Flightless is not a general rule on islands: ability of long-distance flight has been maintained by pigeons in highly insular habitat

Reduction in dispersal ability represented by the shifts in energetic investment from forelimb to hindlimb has been thought to be a general trend for island landbirds. Whereas, recent studies suggested wide-range movements of some pigeons among islands, which might be related to food resource availability. For some island pigeons, it may be more adaptive to maintain dispersal ability rather than to reduce it. Here we investigated whether island pigeons can maintain high dispersal ability, comparing two subspecies of Japanese Wood Pigeon *Columba janthina* distributed on islands with different levels of insularity. *C. j. nitens* on higher-insularity islands showed larger investment in hindlimb but had a wing shape better suited for long-distance flight. Genome-wide MIG-seq SNPs data indicated that both subspecies maintained sufficient gene flow across each habitat with no evidence of isolation by distance. Using MIG-seq SNPs and whole-genome sequencing data, the divergence time of each subspecies was estimated to be 0.6 million years ago, which was sufficient to reduce dispersiveness compared with other cases of island landbirds. Our findings indicated a crucial case in the evolutionary studies on island landbirds, that is, the increased investment in hindlimb does not always reduce their dispersal ability, and maintaining dispersiveness could be adaptive even in a highly insular environment.