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 equal sex ratios (C). Such treatment alters the level of intersexual conflict. Our studies show that males from the M populations rapidly evolve to be more harming 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. This is not unexpected since M females are known to have 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 these females, 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 would be 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 for the first time show that male reproductive behaviors can non-linearly be affected by the number of co-habitants experienced by a male in its early life. We found that copulation duration, an important component of male reproductive success showed an inverted u type relation with number of male co -habitants early in life. The copulation duration was positively correlated with sperm defense, another important component of fitness.

Our studies for the first time have shown 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 was positively correlated with variance in fitness of females indicating that males are capable of estimating the fitness differences among females.