Migration is a complex trait that often has genetic underpinnings. However, it is unclear if migratory behaviour itself is inherited (direct genetic control), or if the decision to migrate is instead the outcome of a set of physiological traits (indirect genetic control). For steelhead/rainbow trout (Oncorhynchus mykiss), migration is strongly linked to a large genomic region across their range. Here, we demonstrate a shared allelic basis between early life growth rate and migratory behaviour. Next, we demonstrate that early life growth differs among resident/migratory genotypes in wild juveniles several months prior to migration, with resident genotypes achieving a larger size in their first few months of life than migratory genotypes. We suggest that the genetic basis of migration is likely indirect and mediated by physiological traits such as growth rate. Evolutionary benefits of this indirect genetic mechanism likely include flexibility among individuals and persistence of life-history diversity within and among populations.

迁移是一个复杂的特征，通常具有遗传基础。然而，目前尚不清楚迁移行为本身是遗传的（直接遗传控制），还是决定迁移的决定是一组生理特征的结果（间接遗传控制）。对于硬头/虹鳟鱼（Oncorhynchus mykiss），迁移与整个范围内的大基因组区域紧密相关。在这里，我们证明了早期生命增长率和迁徙行为之间共有的等位基因基础。接下来，我们证明了在迁徙前几个月，野生少年的居民/迁徙基因型的早期生活增长有所不同，居民基因型在生命的前几个月中比迁徙基因型实现了更大的规模。我们建议迁移的遗传基础可能是间接的，并由诸如生长速率的生理特征介导。这种间接遗传机制的进化优势可能包括个体之间的灵活性以及种群内部和种群之间生命历史多样性的持久性。