Data from: Relationship between effective population size, inbreeding, and adult fitness-related traits in a steelhead (Oncorhynchus mykiss) population released in the wild

Inbreeding is of concern in supportive breeding programmes in Pacific salmonids, Oncorhynchus spp, where the number of breeding adults is limited by rearing space or poor survival to adulthood, and large numbers are released to supplement wild stocks and fisheries. We reconstructed the pedigree of 6602 migratory hatchery steelhead (Oncorhynchus mykiss) over four generations, to determine the incidence and fitness consequences of inbreeding in a northwest USA programme. The hatchery maintained an effective population size, = 107.9 from F0 to F2, despite an increasing census size (N), which resulted in a decreasing Ne/N ratio (0.35 in F0 to 0.08 in F2). The reduced ratio was attributed to a small broodstock size, nonrandom transfers and high variance in reproductive success (particularly in males). We observed accumulation of inbreeding from the founder generation (in F4, percentage individuals with inbreeding coefficients Δf > 0 = 15.7%). Generalized linear mixed models showed that body length and weight decreased significantly with increasing Δf, and inbred fish returned later to spawn in a model that included father identity. However, there was no significant correlation between Δf and age at return, female fecundity or gonad weight. Similarly, there was no relationship between Δf and reproductive success of F2 and F3 individuals, which might be explained by the fact that reproductive success is partially controlled by hatchery mating protocols. This study is one of the first to show that small changes in inbreeding coefficient can affect some fitness-related traits in a monitored population propagated and released to the wild.

太平洋鲑属（Oncorhynchus spp.）鱼类的支持性繁育计划中，近亲繁殖始终是广受关注的问题。此类计划中，繁殖亲体的数量常受限于养殖空间不足或成体存活率低下，随后会放流大量幼体以补充野生种群及渔业资源。本研究对美国西北部某繁育计划下的6602尾洄游型孵化场养殖钢头鳟（Oncorhynchus mykiss）开展了跨四个世代的家系重建工作，以明确该计划中近亲繁殖的发生率及其适合度相关后果。该孵化场的有效种群大小（effective population size, Ne）在F0至F2世代间维持为107.9；尽管普查种群数量（N）持续增长，却导致Ne/N比值逐步下降，从F0世代的0.35降至F2世代的0.08。该比值降低的原因可归结为亲本群体规模偏小、非随机转移以及繁殖成功率的高变异（尤以雄性个体为甚）。研究观测到自奠基世代起的近亲繁殖累积现象：在F4世代中，近交系数Δf＞0的个体占比达15.7%。广义线性混合模型（Generalized Linear Mixed Models, GLMM）分析结果显示，随着Δf升高，个体体长与体重显著降低；在纳入父本身份作为变量的模型中，近交个体的洄游产卵时间显著延后。但Δf与回归产卵年龄、雌性繁殖力或性腺重量之间并未呈现显著相关性。同理，Δf与F2、F3世代个体的繁殖成功率也无关联，这一结果可由繁殖成功率部分受孵化场交配方案调控的事实得到解释。本研究是首批证实：在人工繁育并放归野外的监测种群中，近交系数的小幅变化即可对部分与适合度相关的性状产生影响。