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Exposure to juvenile males during development suppresses female capacity for parthenogenesis in a stick insect

Burke, Nathan W., Bonduriansky, Russell
Animal behaviour 2019 v.154 pp. 85-94
Extatosoma tiaratum, adults, animals, asexual reproduction, eggs, fecundity, females, hatching, juveniles, leaves, males, parthenogenesis, prediction, rearing
The rarity of facultative asexuality in animals is an evolutionary puzzle. It has been hypothesized that male factors that influence female performance could be key to this paradox because parthenogens that fail to obtain fitness-increasing stimulation from males at certain life stages may reproduce poorly via parthenogenesis. However, given that certain male factors can reduce female fitness, an alternative hypothesis is that exposure to male factors could exert a sexually antagonistic suppressive effect on females' capacity for parthenogenesis. To test the contrasting predictions of these two hypotheses, we used the spiny leaf stick insect, Extatosoma tiaratum, a species capable of both sexual and asexual reproduction, to investigate developmental age-dependent effects of nonmating exposure to males on female behaviour and parthenogenetic performance, with exposure to other females as a control. We found that females reared with immature males were more likely than controls to show resistance-like behaviours as juveniles. Moreover, as adults, females reared with immature males produced asexual eggs with greatly depressed hatching success, resulting in a two-fold reduction in asexual performance compared to controls. By contrast, nonmating exposure to adult males at maturity had little effect on female behaviour or performance. However, females maintained exclusively with other females had slightly reduced fecundity, perhaps due to deprivation of fecundity-increasing male stimulation. Our results suggest that interactions with juvenile males can suppress the development of females’ parthenogenetic capacity, an effect that appears to be sexually antagonistic. Such effects could help to explain the rarity of facultative asexuality in animal systems.