Curiously, I have been reading up on roe deer in Europe and I have encountered two claims regarding the genetic status of the populations.
The curious aspect to this is that one of the claims might lead to an additional extant resident roe deer species included in the European Union mammal list.
Currently, European roe deer (Capreolus capreolus) is recognized as the ‘roe deer of Europe’ but study by Lorenzini, R. et al., 2014 points at presence of Siberian roe deer (Capreolus pygargus) in Poland and Lithuania (and possibly, for example, Latvia and Estonia) drawing the sympatry line between the European and the Siberian roe deer not between the rivers Volga and Don as previously assumed but rather much closer in the Baltic region.
I wonder why this matter has not been addressed.
While the current zone of sympatry also lies in Europe (European Russia) and therefore, the Siberian roe deer would not constitute a new species in Europe, it would constitute a new species on a European Union level.
Moreover, it would constitute a rare species on EU scale.
It is not really known yet what the population might be regarding its distribution and abundance in the Baltic countries and whether the Siberian roe deer is rare on a regional scale, as well, according to assumption that a species is frequently less abundant closer to the limits of its geographic range.
If it were scarce, the Siberian roe deer might become enlisted as a protected species even in the countries of residence.
Research should be conducted in order to study the species ecology in the Baltic region and to determine the status of the species on a EU level as well as to assess implications regarding the hybridization with European roe deer (even though evidence suggests it could be limited) and the differences in behaviour / habitat use of both species (bearing in mind that Siberian roe deer are a steppe species that could be better adapted to exploiting agricultural lands and that would be in a greater need of wild and semi-wild grassland restoration measures than the European roe deer which is a more pronounced forest species).
It is inconclusive whether extant Siberian roe deer, indeed, reside in the Baltic countries.
It is rather universally accepted that Siberian roe deer lived in this region even during the last ice age when the habitat was colder and drier, hosting a steppe vegetation.
The European roe deer, meanwhile, had retreated to the glacial refugias (along with the trees and other woody plants).
After the Last Glacial Maximum, the European roe deer (and other forest species including vegetation species) advanced north where they met the Siberian roe deer and possibly interbred.
The study by Lorenzini, R. et al., 2014 notes that hybridization is difficult to achieve between the two species due to different body size (Siberian roe deer are larger and European roe deer female pregnancy with hybrids can result in mortality of the female) as well as due to divergent karyotypes.
F1 hybrids are usually infertile and more recent (since the 19th century) introductions of Siberian roe deer in Europe for hunting purposes have resulted in extinction of the Siberian roe deer populations rather than hybridization with the European roe deer.
However, the ancient hybridization may have occurred at rates far exceeding those between a small introduced population and the native population.
As a result, Siberian roe deer haplotype is present in European roe deer individual genome within a region as vast as that from Finland to Romania and from Slovakia to European Russia (Plis, K. et al., 2022a and Plis, K. et al., 2022b).
However, this is where the two lines of research disagree.
While Plis, K. et al., 2022a and Plis, K. et al., 2022b maintain that there are only European roe deer with Siberian roe deer haplotypes inherited due to ancient introgression events (after the end of LGM when the European roe deer arrived in Eastern Europe from the refugia in Balkans and when hybridization with the Siberian roe deer occurred before the Siberian roe deer range retreated eastward to European Russia and Asia), Lorenzini, R. et al., 2014 suggest that, on a narrower scale (Lithuania and Poland but possibly other neighbouring countries), the Siberian roe deer never went extinct and extant Siberian roe deer populations still live in sympatry in the Baltic region with the European roe deer.
I believe it is very exciting and this might mean that we have a new species in the Baltic region and the European Union to learn about and to determine the conservation status and needs of.
I hope it becomes established whether the zone of sympatry between the two roe deer species, indeed, lies in the Baltic countries or it is only a case of haplotypes inherited from these ancient introgression events.
Recent immigration (introduction) was excluded due to lack of signature of admixture detected at microsatellite loci level.
The haplotypes detected in Lithuania and Poland appear to belong to a lineage different from both haplotypes identified in Eastern-Northeastern Europe and Central Asia which, in my view, would be suggestive of the following scenario:
- Lithuanian and Polish haplotypes have been ‘in active circulation’ after the haplotypes in other Eastern European countries became embedded in the European roe deer genotype and disused in active breeding with Siberian roe deer individuals (i.e., they became a legacy rather than a maintained resource because active breeding with Siberian roe deer did not occur any longer);
- Lithuanian and Polish haplotypes have diverged both from the ancient Siberian roe deer genetic make-up and from the Central Asian extant genotype indicating a separate Siberian roe deer subpopulation in the region that is still actively breeding but that is not interbreeding with other Siberian roe deer from Central Asia due to perhaps geographic constraints.
Difference among Eastern European / Lithuanian + Polish / Asian Siberian roe deer haplotypes might even point at a putative subspecies.
Regardless of the final conclusions, I also think it might be interesting to learn if the Siberian roe deer haplotypes perhaps have endowed the European roe deer individuals with traits that might have been helpful in adapting to the agricultural landscape that is more similar to the steppe habitats than the European roe deer-preferred largely forested landscape.
European roe deer are not grazers and the abundance of graminoids is not very favourable to the European roe deer digestive specification.
Perhaps the ancient hybridization with the Siberian roe deer in Eastern Europe has equipped the European roe deer populations to adjust more efficiently to the new foraging conditions.
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Ms. Lorenzini (personal correspondence through Mr. Sandro Lovari) has confirmed that the individuals screened in Lithuania were Siberian roe deer, not hybrids (Sep, 2023).
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I was also wondering about the behaviour observed in some ungulates whereby they prefer staying on their natal range or close to it and possibly also choose habitats similar to their natal one upon dispersal (thus ensuring, for example, familiarity with the diet and behavioural choices necessary to survive and reproduce successfully).
Ungulates are typically somewhat of traditionalists, and this tendency might have (alongside poor hybridization potential) ensured separation between Siberian roe deer (more open habitats) and European roe deer (forested habitats).
In fact, if the Siberian roe deer are in great enough numbers, they might have formed subpopulations that lead relatively separate lives than those of the European roe deer; and the two deer species might not attempt to interfere with one another’s habitat because they ‘stick to what works’, namely, they rather choose habitats similar to what they knew during their ‘fawnhood’ because in such habitats they already know what to eat, where to seek shelter, how to avoid predators etc.
Perhaps the spatial situation of the two species where they are sympatric is characterized by a high enough degree of habitat segregation to form populations that are not intermingling but that are composed of separate subunits of either one or the other species but more rarely a mix of both within the same type of habitat.
As both species need some forest cover, their ‘meeting zone’ might be one between forest and agricultural lands and as both species can use arable lands and hayfields for foraging, one of the species (the dominant one) might have a slightly greater prevalence in both types of habitats while the other might be observed in its preferred habitat but not in all areas where such habitat is available (only in those where it is not dominated by the other species).
Notes by Ieva 