Copulatory plugs(CP)are substances produced during copulation that block the genital openings of the female.In several species of Nematoda,males produce CP that are thought to impede female remating and thus sperm com...Copulatory plugs(CP)are substances produced during copulation that block the genital openings of the female.In several species of Nematoda,males produce CP that are thought to impede female remating and thus sperm competition.The relatively large size of the CP in several nematodes,and its evolutionary loss in self-fertilizing populations of Caenorhabditis elegans,suggests that CP are costly to produce.If CP production is costly,the application of basic concepts of strategic ejaculation theory suggests a modulated allocation of CP in response to sperm competition risk.This hypothesis led us to predict that males perceiving a higher risk of sperm competition will produce larger CP.We tested these ideas with the entomopathogenic,gonochoristic nematode Rhabditis regina.Our first experiment provides evidence suggesting that production of CP is costly,because the size of CP is negatively affected by stressful conditions(high population density,small male adult size,and suboptimal food type).The results of our second experiment support the prediction that males adjust the size of CP to sperm competition risk:the average size of CP increased as the number of males competing for one female increased.Overall,our study supports the idea that in R.regina the production of CP is costly for males and that the size of the CP produced is influenced by sperm competition risk.展开更多
It has been proposed that given that males should invest in sexual traits at the expense of their investment in immune response, females are better immunocompetent than males. Typically, this idea has been tested in m...It has been proposed that given that males should invest in sexual traits at the expense of their investment in immune response, females are better immunocompetent than males. Typically, this idea has been tested in monomorphic species, but rarely has been evaluated in polymorphic male species. We used Paraphlebia zoe, a damselfly with two male morphs： the black-winged morph （Black-W） develop black spots as sexual traits and the hyaline-winged morph （Hyaline-W） resembles a female in size and wings color. We predicted that Black-W should have a lower immune response than Hyaline-W, but that the latter males should not differ from females in this respect. Nitric oxide （NO） and phenoloxidase （PO） production, as well as hemolymph protein content, were used as immune markers. Body size （wing length） was used as an indicator of the male condition. The results show that, as we predicted, females and Hyaline-W had higher values of NO than Black-W, corresponding to differences in size. However, the opposite was found in relation to PO production. Females had the highest levels of hemolymph protein content, whereas no differences were found between Black-W and Hyaline-W. These results partially support the sexual selection hypothesis and are discussed in the context of the life history of this species. Black-W, Hyaline-W, and females could express the immune markers that are prioritized by their particular condition, and probably neither of them could express all immune markers in an elevated manner, as this would result in an excessive accumulation of free radicals.展开更多
文摘Copulatory plugs(CP)are substances produced during copulation that block the genital openings of the female.In several species of Nematoda,males produce CP that are thought to impede female remating and thus sperm competition.The relatively large size of the CP in several nematodes,and its evolutionary loss in self-fertilizing populations of Caenorhabditis elegans,suggests that CP are costly to produce.If CP production is costly,the application of basic concepts of strategic ejaculation theory suggests a modulated allocation of CP in response to sperm competition risk.This hypothesis led us to predict that males perceiving a higher risk of sperm competition will produce larger CP.We tested these ideas with the entomopathogenic,gonochoristic nematode Rhabditis regina.Our first experiment provides evidence suggesting that production of CP is costly,because the size of CP is negatively affected by stressful conditions(high population density,small male adult size,and suboptimal food type).The results of our second experiment support the prediction that males adjust the size of CP to sperm competition risk:the average size of CP increased as the number of males competing for one female increased.Overall,our study supports the idea that in R.regina the production of CP is costly for males and that the size of the CP produced is influenced by sperm competition risk.
文摘It has been proposed that given that males should invest in sexual traits at the expense of their investment in immune response, females are better immunocompetent than males. Typically, this idea has been tested in monomorphic species, but rarely has been evaluated in polymorphic male species. We used Paraphlebia zoe, a damselfly with two male morphs： the black-winged morph （Black-W） develop black spots as sexual traits and the hyaline-winged morph （Hyaline-W） resembles a female in size and wings color. We predicted that Black-W should have a lower immune response than Hyaline-W, but that the latter males should not differ from females in this respect. Nitric oxide （NO） and phenoloxidase （PO） production, as well as hemolymph protein content, were used as immune markers. Body size （wing length） was used as an indicator of the male condition. The results show that, as we predicted, females and Hyaline-W had higher values of NO than Black-W, corresponding to differences in size. However, the opposite was found in relation to PO production. Females had the highest levels of hemolymph protein content, whereas no differences were found between Black-W and Hyaline-W. These results partially support the sexual selection hypothesis and are discussed in the context of the life history of this species. Black-W, Hyaline-W, and females could express the immune markers that are prioritized by their particular condition, and probably neither of them could express all immune markers in an elevated manner, as this would result in an excessive accumulation of free radicals.
