Demographic histories and genetic diversities of Fennoscandian marine and landlocked ringed seal subspecies

Abstract

Island populations are on average smaller, genetically less diverse, and at a higher risk to go extinct than mainland populations. Low genetic diversity may elevate extinction probability, but the genetic component of the risk can be affected by the mode of diversity loss, which, in turn, is connected to the demographic history of the population. Here, we examined the history of genetic erosion in three Fennoscandian ringed seal subspecies, of which one inhabits the Baltic Sea ‘mainland’ and two the ‘aquatic islands’ composed of Lake Saimaa in Finland and Lake Ladoga in Russia. Both lakes were colonized by marine seals after their formation c. 9500 years ago, but Lake Ladoga is larger and more contiguous than Lake Saimaa. All three populations suffered dramatic declines during the 20th century, but the bottleneck was particularly severe in Lake Saimaa. Data from 17 microsatellite loci and mitochondrial control-region sequences show that Saimaa ringed seals have lost most of the genetic diversity present in their Baltic ancestors, while the Ladoga population has experienced only minor reductions. Using Approximate Bayesian computing analyses, we show that the genetic uniformity of the Saimaa subspecies derives from an extended founder event and subsequent slow erosion, rather than from the recent bottleneck. This suggests that the population has persisted for nearly 10,000 years despite having low genetic variation. The relatively high diversity of the Ladoga population appears to result from a high number of initial colonizers and a high post-colonization population size, but possibly also by a shorter isolation period and/or occasional gene flow from the Baltic Sea.

Bioinformatic processing of RAD‐seq data dramatically impacts downstream population genetic inference

“…Nyman et al . ), researchers should assess the robustness of demographic parameters by screening a variety of bioinformatic pipelines.…”

“…Thus, in the absence of external references, such as a known date of a bottleneck or isolation (e.g. Nyman et al 2014), researchers should assess the robustness of demographic parameters by screening a variety of bioinformatic pipelines.…”

Rapid growth and genetic diversity retention in an isolated reintroduced black bear population in the central appalachians

“…Although it is widely accepted that small founder groups are at an increased risk of diversity loss (Allendorf and Luikart 2007), recent studies have posited that this may not always be the case for iteroparous mammals because the loss of alleles may be reduced because of generation overlap (Kaeuffer et al , Kekkonen et al , Nyman et al ). Additionally, because offspring diversity (i.e., heterozygosity) depends on the genetic composition of parents, and 2 homozygous parents can produce heterozygous offspring, repetitive selection for heterozygotes could increase diversity in reintroduced iteroparous species (Kaeuffer et al ).…”

Morphometrics, body condition, and growth of the ringed seal (Pusa hispida saimensis) in Lake Saimaa: Implications for conservation

“…, Nyman et al . ), and its microsatellite diversity is the lowest ever recorded among pinnipeds (Valtonen et al . ).…”

“…Geographic isolation of some 9,500 yr (Nyman et al . ) of the Saimaa ringed seal in the lacustrine environment has resulted distinctive characteristics in some aspects of the biology, when compared to other subspecies of ringed seals. They have relatively larger eyes and brains (Hyvärinen and Nieminen , Amano et al .…”