SamOtos_withStrayAssignment.csv from High dispersal rates in hybrids drive expansion of maladaptive hybridization

Hybridization between native and invasive species, a major cause of biodiversity loss, can spread rapidly even when hybrids have reduced fitness. This paradox suggests that hybrids have greater dispersal rates than non-hybridized individuals, yet this mechanism has not been empirically tested in animal populations. Here, we test if non-native genetic introgression increases reproductive dispersal using a human-mediated hybrid zone between native cutthroat trout (Oncorhynchus clarkii) and invasive rainbow trout (Oncorhynchus mykiss) in a large and connected river system. We quantified the propensity for individuals to migrate from natal rearing habitats (migrate), reproduce in non-natal habitats (stray), and the joint probability of dispersal as a function of genetic ancestry. Hybrid trout with predominantly non-native rainbow trout ancestry were more likely to migrate as juveniles and to stray as adults. Overall, hybrids with greater than 50% rainbow trout ancestry were 5.7 times more likely to disperse than native or hybrid trout with small amounts of rainbow trout ancestry. Our results show a genetic basis for increased dispersal in hybrids that is likely contributing to the rapid expansion of invasive hybridization between these species. Management actions that decrease the probability of hybrid dispersal may mitigate the harmful effects of invasive hybridization on native biodiversity.本土物种与入侵物种的种间杂交是引发生物多样性丧失的关键诱因之一，即便杂交后代的适合度有所下降，该杂交过程仍可快速扩散。这一悖论表明杂交个体的扩散速率高于非杂交个体，但该机制尚未在动物种群中得到实证验证。本研究依托大型连通水系中由人类活动介导的本土割喉鳟（Oncorhynchus clarkii）与入侵虹鳟（Oncorhynchus mykiss）的杂交带体系，检验非本土遗传渐渗是否会提升繁殖扩散能力。我们量化了个体从出生育幼栖息地迁出的倾向（洄游）、在非出生栖息地完成繁殖的倾向（异域繁殖），并以遗传祖先比例为协变量构建了扩散行为的联合概率模型。遗传背景以入侵虹鳟为主的杂交鳟，其幼体阶段的洄游概率与成体阶段的异域繁殖概率均显著更高。总体而言，虹鳟遗传成分占比超过50%的杂交个体，其扩散概率是本土割喉鳟或虹鳟遗传占比极低的杂交个体的5.7倍。本研究结果证实了杂交个体扩散能力提升的遗传基础，该机制极有可能推动了两物种种间入侵杂交的快速扩散。通过采取降低杂交个体扩散概率的管理措施，可有效缓解入侵杂交对本土生物多样性造成的负面影响。