We still have a limited understanding of why animals colonize extreme environments, but one hypothesis (the Pathogen Refuge Hypothesis, PRH) posits that they might represent a safe haven from parasites and other pathogens. We tested this idea by quantifying endoparasite infections in five populations of the neotropical freshwater fish Poecilia mexicana, three populations from toxic, H₂S-rich habitats and two control populations from nearby rivers and creeks. Counter to predictions derived from the PRH, only P. mexicana from toxic habitats harboured heterophyid metacercariae in their hearts. We further uncovered differences in parasite prevalences and abundances between the three toxic habitats. Our results provide evidence against the PRH and add depth to our understanding of life in (and adaptation to) extreme environments.

对于动物为何在极端环境中定居，我们仍知之甚少，但一种假设（病原体避难所假说，PRH）认为它们可能代表寄生虫和其他病原体的避风港。我们通过量化五种新热带淡水鱼类Poecilia mexicana，三种来自有毒，富含H ₂ S的栖息地的种群以及两个来自附近河流和小溪的控制种群的内寄生虫感染来测试了这一想法。与PRH得出的预测相反，只有P. mexicana来自有毒栖息地的心脏在他们的体内隐匿着异生meta虫。我们进一步发现了三个有毒生境之间的寄生虫流行率和丰度之间的差异。我们的研究结果提供了反对公共卫生的证据，并加深了我们对极端环境（和适应极端环境）生活的理解。