Genetic structure of the Japanese Robin (Larvivora akahige) endemic to East Asian islands

Abstract

Geographical isolation is a key factor in allopatric speciation although divergence with gene flow has been detected in an increasing number of studies, even in island systems. To understand the divergence in island taxa, it is necessary to examine historical gene flow with mainland sister groups, which largely differ due to the various geological and ecological characteristics of each region. The Izu Islands are a chain of young and active volcanic islands in a warm‐temperate climate zone that branch off from the middle of the Japanese mainland. Despite the chain's relatively limited isolation, given its proximity to the mainland, the Izu Islands feature endemic bird species and subspecies. The Japanese Robin Larvivora akahige is an endemic breeder on East Asian islands, and there is also a subspecies on the Izu Islands that is different in feather coloration and ecological traits. The population genetic structure of this robin was investigated using nine nuclear microsatellite markers and mitochondrial cytochrome b region sequences. Distinct and recent differentiation between the groups from the Izu Islands and mainland was detected from nuclear loci, although the genetic structure within the mainland group was unclear over the 1900‐km habitat chain. The mitochondrial haplotypes were divided into two distant clades, one dominated throughout the robin's range and the other coexisting only on the Izu Islands as a minor type. Those clades were inferred to have diverged independent of the recent differentiation of the two nuclear clusters, although their origins and the mechanism underlying their distribution remain unclear. The geographical characteristics of the Izu Islands may have formed a moderate but long‐lasting barrier for gene flow and promoted speciation, as well as serving as refugia for the preservation of relict lineages, particularly for migratory species, which usually move along the mainland chain.