Biology subjects

Valtonen, M.

Publications and source records attributed to Valtonen, M..

4 recordsLinked to original sources

bioRxiv2025

Deep origins and distinct adaptations indicated for a glacial relict seal

Isolated populations of postglacial relicts are known from many regions and are typically found on mountains for terrestrial species and in lakes for aquatic species. Among the few aquatic mammalian relicts, the Saimaa ringed seal (Pusa hispida saimensis) has been landlocked in Lake Saimaa, Finland, for the last 10,000 years. Saimaa ringed seals show genetic, behavioral, and morphological differences to the other ringed seal subspecies, but the extent these differences stem from the end of the last glacial period remains unclear. Here, we demonstrate with comprehensive sampling and state-of-the-art genomic methods that the Saimaa ringed seals are much older than the lake they inhabit, having formed a separate evolutionary branch for at least 60,000 years. This deep evolutionary origin of the Saimaa ringed seals is further underscored by our ecomorphological analyses revealing adaptively distinct features in their dentition and tongue. Overall, glacial relicts, many threatened by extinction, may harbor a richer selection of evolutionary history than might be expected from their recent isolation history alone.

zoology↗

bioRxiv2022

Museum specimens of a landlocked pinniped reveal recent loss of genetic diversity and unexpected population connections

AimThe Saimaa ringed seal (Pusa hispida saimensis) is endemic to Lake Saimaa in Finland. The subspecies is thought to have originated when parts of the ringed seal population of the Baltic region were trapped in lakes emerging due to post-glacial bedrock rebound around 9,000 years ago. During the 20th century, the population experienced a drastic human-induced bottleneck. Today encompassing a little over 400 seals with extremely low genetic diversity, it is classified as endangered. Our main aim was to evaluate the role of the 20th century bottleneck in the erosion of genetic diversity in the Saimaa seal population. We also evaluated connections with other ringed seals from the Baltic Sea, Lake Ladoga, North America, Svalbard and the White Sea. LocationLake Saimaa, Finland, together with the Baltic Sea and the Arctic Ocean. MethodsWe sequenced sections of the mitochondrial control region from 60 up to 125 years old museum specimens of the Saimaa ringed seal. The generated dataset was combined with publicly available sequences. We studied how genetic variation has changed through time in this subspecies, and how it is phylogenetically related to other ringed seal populations. ResultsWe observed temporal fluctuations in haplotype frequencies and loss of haplotypes accompanied by a recent reduction in female effective population size. In apparent contrast with the traditionally held view of the Baltic origin of the population, the Saimaa ringed seal mtDNA variation shows also affinities to North American ringed seals. Main conclusionsOur results suggest that the Saimaa ringed seal has experienced recent genetic drift associated with small population size. The results further suggest that extant Baltic ringed seals do not represent well the ancestral population of the Saimaa ringed seal, which calls for re-evaluation of the deep history of this subspecies.

evolutionary biology↗

bioRxiv2022

Fragmented habitat compensates for the adverse effects of genetic bottleneck

In the face of human-caused biodiversity crisis, understanding the theoretical basis of conservation efforts of endangered species and populations has become increasingly important. According to population genetics theory, population subdivision helps organisms retain genetic diversity, crucial for adaptation in a changing environment. Habitat shape is thought to be important for generating and maintaining population subdivision, but empirical cases are needed to test this assumption. We studied Saimaa ringed seals, landlocked in a labyrinthine lake and recovering from a drastic bottleneck, by whole-genome sequencing 105 individuals and additional individuals from three other ringed seal subspecies. We analyzed the distribution of variation and genetic relatedness among the individuals in relation to the habitat shape. Despite a severe history of a genetic bottleneck with prevalent homozygosity in Saimaa ringed seals, we found evidence for population structure mirroring the subregions of the lake. Highlighting the significance of habitat connectivity in conservation biology and the power of genomic tools in understanding its impact, genome-wide analyses showed that the subpopulations had retained unique variation and largely complementary patterns of homozygosity. Integration of genetic analyses in conservation decisions gives hope to Saimaa ringed seals and other endangered species in fragmented habitats.

evolutionary biology↗

bioRxiv2018

Bracketing phenotypic limits of mammalian hybridization

An increasing number of mammalian species have been shown to have a history of hybridization and introgression based on genetic analyses. Only relatively few fossils, however, preserve genetic material and morphology must be used to identify the species and determine whether morphologically intermediate fossils could represent hybrids. Because dental and cranial fossils are typically the key body parts studied in mammalian paleontology, here we bracket the potential for phenotypically extreme hybridizations by examining uniquely preserved cranio-dental material of a captive hybrid between gray and ringed seals. We analyzed how distinct these species are genetically and morphologically, how easy it is to identify the hybrids using morphology, and whether comparable hybridizations happen in the wild. We show that the genetic distance between these species is more than twice the modern human-Neanderthal distance, but still within that of morphologically similar species-pairs known to hybridize. In contrast, morphological and developmental analyses show gray and ringed seals to be highly disparate, and that the hybrid is a predictable intermediate. Genetic analyses of the parent populations reveal introgression in the wild, suggesting that gray-ringed seal hybridization is not limited to captivity. Taken together, gray and ringed seals appear to be in an adaptive radiation phase of evolution, showing large morphological differences relative to their comparatively modest genetic distance. Because morphological similarity does not always correlate with genetic distance in nature, we postulate that there is considerable potential for mammalian hybridization between phenotypically disparate taxa.

evolutionary biology↗