Monday, June 30, 2025

Genomes reveal the Norwegian lemming as one of the youngest mammal species

Stockholm University

Ancient lemming — image:
Jaw from an ancient lemming.
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Credit: Vendela K. Lagerholm

Using whole genome sequencing and cutting-edge analyses researchers at Stockholm University have uncovered the surprising evolutionary history of the Norwegian lemming (Lemmus lemmus), revealing it to be one of the most recently evolved mammal species. The results published in Proceedings of the National Academy of Sciences (PNAS), reveal that the Norwegian lemming is a distinct species that split from its closest relative, the Western Siberian lemming, approximately 35,000 years ago — just before the peak of the last Ice Age.

“The Norwegian lemming is a key ecological species in the Fennoscandian tundra. Among other things, it serves as primary food for many predator species, including some threatened ones such as the Arctic fox. However, it is also a very interesting species from an evolutionary perspective, which so far has not been studied using genomics. Our study starts to fill that gap,” says David Díez del Molino, Researcher at the Centre for Palaeogenetics and the Department of Zoology at Stockholm University, senior author of the study.

The study, that compared genomes from nine modern and two ancient lemming specimens, not only confirms that the Norwegian and Siberian lemmings are separate evolutionary lineages, but also finds no evidence of interbreeding — a surprising result given how recently they diverged and that their distributions nearly overlap. This lack of gene flow stands in contrast to many other mammalian species, where recent splits are often accompanied by hybridization.

“Our findings indicate that the Norwegian lemming is among the most recently evolved mammals, diverging from its sister taxon, the Western Siberian lemming, at a remarkably shallow time depth. After this, these species seem to have remained isolated, as we don’t find any indication of interbreeding between them”, says Edana Lord, Postdoctoral Researcher at the Centre for Palaeogenetics and the Department of Zoology at Stockholm University lead author of the study.

The researchers also identified hundreds of mutations unique to the Norwegian lemming, particularly in genes related to coat colour, fat metabolism, and possibly even behaviour. These genomic differences likely contribute to its iconic black-yellow fur, as well as helping the lemmings stay active during winter, traits thought to be adaptations to the harsh Fennoscandian tundra and to predator pressure.

In resolving the phylogeny of the Lemmus genus, the study also supports the classification of the Eastern Siberian lemming as a separate species — Lemmus paulus — and clarifies the taxonomy of a group long muddled by uncertain evolutionary relationships.

“This work represents a big step in our understanding of lemming speciation and evolution. It paves the way for exciting future research, particularly in exploring ancient gene flow and precisely dating the emergence of the unique genetic adaptations we see in the Norwegian lemming.”, says Love Dalén, Professor in Evolutionary Genomics at the Centre for Palaeogenetics and the Department of Zoology at Stockholm University, co-author of the study.

This work highlights the powerful insights genomic tools can bring to longstanding evolutionary questions and shows how even recent climatic changes can drive rapid species formation and isolation.

Find the article “Genome analyses suggest recent speciation and post-glacial isolation in the Norwegian lemming” by Edana Lord et al., published in PNAS, 2025.
DOI: 10.1073/pnas.2424333122

About the Centre for Palaeogenetics (CPG)

The Centre for Palaeogenetics (CPG) is a joint venture between Stockholm University and the Swedish Museum of Natural History.
Read more about the research at CPG: https://palaeogenetics.com/

Journal

Proceedings of the National Academy of Sciences

A Norwegian lemming runs across rocks in Sarek National Park, Sweden.

A Norwegian lemming peeks out from under rocks in Sarek National Park, Sweden.

Credit

Love Dalén

DOI

10.1073/pnas.2424333122

Method of Research

Experimental study

Subject of Research

Animal tissue samples

Article Title

Genome analyses suggest recent speciation and post-glacial isolation in the Norwegian lemming

Article Publication Date

30-Jun-2025

Groundbreaking analysis provides day-by-day insight into prehistoric plankton’s capacity for change

University of Southampton

Foraminifera being picked — image:
Washed foraminifera being picked for computer tomography and geochemical analysis
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Credit: University of Southampton

Scientists at the University of Southampton have developed a new way of analysing fossils allowing them to see how creatures from millions of years ago were shaped by their environment on a day-to-day basis for the first time.

The research published today [30 June] in Proceedings of the National Academy of Sciences could revolutionise our understanding of how character traits driven by environmental changes shaped evolutionary history and life on earth.

It could help scientists to understand how much of a species’ evolutionary journey is down to ‘nature vs nurture’.

Researchers from the University of Southampton studied the fossilised remains of prehistoric plankton using high-resolution 3D scanning, like a medical CT scan, to examine tiny fossil shells about the size of a grain of sand.

These plankton, called foraminifera or ‘forams’ for short, are tiny floating seashells that still live in the ocean today. Their shells are made of calcium carbonate and grow every few days by adding a new chamber to their shell in a spiralling pattern.

These chambers act a little like the rings of a tree trunk, providing a permanent record of the growth and lived environment of forams over time.

The shells’ chemical composition also tells us about the conditions the organism lived in, including the chemistry, depth and temperature of the water.

“The fossil record provides the most powerful evidence of biodiversity change on Earth, but it traditionally does so at a scale of thousands and millions of years,” says Dr Anieke Brombacher, lead author of the paper how carried out the research at the University of Southampton and now works at the National Oceanography Centre.

“These fossils however act a bit like chapter summaries of a species’ evolutionary story. This new way of analysing them lets us read the pages within each chapter – allowing us to see how individual organisms adapted to their changing environment, not over the course of generations but within an individual life span at day-to-day resolution.”

The key advance the researchers developed was to combine highly advanced CT scanning with chemical analysis by laser ablation techniques. This combination of methods meant the team was able to ‘zoom in’ and ‘read’ the individual pages of those chapters to reveal how the forams grew and estimate the environment they experienced while growing.

The growth rates of all three species were similar at low temperatures, but one species grew much faster in higher temperatures despite reaching the same average size.

“If you’re a foram, temperature appears to be a bigger determinant of your growth rate than even how old you are,” says Dr Brombacher.

“Temperatures change throughout the depth of the ocean water column so being able to optimise growth at different temperatures would have allowed each foram to live in a greater variety of habitats.”

James Mulqueeney a PhD researcher from the University of Southampton and co-author of the study said: “We also found that of the two species with similar environmental sensitivities, one was able to reach the same size but with a thinner shell, indicating a lower energetic cost and potential evolutionary advantage.”

Researchers say the same analysis techniques could be applied to other creatures which preserve their environmental and lifespan information including ammonoids, corals and bivalves like clams, oysters and mussels.

“This sort of data is routine in how we study adaptation in modern populations but has only now been gathered for fossils. By bringing together experts and facilities across the University of Southampton, we’ve been able to make progress on a foundational question in biology that wouldn’t have been possible within a single discipline,” says Prof Thomas Ezard, supervising author on the paper from the University of Southampton.

The research is part of a wider project which aims to scale up the analysis across a wider sample of two thousand plankton specimens to determine if a species’ adaptive flexibility is likely to lead it to diverge into separate, distinct species over time.

Detecting environmentally dependent developmental plasticity in fossilised individuals is published in Proceedings of the National Academy of Sciences and is available online.

The study was funded by the Natural Environment Research Council (NERC).

Ends

Contact

Steve Williams, Media Manager, University of Southampton, press@soton.ac.uk or 023 8059 3212.

Notes for editors

Detecting environmentally dependent developmental plasticity in fossilised individuals will be published in Proceedings of the National Academy of Sciences. An advanced copy is available upon request.
For Interviews with Prof Thomas Ezard please contact Steve Williams, Media Manager, University of Southampton press@soton.ac.uk or 023 8059 3212.
Images and video available here: https://safesend.soton.ac.uk/pickup?claimID=cttMNqAAKbarUFDw&claimPasscode=tHti2hkZabikVEtq

All images and videos should be credited to University of Southampton

Additional information

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www.southampton.ac.uk/news/contact-press-team.page

CT models of internal or external growth structures, as well as shell thickness, of individual foraminifera

Credit

University of Southampton

Video of CT scan of foraminifera [VIDEO] |