Estonian bears still recovering from a century-old genetic bottleneck ({{contentCtrl.commentsTotal}})

Brown bear in a forest.
Brown bear in a forest. Source: Zdeněk Macháček/Unsplash

Do bears have as good a life in Estonia as we think? A doctoral student at the University of Tartu, Peeter Anijalg, explains why we need Russian bears; what happened to Estonian bears during the bottleneck a century ago; where Estonian bears take refuge in tough times, and why genetic diversity is important.

Today there are estimated to be approximately 700 to 800 bears in Estonia, but their life in this region has not always been easy.

Maps from the middle of the 19th century show the distribution of bears gradually declined in Estonia and was by far the lowest in the 1920s. At that time, the bear population was estimated to be only a few dozen animals who managed to find refuge from hunters probably in the forests of Alutaguse, as well as in the forests of south-western Estonia.

After protective measures were implemented in the mid-1930s, the bear population slowly started to grow and at the beginning of the 1990s, the local population exceeded 800.

This drastic drop in a population's abundance is called a population's bottleneck and the survivors of the bottleneck are known as the founder population.

The historic and contemporary spread of bears in Estonia. On the contemporary image, every green circle represents a mother bear with an offspring of the same year. Source: Anijalg at al., 2019

The objective of mammalogists at the University of Tartu's Institute of Ecology and Earth Sciences was to find out whether there are still signs of the century-old bottleneck in the Estonian bear population. Whether or not the local population is panmictic, i.e. if there are factors preventing the unrestrained mating of individuals, and what the genetic diversity of the Estonian bear population is compared to other populations.

For this, they used over 200 tissue samples from bears hunted or killed by accident between 1999 and 2011.

Their DNA analyses showed that the local bears divide into three genetically distinct groups:

One distributed over the eastern part of Estonia, being the most frequent in Põlva County, but this group is also present on the western shore of Lake Peipus and in Ida-Viru County. The other two groups are spread over the entire distribution area and are geographically mixed. The south-eastern corner of the distribution area is the only place where fewer representatives of these two groups can be found.

These two groups were most likely founded after the bottleneck by the two founder populations, one of which was preserved in the forests of Alutaguse, and the other in the forests of south-western Estonia. Even though these two groups are geographically mixed, the genetic signal from this bottleneck is still identifiable.

Regarding the third group distributed in the eastern part of Estonia, the author of the study believes it to be related to the Russian bear population. This is firstly confirmed by the group's distribution around Lake Peipus. These bears are especially common in Põlva County where the Russian bears can get to by crossing the relatively narrow Lake Lämmijärv. In addition, the bears of this group are much more genetically diverse. The Russian bear population has not gone through such a severe bottleneck so their genetic diversity is higher. This is also exemplified by comparisons with other studies, where this group also stands out for its large genetic diversity, being comparable with Romanian bears.

The three distinct genetic groups of bears. Source: Anijalg at al., 2019

The study showed that despite the bottleneck having occurred a century ago, its genetic mark is still identifiable. The lower genetic diversity of the two local groups and the fact that the bears have yet not been able to repopulate their previous habitats shows that the population is still in a recovery phase.

At the same time, it is positive that there are additions coming from the east, but it must also be taken into account that this journey might not be that easy for animals – there are various water obstacles on the way (either in the form of Lake Peipus or Narva River), a border infrastructure, but also a high population density of bears, mostly true in Northeastern Estonia.

The results are significant from the viewpoint of nature conservation and can be of help for making decisions when planning to build roads and railways. This way, it is possible to reduce the negative impacts on the population and on the free movement of animals.

The article was originally published on the Estonian zoology blog Zooloogid 2.0.

The translation of this article from Estonian Public Broadcasting science news portal Novaator was funded by the European Regional Development Fund through Estonian Research Council. 

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Editor: Helen Wright

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