Data from: Evolution of Drosophila resistance against different pathogens and infection routes entails no detectable maintenance costs

Pathogens exert a strong selective pressure on hosts, entailing host adaptation to infection. This adaptation often affects negatively other fitness-related traits. Such trade-offs may underlie the maintenance of genetic diversity for pathogen resistance. Trade-offs can be tested with experimental evolution of host populations adapting to parasites, using two approaches: (1) measuring changes in immunocompetence in relaxed-selection lines and (2) comparing life-history traits of evolved and control lines in pathogen-free environments. Here, we used both approaches to examine trade-offs in Drosophila melanogaster populations evolving for over 30 generations under infection with Drosophila C Virus or the bacterium Pseudomonas entomophila, the latter through different routes. We find that resistance is maintained after up to 30 generations of relaxed selection. Moreover, no differences in several classical life-history traits between control and evolved populations were found in pathogen-free environments, even under stresses such as desiccation, nutrient limitation, and high densities. Hence, we did not detect any maintenance costs associated with resistance to pathogens. We hypothesize that extremely high selection pressures commonly used lead to the disproportionate expression of costs relative to their actual occurrence in natural systems. Still, the maintenance of genetic variation for pathogen resistance calls for an explanation.病原体对宿主施加了强烈的选择压力，迫使宿主演化出对感染的适应性。这类适应性往往会对其他与适合度相关的性状产生负面影响。这种适合度权衡可能是维持病原体抗性遗传多样性的潜在机制。可通过宿主种群适应寄生虫的实验演化来检验这类权衡，具体采用两种方法：（1）测定松弛选择品系的免疫能力变化；（2）在无病原体环境中比较演化种群与对照种群的生活史性状。本研究同时采用这两种方法，对在果蝇C病毒（Drosophila C Virus）或嗜虫假单胞菌（Pseudomonas entomophila，后者通过不同侵染途径）感染下演化超过30代的黑腹果蝇（Drosophila melanogaster）种群进行权衡分析。我们发现，即使经过多达30代的松弛选择，病原体抗性仍得以维持。此外，在无病原体环境中，即使面临脱水、营养限制和高密度等胁迫条件，对照种群与演化种群的多项经典生活史性状均未出现显著差异。因此，我们未检测到与病原体抗性维持相关的任何适合度成本。我们推测，实验中常用的极高选择压力，导致了适合度成本的表达比例高于其在自然系统中的实际发生水平。尽管如此，病原体抗性相关遗传变异的维持仍需要合理的解释。