Understanding the drivers of species distribution is necessary in order to properly predict the future geographical ranges of colonizing species. Yet this task is challenging for species involved in intimate interactions, such as parasites, since their distribution is likely shaped by a complex interplay between environmental‐related and host‐related factors. Here we developed an original approach combining species distribution models (SDMs) and population genomics to test whether the local environmental conditions or the host genomic background most likely limits the colonization of an emerging freshwater fish ectoparasite, Tracheliastes polycolpus. We hypothesized that the absence of T. polycolpus in some areas may be due to an unsuitable environment in these areas (the ‘environmental suitability hypothesis') and/or to the presence of resistant hosts in these areas (the ‘genomic background hypothesis'). Using a SDM set at the French spatial extent, we first found that the environmental conditions of an uninfected area were as suitable for the parasite as those of infected areas. Then, using single nucleotide polymorphisms (SNPs) data at the host genome scale, we demonstrated that there was a strong association between the spatial occurrence of parasites and the host genomic background. In particular, the area in which the parasite was absent sustained a unique host population from a genomic standpoint, and ninety SNPs were significantly associated to the infection status (parasitized versus unparasitized) of individual hosts. We concluded that the spatial distribution of T. polycolpus (and its colonization potential) was more likely limited by intrinsic host characteristics associated to parasite resistance, rather than to the local environmental conditions. This study illustrates the usefulness of combining modeling and genomic approaches to reveal the determinants of species distribution and to improve predictions about their future ranges.

中文翻译：

---

物种分布模型和种群基因组学的结合强调了新兴寄生虫范围限制的决定因素

为了正确预测殖民物种的未来地理范围，有必要了解物种分布的驱动因素。然而，对于涉及亲密相互作用的物种（例如寄生虫）而言，这项任务是具有挑战性的，因为它们的分布可能由环境相关因素与寄主相关因素之间复杂的相互作用所决定。在这里，我们开发了一种结合物种分布模型（SDMs）和种群基因组学的原始方法，以测试当地的环境条件或宿主基因组背景是否最有可能限制新兴淡水鱼外寄生物Tracheliastes polycolpus的定殖。我们假设不存在T. polycolpus在某些地区，可能是由于这些地区的环境不适合（“环境适宜性假设”）和/或这些地区中存在抗性宿主（“基因组背景假设”）所致。我们首先使用法国空间范围内的SDM设置，首先发现未感染区域的环境条件与感染区域一样适合寄生虫。然后，使用宿主基因组规模的单核苷酸多态性（SNPs）数据，我们证明了寄生虫的空间发生与宿主基因组背景之间有很强的联系。特别地，从基因组的角度来看，没有寄生虫的区域维持了独特的宿主种群，并且90个SNP与单个宿主的感染状况（被寄生或未被寄生）显着相关。T. polycolpus（及其定殖潜力）更可能受到与寄生虫抗性相关的固有宿主特征的限制，而不是受当地环境条件的限制。这项研究说明了结合建模和基因组方法来揭示物种分布的决定因素并改善对它们未来范围的预测的有用性。