Evolution of divergent female mating preference in response to experimental sexual selection.

Sexual selection is predicted to drive the coevolution of mating signals and preferences (mating traits) within populations, and could play a role in speciation if sexual isolation arises due to mating trait divergence between populations. However, few studies have demonstrated that differences in mating traits between populations result from sexual selection alone. Experimental evolution is a promising approach to directly examine the action of sexual selection on mating trait divergence among populations. We manipulated the opportunity for sexual selection (low vs. high) in populations of Drosophila pseudoobscura. Previous studies on these experimental populations have shown that sexual selection manipulation resulted in the divergence between sexual selection treatments of several courtship song parameters, including interpulse interval (IPI) which markedly influences male mating success. Here, we measure female preference for IPI using a playback design to test for preference divergence between the sexual selection treatments after 130 generations of experimental sexual selection. The results suggest that female preference has coevolved with male signal, in opposite directions between the sexual selection treatments, providing direct evidence of the ability of sexual selection to drive the divergent coevolution of mating traits between populations. We discuss the implications in the context sexual selection and speciation.

What do we need to know about speciation?

Speciation has been a major focus of evolutionary biology research in recent years, with many important advances. However, some of the traditional organising principles of the subject area no longer provide a satisfactory framework, such as the classification of speciation mechanisms by geographical context into allopatric, parapatric and sympatry classes. Therefore, we have asked where speciation research should be directed in the coming years. Here, we present a distillation of questions about the mechanisms of speciation, the genetic basis of speciation and the relationship between speciation and diversity. Our list of topics is not exhaustive; rather we aim to promote discussion on research priorities and on the common themes that underlie disparate speciation processes.

Plasticity, canalization, and developmental stability of the Drosophila wing: joint effects of mutations and developmental temperature.

The phenotypic effects of genetic and environmental manipulations have been rarely investigated simultaneously. In addition to phenotypic plasticity, their effect on the amount and directions of genetic and phenotypic variation is of particular evolutionary importance because these constitute the material for natural selection. Here, we used heterozygous insertional mutations of 16 genes involved in the formation of the Drosophila wing. The flies were raised at two developmental temperatures (18 degrees C and 28 degrees C). Landmark-based geometric morphometrics was used to analyze the variation of the wing size and shape at different hierarchical levels: among genotypes and temperatures; among individuals within group; and fluctuating asymmetry (FA). Our results show that (1) the phenotypic effects of the mutations depend on temperature; (2) reciprocally, most mutations affect wing plasticity; (3) both temperature and mutations modify the levels of FA and of among individuals variation within lines. Remarkably, the patterns of shape FA seem unaffected by temperature whereas those associated with individual variation are systematically altered. By modifying the direction of available phenotypic variation, temperature might thus directly affect the potential for further evolution. It suggests as well that the developmental processes responsible for developmental stability and environmental canalization might be partially distinct.