Dávila Francisco, Botteaux Anne, Bauman David, Chérasse Sarah, Aron Serge
Evolutionary Biology and Ecology, Université Libre de Bruxelles, 1050 Brussels, Belgium.
Laboratory of Molecular Bacteriology, Université Libre de Bruxelles, 1070 Brussels, Belgium.
J Exp Biol. 2018 Mar 26;221(Pt 6):jeb175158. doi: 10.1242/jeb.175158.
Bacteria can damage sperm and thus reduce the reproductive success of both males and females; selection should therefore favour the evolution of antimicrobial protection. Eusocial hymenopterans might be particularly affected by such bacterial infections because of their mating ecology. In both sexes, mating is restricted to a short window early in the adult stage; there are no further chances to mate later in life. Males die shortly after mating, but queens use the acquired sperm to fertilise their eggs for years, sometimes decades. The reproductive success of both sexes is, thus, ultimately sperm-limited, which maintains strong selection for high sperm viability before and after storage. We tested the antibacterial activity of the contents of the male and female sperm-storage organs - the accessory testes and the spermatheca, respectively. As our study species, we used the bacterium and the garden ant , whose queens can live for several decades. Our results provide the first empirical evidence that male and female sperm-storage organs display different antibacterial activity. While the contents of the accessory testes actually enhanced bacterial growth, the contents of the spermatheca strongly inhibited it. Furthermore, mating appears to activate the general immune system in queens. However, antimicrobial activity in both the spermatheca and the control tissue (head-thorax homogenate) declined rapidly post-mating, consistent with a trade-off between immunity and reproduction. Overall, this study suggests that ejaculates undergo an immune 'flush' at the time of mating, allowing storage of sperm cells free of bacteria.
细菌会损害精子，从而降低雄性和雌性的繁殖成功率；因此，自然选择应有利于抗菌保护机制的进化。群居膜翅目昆虫可能因其交配生态而特别容易受到此类细菌感染的影响。在雄性和雌性中，交配都局限于成年早期的一个短暂窗口期；成年后没有再次交配的机会。雄性在交配后不久就会死亡，但蚁后会利用获取的精子为其卵子受精数年，有时甚至数十年。因此，雄性和雌性的繁殖成功率最终都受到精子数量的限制，这使得在精子储存前后对高精子活力的选择压力很大。我们分别测试了雄性和雌性精子储存器官——副睾和受精囊——内容物的抗菌活性。作为我们的研究物种，我们使用了细菌和花园蚁，其蚁后可以存活数十年。我们的结果提供了首个实证证据，表明雄性和雌性精子储存器官具有不同的抗菌活性。虽然副睾的内容物实际上促进了细菌生长，但受精囊的内容物却强烈抑制了细菌生长。此外，交配似乎会激活蚁后的全身免疫系统。然而，受精囊和对照组织（头胸部匀浆）中的抗菌活性在交配后迅速下降，这与免疫和繁殖之间的权衡一致。总体而言，这项研究表明，射精在交配时会经历一次免疫“冲洗”，从而使精子细胞能够在无细菌的情况下储存。
