LAUSR

ABSTRACT Great reed warblers (Acrocephalus arundinaceus) have become an important species for understanding long-distance avian migration, yet the genetic basis of their migratory timing remains unknown. While previous studies have identified candidate genes influencing migration timing in other species, their role in great reed warblers remains unexplored. Additionally, it is unclear whether the genetic basis of migratory timing differs between spring and autumn migrations. This study aims to uncover genetic factors influencing migration timing, providing insights into the evolutionary and ecological processes shaping long-distance migration. We conducted pooled whole-genome sequencing representing four great reed warbler migratory chronotypes: early spring, late spring, early autumn, and late autumn. By comparing FST and allele frequency differences, we determined that the spring migration had a larger genetic contribution than the autumn migration; however, the effect sizes were small (0.03 and 0.001, respectively). When comparing the early and late spring pools, we identified 93 candidate genes enriched for functions related to lipid hydrolysis that putatively influence great reed warbler migratory behavior. Our results provide insight into the genetic differentiation underlying migratory timing in great reed warblers, which is crucial for predicting how they will adapt to shifting environmental conditions due to climate change and habitat loss.