Landscape structure is important for determining the sizes and connectivity of local populations. Consequently, it can affect gene flow between local populations and their proneness to genetic drift. Landscape structure can therefore have large influences on the amount of genetic diversity as well as mixing and routing of genetic variation in spatially structured populations. Because of these effects, the degree of inbreeding in spatially structured populations may vary depending on landscape structure. Previous empirical studies have shown that inbreeding can negatively impacts fitness of individuals and also can increase extinction risk of small populations. These findings suggest that inbreeding can potentially decrease the persistence of metapopulations. The objective of this study is to understand the role of landscape structure on the level of inbreeding depression, loss of heterozygosity, and metapopulation persistence, using a genetically explicit individual-based model developed for the Glanville fritillary butterfly in the Åland islands. The butterfly inhabit a network of 4000+ meadow patches composed of 130+ semi-independent networks of various sizes and connectivities. In addition to detailed long-term demographic and environmental data, about 10,000 individuals have been genotyped for 271 SNPs. These data enable us to develop and parameterize a mechanistic model for this species.
Results/Conclusions
The results indicate that inbreeding can increase extinction risk of metapopulations, but the extent depends on landscape structure. Networks composed of smaller, less connected patches experience greater loss of heterozygosity and elevated extinction risk from inbreeding. Dispersive individuals disproportionately contribute to elevated heterozygosity and reduce the overall level of inbreeding. We conclude that inbreeding depression can pose a significant threat to persistence of small metapopulations that lack well-connected large patches and that dispersive individuals not only can increase metapopulation persistence but also can contribute to maintain genetic diversity in a metapopulation. Because dispersiveness of individuals is known to evolve rapidly in response to change in landscape structure in certain conditions, conservation planning for declining fragmented populations should consider how dispersal might affect both inbreeding and population dynamics simultaneously to elevate extinction risk.