Field of Genetics, Genomics, and Development, Cornell University, Ithaca, NY 14853, USA; Department of Entomology, Cornell University, Ithaca, NY 14853, USA.
Field of Genetics, Genomics, and Development, Cornell University, Ithaca, NY 14853, USA; Department of Entomology, Cornell University, Ithaca, NY 14853, USA.
J Insect Physiol. 2022 Jul;140:104414. doi: 10.1016/j.jinsphys.2022.104414. Epub 2022 Jun 18.
In many species, female reproductive investment comes at a cost to immunity and resistance to infection. Mated Drosophila melanogaster females are more susceptible to bacterial infection than unmated females. Transfer of the male seminal fluid protein Sex Peptide reduces female post-mating immune defense. Sex Peptide is known to cause both short- and long-term changes to female physiology and behavior. While previous studies showed that females were less resistant to bacterial infection as soon as 2.5 h and as long as 26.5 h after mating, it is unknown whether this is a binary switch from mated to unmated state or whether females can recover to unmated levels of immunity. It is additionally unknown whether repeated mating causes progressive reduction in defense capacity. We compared the immune defense of mated females when infected at 2, 4, 7, or 10 days after mating to that of unmated females and saw no recovery of immune capacity regardless of the length of time between mating and infection. Because D. melanogaster females can mate multiply, we additionally tested whether a second mating, and therefore a second transfer of seminal fluids, caused deeper reduction in immune performance. We found that females mated either once or twice before infection survived at equal proportions, both with significantly lower probability than unmated females. We conclude that a single mating event is sufficient to persistently suppress the female immune system. Interestingly, we observed that induced levels of expression of genes encoding antimicrobial peptides (AMPs) decreased with age in both experiments, partially obscuring the effects of mating. Collectively, the data indicate that being reproductively active versus reproductively inactive are alternative binary states with respect to female D. melanogaster immunity. The establishment of a suppressed immune status in reproductively active females can inform our understanding of the regulation of immune defense and the mechanisms of physiological trade-offs.
在许多物种中，雌性生殖投资会对免疫和抗感染能力造成代价。交配后的黑腹果蝇雌蝇比未交配的雌蝇更容易受到细菌感染。雄性精液蛋白性肽的转移会降低雌性交配后的免疫防御能力。性肽被认为会导致雌性的生理和行为发生短期和长期的变化。虽然之前的研究表明，雌性在交配后 2.5 小时和 26.5 小时后对细菌感染的抵抗力下降，但尚不清楚这是从交配到未交配状态的二元转换，还是雌性可以恢复到未交配状态的免疫水平。此外，尚不清楚重复交配是否会导致防御能力逐渐降低。我们比较了交配后 2、4、7 或 10 天感染的交配雌性的免疫防御能力与未交配雌性的免疫防御能力，发现无论交配和感染之间的时间长短如何，免疫能力都没有恢复。由于黑腹果蝇雌蝇可以多次交配，我们还测试了第二次交配，也就是第二次精液转移，是否会导致免疫性能更深的降低。我们发现，感染前交配一次或两次的雌性以相等的比例存活，其存活概率均显著低于未交配的雌性。我们得出结论，单次交配事件足以持续抑制雌性免疫系统。有趣的是，我们观察到，在两个实验中，编码抗菌肽（AMPs）的基因的诱导表达水平随着年龄的增长而下降，这部分掩盖了交配的影响。总的来说，这些数据表明，相对于雌性黑腹果蝇的免疫力，生殖活跃与生殖不活跃是两种替代的二元状态。在生殖活跃的雌性中建立受抑制的免疫状态可以为我们理解免疫防御的调节和生理权衡的机制提供信息。
