Signatures of aestivation and migration in Sahelian malaria mosquito populations

摘要

携带疟疾的蚊子在旱季会消失，但当雨季来到撒哈拉以南非洲时它们则会突然出现。它们在一年中干旱的一半时间里的行为长期以来都像谜一样。在这篇论文中，Tovi Lehmann及同事报告了对蚊子密度所做的为期五年的考察，其结果显示了携带疟疾的三种主要蚊子的种群动态的季节模式，然后他们又用这些模式来推断蚊子在旱季的行为。对两种蚊子（Anopheles arabiensis和A. gambiae s.s.）来说，其种群动态与长距离迁移相一致；对第三种蚊子Anopheles coluzzii），其种群动态与成年个体在旱季休眠或夏蛰相一致。这些自然史发现为改进疟疾控制（目前仍是一大公共卫生挑战）提供了基本机会。%During the long Sahelian dry season, mosquito vectors of malaria are expected to perish when no larval sites are available; yet, days after the first rains, mosquitoes reappear in large numbers. How these vectors persist over the 3-6-month long dry season has not been resolved, despite extensive research for over a century. Hypotheses for vector persistence include dry-season diapause (aestivation) and long-distance migration (LDM); both are facets of vector biology that have been highly controversial owing to lack of concrete evidence. Here we show that certain species persist by a form of aestivation, while others engage in LDM. Using time-series analyses, the seasonal cycles of Anopheles coluzzii, Anopheles gambiae sensu stricto (s.s.), and Anopheles arabiensis were estimated, and their effects were found to be significant, stable and highly species-specific. Contrary to all expectations, the most complex dynamics occurred during the dry season, when the density of A. coluzzii fluctuated markedly, peaking when migration would seem highly unlikely, whereas A. gambiae s.s. was undetected. The population growth of A. coluzzii followed the first rains closely, consistent with aestivation, whereas the growth phase of both A. gambiae s.s. and A. arabiensis lagged by two months. Such a delay is incompatible with local persistence, but fits LDM. Surviving the long dry season in situ allows A. coluzzii to predominate and form the primary force of malaria transmission. Our results reveal profound ecological divergence between A. coluzzii and A. gambiae s.s., whose standing as distinct species has been challenged, and suggest that climate is one of the selective pressures that led to their speciation. Incorporating vector dormancy and LDM is key to predicting shifts in the range of malaria due to global climate change, and to the elimination of malaria from Africa.