Cover: Picture by Greenland Institute of Natural Resources

When I need to take a break from work, I often stroll around the Oslo Natural History Museum. Zoological collections have always fascinated me since I was a child, and now that I work for one of them I`m able to appreciate the many facets that characterize them. Every specimen has a unique history and educational value, letting you get a hint at its life history or its connection with human culture. I get closer to a diorama showing a reproduction of the pack ice. Inside of it, three small seals welcome the visitors, seemingly not considering the polar bear that is approaching them.

The three taxidermies belong to ringed seals (Pusa hispida Schreber, 1775), the smallest and most abundant earless seal species in the Arctic. The name derives from the presence of ring-shaped light spots in the pelage extending on the animals` back and sides. Ringed seals are what can be called pagophilic organisms, which means that they heavily depend on sea ice for critical aspects of their lives such as reproduction (Ringed seal, 2024).

Pictures of polar environments often portraits vast stretch of ice, something very difficult to replicate inside a diorama. What could happen however if seals were to live for generations in an enclosed environment, isolated from neighboring populations?

As highlighted in Rosing-Asvid et al. (2023), Kangia ringed seals seem to provide a valuable case study. The distribution of these peculiar seals is limited to the Ilulissat Icefjord (i.e. Kangia in the local language), located in western Greenland. Furthermore, they have several unique features that make them easily recognizable. Not only Kangia ringer seals show an average larger body size than other Arctic ringed seals, but their pelage is also characterized by marked ring-light spots covering wider areas of the animal body, often extending to the neck and belly regions (Figure 1a). Data from tracking (Figure 1b) and visual surveys support both high population densities and high level of site fidelity. The limited dispersal range is unusual for the species, with evidence from other Arctic ringed seal populations showing how juveniles can travel up to thousands of kilometers.

Figure 1a: The pelage of Kangia ringed seals (left) is darker and with more marked and extended ring-like spots than the pelage of typical Arctic ringed seals (right). Figure 1b: Satellite tags were deployed to get a better understanding of the movement patters of Kangia ringed seals in the Ilulissat Icefjord and neighboring areas. Pictures by Greenland Institute of Natural Resources.

The distinctness of Kangia ringed seals was confirmed by molecular analyses, showing a clear separation of this population from other ringed seals. Furthermore, the genetic diversity levels are lower than the ones obtained for other Arctic ringed seals, but similar to the one found for Baltic ringed seals, which also represent an isolated population. The origin of this uniqueness is to be found in the environmental and geomorphological evolution that have shaped the region over time. As a results of sea-level changes and isostatic rebounds (rise of land masses following the retreat of ice sheets), Kangia ringed seals have been isolated in a glacial freshwater environment between 240 thousand years ago and 24.4 thousand years ago, the lower boundary coinciding with the Last Glacial Maximum. During this time, it is possible that specific expressions for some genes were selected, leading to the appearance of the unique morphological traits observed today. In particular – gene Grb10, possibly associated with larger body size, could also be involved in the increased aggressivity and territoriality observed for Kangia ringed seals.

As Kangia ringed seals are now connected to neighboring ringed seals populations, such local adaptations still survive as a result of both genetic and behavioral barriers to introgression. While in the past Polar regions were seen as harboring low levels of intraspecific diversity, cases as the one of Kangia ringed seals are helping to understand the extent of a previously unknown cryptic variation. As human-cause climate change continue to pose a great threat to polar biota, different populations of the same species could show different levels of resilience, highlighting the need for the development of more specific management plans.

References

Rosing‐Asvid, A. et al. (2023). An evolutionarily distinct ringed seal in the Ilulissat Icefjord. Molecular Ecology, 32(22), 5932–5943. https://doi.org/10.1111/mec.17163

Ringed seal. (2024, November 27). NOAA Fisheries. Ringed Seal | NOAA Fisheries