Initial theories on glacier refuges suggested that after the conclusion of the glaciations during the ice age, bears from northern Europe fled to the south for shelter.
A team from Coruña University have challenged this theory by reconstructing the colonisation of brown bears in the Iberian Peninsula that has resulted in the lineage of the Pleisocene bears being lost.
Aurora Grandal Danglade of Coruña University said: “We have investigated the mitochondrial DNA [the cellular energy ‘factories’] of a significant number of samples of current bears, from the Holocene the and Pleistocene, in the European context, and we have seen that the glacier refugee theory, commonly accepted, does not work for this species”
The compiled data on mitochondrial genomes and chronology of brown bears
In their work, they compiled data on the chronology and mitochondrial genome of brown bears, adding new sequences of the current ones from the Cantábrico Mountains.
“Through the study of today’s´ bears, it had been seen that the brown bears of southern Scandinavia were of the same lineage as the current Iberian ones. This led to the hypothesis that the Peninsula would have served as a glacier refuge for the brown bears, which at the end of the last glacial maximum, would have colonized again Western Europe from here, “explains Ana García Vázquez, co-author of the research.
The northern region of the Iberian Peninsula had three maternal lineages of the bear during the Pleistocene. One large group, whilst the other two lineages have remains of just a single individual remaining. They co-existence of lineages is still common today in parts of the world such as the remote regions of Russia, however, on the Peninsula there is only one, which means that the other two lineages arrived from very distant areas and did not have continuity over time.
The data suggests that the Pleistocene lineage was lost, and the Holocene bears, after the last glacial maximum, entered the peninsula from some unidentified area -probably France- and they did it 5,000 years after having colonized the British Isles.
“It would be necessary to obtain more mitochondrial sequences from bears from other regions of Western Europe to clarify if the presence of these maternal lineages is casual or, on the contrary, no other representatives were found due to the scarcity of data,” the scientist points out.
The delay in the re-colonization of the Iberian Peninsula could be due to the orographical characteristics of the Pyrenees and the abundant presence of human beings in the natural entrance to the Peninsula. However, as there is no continuity of any of the Pleistocene lineages in the Holocene, Grandal and her team propose the existence of a cryptic refuge on the Atlantic slopes of continental Europe, “”from where the bears expanded as the ice receded”, she concludes.