Data from: Evolution of behavioral and cellular defenses against parasitoid wasps in the Drosophila melanogaster subgroup

It may be intuitive to predict that host immune systems will evolve to counter a broad range of potential challenges through simultaneous investment in multiple defenses. However, this would require diversion of resources from other traits, such as growth, survival, and fecundity. Therefore, ecological immunology theory predicts that hosts will specialize in only a subset of possible defenses. We tested this hypothesis through a comparative study of a cellular immune response and a putative behavioral defense used by eight fruit fly species against two parasitoid wasp species (one generalist and one specialist). Fly larvae can survive infection by melanotically encapsulating wasp eggs and female flies can potentially reduce infection rates in their offspring by laying fewer eggs when wasps are present. The strengths of both defenses varied significantly but were not negatively correlated across our chosen host species; thus, we found no evidence for a trade-off between behavioral and cellular immunity. Instead, cellular defenses were significantly weaker against the generalist wasp, whereas behavioral defenses were similar in strength against both wasps and positively correlated between wasps. We investigated the adaptive significance of wasp-induced oviposition reduction behavior by testing whether wasp-exposed parents produce offspring with stronger cellular defenses, but we found no support for this hypothesis. We further investigated the sensory basis of this behavior by testing mutants deficient in either vision or olfaction, both of which failed to reduce their oviposition rates in the presence of wasps, suggesting that both senses are necessary for detecting and responding to wasps.人们可直观推测，宿主免疫系统会通过同时投入多种防御机制，进化出应对广泛潜在挑战的能力，但这需要将资源从生长、存活与繁殖力（fecundity）等其他性状中转移。因此，生态免疫学理论（ecological immunology theory）预测，宿主仅会专攻部分潜在防御策略。我们通过比较8个果蝇物种针对2种寄生蜂（1种广食性寄生蜂与1种专食性寄生蜂）所采用的细胞免疫应答（cellular immune response）与推定行为防御（putative behavioral defense），对该假说进行了验证。果蝇幼虫可通过黑色素包囊化寄生蜂卵从而抵御感染，而雌性果蝇在寄生蜂存在时可通过减少产卵量，降低子代的感染风险。两种防御的强度在所选宿主物种间均存在显著差异，但二者之间未呈现负相关；因此，我们未发现行为免疫与细胞免疫之间存在权衡（trade-off）的证据。进一步分析显示，细胞免疫对广食性寄生蜂的防御强度显著更弱，而行为防御对两种寄生蜂的防御强度均相近，且在不同寄生蜂处理下呈正相关。我们通过检验寄生蜂暴露的亲代是否会产生细胞免疫更强的子代，探究了寄生蜂诱导的产卵量降低行为的适应性意义，但未找到支持该假说的证据。我们还通过分别测试视觉（vision）或嗅觉（olfaction）缺陷的突变体（mutants），探究了该行为的感官基础，结果发现两类突变体均无法在寄生蜂存在时降低产卵量，这表明两种感官均是检测并响应寄生蜂所必需的。