EVOLUTIONARY HISTORY OF SEALS IN THE BALTIC SEA

In the last three years, I have been working on a project aimed at reconstructing the evolutionary history of seals in the Baltic Sea. The project was funded from Marie Curie Intra-European Fellowship awarded by the European Commission, and carried out at Durham University in the Molecular Ecology Group led by Prof. Rus Hoelzel.

INTRODUCTION
This project is focused on the populations of four species that have inhabited the Baltic Sea: the extant ringed seal Pusa hispida, grey seal Halichoerus grypus, and harbour seal Phoca vitulina, as well as the extinct harp seal Pagophilus groenlandicus. The Baltic Sea is an isolated sea basin, with a short but complex geological history that influenced the occurrence of different species of seals during the Holocene. The Baltic Sea originated as an ice lake after the Last Glacial Maximum; in the early Holocene, a connection to the ocean was opened, then lost and re-opened again. From this geological history we know that populations of Baltic seals have recent origins, which gives a potential to study the evolutionary history of each population from the time of its founding. With the four seal species that have inhabited its waters throughout the Holocene, the Baltic Sea has been reach in seal species as compared with other sea basins around Europe at the same latitude. These four species are closely related and their general biology is similar, but each of them has distinct life history traits and habitat requirements. Therefore, the Baltic seals provide a good model to study the dependence of past population dynamics on intrinsic and extrinsic factors.

PROJECT AIMS
The aim of this project is to understand the long-term dynamics of genetic and demographic changes in four closely related species of seals inhabiting the same environment. This aim should be achieved through: (I) reconstructing demographic and genetic changes in each population during the Holocene, using Bayesian coalescent inference from mtDNA sequences; (II) comparing the population dynamics of the four species in the context of climate change, human exploitation, and their respective life histories; (III) reconstructing the evolutionary and demographic processes leading to the extinction of the Baltic harp seal, in comparison with the demographic changes in populations of the three extant Baltic seal species.

METHODS
Genetic and demographic changes in seal populations are reconstructed based on mtDNA sequence data obtained from the analysis of bones from archaeological sites and natural deposits dating from the early Holocene to the Middle Ages. The age of the samples is known from earlier radiocarbon-dating studies or from geological/archaeological context; some samples have been radiocarbon-dated in this study. For the three extant species, the data on genetic diversity of the “ancient” populations are compared with the modern data. Because each of the extant species went through a severe decline in the Baltic Sea during the 1970s, which resulted in a genetic bottleneck, we use museum specimens from the 19th and early 20th century for this comparison.

Seal bones from archaeological sites that have been analysed in this project

OUTCOME AND POTENTIAL APPLICATIONS
Besides contributing to the general knowledge of the processes underlying population extinction or survival, this project can be also applied to a particular case of conservation of seals in the Baltic Sea. Our results suggest that climate change was not the most important driver of population dynamics of Baltic seals, including the two exclusively ice-breeding species (the ringed seal and the harp seal), which has important conservation implications. The knowledge obtained in this project may be applied towards the development of predictive models on the impact of ongoing human activities (including culling) and climate change on the Baltic seals, which may help to develop effective strategies for their conservation. In this way, the project may contribute to the implementation of the European Union’s Marine Strategy, and to the Baltic Sea Action Plan of the Helsinki Commission.

COLLABORATORS
This project could not be carried out without the help and support from my collaborators:
Rus Hoelzel (Durham University) – the project supervisor
– Andre Moura (Durham University)
Daniel Makowiecki (Department of Archaeology, Nicolaus Copernicus University in Torun)
– Danuta Krol (Archaeological Museum in Gdansk)
– Iwona Pawliczka (Marine Station of the Institute of Oceanography, University of Gdansk)
– Krzysztof Skora (Marine Station of the Institute of Oceanography, University of Gdansk)
– Linas Daugnora (Osteological Laboratory, Lithuanian Veterinary Academy)
Olle Karlsson (Swedish Museum of Natural History)
– Pirkko Ukkonen (Finnish Museum of Natural History)

SUPPORTING INSTITUTIONS
European Commission – funded the project through the Marie Curie Intra-European Fellowship programme

Foundation for Polish Science – provided funding for a pilot study that allowed me to develop this project

Durham University – the host institution were this project has been carried out

Museum and Institute of Zoology, Polish Academy of Sciences – my former workplace, a source of continuous support for my research, and a source of museum specimens analysed in this project

Archaeological Museum in Gdansk – a source of museum specimens analysed in this project
Finnish Museum of Natural History – a source of museum specimens analysed in this project
Gothenburg Museum of Natural History – a source of museum specimens analysed in this project
Swedish Museum of Natural History – a source of museum specimens analysed in this project
Marine Station of the Institute of Oceanography, University of Gdansk – a source of contemporary seal specimens analysed in this project
Poznan Radiocarbon Laboratory – performed the radiocarbon dating

ACKNOWLEDGEMENTS
– Anne Kirstine Frie (Institute of Marine Research, Tromso) – kindly provided samples of contemporary harp seals from Norway
– Friederike Johansson (Gothenburg Museum of Natural History) – introduced me to the seal bone collection at the Gothenburg Museum of Natural History and provided me with help and support during my visit there
Greger Larson (Durham University, Department of Archaeology) – kindly allowed me to use the equipment in his lab, which greatly accelerated my labwork
– Ilpo Hanski (Finnish Museum of Natural History) – made a collection of the seal bones at the Finnish Museum of Natural History available for my research
– Martti Hilden (Finnish Museum of Natural History) – introduced me to the seal bone collection at the Finnish Museum of Natural History and provided me with help and support during my visit there
Risto Vainola (Finnish Museum of Natural History) – kindly agreed to share his samples of contemporary grey seals and ringed seals
– Tomasz Goslar (Poznan Radiocarbon Laboratory) – provided an excellent radiocarbon-dating service and patiently answered my questions related to the dating of my samples
– Ulf Johansson (Swedish Museum of Natural History) – kindly provided me with the access to the seal bone collection at the Swedish Museum of Natural History