Fishing for parasite genomes: host-parasite co-evolution of an emerging salmonid disease

气候和环境的变化与疾病的出现有关，可能对生态系统健康和服务造成严重后果。流行病可能通过范围变化或宿主易感性和寄生虫毒力的温度敏感性产生。这意味着，在正常条件下毒性较低的寄生虫，在环境条件发生变化时，可能在其通常范围内成为主要的疾病媒介。在这种情况下，导致疾病爆发的机制在很大程度上取决于病原体的共同进化史。例如，具有较高传染性或毒力的寄生虫菌株在变暖条件下可能更受欢迎，或者寄生虫菌株之间的宿主特异性程度可能使某些宿主物种或种群的死亡率更高。本项目旨在研究气候变化驱动水生新发疾病系统中疾病出现是否存在基因组基础，或者多个应激源下宿主易感性和耐受性之间的动态是否可以驱动疾病暴发。我们将重点关注增殖性肾脏疾病(PKD) -一种在欧洲和北美养殖和野生鲑鱼中出现的新疾病。预计PKD的频率和严重程度会随着气候变化而增加，因为感染期间病理改变的发展是强烈的温度驱动的。所有的沙门氏菌都可以被致病寄生虫——苔藓沙门氏菌四纲（刺胞门）感染，但人们对这种广泛存在的、具有重要生态和经济意义的寄生虫的遗传结构和菌株特异性毒力知之甚少。该项目将1)在其已知和新兴的全北极分布中描述布氏沙门氏菌的种群基因组结构和分化特征；2)通过关注广泛的沙门氏菌宿主来评估宿主特异性适应模式；3)通过全基因组关联研究将寄生虫遗传分化模式与疾病爆发期间的致病性估计联系起来。

Changing climates and environments are linked with the emergence of diseases - with potentially severe consequences for ecosystem health and services. Epidemics may arise through range-shifts, or via temperature-sensitivity of host susceptibility and parasite virulence. This implies that parasites with low virulence under normal conditions, may emerge as major disease agents in their usual ranges when the environmental conditions change. Under such scenarios, the mechanisms leading to disease outbreaks crucially depend on the coevolutionary history of the pathogen. For example, parasite strains with higher infectivity or virulence may be favoured under warming conditions, or the degree of host specificity among parasite strains may pre-dispose certain host species or populations to higher mortality. This project aims to investigate whether there is a genomic basis to climate change driven disease emergence in an aquatic emerging disease system, or whether the dynamic between host susceptibility and tolerance under multiple stressors alone can drive disease outbreaks. We will focus on Proliferative Kidney Disease (PKD) - an emerging disease farmed and wild salmonids in Europe and in North America. PKD is predicted to increase in frequency and severity with climate change, as the development of the pathological alterations during infection is strongly temperature driven. All salmonids can be infected by the causative parasite Tetracapsuloides bryosalmonae (Phylum Cnidaria), but little is known about the genetic structure and strain specific virulence in this widespread, ecologically and economically important parasite. This project will 1) characterise the population genomic structure and divergence of T. bryosalmonae across its known and emerging Holarctic distribution, 2) evaluate patterns of host-specific adaptation by focusing on a broad range salmonid hosts, and 3) link patterns of parasite genetic differentiation with estimates of pathogenicity during a disease outbreak using a genome-wide association study.