Sexual Selection and Sexual Conflict
We are studying antagonistic co-evolution between the sexes and its influence on life-history traits. We have created three different regimes (with three replicates in each regime) in which flies are held at male-biased (M), female-biased (F) or unbiased sex ratios (C). Such a treatment alters the level of intersexual conflict.
Our studies show that males from the M populations rapidly evolve to be more harmful to the females. Females housed with M males tend to die more often than females housed with F males. Interestingly, males from the base population housed with females from the M population tend to die more often too. This is not unexpected since M females are known to have a higher mating latency. Additionally, M females have higher locomotor activity. Hence, it is quite possible that males housed with M females expend more energy courting and chasing them, leading to accelerated rates of death.
We have found that the mean life-span of M individuals is lower than that of F individuals when measured as virgins, indicating that the intrinsic rates of aging in these populations has increased as expected. However, under mated conditions, the mean longevity of M females is higher than that of the F females indicating that M females have evolved greater resistance to male-induced harm.
Our studies are the first to show that male reproductive behaviour can be affected non-linearly by the number of co-habitants experienced by a male early in his life. We have found that copulation duration, an important component of male reproductive success, shows an inverted u type relation with the number of male co -habitants early in life. Copulation duration is positively correlated with sperm defence, another important component of fitness.
Our studies also show adaptive male mate choice based on female age and nutritional status. Males tended to mate more with younger and/or well-fed females when offered a choice. Interestingly, variance in male mate choice is positively correlated with variance in the fitness of females, indicating that males are capable of estimating fitness differences among females.