Rapid Evolution of Genomic Acp Complement in the melanogaster Subgroup of Drosophila

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Abstract
Unusual properties of molecular evolution in reproduction-related Drosophila genes, including atypically rapid rates of protein evolution, support the idea that natural selection plays an important role in divergence of reproductive function in Drosophila. We used subtractive hybridization to investigate another potential side of evolution of the male reproductive transcriptome. We carried out a screen for genes with much greater transcript abundance in Drosophila simulans reproductive tracts than in Drosophila melanogaster reproductive tracts. Such genes could be present in both species but diverged dramatically in transcript abundance or could be present in D. simulans but absent from D. melanogaster. Here we report data from melanogaster subgroup species for three previously unknown accessory gland protein genes (Acps) identified in this screen. We found multiple Acps that were present in some lineages yet absent from other closely related melanogaster subgroup lineages, representing several losses of genes. An Acp that may have been lost in D. melanogaster and Drosophila erecta is segregating a null allele in Drosophila yakuba, yet shows evidence of adaptive protein evolution in contrasts of polymorphism and divergence within and between D. yakuba and its close relative, Drosophila teissieri. These data suggest that turnover of Acps occurs rapidly in Drosophila, consistent with rapid evolution of seminal fluid function.