Experimental evidence for chemical mate guarding in a moth

Abstract

In polyandrous species, males seek to maximize their reproductive output by monopolizing their mate. Often the male transfers substances to the female that suppress her sexual receptivity or antagonize the behavior of competing males; both are usually transferred in seminal fluids and represent forms of chemical mate guarding. In moths, more long-range female sex pheromones have been identified than in any other animal group, and males often display with close-range sex pheromones, yet odor-based post-copulatory mate guarding has not been described in moths so far. We tested the hypothesis that the male sex pheromone in the noctuid moth Heliothis virescens perfumes the female and functions as an anti-aphrodisiac. Indeed, virgin females perfumed with male pheromone extract, or with its main component, mated significantly less than control virgin females, and this effect persisted for two successive nights. This chemical mate guarding strategy was disadvantageous for H. virescens females, because the reproductive output of twice-mated females was significantly higher than that of once-mated females. Since the female and male sex pheromones are biosynthetically related in this and other moth species, chemical mate guarding may also impose selection pressure on the long-range female sex pheromone channel and consequently affect the evolution of sexual communication.

A Life-History Perspective On Sexual Selection in a Polygamous Species

“…Field-caught females have been found to contain 7 spermatophores [39] and females mate up to 12 times under laboratory conditions [42]. Both males and females can mate only once a night [39,43], as each mating lasts on average 3 hours [43] and adults are sexually active only for 3-5 h during the night [44,45]. However, both sexes mate multiple nights [37][38][39][40][41]; this study.…”

“…Mate choice experiments indicate that females do not discriminate between virgin or mated males [43].…”

“…Sperm precedence and paternity allocation studies in H. virescens have shown that paternity patterns are quite variable, ranging from 100 % first or last male sperm precedence to complete sperm mixing [37,38,40,41,52,53], although on average the last male gains ~ 66 % paternity [53]. In mate choice experiments, we recently found that males choose virgin partners over mated partners [43].…”

“…Of course, the reduced mating of males with the same female may also be due to a female's change in behavior or physiology. For example, a female may decide not to remate with the same male, which she may recognize by the same 'perfume' that males apply with their hair pencils to the female during mating [43].…”

“…Moths are completely inactive during the daytime and become sexually active at specific hours at night [69]. Heliothis virescens is sexually active between three and 6-7 hours after sunset [44,45] and matings last on average 3 h [43]. Therefore, for five consecutive nights individual moths of all four treatments were observed every half hour with a red light to note copulating pairs, starting at the onset of the dark period (scotophase), in a climate chamber with the same conditions as described above.…”