Data from: Fitness consequences of altered feeding behavior in immune-challenged mosquitoes

Background: Malaria-infected mosquitoes have been reported to be more likely to take a blood meal when parasites are infectious than when non-infectious. This change in feeding behavior increases the likelihood of malaria transmission, and has been considered an example of parasite manipulation of host behavior. However, immune challenge with heat-killed Escherichia coli induces the same behavior, suggesting that altered feeding behavior may be driven by adaptive responses of hosts to cope with an immune response, rather than by parasite-specific factors. Here we tested the alternative hypothesis that down-regulated feeding behavior prior to infectiousness is a mosquito adaptation that increases fitness during infection. Methods: We measured the impact of immune challenge and blood feeding on the fitness of individual mosquitoes. After an initial blood meal, Anopheles stephensi Liston mosquitoes were experimentally challenged with heat-killed E. coli at a dose known to mimic the same temporal changes in mosquito feeding behavior as active malaria infection. We then tracked daily egg production and survivorship of females maintained on blood-feeding regimes that either mimicked down-regulated feeding behaviors observed during early malaria infection, or were fed on a four-day feeding cycle typically associated with uninfected mosquitoes. Results: Restricting access to blood meals enhanced mosquito survival but lowered lifetime reproduction. Immune- challenge did not impact either fitness component. Combining fecundity and survival to estimate the population- scale intrinsic rate of increase (r), we found that, contrary to the mosquito adaptation hypothesis, mosquito fitness decreased if blood feeding was delayed following an immune challenge. Conclusions: Our data provide no support for the idea that malaria-induced suppression of blood feeding is an adaptation by mosquitoes to reduce the impact of immune challenge. Alternatively, the behavioral alterations may be neither host nor parasite adaptations, but rather a consequence of constraints imposed on feeding by activation of the mosquito immune response, i.e. non-adaptive illness-induced anorexia. Future work incorporating field conditions and different immune challenges could further clarify the effect of altered feeding on mosquito and parasite fitness.背景：已有研究表明，感染疟原虫的蚊子在寄生虫具备感染性时，相较于寄生虫无感染性时，更倾向于吸食血液。这种取食行为的改变会提升疟疾传播概率，此前被视为寄生虫操纵宿主行为的典型案例。然而，用热灭活大肠杆菌（Escherichia coli）进行免疫刺激同样会诱发此类行为，这提示取食行为的改变可能是宿主为应对免疫反应而产生的适应性应答所致，而非寄生虫特异性因子的作用。本研究对另一假说展开验证：即蚊子在寄生虫具备感染性前下调取食行为，是一种可提升感染期自身适合度的适应性策略。 方法：本研究测定了免疫刺激与吸血行为对单只蚊子适合度的影响。实验先让斯氏按蚊（Anopheles stephensi Liston）吸食初始血液餐，随后以已知可模拟活动性疟原虫感染时蚊子取食行为时序变化的剂量，注射热灭活大肠杆菌（E. coli）进行免疫刺激。随后，我们追踪了两组雌蚊的每日产卵量与存活情况：一组的取食制度模拟疟疾早期感染时出现的取食下调行为，另一组则采用通常对应未感染蚊子的4天取食周期。 结果：限制吸血频次可提升蚊子的存活能力，但会降低其终身繁殖力。免疫刺激并未对这两项适合度指标产生影响。结合繁殖力与存活数据估算种群水平的内禀增长率（r）后，我们发现：与蚊子适应性假说相悖，免疫刺激后延迟吸血会降低蚊子的适合度。 结论：本研究数据不支持“疟疾诱导的吸血行为抑制是蚊子为减轻免疫反应影响而产生的适应性策略”这一观点。换言之，此类行为改变既非宿主的适应性应答，也非寄生虫的操纵行为，而是蚊子免疫应答激活后对取食行为产生限制的结果，即非适应性的疾病诱发性厌食。未来可结合野外环境与不同免疫刺激场景开展研究，以进一步明确取食行为改变对蚊子与疟原虫适合度的影响。