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.

研究背景：已有研究表明，疟原虫具有感染性时，感染疟疾的蚊子更易吸食血液，相较疟原虫无感染性时更为明显。这种取食行为的改变会提升疟疾传播概率，曾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）进行免疫激发也能引发相同的行为变化，这提示取食行为的改变可能源于宿主应对免疫应答的适应性反应，而非寄生虫特异性因子所致。本研究旨在验证另一假说：疟原虫具有感染性前取食行为下调是蚊子的适应性策略，可提升感染期间的适合度。

研究方法：本研究检测了免疫激发与血液取食对单只蚊子适合度的影响。在初始血餐后，我们用已知可模拟活动性疟疾感染时蚊子取食行为时间动态变化的剂量的热灭活大肠杆菌（E. coli）对斯氏按蚊（Anopheles stephensi Liston）进行实验性免疫激发。随后，我们追踪了两类雌蚊的每日产卵量与存活情况：一类的取食制度模拟疟疾感染早期出现的取食行为下调模式，另一类则采用未感染蚊子典型的四天取食周期。

研究结果：限制血液取食可提升蚊子的存活能力，但会降低其终身繁殖力。免疫激发对这两项适合度指标均无影响。结合繁殖力与存活数据估算种群水平的内禀增长率（intrinsic rate of increase, r）后，我们发现：与蚊子适应性假说相悖，若免疫激发后延迟血液取食，蚊子的适合度会下降。

研究结论：本研究数据不支持"疟疾诱导的血液取食抑制是蚊子为减轻免疫激发影响而产生的适应性策略"这一观点。换言之，这种行为改变既非宿主的适应性反应，也非寄生虫的适应性操纵，而是蚊子免疫应答激活后对取食行为造成约束的结果，即非适应性的疾病诱导性厌食。未来可结合野外环境与不同免疫激发场景开展研究，以进一步阐明取食行为改变对蚊子与疟原虫适合度的影响。