MOLE-RATS NANNOSPALAX LEUCODON AND SPALAX ZEMNI IN UKRAINE: IDENTIFICATION CRITERIA AND BORDER BETWEEN THEIR RANGES

Mole-rats Nannospalax leucodon and Spalax zemni in Ukraine: identification criteria and border between their ranges. — Zagorodniuk, I., Korobchenko, M., Kirichenko, V. — The differences between two mole-rat species are shown according to the complex of exterior and cranial characters, each of which is reliable in species diagnostics. In particular, they include the color of rhinarium, shape of the rostrum, development of lateral occipital apertures and pharyngeal tubules, also the flexion of the base of the skull, and expressiveness of the intercrestal fossa in the mandible. A number of collection materials were re-identified, which significantly changed the views on geographical ranges of these species. The boundary between species should be considered substantially shifted to the west: the Bug–Tylihul interriver area is inhabited not by N. leucodon, as it was believed so far, but by S. zemni. It is confirmed by both old specimens (1930–1950s) and modern materials (2010–2016), thus it is not associated with habitat changes. At the same time, monitoring of the dynamics of settlements of these species shows significant changes in the scope of inhabited areas, as well as recent colonization of the most part of the region from coastal refugia.


Introduction
Distribution of steppe terrestrial animals is very severely limited by the influence of a number of factors, among which hydrography has a leading role. The significance of river valleys in geographical distribution of steppe animals, including mammals, was repeatedly considered in the literature (e.g., Pidoplichko, 1936;Tsemsh, 1941;Zagorodniuk, 1999). Rivers are especially important in formation of geographical ranges of steppe underground mammals, in particular of mole-rats (Reshetnyk, 1941;Korobchenko, Zagorodniuk, 2009, 2016. In fact, distribution range borders of all species of Spalacidae are associated with large rivers, and the pair of species Nannospalax leucodon and Spalax zemni is not an exception (Topachevsky, 1969).
However, it is obvious that the fauna is in constant dynamics, and the boundaries of species ranges are constantly changing as well. In case of mole-rats it means the regular appearance of such factor of evolution and species distribution as interspecific competition, because mole-rats occupy similar ecological niches, regarding both trophic (feeding by bulbous plants and rhizomatous grasses) and spatial components (meadow and steppe habitats within a narrow underground ecotope). According to eco-morphological criteria, all mole-rats known in the European fauna are very close species, and their existence is possible only in the form of vicarious populations replacing each other in the space (Korobchenko, Zagorodniuk, 2009).
In this regard, the following two facts established during identification of new samples and reidentification of old collection specimens of mole-rats (Nannospalax leucodon and Spalax zemni) distributed in the Black Sea region appear important (and also unexpected before this research): 1) within the known by now range of Nannospalax leucodon there are records of another species, Spalax zemni, in particular in vicinities of Shyrokolanivka (Korobchenko, Zagorodniuk, 2009: based on samples obtained from K. Redinov) and in Berezivla district, Mykolaiv region (this article), as well as in Lyman (former Kominternove) district, Odesa region (ibid.); 2) denial of the previously prevalent and generally accepted idea that the distribution boundary between the two mentioned mole-rat species (and essentially two genera) is the Southern Bug river.
According to these facts and some other findings and sample re-identifications, it is obvious now that the boundary between the species runs to the west, most likely along the Tylihul river and the Tylihul estuary, however it requires further clarification. The purpose of this work is to describe the diagnostic characters and distribution features of two mole-rat species in the contact zone of their ranges and to compile the inventory of their records to specify the boundary between them 1 .

Materials
Collections of mole-rats deposited in the National Museum of Natural History of Ukraine (see: Korobchenko, 2014) were investigated, in both the Paleontological and Zoological departments (NMNHU-P and NMNHU-Z). Some morphological materials were studied using samples from the authors' working collection. Criteria for species diagnostics were described by the authors earlier (Korobchenko, Zagorodniuk, 2009; and revised in this work in the light of identification of the pair of species Nannospalax leucodon and Spalax zemni.

Criteria for species identification
Key differences between the two species are compiled based on the authors' previous review (Korobchenko, Zagorodniuk, 2009) and some old publications (Yanholenko, 1966;Topachevsky, 1969). These characters are compiled and described in table 1 and illustrated on figs. 1-5. Metric characters were not analyzed. Characters were studied on samples deposited in NMNHU.
The main external identification criteria for this pair of species (and for Nannospalax and Spalax in general) that can be used in the field, as well as in identification by photo records, is the color of rhinarium, which is light-pink in N. leucodon and gray, dark gray, or black in all Spalax s. str., including S. zemni ( fig. 1). This character was described first by Reshetnyk (1941), but it was lost in all identification keys, and re-described just a few years ago (Korobchenko, 2012 b).
Nannospalax leucodon and Spalax zemni have 5 distinct cranial differences, which, according to our research, play key role in diagnostics of these pair of species. Regarding the distal rostrum, an important feature is the form of the nasal part: in N. leucodon, the contour of the nasal part (top view) is rounded on the sides, whereas in S. zemni it has a trapezoidal shape with almost straight lateral edges ( fig. 2). Clear differences between these species were also revealed in the structure of the occipital region: a characteristic feature is the presence of condylar canals above occipital condyles in N. leucodon, distinguishing it from the genus Spalax ( fig. 3). In addition, an important character is the large development of pharyngeal tubercles and a flexion at the border of basioccipital and sphenoid bones in Nannospalax ( fig. 4). On the mandible, an important character of Spalax is the development of lateral crest that runs from the alveolar to coronary process and limits the intercrestal fossa, which is typical for this genus (fig. 5). The nasal part has an elliptical shape with an expressive extension of its lateral contours formed by the intermaxillar bones ( fig. 2 l) The nasal part has almost straight lateral outlines of the intermaxillar bones, which converge only at the level of posterior ends of nasal bones (fig. 2 z) Condylar canals above occipital condyles (on both sides of foramen magnum) On the sides of foramen magnum, there are small lateral condylar canals above the occipital condyles, occasionally they can be absent (

Peculiarities of geographical distribution
The main attention is paid to the records of mole-rats in the area between the east and north of Odesa region and the Dnister river. From the west, the area of records is limited by the Odesa-Podolsk imaginary line; in biogeographic coordinates, this is the territory extending east of the Maly Kuialnyk river that flows southwest from Zakharivsky district (Birnosove vil.) to the Hadzhibei estuary near Odesa. This area drew attention after identification Spalax zemni in samples from Shyrokyi Lan (Korobchenko, Zagorodniuk, 2009), for which another species, Nannospalax leucodon, was indicated earlier (Rusev et al., 2014) 2 , just as for the right bank of the Dnister river in general (Reshetnyk, 1941;Topachevsky, 1969;Filipchuk, Yangolenko, 1986 etc.) 3 .
The complied cadaster includes only materials species identification for which has been carried out based mainly on cranial characters, studying collections, or (in some cases) specimen descriptions published in works of colleagues who specialize in the study of cranial characters of mole-rats (works by O. Myhulin, E. Reshetnyk, and V. Topachevsky). All localities are marked by the names of the nearest settlements, with indications of administrative districts.

Records of Nannospalax leucodon
The descriptions of 9 locations are divided into two groups: the first one includes localities in the north of Odesa region and the west of Mykolaiv region (4 localities), while the second group deals with the south of the Odesa region, i.e. strictly the Black Sea region (5 localities). In this score, there are also 17 locations in which mole-rats were recorded, but without species identification.

Records of Spalax zemni
Descriptions of 9 locations divided in two groups are given below. The first group includes records from the south of Mykolaiv region, namely from the right bank of the Southern Bug river (6 localities), while the second group includes records from the north of Mykolaiv region and from Kryvorizhia, i.e. the left bank of the Southern Bug river (5 localities). The first group is the most important because it regards the territory, which researchers attributed to geographical ranges of Nannospalax leucodon ( fig. 6). In these limits there are also 6 locations in which mole-rats were found, but without data needed for diagnostics. Most of the known localities tend to the south of the region, where refugium settlements of the species occurred in the recent past.
In field conditions, it is also noteworthy that mole-hills of Spalax zemni are often much larger than those in the Odesian N. leucodon. It was repeatedly noted by the authors, in particular when comparing observations of mole-rat settlements in Shyrokolanivka (Spalax zemni) and adjacent locations (see below) with mole-rat settlements in the area located westwards of the Tylihul estuary, to the west from Kobleve (Nannospalax leucodon). 5 The labels indicate only the district "Kominternivsky." The name of the village was clarified based on the collector's work (Reshetnyk, 1941: 24). However, there are two villages with similar names, Stari and Novi Shompoly, situated next to each other. 6 The mandible of this sample with the same number (No. 3568) was found in NMNHU-P. 7 The sample's mandible was found in NMNHU-Z with the old (4845) and a new number (14925). These numbers (4845 and 14925) are in the catalogues of NMNHU-P and NMNHU-Z with the same original data ("leucodon, Reshetnyk, 1938, Kominter. dstr."), which are also written on the samples by Y. Reshetnyk's hand. However, on the skull 14925 in NMNHU-Z the old number was erased. Both samples are N. leucodon, but the second one has no lateral condylar canals (it was mentioned earlier as a character common for S. zemni: Korobchenko, Zagorodniuk, 2009). We believe that the error occurred in NMNHU-Z because of destruction of the original information. □ Nannospalax leucodon, ∆ Spalax zemni, Λ Spalax zemni subfoss., ○ Spalax indet.
Dark signs indicate localities with available morphological data, white circles indicate records without species identification. The big circle is the area between the Tylihul and Berezan estuaries, where colonies of S. zemni probably existed in the period of depression in 1940-2000, and from which the species expanded to north (localities Z2-Z6).

C) Records in the south of Mykolaiv region (right bank of the Southern Bug river)
Z1) Osnova (Berezivka district, Odesa reg.). In the catalogue of NMNHU-P, there is a record No. 641 (313) "Spalax podolicus, skull, Osnova vil., Kherson reg., 28.07.1925, male, [leg.] Z. Holovianko (from Pidoplichka's collection)." This sample was not found in NMNHU-P. In the catalogue of NMNHU-Z, there is a record No. 2993 ("skin"): "Spalax arenarius, Osnova vil., Berezivka district, leg. Z. Holovianko, 28.07.1925" (Shevchenko, Zolotukhina, 2005, i.e. the same specimen, but only the label was found, with an additional No. 2369. We accept the species identification (zemni) after I. Pidoplichko. Z2) Berezivka (Berezivka district, Odesa reg.), 3 km E, 25.05.2009. Direct observation; the color of rhinarium is dark-gray (E. Yablonovska-Grishchenko, pers. comm.). Z3) Danylivka (Berezanka district, Mykolaiv reg.). Stable settlement, isolated for a long time; in 1998-2000 the mole-rat began to expand to the north, to Shyroky Lan, then to Ulianivka, and it was often registered in forest bands and fields. Then it spread further to the north, towards Voznesensk. Species identification is provisional and based on data about mole-rats expansion from here to Shyrokolanivka. Z4a) Shyrokolanivka (Veselynove district, Mykolaiv reg.). In July 2005, in the Shyroky Lan military training ground, 6 samples from nests of Buteo rufinus were collected (leg. K. Redinov), which are deposited in the authors' collection (in NMNHU) (Korobchenko, Zagorodniuk, 2009) 8 . Another sample was collected nearly in 2012 and passed to the Mykolaiv Local History Museum (K. Redinov, pers. comm.). The species appeared here in the 2000s; in 2002-2005 it settled the whole military area, adjacent villages, and fields. The description of mole-rat population in this locality as "S. leucodon" (Rusev et al., 2015) was not based on morphological characters, but on the old views on mole-rat species ranges.
Z4b) Shyrokolanivka-2. A mole-rat was captured in the Shyroky Lan military area in autumn 2013, and the specimen was passed to the Mykolaiv Local History Museum (K. Redinov, pers. comm.). Species identification was carried out based on exterior features, including dark rhinarium (S. zemni).

Conclusions
The differences between two mole-rat species Nannospalax leucodon and Spalax zemni were evaluated by 6 revised exterior and cranial characters. Each of them is reliable in species identification, including the color of rhinarium, shape of rostrum, presence or absence of condylar canals, development of pharyngeal tubercles, flexion at the border of basioccipital and sphenoid bones, development of mandibular crest separating the intercrestal fossa. This complex of features allowed reidentifying a number of collection specimens that significantly changed the view on geographical ranges of the studied species.
The new data clearly showed that the boundary between the species ranges that has been considered so far along the Southern Bug river (e.g., in the Red Data Book of Ukraine (2009) and many other sources cited above) should be significantly shifted to the west: between the Southern Bug and Tylihul rivers occurs not Nannospalax leucodon, as it was believed by now, but another species Spalax zemni. This is confirmed by both old (1930s to 1950s) and modern samples (2010)(2011)(2012)(2013)(2014)(2015)(2016). Therefore, it is not associated with long-term changes in species ranges, and the boundary between species as earlier as now run along the Tylihul river.
At the same time, monitoring of mole-rat settlement dynamics demonstrates significant changes in the scope of inhabited areas. During at least 1958-2000, the territory of Mykolaiv region was free from mole-rats (data of the Mykolaiv Regional SES). Therefore, it is worthwhile to talk about a secondary occupation by mole-rats the most part of the Black Sea region from small refugia, which survived in the south, on the steppes near estuaries in Odesa and Mykolaiv regions.
The geographical boundary between the two species in the north of the region, obviously, runs along the Southern Bug river and through the Southern Bug-Dnister interriver area. Summarizing all data it can be assumed that Nannospalax leucodon is a recent entrant in the region.