. The team suggest that the loss of this one gene was enough to prompt the evolution of hair loss in different fly species.

The Winconsin duo discovered, in the 13 species of fruit fly they examined, that the products of two 'bric-a-brac' genes - bab1 and bab2 - are responsible for abdominal patterning and hair development. It turns out that in one case 'bric-a-brac' function is not only responsible for pigmentation, but also for hair development.

"Although pigmentation and trichome patterning changes are often coupled, their evolution has become uncoupled in some groups," writes Richardson.

Developmental change
The new research seems to prove that adjusting only a few genes regulating embryonic or larval development can cause natural selection to produce evolutionary change. But changes to developmental genes can cause devastating results, such as legs growing on a fly's head, so the researchers wanted to find out how developmental genes are altered during the normal course of evolution in natural populations.

"[The researchers] show that modifications at just a few developmental hotspots underlie 'parallel' evolutionary changes that occurred independently in different species," said Richardson. "Although not all instances of trait convergence rely on the same genetic mechanism, these studies have uncovered several instances that do."

The next step is to understand the function of the physical characteristics and the causes of evolutionary change, he said: "The brightest future for evolutionary developmental biology might lie with the study of systems in which we can analyse the cause as well as the function of evolutionary change."