Department of Evolutionary Ecology, MNCN-CSIC, c/ José Gutiérrez Abascal 2, Madrid, E-28006, Spain; CIBIO, InBIO - Research Network in Biodiversity and Evolutionary Biology, Universidade do Porto, Campus de Vairão, Rua Padre Armando Quintas, 4485-661, Vairão, Portugal.
Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, 95064, CA, USA; Department of Biodiversity, Abasaheb Garware College, Pune, India.
Ticks Tick Borne Dis. 2020 Jan;11(1):101275. doi: 10.1016/j.ttbdis.2019.101275. Epub 2019 Aug 21.
It is generally accepted that parasites exert negative effects on their hosts and that natural selection favors specific host responses that mitigate this impact. It is also known that some components of the host immune system often co-evolve with parasite antigens resulting in a host-parasite arms race. In addition to immunological components of the anti-parasitic response, host behavioral responses are also important in this arms race and natural selection may favor avoidance strategies that preclude contact with parasites, or shifts in the host's thermoregulatory strategy to combat active infections (e.g., behavioral fever). Ticks are widespread parasites with direct and indirect costs on their vertebrate hosts. Their saliva provokes hemolysis in the blood of their hosts and can transmit a plethora of tick-borne pathogens. We enquired whether tick infestation by Ixodes pacificus can provoke a thermoregulatory response in Sceloporus occidentalis. For this, we compared the thermoregulatory behavior of tick-infested lizards against tick-infested lizards co-infected with two different species of coccidians (Lankesterella occidentalis and Acroeimeria sceloporis). After this, lizards were kept in individual terraria with a basking spot and fed ad libitum. We found that tick-infested lizards sought cooler temperatures in proportion to their tick load, and this response was independent of the co-infection status by L. occidentalis. This was consistent in April and June (when tick loads were significantly lower) and suggests a conservative strategy to save energy which might have been selected to overcome tick infestations during phenological peaks of this parasite. However, this behavior was not observed in lizards co-infected with A. sceloporis, suggesting that co-infection with this intestinal parasite prompt lizards to be active. Cost of tick infestation was confirmed because housed lizards lost weight at a constant ratio to initial tick load, independently of other infections. The broader implications of these findings are discussed in the context of climate change.
人们普遍认为寄生虫对宿主产生负面影响，而自然选择有利于宿主产生特定的反应来减轻这种影响。此外，我们已知宿主免疫系统的某些成分通常与寄生虫抗原共同进化，从而导致宿主-寄生虫的军备竞赛。除了抗寄生虫反应的免疫成分外，宿主的行为反应在这场军备竞赛中也很重要，自然选择可能有利于避免与寄生虫接触的策略，或者改变宿主的体温调节策略来对抗活动性感染（例如，行为性发热）。蜱是广泛存在的寄生虫，对其脊椎动物宿主有直接和间接的成本。它们的唾液会引起宿主血液中的溶血，并能传播大量蜱传病原体。我们询问了太平洋硬蜱的寄生是否会引起西部锦蛇的体温调节反应。为此，我们比较了感染蜱的蜥蜴与感染两种不同球虫（西部曼氏球虫和西部蛇孢球虫）的感染蜱的蜥蜴的体温调节行为。之后，将蜥蜴放入单独的饲养箱中，有一个晒点，并自由喂食。我们发现，感染蜱的蜥蜴会根据其蜱的负载寻求更凉爽的温度，而这种反应与西部曼氏球虫的共感染状态无关。这在 4 月和 6 月（当蜱的负载明显较低时）是一致的，这表明这是一种节省能量的保守策略，可能是为了在这种寄生虫的物候高峰期克服蜱的寄生而选择的。然而，在感染了 A. sceloporis 的蜥蜴中没有观察到这种行为，这表明与这种肠道寄生虫的共感染促使蜥蜴更加活跃。寄生蜱的成本得到了证实，因为饲养的蜥蜴以与初始蜱负载成正比的恒定比例减重，而与其他感染无关。这些发现的更广泛意义在气候变化的背景下进行了讨论。
