Data from: Can interbreeding of wild and artificially propagated animals be prevented by using broodstock selected for a divergent life history?

Two strategies have been proposed to avoid negative genetic effects of artificially propagated individuals on wild populations: (i) integration of wild and captive populations to minimize domestication selection, and (ii) segregation of released individuals from the wild population to minimize interbreeding. We tested the efficacy of the strategy of segregation by divergent life history in a steelhead trout, Oncorhynchus mykiss system, where hatchery fish were selected to spawn months earlier than the indigenous wild population. Up to 80% of the naturally produced steelhead in any given year were hatchery-wild hybrids. The proportion of wild ancestry smolts and adults declined by 10 to 20% over the three generations since the beginning of the program, due to an increase in hybrids. Regression model selection analysis suggested that proportions of hybrid smolts and adults were positively correlated with the number of naturally spawning hatchery-produced adults. Furthermore, the proportion of smolt hybrids was higher in years with high stream discharge allowing hatchery fish to bypass the weir protecting wild spawning habitat. Divergent life history failed to prevent interbreeding when physical isolation was compromised following changes in environmental conditions, an inadequacy of the segregation strategy that is likely to prevail in many other situations.

为规避人工繁育个体对野生种群产生的负面遗传影响，学界已提出两类应对策略：（一）整合野生种群与圈养种群，以最大限度降低驯化选择的影响；（二）将放归个体与野生种群隔离，以尽可能减少种群间杂交繁殖。我们以硬头鳟（steelhead trout，*Oncorhynchus mykiss*）为研究对象，检验了基于分化生活史的隔离策略的有效性——该系统中，孵化场繁育的个体产卵时间较本土野生种群提前数月。

在任意给定年份，天然产出的硬头鳟中最高可达80%为孵化场-野生种群杂交个体。自该项目实施以来的三代间，具有野生血统的降海幼体与成体的占比因杂交个体数量增加而下降了10%至20%。回归模型遴选分析结果显示，杂交降海幼体与成体的占比与天然产卵的孵化场繁育成体数量呈正相关。

此外，在河流径流量较高的年份，孵化场繁育的个体可绕过保护野生产卵栖息地的堰坝，此时杂交降海幼体的占比更高。

当环境条件变化导致物理隔离失效时，基于分化生活史的隔离策略无法阻止杂交繁殖；这一隔离策略的缺陷很可能在诸多其他场景中普遍存在。