The genomic and adaptive consequences of extreme, human-mediated population decline

人们对野生生物种群严重减少的后果知之甚少。经历这种衰退的物种的生存可能会受到以下因素的阻碍：适应不断变化的环境的能力有限、生育力下降以及对疾病的易感性--所有这些都源于低遗传多样性。当应用于由于人类活动而经历了种群瓶颈的系统时，基因组工具使我们能够从近亲交配、遗传负载、抗病和适应性方面检查基因组的后果。我们的目的是通过一个剧烈的人类干预的例子来了解种群极端快速下降的后果，在这个例子中，整个湖泊的鱼类种群被根除并重新繁殖。鲑鱼体外寄生虫Gyrodactylus Salaris引入挪威导致野生大西洋鲑鱼种群的崩溃。因此，当局将鱼藤酮-一种广谱杀菌剂-应用于整个河流流域，以杀死所有鱼类宿主。一旦经过处理，水道就会重新放养当地鱼类种群中未受感染的人工饲养的幼鱼。2012年，福斯塔集水区(四个线性连接的亚北极湖泊)经历了鱼藤酮计划。在治疗之前，鱼类群落包括湖间迁徙的褐鲑鱼。遗传评估显示出显著的种群结构，在海上捕获的滨河鲑鱼有很高比例可以归入Fusta种群。此外，这些分析检测到选择中的基因座，表明整个系统的局部适应。尤其是褐鲑鱼和淡水型鲑鱼，近年来经历了大幅下降，这种治疗可能会威胁到褐鲑鱼的遗传健康。这个系统提供了一个独特的机会来了解(I)极端瓶颈对物种基因组的影响，(Ii)遗传多样性的丧失如何影响对寄生虫的免疫力，以及(Iii)在遗传恶化的种群中发生快速适应的过程。

The consequences of severe population decline in wild organisms are poorly understood. Survival of species experiencing such declines may be hampered by a limited ability to adapt to changing environments, reduced fertility and greater susceptibility to disease - all stemming from low genetic diversity. When applied to systems that have experienced population bottlenecks as a result of human activities, genomic tools allow us to examine the genomic consequences in terms of inbreeding, genetic load, disease resistance and adaptability. Our aim is to understand the consequences of extreme, rapid population decline using an example of drastic human intervention in which the fish stocks of entire lakes were eradicated and repopulated.The introduction of the salmonid ectoparasite Gyrodactylus salaris to Norway resulted in the collapse of wild Atlantic salmon populations. Consequently, authorities applied Rotenone - a broad-spectrum biocide - to entire river catchments to kill all fish hosts. Once treated, waterways are restocked with uninfected captive-bred juveniles from local fish stocks. In 2012 the Fusta catchment (four linearly-connected sub-arctic lakes) underwent a rotenone program. Prior to treatment, fish communities included inter-lake migratory brown trout. Genetic assessment revealed significant population structure and a high proportion of anadromous trout caught at sea could be assigned to Fusta populations. Furthermore, these analyses detected loci under selection suggesting local adaptation across the system. Brown trout and the anadromous form, in particular, have experienced substantial declines in recent years and such treatments may threaten the genetic health of brown trout. This system represents a unique opportunity to understand (i) the impact of extreme bottlenecks on the genome of a species, (ii) how loss of genetic diversity influences immunity to parasites and (iii) the processes by which rapid adaptation occurs in genetically depauperate populations.