Scientists see new species born
By Dr David Whitehouse
BBC News Online science editor

Scientists at the University of Arizona may have witnessed the birth of a
new species for the first time.
Biologists Laura Reed and Prof Therese Markow made the discovery by
observing breeding patterns of fruit flies that live on rotting cacti in
deserts.

The work could help scientists identify the genetic changes that lead one
species to evolve into two species.

The research is published in the Proceedings of the National Academy of
Sciences.

One becomes two

Whether the two closely related fruit fly populations the scientists
studied - Drosophila mojavensis and Drosophila arizonae - represent one
species or two is still debated by biologists.

However, the University of Arizona researchers believe the insects are in
the early stages of diverging into separate species.

The emergence of a new species - speciation - occurs when distinct
populations of a species stop reproducing with one another.


When the two groups can no longer interbreed they cease exchanging genes and
eventually go their own evolutionary ways becoming separate species.
Though speciation is a crucial element of understanding how evolution works,
biologists have not been able to discover the factors that initiate the
process.

In fruit flies there are several examples of mutant genes that prevent
different species from breeding but scientists do not know if they are the
cause or just a consequence of speciation.

Sterile males

In the wild, Drosophila mojavensis and Drosophila arizonae rarely, if ever,
interbreed - even though their geographical ranges overlap.

In the lab, researchers can coax successful breeding but there are
complications.

Drosophila mojavensi s mothers typically produce healthy offspring after
mating with Drosophila arizonae males, but when Drosophila arizonae females
mate with Drosphila mojavensis males, the resulting males are sterile.

Laura Reed maintains that such limited capacity for interbreeding indicates
that the two groups are on the verge of becoming completely separate
species.

Another finding that adds support to that idea is that in a strain of
Drosophila mojavensis from southern California's Catalina Island, mothers
always produce sterile males when mated with Drosophila arizonae males.

Because the hybrid male's sterility depends on the mother's genes the
researchers say the genetic change must be recent.

Reed has also discovered that only about half the females in the Catalina
Island population had the gene (or genes) that confer sterility in the
hybrid male offspring.

However, when she looked at the Drosophila mojavensi s females from other
geographic regions, she found that a small fraction of those populations
also exhibited the hybrid male sterility.

The newly begun Drosophila mojavensis genome sequencing project, which will
provide a complete roadmap of every gene in the species, will help
scientists pin down which genes are involved in speciation.


Story from BBC NEWS:
http://news.bbc.co.uk/go/pr/fr/-/2/hi/science/nature/3790531.stm

Published: 2004/06/09 12:34:02 GMT

Posted by,
Robert Karl Stonjek.
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