320A Poster - 03. Evolution
Thursday April 07, 2:00 PM - 4:00 PM

Authors:
Ivan D. Mendez Gonzalez ¹; Mark Rebeiz ¹; Thomas M. Williams ²

Affiliations:
1) University of Pittsburgh, Pittsburgh, PA; 2) University of Dayton, Dayton, OH

Keywords:
l. evo-devo; e. enhancers

A fundamental question in evolutionary biology is how the diversity of forms and colors that we observe in the animal kingdom originated. Hox genes are highly conserved genes often implicated in phenotypic evolution, and yet the molecular mechanisms of Hox gene evolution have been difficult to pinpoint.
In Drosophila melanogaster, the Hox gene Abd-B regulates the production of melanin covering the A5 and A6 segments of the male’s abdomen. This trait evolved from a non-melanic ancestor and in the melanogaster species group, within which it was extensively diversified. We tested whether temporal changes in Abd-B expression have played a role during the origination and diversification of abdominal melanic pigmentation. We identified two cis-regulatory elements (CREs) in D. melanogaster that are necessary for Abd-B expression in the A5 abdominal segment during late pupal development. Deletion of either CRE disrupts the formation of melanic pigmentation, suggesting that they have partially redundant activities. To test for intraspecific differences in the activity of these CREs, we replaced the melanogaster allele with the orthologous region from species with different melanic pigmentation. Our preliminary data suggests that the function of one of these CREs is highly conserved. Our current model is that partially redundant CREs form a relay to maintain Abd-B expression over time, and that evolutionary changes in this process that construct and deconstruct these CREs may be involved in the evolution of abdominal melanic pigmentation. Furthermore, the identification of these CREs offers the opportunity to manipulate Abd-B expression across different species to causally test how animal morphology evolves in response to changes in the expression of Hox-genes.
We propose that regulatory evolution of genes with multiple developmental functions, like Abd-B, should favor temporal rather than spatial changes, potentially limiting negative pleiotropic effects.