Genetic variation in male-induced harm in Drosophila melanogaster

Abstract

In Drosophila melanogaster, prolonged exposure to males reduces the longevity and fecundity of females. This harm arises from the effects of male courtship behaviours and the toxic side effects of the accessory gland proteins (Acps) in their seminal fluids. Here, we examine the relationship between male exposure and its harmful effect on the lifetime fitness of his mates, and quantify the genetic basis for this variation. We found significant additive genetic variation in the magnitude of harm that males impose on females by exposing females to males from a variety of hemiclonal backgrounds for either a brief or prolonged period of time and measuring their fecundity, a meaningful fitness index. Furthermore, we discovered a strong negative correlation between the magnitude of harm and the short-term effects of male exposure on female fitness. We discuss the evolutionary significance of these results with regards to potential life-history trade-offs in females, and its relationship to male body size.

Keywords: Drosophila melanogaster; fitness; male-induced harm; mate choice; population genetics; sexual conflict.

Figure 1.

Effect of male genotype and exposure treatment on fecundity (number of eggs laid on day 14 of the culture cycle) of female Drosophila melanogaster. The reaction norm plot at the centre depicts female fecundity for each of the 26 hemiclone lines across the two male-exposure duration treatments, while boxplots illustrate the overall differences between the treatments. The boxes enclose the middle 50% of each distribution (inter-quartile range, IQR), with the horizontal bars indicating the location of the medians. Values > ±1.5 × IQR are outliers, and are indicated by closed circles, and whiskers extend from the margins of the box to the minimum and maximum values that are not outliers.

Figure 2.

Scatterplot and regression line illustrating the negative relationship between fecundity of females in the short-term treatment, and the net-cost of prolonged male exposure in female Drosophila melanogaster that had been exposed to 26 different male hemiclone lines. Fecundity is defined as the number of eggs laid by females on day 14 of their culture cycle.