Flies May Reveal Evolutionary Step To Live Birth

A species of fruit fly from the Seychelles Islands often lays larvae
instead of eggs, UC San Diego biologists have discovered. Clues to how
animals switch from laying eggs to live birth may be found in the well-
studied species’ ecology and genes.
The fly is one of a dozen species of Drosophila to have recently had
their genomes sequenced, information that should provide abundant
opportunities for identifying genetic changes that cause females of
this species, and not others, to retain their fertilized eggs until
they are ready to hatch.

The result was so surprising that the scientists initially thought it
was a mistake.

“The student who was timing things came a said ‘wow, these eggs in
this species really develop quickly,’ sometimes in less than an hour.
That’s not possible,” said Therese Markow, a professor of biology who
led the project. “When I went and actually looked at them I saw that
they were depositing something that was very advanced, that hatched
into a larva right away. In several cases they were hatching as they
were being laid.”

Even those Seychelles fly eggs that emerged unhatched were at an
advanced state of development, the team reports in forthcoming issue
of the Journal of Evolutionary Biology. Most larvae emerged within two
hours compared to an average of nearly 23 hours for the other 10
species in the study.

Tonny
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