The developmental plasticity and functional significance of an additional sperm storage compartment in female yellow dung flies

1. The mechanistic basis for, and adaptive significance of variation in female sperm storage organs is important for a range of questions concerning sexual selection and speciation, as such variation influences the evolutionary trajectories of male fertilization related traits and may facilitate speciation through its effects on gamete recognition. 2. Female yellow dung flies (Scathophaga stercoraria) usually develop three sperm storage compartments, and this subdivision may be an adaptation for sorting sperm during post-copulatory choice. 3. Using lines artificially selected to express four spermathecae (4s), we explored the fitness consequences of the novel phenotype relative to the naturally prevalent three-spermatheca (3s) phenotype by manipulating the opportunity for post-copulatory sexual selection (females mated either with three or only one male prior to oviposition). In addition, we examined the developmental plasticity of spermathecal number in response to different larval foo...