McNamara K B, Simmons L W
Centre for Evolutionary Biology, School of Biological Sciences (M092), The University of Western Australia, Crawley, WA, Australia.
J Evol Biol. 2017 Sep;30(9):1763-1771. doi: 10.1111/jeb.13139. Epub 2017 Aug 4.
Group living can select for increased immunity, given the heightened risk of parasite transmission. Yet, it also may select for increased male reproductive investment, given the elevated risk of female multiple mating. Trade-offs between immunity and reproduction are well documented. Phenotypically, population density mediates both reproductive investment and immune function in the Indian meal moth, Plodia interpunctella. However, the evolutionary response of populations to these traits is unknown. We created two replicated populations of P. interpunctella, reared and mated for 14 generations under high or low population densities. These population densities cause plastic responses in immunity and reproduction: at higher numbers, both sexes invest more in one index of immunity [phenoloxidase (PO) activity] and males invest more in sperm. Interestingly, our data revealed divergence in PO and reproduction in a different direction to previously reported phenotypic responses. Males evolving at low population densities transferred more sperm, and both males and females displayed higher PO than individuals at high population densities. These positively correlated responses to selection suggest no apparent evolutionary trade-off between immunity and reproduction. We speculate that the reduced PO activity and sperm investment when evolving under high population density may be due to the reduced population fitness predicted under increased sexual conflict and/or to trade-offs between pre- and post-copulatory traits.
鉴于寄生虫传播风险的增加，群居生活可能会选择增强免疫力。然而，鉴于雌性多次交配风险的提高，群居生活也可能会选择增加雄性的生殖投入。免疫与生殖之间的权衡已有充分记录。从表型上看，种群密度介导了印度谷螟（Plodia interpunctella）的生殖投入和免疫功能。然而，种群对这些性状的进化反应尚不清楚。我们创建了两个重复的印度谷螟种群，在高或低种群密度下饲养并交配14代。这些种群密度会引起免疫和生殖方面的可塑性反应：在数量较多时，两性都会在一种免疫指标[酚氧化酶（PO）活性]上投入更多，而雄性会在精子上投入更多。有趣的是，我们的数据显示PO和生殖方面的差异与先前报道的表型反应方向不同。在低种群密度下进化的雄性转移了更多精子，并且雄性和雌性的PO都高于高种群密度下的个体。这些对选择的正相关反应表明免疫与生殖之间没有明显的进化权衡。我们推测，在高种群密度下进化时PO活性和精子投入的降低可能是由于性冲突增加时预测的种群适应性降低和/或交配前和交配后性状之间的权衡。
