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Dr. Trudy Mackay, 919/515-5810
Mick Kulikowski, News Services, 919/515-3470

May 2, 2005

Artificial Selection of Mating Behavior Results in Larger-Than-Expected Changes to Fruit Fly Genes

FOR IMMEDIATE RELEASE

Research by North Carolina State University geneticists has found that artificially promoting certain traits in an organism can result in major changes to the organism’s genome, or set of all genes.

Dr. Trudy Mackay, William Neal Reynolds Professor of Genetics, and research colleagues at NC State made the unexpected discovery while studying the mating behavior of the model research organism Drosophila melanogaster, or fruit fly.

The research showed that after 29 generations of mating quick-copulating males and females while also separately mating slow-copulating males and females – thereby artificially selecting for mating behavior – 21 percent of the genome changed between the fast-mating flies and the slow-mating flies. That is, 3,727 genes in the genome – which contains more than 14,000 genes – had differing levels of activity when comparing slow-mating flies and fast-mating flies.

The research results are published online in Proceedings of the National Academy of Sciences.

Mackay said the results were surprising; she and her colleagues expected the percentage of changed genes would be well less than a few percent of the genome. But, she said, the results could lead to clues to the biological puzzle of speciation, in which reproductively breeding organisms diverge into two groups incapable of breeding.

“Artificial selection has been used to improve crop science and to improve animal species; the more general question now is, ‘What are the genomic responses to artificial selection?’” Mackay said. “Our results suggest the changes are a lot larger and more profound than we previously thought.

After 29 generations, the slow-mating flies took two and sometimes three hours to mate while the fast-mating flies generally mated within 20 minutes, the research showed.

Mackay said the females in the slow-mating lines became more selective through succeeding generations.

“The slow lines were slow because the females became very picky; they wouldn’t mate with males from their (slow) line or the fast line,” Mackay said.

Mackay says Drosophila mating involves a set of stereotyped exchanges or cues, beginning with a male sensing a nearby female through olfaction. The wooing male then taps on the female’s abdomen with a leg; Mackay says doing this allows the male to sense whether the female is of an acceptable species by interpreting the female’s sex chemicals, or pheromones.

If the female is the correct species, the male will perform a courtship song by beating his wings. If the song is acceptable to the female, Mackay says, she becomes receptive to the male’s advances and mates with the male. In essence, the female dictates if mating will occur or not.

“The study results could parallel what appears in nature when signals between males and females become unrecognizable,” Mackay said. “The questions we want to ask now are ‘Why are the females picky?’ and ‘What is changing in the picky females?’”

The research was funded by grants from the National Institutes of Health.

- kulikowski -

Note to editors: An abstract of the paper follows.

“Genetics and Genomics of Drosophila Mating Behavior”
Authors: Trudy Mackay, Stefanie Heinsohn, Richard Lyman, Amanda Moehring, Theodore Morgan and Stephanie Rollmann, North Carolina State University
Published: April 25, 2005, in the online version of Proceedings of the National Academy of Sciences

Abstract: The first steps of animal speciation are thought to be the development of sexual isolating mechanisms. In contrast to recent progress in understanding the genetic basis of postzygotic isolating mechanisms, little is known about the genetic architecture of sexual isolation. Here, we have subjected Drosophila melanogaster to 29 generations of replicated divergent artificial selection for mating speed. The phenotypic response to selection was highly asymmetrical in the direction of reduced mating speed, with estimates of realized heritability averaging 7%. The selection response was largely attributable to a reduction in female receptivity. We assessed the whole genome transcriptional response to selection for mating speed using Affymetrix GeneChips and a rigorous statistical analysis. Remarkably, >3,700 probe sets (21% of the array elements) exhibited a divergence in message levels between the Fast and Slow replicate lines. Genes with altered transcriptional abundance in response to selection fell into many different biological process and molecular function Gene Ontology categories, indicating substantial pleiotropy for this complex behavior. Future functional studies are necessary to test the extent to which transcript profiling of divergent selection lines accurately predicts genes that directly affect the selected trait.