Sperm competition and mate harm unresponsive to male-limited selection in Drosophila: an evolving genetic architecture under domestication.

Earlier research by W.R. Rice showed that experimentally limiting gene expression to males in Drosophila melanogaster leads to the rapid evolution of higher fitness. Using a similar male-limited (ML) selection protocol, we confirmed that result and showed that eliminating intralocus sexual conflict results in a comprehensive remodeling of the sexually dimorphic phenotype. However, despite starting from laboratory-evolved descendants of the same founder population used in earlier work, we found no evidence for the increased performance in sperm competition or increased postmating harm to females previously demonstrated. We employed females with both ancestral population genotypes and those of the special "clone generator" females used in ML selection. Despite strong differences in sperm storage or usage patterns between these females, there was no detectable adaptation by males to the specific female stock used in the selection protocol. The lack of evolution of postcopulatory traits suggests either that requisite genetic variation was eliminated by long-term domestication of the base population, or that complex male-by-male-by-female interactions made these traits unavailable to selection. The different evolutionary outcomes produced by two very similar experiments done at different time points underscores the potential for cryptic adaptation in the laboratory to qualitatively affect inferences made using quantitative genetic methodologies.