Data from: No apparent cost of evolved immune response in Drosophila melanogaster

Maintenance and deployment of the immune system are costly and are hence predicted to trade-off with other resource demanding traits, such as reproduction. We subjected this long standing idea to test using laboratory experimental evolution approach. In the present study, replicate populations of Drosophila melanogaster were subjected to three selection regimes – I (Infection with Pseudomonas entomophila), S (Sham-infection with MgSO4) and U (Unhandled Control). After 30 generations of selection flies from the I-regime had evolved better survivorship upon infection with P. entomophila compared to flies from U and S regimes. However, contrary to expectations and previous reports, we did not find any evidence of trade-offs between immunity and other life-history related traits, such as longevity, fecundity, egg hatchability or development time. After 45 generations of selection, the selection was relaxed for a set of populations. Even after 15 generations, the post-infection survivorship of populations under relaxed selection regime did not decline. We speculate that either there is a negligible cost to the evolved immune response or that trade-offs occur on traits like reproductive behaviour or other immune mechanisms that we have not investigated in this study. Our research suggests that at least under certain conditions, life-history trade-offs might play little role in maintaining variation in immunity.

免疫系统的维持与运作均需消耗资源，因此理论上其会与繁殖等其他高资源需求性状存在进化权衡。我们采用实验室实验进化研究方法，对这一长期存在的假说开展实证检验。本研究中，黑腹果蝇（Drosophila melanogaster）的重复种群被分为三种选择处理组：I组（感染昆虫假单胞菌（Pseudomonas entomophila））、S组（以硫酸镁（MgSO₄）进行假感染）以及U组（未处理对照组）。经过30代选择后，相较于U组与S组的果蝇，I组果蝇在感染P. entomophila后的存活率显著提升。然而与预期及既往研究结果相悖的是，我们未发现免疫系统与寿命、繁殖力、卵孵化率或发育时间等其他生活史相关性状间存在进化权衡的证据。在第45代选择完成后，我们对部分种群实施了松弛选择。即便经过15代松弛选择后，经松弛选择的种群在感染后的存活率也未出现下降。我们推测，要么是进化获得的免疫应答几乎不存在能量成本，要么是进化权衡效应出现在本研究未考察的繁殖行为或其他免疫机制等性状上。本研究表明，至少在特定条件下，生活史权衡在维持免疫性状遗传变异方面的作用可能微乎其微。