Abstract
BackgroundSmall, genetically uniform populations may face an elevated risk of extinction due to reduced environmental adaptability and individual fitness. Fragmentation can intensify these genetic adversities and, therefore, dispersal and gene flow among subpopulations within an isolated population is often essential for maintaining its viability. Using microsatellite and mtDNA data, we examined genetic diversity, spatial differentiation, interregional gene flow, and effective population sizes in the critically endangered Saimaa ringed seal (Phoca hispida saimensis), which is endemic to the large but highly fragmented Lake Saimaa in southeastern Finland.ResultsMicrosatellite diversity within the subspecies (HE = 0.36) ranks among the lowest thus far recorded within the order Pinnipedia, with signs of ongoing loss of individual heterozygosity, reflecting very low effective subpopulation sizes. Bayesian assignment analyses of the microsatellite data revealed clear genetic differentiation among the main breeding areas, but interregional structuring was substantially weaker in biparentally inherited microsatellites (FST = 0.107) than in maternally inherited mtDNA (FST = 0.444), indicating a sevenfold difference in the gene flow mediated by males versus females.ConclusionsGenetic structuring in the population appears to arise from the joint effects of multiple factors, including small effective subpopulation sizes, a fragmented lacustrine habitat, and behavioural dispersal limitation. The fine-scale differentiation found in the landlocked Saimaa ringed seal is especially surprising when contrasted with marine ringed seals, which often exhibit near-panmixia among subpopulations separated by hundreds or even thousands of kilometres. Our results demonstrate that population structures of endangered animals cannot be predicted based on data on even closely related species or subspecies.
Highlights
Small, genetically uniform populations may face an elevated risk of extinction due to reduced environmental adaptability and individual fitness
The landlocked Saimaa ringed seal (Phoca hispida saimensis) provides an excellent model system for studying how small population size and spatial subdivision influence key genetic and demographic parameters and processes. This endemic ringed seal subspecies derives from marine seals that became trapped in Lake Saimaa in southern Finland after the last glacial period, i.e., nearly 10,000 years ago [12]
Genetic diversity, and effective population size Genotypes for all 17 microsatellite loci were obtained for 168 individuals, while four individuals lacked data for one locus each (Additional file 2: Table S2) [22]
Summary
Genetically uniform populations may face an elevated risk of extinction due to reduced environmental adaptability and individual fitness. Using microsatellite and mtDNA data, we examined genetic diversity, spatial differentiation, interregional gene flow, and effective population sizes in the critically endangered Saimaa ringed seal (Phoca hispida saimensis), which is endemic to the large but highly fragmented Lake Saimaa in southeastern Finland. The landlocked Saimaa ringed seal (Phoca hispida saimensis) provides an excellent model system for studying how small population size and spatial subdivision influence key genetic and demographic parameters and processes. This endemic ringed seal subspecies derives from marine seals that became trapped in Lake Saimaa in southern Finland after the last glacial period, i.e., nearly 10,000 years ago [12]. As the population has remained completely isolated for hundreds of generations, the trajectory of its gene pool is determined largely by population size and internal population structure
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