Enforced monoandry over generations induces a reduction of female investment into reproduction in a promiscuous bird

Abstract

While uncovering the costs and benefits of polyandry has attracted considerable attention, assessing the net effect of sexual selection on population fitness requires the experimental manipulation of female mating over generations, which is usually only achievable in laboratory populations of arthropods. However, knowing if sexual selection improves or impairs the expression of life-history traits is key for the management of captive populations of endangered species, which are mostly long-lived birds and mammals. It might therefore be questionable to extrapolate the results gathered on laboratory populations of insects to infer the net effect of sexual selection on populations of endangered species. Here, we used a longitudinal dataset that has been collected on a long-lived bird, the houbara bustard, kept in a conservation breeding program, to investigate the effect of enforced monoandry on female investment into reproduction. In captivity, female houbara bustards are artificially inseminated with sperm collected from a single male (enforced monoandry), or sequentially inseminated with semen of different males (polyandry), allowing postcopulatory sexual selection to operate. We identified female lines that were produced either by monoandrous or polyandrous inseminations over three generations, and we compared reproductive investment of females from the two mating system groups. We found that females in the polyandrous lines had higher investment into reproduction as they laid more eggs per season and produced heavier hatchlings. Higher reproductive investment into reproduction in the polyandrous lines did not result from inherited differences from females initially included in the two mating system groups. These results show that removal of sexual selection can alter reproductive investment after only few generations, potentially hindering population fitness and the success of conservation breeding programs.

Ranking parameters driving siring success during sperm competition in the North African houbara bustard

“…Before the first egg of the clutch is laid, two sequential inseminations are performed with a 48 h interval (but occasionally females can lay after the first insemination); a third, fourth (and so on) insemination can be added if required (i.e., if the first egg of the clutch takes longer to come than expected) 53 . Therefore, depending on when the egg is laid, females can be inseminated once, twice, or more.…”

“…Therefore, depending on when the egg is laid, females can be inseminated once, twice, or more. Such successive inseminations can involve sperm collected from the same male or from different males [with each insemination involving sperm from a single male (e.g., no mix of sperm was used)] 53 . When females are successively inseminated with sperm from different males, sperm competition can occur 53 .…”

“…These inclusion rules were based on the following rationale. Female houbara bustards can store sperm in dedicated structure and use them well after insemination has occurred 53 . However, the probability of egg fertilization decreases as a function of the time elapsed between insemination and egg laying; therefore, we set a conservative limit to 30 days before egg laying for data inclusion.…”