PgmNr D120: Evolution of the Sex Peptide Network: Lineage-specific adaptive evolution and gene duplication.

Authors:
Meaghan McGeary; Geoffrey Findlay


Institutes
College of the Holy Cross, Worcester, MA.


Keyword: genome evolution

Abstract:

The sex peptide (SP) network consists of at least 13 proteins from males and females that interact to control female behavior and physiology after mating.  In Drosophila melanogaster, these changes can last for several days and include increased egg production, efficient sperm storage, and a decrease in female receptivity to remating. However, other Drosophila species show dramatically different reproductive phenotypes, including faster female remating and differences in sperm size and sperm storage patterns.  We thus investigated the molecular evolution of the SP network proteins across the Drosophila genus.  After bioinformatically identifying SP network proteins in up to 22 species, we used PAML to test whether any proteins had sites that had evolved under recurrent positive selection and to test for adaptive evolution on specific phylogenetic branches that correlate with major changes in reproductive phenotypes.   While only 2 of 11 tested genes showed evidence of recurrent positive selection across the phylogeny, we identified bursts of adaptive evolution on lineages correlating with phenotypic changes. For example, the lineage leading to the melanogaster species group showed evidence of adaptive evolution on three genes.  This lineage corresponds to a change in the expression level of the SP receptor in the female reproductive tract and to two gene duplication events of the network member, seminase.  We then investigated the importance of gene duplication in the network’s evolution by studying seminase in further detail.  Three copies of this gene are present in the melanogaster group of Drosophila, while only a single copy is found in other species.  PAML analysis showed no evidence for adaptive evolution of seminase following duplication, and gene expression analysis in seven species showed that seminase and both paralogs are expressed specifically in males. Taken together, these results paint a dynamic picture of SP network evolution, with different lineages and genes having experienced different selective pressures.



Flybase Genetic Index:
1. FlyBase gene symbol: SP; FBgn: FBgn0003034
2. FlyBase gene symbol: Sems; FBgn: FBgn0037036
3. FlyBase gene symbol: SPR; FBgn: FBgn0029768