Reproductive character displacement of epicuticular compounds and their contribution to mate choice in Drosophila subquinaria and Drosophila recens

Abstract

Interactions between species can alter selection on sexual displays used in mate choice within species. Here we study the epicuticular pheromones of two Drosophila species that overlap partially in geographic range and are incompletely reproductively isolated. Drosophila subquinaria shows a pattern of reproductive character displacement against Drosophila recens, and partial behavioral isolation between conspecific sympatric versus allopatric populations, whereas D. recens shows no such variation in mate choice. First, using manipulative perfuming experiments, we show that females use pheromones as signals for mate discrimination both between species and among populations of D. subquinaria. Second, we show that patterns of variation in epicuticular compounds, both across populations and between species, are consistent with those previously shown for mating probabilities: pheromone compositions differ between populations of D. subquinaria that are allopatric versus sympatric with D. recens, but are similar across populations of D. recens regardless of overlap with D. subquinaria. We also identify differences in pheromone composition among allopatric regions of D. subquinaria. In sum, our results suggest that epicuticular compounds are key signals used by females during mate recognition, and that these traits have diverged among D. subquinaria populations in response to reinforcing selection generated by the presence of D. recens.

Keywords: Mate choice; pheromones; reinforcement; sexual selection; speciation.

Figure 1

Map of population locations used in this study. Locations are noted by their abbreviation in Table 1.

Figure 2

Individual variation in epicuticular compounds among male Drosophila recens (circles) and Drosophila subquinaria (squares) in response to perfuming. Pure (i.e., nonperfumed) individuals (open symbols) are shown in relation to perfumed individuals (filled symbols), with the latter including those individuals perfumed with their own (conspecific) males and those perfumed with sympatric D. subquinaria males. Ninety percent bivariate normal density ellipses are also shown for the various combinations of perfumed (solid lines) and nonperfumed (broken lines) groups.

Figure 3

Individual variation in epicuticular compounds of (A) female and (B) male Drosophila recens (circles) and Drosophila subquinaria (squares) collected from sympatric (filled symbols) and allopatric (open symbols) locations. Axes are the first and second canonical variates from a discriminate function analysis, conducted separately by sex, which discriminated among individuals according to species and population. Circles depict the 95% confidence limits for the means of the various sympatric (solid line) and allopatric (broken line) populations.