Evolution Under Relaxed Sexual Conflict in the Bulb Mite Rhizoglyphus Robini

Abstract

The experimental evolution under different levels of sexual conflict have been used to demonstrate antagonistic coevolution in muscids, but among other taxa a similar approach has not been employed. Here, we describe the results of 37 generations of evolution under either experimentally enforced monogamy or polygamy in the bulb mite Rhizoglyphus robini. Three replicates were maintained for each treatment. Monogamy makes male and female interests congruent; thus selection is expected to decrease harmfulness of males to their partners. Our results were consistent with this prediction in that females from monogamous lines achieved lower fecundity when housed with males from polygamous lines. Fecundity of polygamous females was not affected by mating system under which their partners evolved, which suggests that they were more resistant to male-induced harm. As predicted by the antagonistic coevolution hypothesis, the decrease in harmfulness of monogamous males was accompanied by a decline in reproductive competitiveness. In contrast, female fecundity and embryonic viability, which were not expected to be correlated with male harmfulness, did not differ between monogamous and polygamous lines. None of the fitness components assayed differed between individuals obtained from crosses between parents from the same line and those obtained from crosses between parents from different lines within the same mating system. This indicates that inbreeding depression did not confound our results. However, interpretation of our results is complicated by the fact that both males and females from monogamous lines evolved smaller body size compared to individuals from polygamous lines. Although a decrease in reproductive performance of males from monogamous lines was still significant when body size was taken into account, we were not able to separate the effects of male body size and mating system in their influence on fecundity of their female partners.

The consequences of polyandry for population viability, extinction risk and conservation

“…water striders [32], lizards [33], sea lions [34], Drosophila [35]). Experimental evolution studies manipulating the mating system have provided some of the strongest evidence that polyandry selects for both elevated male harm and costly female resistance to that harm [36][37][38][39][40]; for example, Crudgington et al [41] showed that males evolved under polyandry courted females more frequently, and that females housed with these males produced fewer progeny than females interacting with males evolved under monogamy. Additionally, female dung flies evolved under polyandry were found to be less fecund than monogamous females when mating only once, implying that female adaptations to male harm have a cost that outweighs the potential genetic benefits of sexual selection [40].…”

Female responses to experimental removal of sexual selection components in Drosophila melanogaster

“…They found that monogamous populations had greater net reproductive rate than (promiscuous) controls, while fecundity of monogamous females was reduced after mating with ancestral (promiscuous) males [23]. After this seminal paper, several other studies employed a similar methodology in different taxa [24][25][26][27][28][29][30][31][32][33][34], briefly reviewed by Edward et al [20], with some degree of variation in experimental design and outcome.…”

Mating system affects population performance and extinction risk under environmental challenge

“…Indeed, a polygamous mating system has been shown to help purge inbreeding depression and decrease extinction rate, compared with a monogamous system, in bottlenecked bulb mite populations [34]. On the other hand, sexual conflict has been shown to negatively affect reproductive success of bulb mite females, and the harmful effects of males on females were selected against under enforced monogamy [35]. These harmful effects of polygamy may actually increase the risk of the population being caught into an extinction vortex.…”