During the Pleistocene interglacials in Europe, there were three varieties of large bovine present in various habitats across the continent. These were the bison (Bos bison priscus/schoetensacki), the aurochs (Bos taurus primigenius), and the water buffalo (Bubalus (bubalis?) murrensis). Like the ass and the horse, these three species managed to live alongside each other through slight but significant differences in habitat and dietary preference. Where the buffalo preferred river valleys, swamps, and wetlands, the bison preferred drier mountain, steppe, and shrubland environments. In the meadows, pastures, and mixed woodlands in between is where you would find the aurochs. This is a similar situation to that seen in three sympatric bovines today in southeast Asia where the gaur (Bos gaurus hubbacki), banteng (Bos javanicus birmanicus), and water buffalo (Bubalus bubalis theerapati) coexist through a similar dynamic. Today, with modern rewilding initiatives, we have the opportunity to re-establish this ecological relationship in Europe again, the question is how to go about doing it, when all three of the native bovines have been reduced or altered with time. For this first article I will be discussing the process of rewilding European bison.
The modern European bison (Bos bison bonasus) has a complicated taxonomic history. A couple years ago there was a lot of buzz around new findings that suggested it was the result of limited interbreeding between the steppe bison (Bos bison priscus) and the aurochs. However, several newer studies have rejected this theory, with more complete genetic evidence suggesting instead that they are a non-hybrid offshoot of the steppe bison that gradually adapted to different conditions. It is also becoming increasingly evident that the previous designation of bison as belonging to their own genus, Bison, is unwarranted, as they remain more closely related to some members of Bos(ex. Bos grunniens, the yak) than said members are to other species within the genus. Consequently it is now considered more appropriate to group bison into Bos, with the two previously recognized species in the genus, the American and European bison, being lowered to subspecies status, with each being a derivation of the ancestral steppe bison, and each remaining completely interfertile. All previously recognized subspecies are now better considered to be varieties or ecotypes. Another new study suggested that the European bison was a descendant of the Pleistocene species Bos bison schoetensacki, but that species has not been proven to have made it to the end of the Pleistocene, and it may be moot anyway since it was likely just an interglacial variety of the steppe bison in the first place. Bison morphology has been quite variable over time, responding to differing conditions and changing distributions, and there has been a tendency to overclassify, as is often the case when making taxonomic decisions based on morphology alone.
Regardless of ancestry, the European bison is the only remaining member of the lineage in Europe, and consequently it is the most appropriate for use in European rewilding areas. This is already an ongoing process, with new herds being formed in many reserves across the continent. There does remain one problem however, and that is that the European bison suffers from interbreeding. To understand why, you would need some background on its conservation history. The European bison has been hunted by humans, both for food and for sport, for as long as the two have coexisted. The slaughter of the animal was so excessive that by the nineteenth century, there were only three populations remaining: one in the Polish lowlands (Bos bison bonasus var. bonasus), one in the Caucasus mountains (Bos bison bonasus var. caucasicus), and one in the Carpathian mountains (Bos bison bonasus var. hungarorum). The last of the Carpathian variety was shot in 1850, and the last of the Caucasian variety met a similar fate in 1927. Only the Polish variety survived, and only in captivity. Today there are two surviving lineages: the Lowland line which descends from seven “pure” Polish bison, and the Lowland-Caucasian line which descends from twelve polish bison as well as the last captive Caucasian individual. The first lineage understandably has a higher inbreeding coefficient than the second (44% versus 26%), but both lineages still have a high incidence of skeletal deformity, in addition to problems with their immune functionality and a general lack of robustness or adaptability. Genetic diversity has continued to decrease, and generations of captivity and/or winter feeding have left them less able to thrive on their own. Consequently, we need to look into strategies for increasing their genetic diversity and adaptability. It happens that there is already a very viable and effective option, but not everyone thinks it would be a good idea.
In my opinion the best thing to do would be to experiment with controlled introgression of American bison (Bos bison bison) DNA into the European bison gene pool. Considering they are now considered by many to be the same species, it wouldn’t be entirely unreasonable. The same process I proposed for crossing wild and domestic horses in my previous article could also be used for crossing the two subspecies of bison, only I would recommend a greater number of backcrosses in order to preserve the phenotypic integrity of the European subspecies. The process would be something like the following:
Male bison x Female bonasus
- F1 hybrid male, 1/2 bison, 1/2 bonasus
- bison Y-Chromosome, bonasus X-chromosome and mDNA
Male F1 x Female bonasus
- F2 hybrid female, 1/4 bison, 3/4 bonasus
- bonasus X-Chromosomes and mDNA
Male bonasus x Female F2
- F3 hybrids, 1/8bison, 7/8 bonasus
- bonasus Y/X-Chromosomes and mDNA
F3 x bonasus
- F4 hybrids, 1/16 bison, 7/16 bonasus
- bonasus Y/X-Chromosomes and mDNA
- Intermix these individuals with existing herds to introduce new genetic material
There are two existing varieties of American bison: the American plains bison (Bos bison bison var. bison) and the Canadian wood bison (Bos bison bonasus var. athabascae). Despite not being particularly distinct from a phylogenetic perspective, they do have some noticeable aesthetic differences which might make one more appropriate for the introgression process than the other. Wood bison are perhaps optically more similar to the European bison than are the plains bison, being of a darker colour with larger horns. However it is worth noting that a mixed herd already exists in the Caucasus, where the reintroduced herds have about five percent of their DNA inherited from the plains variety, and seem to be thriving where attempts using pure bonasus herds failed. My thinking is that either of the North American varieties could be used, but maybe they should each be used for improving herds in different areas, with wood bison introgression for herds in the colder areas of central and northern Europe, and plains bison introgression for herds in the more arid and open areas of the south and east. In both cases animals which resemble the American subspecies too heavily will need to be sterilized or removed from the population, with the goal being to introduce new genes to the population without compromising the general appearance of the European subspecies. Attention will also need to be taken to ensure that animals with bisonancestry do not differ from pure bonasus individuals in diet or behaviour, since European bison do have a greater tendency to browse (though they are still primarily grazers) than American bison, and have a slightly different method of fighting for mates. An animal with over 95% bonasus ancestry would probably be basically indistinguishable from a pure individual, the only difference being the improved robustness and diversity.
The Lowland-Caucasian line is sometimes referred to as Bos bison bonasus var. montantus. I would tentatively suggest that a crossing of this line with these experimental bison-bonasushybrids might be called Bos bison bonasus var. robustus. I think these reinvigorated herds could potentially be very useful for rewilding areas of continental and northern Europe. They might also be of use in drier Mediterranean regions, where they actually seem to do quite well, based on observations of a breeding herd of the Lowland line in Extremadura. These areas were not occupied by bison in historic times, but were by various other members of the species during previous interglacials. In general they seem slightly more suited to living freely in arid scrublands than are various breeds of feral cattle. Fossils have also been found in the Anatolian region, suggesting these southern steppic regions are also suited to the European bison.
The European bison is the largest of the remaining European megaherbivores, and is consequently of great importance for re-establishing grazing dynamics across the continent. The regions available for the taxon remain limited, but there also remaining areas which have not yet been exploited, however small. Improving herd connectivity and available habitat is going to be a large part of their recovery. Their wild nature means that areas with large amounts of human traffic are not going to be suitable, further necessitating the need for creation and expansion of nature reserves in depopulating regions. I’ve discussed the generic positive effects of reintroducing large herbivores before, and bison will simply bring a similar, yet distinct version of the same effects. They will also bring benefits for the tourism and sustainable hunting industries, similar to the equids previously discussed.
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