ASSESSING THE POTENTIAL FOR AN ONGOING ARMS RACE WITHIN AND BETWEEN THE SEXES: SELECTION AND HERITABLE VARIATION

Proteomic discovery of previously unannotated, rapidly evolving seminal fluid genes in Drosophila

As genomic sequences become easier to acquire, shotgun proteomics will play an increasingly important role in genome annotation. With proteomics, researchers can confirm and revise existing genome annotations and discover completely new genes. Proteomic-based de novo gene discovery should be especially useful for sets of genes with characteristics that make them difficult to predict with gene-finding algorithms. Here, we report the proteomic discovery of 19 previously unannotated genes encoding seminal fluid proteins (Sfps) that are transferred from males to females during mating in Drosophila. Using bioinformatics, we detected putative orthologs of these genes, as well as 19 others detected by the same method in a previous study, across several related species. Gene expression analysis revealed that nearly all predicted orthologs are transcribed and that most are expressed in a male-specific or male-biased manner. We suggest several reasons why these genes escaped computational prediction. Like annotated Sfps, many of these new proteins show a pattern of adaptive evolution, consistent with their potential role in influencing male sperm competitive ability. However, in contrast to annotated Sfps, these new genes are shorter, have a higher rate of nonsynonymous substitution, and have a markedly lower GC content in coding regions. Our data demonstrate the utility of applying proteomic gene discovery methods to a specific biological process and provide a more complete picture of the molecules that are critical to reproductive success in Drosophila.

The cost of mating rises nonlinearly with copulation frequency in a laboratory population of Drosophila melanogaster

Previous studies of Drosophila melanogaster have demonstrated a cost to females from male courtship and mating, but two critically important parameters remain unresolved: (i) the degree to which harm from multiple-mating reduces lifetime fitness and (ii) how harm from mating might change with successive matings (rematings). Here we use 'laboratory island analysis' to quantify the costs that females incur with each remating, in the currency of lifetime fitness and under conditions that closely match those to which the flies have adapted for hundreds of generations. We experimentally manipulated the number of female matings by varying the order of daily 2-h exposures of females to either sperm-less males (XO) or intact males (XY). Females that mated more often had substantially reduced lifetime fecundity, and importantly, the fitness cost from remating rapidly accelerated.