MBE Advance Access published online on December 4, 2007
Molecular Biology and Evolution, doi:10.1093/molbev/msm270
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Research Article |
Evidence for Positive Selection on Drosophila melanogaster Seminal Fluid Protease Homologs
Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853
* Corresponding author: Room 233 Biotechnology Building, Department of Molecular Biology and Genetics Cornell University Ithaca, NY 14853 USA, phone: 607-254-4826, fax: 607-255-6249, email: aw246{at}cornell.edu
Received for publication September 2, 2007. Revision received November 6, 2007. Accepted for publication November 19, 2007.
Proteins present in the seminal fluid of Drosophila melanogaster (Acps) contribute to female post-mating behavioral changes, sperm storage, sperm competition, and immunity. Consequently, male-female co-evolution and host-pathogen interactions are thought to underlie the rapid, adaptive evolution that characterizes several Acp encoding genes. We propose that seminal fluid proteases are likely targets of selection, due to their demonstrated or potential roles in between-sex interactions and in immune processes. We use within- and between-species sequence data for five predicted protease-encoding Acp loci to test this hypothesis. Our polymorphism-based analyses find evidence for positive selection at two genes, both of which encode predicted serine protease homologs. One of these genes, CG6069, also shows evidence for consistent selection on a subset of codons over a deeper evolutionary time scale. The second gene, CG9997, was previously shown to be essential for normal sperm usage, suggesting that sexual selection may underlie its history of adaptation.
Key Words: seminal fluid Acp protease positive selection adaptation evolution immunity