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联系在一起--可能对生态系统健康和服务造成严重后果。流行可能通过范围转移，或通过寄主易感性和寄生虫毒力的温度敏感性而发生。这意味着，在正常条件下毒力较低的寄生虫，当环境条件发生变化时，可能会在其通常的范围内成为主要病原体。在这种情况下，导致疾病爆发的机制至关重要地取决于病原体的共同进化史。例如，在变暖的条件下，具有较高传染性或毒力的寄生虫菌株可能更受青睐，或者寄生虫菌株之间的寄主专一性程度可能预先使某些寄主物种或种群具有更高的死亡率。该项目旨在调查在水生新出现的疾病系统中，是否存在由气候变化驱动的疾病出现的基因组基础，或者仅在多种应激源下宿主的易感性和耐受性之间的动态是否可以驱动疾病的爆发。我们将重点关注增殖性肾脏病(PKD)--一种在欧洲和北美养殖和野生鲑鱼的新兴疾病。预计PKD的频率和严重程度将随着气候变化而增加，因为感染期间的病理变化的发展是强烈的温度驱动。所有的鲑鱼都可以被引起沙门氏菌(Cnidaria门)的四种寄生虫感染，但人们对这种广泛存在的、具有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)描述苔藓毛滴虫在其已知和新出现的全北极分布中的种群基因组结构和差异，2)通过关注广泛的鲑鱼宿主来评估宿主特异性适应模式，以及3)利用全基因组关联研究将寄生虫遗传分化模式与疾病暴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.