Data from: Estimating the relative fitness of escaped farmed salmon offspring in the wild and modeling the consequences of invasion for wild populations

Throughout their native range, wild Atlantic salmon populations are
threatened by hybridization and introgression with escapees from net-pen
salmon aquaculture. Although domestic-wild hybrid offspring have shown
reduced fitness in lab and field experiments, consequential impacts on
population abundance and genetic integrity remain difficult to predict in
the field, in part because the strength of selection against domestic
offspring is often unknown and context-dependent. Here we follow a single
large escape event of farmed Atlantic salmon in southern Newfoundland and
monitor changes in the in-river proportions of hybrids and feral
individuals over time using genetically-based hybrid identification. Over
a three-year period following the escape, the overall proportion of wild
parr increased consistently (total wild proportion of 71.6%, 75.1%, 87.5%
each year, respectively), with subsequent declines in feral (genetically
pure farmed individuals originating from escaped, farmed adults) and
hybrid parr. We quantify the strength of selection against parr of
aquaculture ancestry and explore the genetic and demographic consequences
for populations in the region. Within-cohort changes in the relative
proportions of feral and F1 parr suggest reduced relative survival
compared to wild individuals over the first (0.15 and 0.81 for feral and
F1, respectively), and second years of life (0.26, 0.83). These relative
survivorship estimates were used to inform an individual-based salmon
eco-genetic model to project changes in adult abundance and overall allele
frequency across three invasion scenarios ranging from short-term to
long-term invasion and three relative survival scenarios. Modeling results
indicate that total population abundance and time to recovery were greatly
affected by relative survivorship and predict significant declines in wild
population abundance under continued large escape events and calculated
survivorship. Overall this work demonstrates the importance of estimating
the strength of selection against domestic offspring in the wild to
predict the long-term impact of farmed salmon escape events on wild
populations.

在其原生分布范围内，野生大西洋鲑（Atlantic salmon）种群正面临与网箱养殖鲑逃逸个体杂交及基因渐渗（introgression）的威胁。尽管室内与野外实验均表明，家养-野生杂交后代的适合度有所下降，但野外环境下其对种群丰度与遗传完整性的实际影响仍难以预测，部分原因在于针对家养后代的选择强度通常未知且依赖具体情境。本研究针对纽芬兰南部发生的单次大规模养殖大西洋鲑逃逸事件，采用基于遗传学的杂交个体鉴定方法，长期监测河流中杂交个体与野化个体的占比变化。逃逸事件发生后的三年内，野生幼鲑（parr）的整体占比持续上升（三年占比分别为71.6%、75.1%与87.5%），而野化幼鲑（即源自逃逸养殖成体的基因纯合养殖个体）与杂交幼鲑的占比则持续下降。本研究量化了针对养殖血统幼鲑的选择强度，并探讨了该区域种群面临的遗传与种群动态后果。野化幼鲑与F1杂交幼鲑的同龄组相对占比变化显示，相较于野生幼鲑，二者在生命第一年（野化与F1分别为0.15与0.81）与第二年（分别为0.26与0.83）的相对存活率均有所降低。我们将这些相对存活率估算值应用于基于个体的鲑鱼生态遗传模型（eco-genetic model），针对三种短期至长期的入侵情景与三种相对存活率情景，预测成体种群丰度与整体等位基因频率（allele frequency）的变化。模型结果显示，种群总丰度与恢复时间均受相对存活率的显著影响；研究预测，若持续发生大规模逃逸事件且选择强度为本次估算值，则野生种群丰度将出现显著下降。综上，本研究证实了野外环境下针对家养后代的选择强度估算的重要性，可为预测养殖鲑逃逸事件对野生种群的长期影响提供依据。