Data from: Limited hatchery introgression into wild brook trout (Salvelinus fontinalis) populations despite reoccurring stocking

Due to increased anthropogenic pressures on many fish populations, supplementing wild populations with captive-raised individuals has become an increasingly common management practice. Stocking programs can be controversial due to uncertainty about the long-term fitness effects of genetic introgression on wild populations. In particular, introgression between hatchery and wild individuals can cause declines in wild population fitness, resiliency, and adaptive potential, and contribute to local population extirpation. However, low survival and fitness of captive-raised individuals can minimize the long-term genetic consequences of stocking in wild populations, and to date the prevalence of introgression in actively stocked ecosystems has not been rigorously evaluated. We quantified the extent of introgression in 30 populations of wild brook trout (Salvelinus fontinalis) in a Pennsylvania watershed, and examined the correlation between introgression and 11 environmental covariates. Genetic assignment tests were used to determine the origin (wild vs. captive-raised) for 1742 wild-caught and 300 hatchery brook trout. To avoid assignment biases, individuals were assigned to two simulated populations that represented the average allele frequencies in wild and hatchery groups. Fish with intermediate probabilities of wild ancestry were classified as introgressed, with threshold values determined through simulation. Even with reoccurring stocking at most sites, over 93% of wild-caught individuals probabilistically assigned to wild origin, and only 6% of wild-caught fish assigned to introgressed. Models examining environmental drivers of introgression explained less than 3% of the among-population variability, and all estimated effects were highly uncertain. This was not surprising given overall low introgression observed in this study. Our results suggest that introgression of hatchery-derived genotypes can occur at low rates, even in actively stocked ecosystems and across a range of habitats. However, a cautious approach to stocking may still be warranted, as the potential effects of stocking on wild population fitness and the mechanisms limiting introgression are not known.由于众多鱼类种群正面临日益加剧的人为压力（anthropogenic pressures），通过投放人工繁育个体以补充野生种群，已成为愈发常见的渔业管理实践。放流计划（stocking programs）常因遗传渐渗（genetic introgression）对野生种群适合度（wild population fitness）的长期影响存在不确定性而颇具争议。具体而言，孵化场繁育个体与野生个体间的遗传渐渗，可能导致野生种群适合度、恢复力（resiliency）及适应潜力（adaptive potential）下降，并加剧局部种群灭绝（extirpation）。不过，人工繁育个体的存活率与适合度较低，可降低放流对野生种群产生的长期遗传后果；但截至目前，针对活跃放流生态系统中遗传渐渗的发生频率，尚未有严谨的评估研究。本研究对宾夕法尼亚州流域（Pennsylvania watershed）内30个野生溪红点鲑（Salvelinus fontinalis）种群的遗传渐渗程度进行了量化，并分析了渐渗与11项环境协变量（covariates）间的相关性。研究采用遗传归属测试（genetic assignment tests），对1742尾野生捕获个体及300尾孵化场溪红点鲑的起源（野生或人工繁育）进行判定。为避免归属偏差，我们将个体划分至两个模拟种群（simulated populations），分别代表野生组与孵化场组的平均等位基因频率（allele frequencies）。将具有中等野生祖先（ancestry）概率的个体归类为渐渗个体，其阈值通过模拟实验确定。尽管多数站点持续开展放流活动，但超过93%的野生捕获个体被概率性判定为野生起源，仅6%的野生捕获个体被归类为渐渗个体。针对渐渗环境驱动因子的模型仅解释了种群间变异的不到3%，且所有估计效应的不确定性均极高。鉴于本研究中观测到的整体低渐渗率，这一结果并不意外。研究结果表明，即便在活跃放流的生态系统中且覆盖多种生境，孵化场来源基因型的遗传渐渗仍可能以低速率发生。不过，仍需采取谨慎的放流策略，因为放流对野生种群适合度的潜在影响，以及限制渐渗的机制，目前仍未明确。