Abstract
Aim Founder effects and recurrent immigration are two major factors that potentially contribute to genetic differentiation and population persistence in the early-stage of remote island colonization. However, their relative importance remains controversial. By conducting population genetics analyses of multiple remote island populations of the bull-headed shrike established naturally within several decades, we examined the relative contributions of founder effects and recurrent immigration on these island populations.
Location Japan
Taxon Lanius bucephalus
Methods We used 15 microsatellite loci to analyze the population genetics of four newly established island populations and five Japanese mainland populations. Allelic richness, heterozygosity, genetic differentiation, and the strength of the genetic bottleneck were compared among the islands. Two analyses, STRUCTURE and the DAPC, were conducted to assess the relative influence of founder effects and recurrent immigration on genetic differentiation. Temporal samples collected over eight years on Minami-Daito Island were used to detect any change in genetic structure due to recurrent immigration.
Results The founder effect strongly influenced genetic differentiation on the most remote oceanic island, Chichi-jima Island. However, this population became extinct 20 years after colonization, possibly owing to a lack of recurrent immigration. The founder effect moderately influenced a land-bridge island, Kikai-jima Island, indicating the presence of a relatively large founder population without recurrent immigration. Surprisingly, another distant oceanic island, Minami-Daito Island, was likely subject to multiple recurrent immigration events from the mainland, which obscured any genetic differentiation previously established by the founder effect.
Main conclusion Underlying the island-specific population dynamics of colonization, founder effects contributed to the genetic differentiation among the three studied island populations. Importantly, however, recurrent immigration strongly affected the population persistence and subsequent evolutionary processes of remote island populations, potentially overwhelming the founder effect. We argue the importance of recurrent immigration in highly remote island colonization, which has been previously overlooked.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
The content was improved by further addressing the core population genetics and was entirely updated (including the Introduction, Methods, Results, Discussion and Figures and Tables). This revised version puts the emphasis on the demography of island colonization, in terms of the relative contributions of founder effects and recurrent immigration, whereas the theme of the previous version was its link with migratoriness of founders. In the revised version, migratoriness in island colonization was only discussed in the second part of the discussion ("Factors affecting the specificity of colonization demography"). This required major revision of the introduction and discussion. Furthermore, methods and results were slightly altered (those for DIY-ABC and wing-shape analyses were removed, and the analyses for temporal genetic structure were added).