Islands are often acknowledged as a refuge for species with declining mainland distributions. However, as the finite size of islands coupled with isolation can lead to genetic deterioration within insular populations, the study of these systems is of great interest to the conservation of biological diversity and persistence. The remote Kimberley region in Western Australia is facing increased impacts from invasive species, habitat fragmentation, grazing, mining and altered fire regimes, and many of the 2633 islands in the Kimberley have come into focus as a significant conservation resource. The Barshouldered skink (Ctenotus inornatus) is a habitat generalist that is highly abundant throughout the Kimberley and its diverse islands. This study encompasses 41 islands and seven mainland populations in the vast Kimberley environment, and genetically characterises them using 18 nuclear (microsatellite) markers. The island populations lost heterozygosity at a rate of 1 % per kilometre from the mainland. Diversity was significantly lower on islands of small size (\500 ha) and greater than 2 km from the coastline. The scope of this study is unparalleled and addresses an important gap in our understanding of the genetic diversity throughout ecosystems. The findings illustrate how populations, operating within these pristine island systems, conform to the general rule of decreased genetic diversity with decreasing island area and increased distance from the mainland and identifies islands that may hold the most potential for conserving biodiversity.

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Islands present a unique scenario in conservation biology, offering refuge yet imposing limitations on insular populations. The Kimberley region of northwestern Australia has more than 2500 islands that have recently come into focus as substantial conservation resources. It is therefore of great interest for managers to understand the driving forces of genetic structure of species within these island archipelagos. We used the ubiquitous bar-shouldered skink (Ctenotus inornatus) as a model species to represent the influence of landscape factors on genetic structure across the Kimberley islands. On 41 islands and 4 mainland locations in a remote area of Australia, we genotyped individuals across 18 nuclear (microsatellite) markers. Measures of genetic differentiation and diversity were used in two complementary analyses. We used circuit theory and Mantel tests to examine the influence of the landscape matrix on population connectivity and linear regression and model selection based on Akaike's information criterion to investigate landscape controls on genetic diversity. Genetic differentiation between islands was best predicted with circuit-theory models that accounted for the large difference in resistance to dispersal between land and ocean. In contrast, straight-line distances were unrelated to either resistance distances or genetic differentiation. Instead, connectivity was determined by island-hopping routes that allow organisms to minimize the distance of difficult ocean passages. Island populations of C. inornatus retained varying degrees of genetic diversity (N A = 1.83 -7.39), but it was greatest on islands closer to the mainland, in terms of resistance-distance units. In contrast, genetic diversity was unrelated to island size. Our results highlight the potential for islands to contribute to both theoretical and applied conservation, provide strong evidence of the driving forces of population structure within undisturbed landscapes, and identify the islands most valuable for conservation based on their contributions to gene flow and genetic Keywords: bar-shouldered skink (Ctenotus inornatus); CIRCUITSCAPE program; connectivity; genetic drift; island biogeography; isolation by resistance; landscape genetics; aislamiento por resistencia; biogeografía de islas; conectividad; deriva génica; genética de paisajes; programa CIRCUITSCAPE; Ctenotus inornatus La Importancia de las Rutas de Dispersión que Minimizan el Movimiento en Mar Abierto de la Estructura Genética de las Poblaciones Insulares ResumenLas islas presentan un escenario único para la biología de la conservación ya que ofrecen refugio pero a la vez imponen limitaciones sobre las poblaciones insulares. La región Kimberley del noroeste de Australia tiene más de 2500 islas que recientemente han llamado la atención como recursos sustanciales para la conservación. Por esto es de gran interés para los manejadores el entender las fuerzas conductoras de la estructura genética de las especies en estos archipiélagos. Usamos a la especie ubicua Ctenotu...