Identification of North Caucasian mole rats ( Spalax ) based on their karyotype description

0000-0002-0523-133X


Introduction
Genus Spalax is represented in the fauna of Eastern Europe by five species, four of which have restricted distribution: S. graecus, S. zemni, S. arenarius, and S. giganteus.In different times, all of them were considered as subspecies of S. microphthalmus (s.l.), but after the revision of this group by V. Topachevsky [1969] all the species were recognised [e.g.Wilson & Reeder 2005].Karyological revision of this group confirmed this viewpoint in general: these species have 2n = 62 against 2n = 60 in S. microphthalmus [Lyapunova et al. 1974 and others].
Moreover, according to the author's hypothesis, the pair of species arenariusgiganteus had in the recent past a single continuous geographical range stretching across the steppes of the Northern Azov and North Caucasus, and some fragmentary data indicate that some southern refugia of the 'common' mole rat ('microphthalmus') actually contain representatives of the 'giganteus' group.This, in particular, was assumed by us for the 'common' mole rat from the Stavropol Krai [Korobchenko & Zagorodniuk 2009] 1 .

Results
Romanian Spalax 'microphthalmus'.A review of cytogenetic characteristics of mole rats together with biogeographical data allows clarifying some earlier identifications of studied samples.So, Spalax 'microphthalmus' from the Romanian Moldavia, Suceava [Raicu et al. 1968], should be re-identified as S. graecus.This erroneous identification happened because of the earlier consideration of all Spalax (s.str.) as S. microphthalmus (s.l.).This re-identification is completely clear and can be accepted without any doubts.
Hypothesis on Spalax giganteus in the North Caucasus.Both traditional and modern views on the taxonomy and distribution of mole rats restrict the range of Spalax giganteus to NE Caucasus [Puzachenko 1993].More recent studies have shown the presence of S. giganteus on sandy arenas in the Kursk district of Stavropol Krai, in particular in the vicinity of 'villages of Aga-Batyr and Yuzhanin, as well as the channel of the Terek-Kuma canal between the villages of Aga-Batyr and Irgakly' [Tsapko 2016].Revision of chromosome data allows re-identifying the North Caucasian mole rats as a new taxonomic form that is not identical to S. microphthalmus and can be attributed to the 'giganteus' group.These data relate to much more western parts of the Stavropol Krai, in particular Zheleznovodsk and Prokhladny (Kabardino-Balkaria), leaving little scope for assumptions about the distribution of S. microphthalmus here.It is also noteworthy that the Stavropolian mole rats are described as the most typical for sandy habitats [Tsapko 2016], which is also very typical for the Lower Dnipro S. arenarius [Selyunina & Tlusta 2001].
Probably, the Kuma-Manych depression that separates the East European Plain from the North Caucasian steppes is the natural border between S. microphthalmus (s.str.) and S. giganteus.Taking into account that the 'giganteus' group includes two mole rat species, S. giganteus (North Caucasus) and S. arenarius (Lower Dnipro region) [Topachevsky 1969], it can be considered as a result of range fragmentation in this species, similarly to many other allospecies pairs of steppe rodents.
In particular, similar situation is observed in such pairs of taxa as Sylvaemus falzfeini and S. fulvipectus (supraspecies Sylvaemus witherbyi), Scirtopoda telum falzfeini and S. t. turovi, Microtus socialis nikolajevi and M. s. parvus, and many other pairs.The author designates the western isolated segment of this group as DEG (Dnipro Endemic Group) [Zagorodniuk 2019].
Thus, data on chromosomal variability of mole rats allow assuming a wide distribution range of the 'giganteus' group in the North Caucasus, from Dagestan to Stavropol Krai, and, probably, up to the Azov Sea.Moreover, these data, including S. arenarius being part of the 'giganteus' superspecies, suggest not only a continuous, but also a much more northern distribution of this superspecies in the Northern Azov and North Caucasus regions in the recent past, after which the range was reduced and fragmented with the formation of 'small' species of this group, including S. arenarius, S. giganteus, and S. uralensis.

Table 1 .
Chromosome numbers of mole rats from Eastern Europe and neighbouring regions