MOLE-RAT FROM KHORTYTSIA IN THE LIGHT OF MORPHOLOGICAL AND GEOGRAPHICAL RELATIONS BETWEEN SPALAX ZEMNI AND S . MICROPHTHALMUS

Mole-Rat from Khortytsia in the Light of Morphological and Geographical Relations between Spalax zemni and S. microphthalmus. — Korobchenko, M., Zagorodniuk, I. — The taxonomic status of the mole-rats from Khortytsia Island which is located between the ranges of Spalax zemni (right bank of the Dnipro) and S. microphthalmus (left bank) are considered. This island population is a unique biogeographical phenomenon that may be an evidence of ancient evolutionary events associated with the migration of steppe animals in the region of Zaporizhia Rapids. The mole-rat forms on Khortytsia a stable population, which is regarded as autochthonous. Osteological characters of mole rats from the island and adjacent areas of the right bank of the Dnipro, as well as comparison of these samples with those of S. zemni and S. microphthalmus from distant parts of their ranges were investigated. By all characters, mole rats of Khortytsia and adjacent areas of the left bank of the Dnipro should be identified as S. zemni. Authors suggest that the mole-rat population in the nearest left-bank steppes may also be S. zemni. Descriptions of craniological characters to distinguish the two species and their distribution map are presented.


Introduction
There are five morphologically close species of mole-rats (Spalacidae) in the Ukrainian fauna, whose reliable diagnosis, as well as taxonomical and biogeographical reconstructions for which are possible, when craniological characters such as proportions of the skull, some details of its structure and the morphology of the tooth surface are analyzed (Решетник, 1941; Топачевський 1969).The peculiarity of this group is the extremely high morphological similarity.Hence, species of mole-rats, occupying almost identical econiches, in fact are strictly allopatric everywhere they occur, and they do not form sympatric settlements.Borders between their ranges, as a rule, are major river valleys, i.e. rivers are key biogeographic coordinates (Загороднюк, 1999).One of such coordinates is the course of the Dnipro, which is a border in distribution of three of five species known in the fauna of Ukraine -Spalax microphthalmus, S. zemni and S. arenarius (Коробченко, Загороднюк, 2009).
One of the main biogeographical "bridges" on the Dnipro is the region of Dnipro Rapids.It is known that in this place intensive faunal exchanges occurred between terrestrial faunas of the leftand right banks of the Dnipro.In particular, in this very area took place the formation of a small but viable group of settlements of the steppe northern mole-rat (Ellobius talpinus) and the great jerboa (Allactaga major): these species, which are distributed mostly in the left bank steppes, form in the region of Zaporizhia Rapids and the Lower Dnipro a series of settlements that occur throughout the right bank from Zaporizhia to Kherson (Селюніна, 2008; Коробченко та ін., 2014).
Especially important are the findings of species limited in their distribution by the Dnipro river, but also occurring on its islands.One of the best known biogeographical units on the Dnipro is the region of Zaporizhia Rapids, especially Khortytsia Island, located near Zaporizhia city.This sizable island is characterized by steppe communities belonging to the Khortytsia National Reserve.Such material is extremely valuable for research on possible faunal exchanges between the right-and left bank parts of the steppe, and it can "carry" the memory of the ancient states of fauna that have survived in conditions of island isolation.
The goal of this work is to analyze the morphological characters of mole-rats from Khortytsia and surrounding areas in comparison with S. zemni and S. microphthalmus, as well as determination of spatial relations between these two species in terms of the hypothesis about faunal exchanges in the region of Dnipro Rapids.

Material and methods
The present work was based on the osteological collection of mole-rats preserved in the National Museum of Natural History (NMNH), and on several samples handed to us from the region of our special attention -Khortytsia and adjacent areas.The key objects of our analysis are a sample captured on Khortytsia and a series of examples from the closest to Khortytsia sites near Zaporizhia city (right bank of the Dnipro).For comparison, several samples of mole-rats from more distant areas, preserved in NMNH and described earlier, were analyzed (Коробченко, 2014).Problematic samples (preserved as "S.microphthalmus"): • 1 ex., sen.(worn teeth), Khortytsia (Zaporizhia reg.), found in ca.1990-2000, deposited in the collection of archeologists in Zaporizhia University, handed by O. Tuboltsev (another "mole-rat" specimen from the same site turned out to be a combination of a skull of Ondatra and a mandible of Spalax, without reliable diagnostic characters1 ); • 5 mole-rat skulls ("S.microphthalmus"), 4 subad.+ 1 ad., collected in the nearest to Khortytsia sites of the Dnipro region, within the urban area of Zaporizhia city on 11. 05.2003, in its left-bank part (preserved in  A set of cranial features allowing to distinguish East European mole-rat species was described in our previous works (Коробченко, Загороднюк, 2009; Коробченко, 2012).Among them, five characters are used in this research to distinguish the pair of S. zemni and S. microphthalmus; (Ukrainian acronyms are in parenthesis): 1) RLN (ВДН): relative length of the nasal bones; 2) PEN (ЗКН): proximal ends of the nasal bones (shape); 3) PNS (ПНШ): postnasal sutures (shape of frontonasal and frontomaxillary sutures); 4) POS (ЗОШ): postorbital sutures (the angle between coronal and frontosquamal sutures); 5) SIP (ФТК): shape of the parietal bones1 .
Another character mentioned by V. Topachevsky ( 1969: p. 206, 217) has been added to the list too: the size of the auditory pore.In S. zemni it is of the same length as of the first molar teeth (M 1 ), but in S. microphthalmus its length is significantly smaller than the length of M 1 .Also, we have analyzed 3 new characters related to the occipital part of the skull: 6) DAP (ДВО) -the greatest diameter of the auditory pore (in relation to the coronar length of the first upper molar M 1 ); 7) COE (СПГ): expression of the external occipital crest (crista occipitalis externa); 8) SGH (ФПО): shape (contours) of the foramen magnum from back view; 9) LLS (БПВ): lateral occipital lines on the squamous part of the occipital bone.
We have measured the skulls by caliper, while measurements of small characters (auditory pore diameter and coronar length of M 1 ) were carried out by eyepiece micrometer in binocular MBS-9.Photos were taken by a digital camera, photographing of skull parts was held by a digital microscope.When taking pictures of sutures we used contrasting by graphite (soft pencil).The distribution of all these features among the samples are presented in tab. 1.

Hypothesis
The settlement of mole-rats on Khortytsia is considered as an old "refugium" in terms of biogeography of Spalax, which is situated between the ranges of Spalax zemni (right bank of the Dnipro) and S. microphthalmus (left bank of the Dnipro).This island population is a unique biogeographical fact which might be an evidence of ancient evolutionary events related to the migration of terrestrial steppe species in the area of Dnipro Rapids.The mole-rat forms on Khortytsia a relatively stable population (fig.1), which is considered as autochthonous.The mole-rat is not a subject of human economic interest, and we do not know about cases of its artificial resettlement; it also avoids water.Therefore, the basis of our hypotheses is that mole rats on the island have remained from the time when the island was connected with one of the banks of the Dnipro river, either right (range of S. zemni), or left (range of S. microphthalmus).It is obvious that each large river island is inhabited by a certain set of species that have existed in the region for a long time, even when some species became extinct or changed their ranges on adjacent lands due to significant alterations in the biome.Insular fauna have for this much fewer opportunities and, in fact, they are conserved and composed of species that were distributed in the region when the island had a connection with one of the banks.This primarily concerns exclusively terrestrial animals unable to fly and avoiding water, and it is fully refers to mole-rats, whose lifestyle is restricted to underground ecotopes.It is important that mole-rats occupy a very narrow econiche, so in one area always only one species is presented (Коробченко, Загороднюк, 2009).Hence, there is no reason to believe that such islands (including Khortytsia) could be inhabited by two mole-rat species simultaneously, but survived just one of them.

The variety of status assessments for mole-rats from Khortytsia
In the published fauna checklist of the Khortytsia National Reserve mole-rats are listed as "Spalax microphthalmus" (Перелік..., 2016).Passed to us samples are labeled also as "Spalax microphthalmus".In the review by V. Topachevsky (1969) this island, as well as the Middle Dnipro region in general, is not mentioned, and the descriptions of species' ranges are very schematic.
In the review on animals' distribution ranges in relation to the Dnipro, I. Tsemsh (Цемш, 1941) mentioned mole-rats as a pair of species separated by the river: S. polonicus (= zemni, westwards from the Dnipro) and S. microphthalmus (eastwards from the Dnipro).However, the researcher, in general, builds his concept on the old taxonomic basis: he assumes that Lower-Dnipro Sands (in the Left Bank) are also inhabited by S. podolicus, which was established by E. Reshetnyk as a subspecies S. polonicus zemni (Решетник, 1939), and later as S. zemni arenarius (Решетник, 1941).After the review by S. Ognev (Огнев, 1940, 1947), the sand mole-rat was recognized as a separate species S. arenarius, and later included into the species group "giganteus" (Топачевский, 1969).Therefore, the issue of transition of Podolian mole-rats over the Dnipro was closed.There had been no information about the existence of mole-rats on Dnipro islands for a long time, and Khortytsia was not mentioned in descriptions of mole-rats' distribution in the reviews by both E. Reshetnyk (Решетник, 1941) and V. Topachevsky (Топачевский, 1969).

Analysis of samples and variants of characters
The main attention has been paid to cranial characters that distinguish the pair of Spalax zemni and S. microphthalmus, and to determination of the place of mole-rats from Khotytsia and Zaporizhia in the space of variation of these characters.Data on morphotypes of cranial characters in the mole-rat from Khotytsia in comparison with typical variants in S. zemni and S. microphthalmus are summarized in tab. 1.It is necessary to remember that each character can be found in other states characteristic for some other species1 (Коробченко, 2012).In the sample from Khortytsia, all the characters are identical to typical characters of S. zemni; the same applies to samples from the vicinities of Zaporizhia.The dental features of the sample from Khortytsia cannot be analyzed because it is of old age with worn crowns.Below, these characters are analyzed in details.
Lengthening of the rostrum.Character RLN (relative length of the nasal bones) as a diagnostic peculiarity for the pair zemni/microphthalmus was analyzed by E. Reshetnyk (1941) and V. Topachevsky (1969).However, these researchers describe it differently: Topachevsky indicates that in microphthalmus the length of the nasal bones exceeds the joint length of the parietal and frontal bones.Reshetnyk indicates that the nasal length in this species is almost equal to the joint length of the frontal and parietal bones.Unlike S. microphthalmus, RLN in S. zemni is much smaller (in this both researchers agree).According to our data, in S. microphthalmus RLN = 48.0-52.4% (n = 17), while in the sample from Khortytsia RLN = 44.6 %, and in the samples from Zaporizhia RLN = 42.9-48.3% (n = 5).Thus, samples from Khortytsia and Zaporizhia clearly differ from S. microphthalmus (fig.2) and are similar to S. zemni (41.5-47.8%, n = 14).* In Nannospalax nehringi this feature is sex-related, well-developed in males (Ketani et al., 2017).
Nasal bones and postnasal sutures.This complex includes two characters: the proximal edge of the nasal bones (PEN) and the shape of postnasal sutures (PNS) (tab.1).In the specimen from Khortytsia, the character PEN corresponds to the morphotype PEN2, i.e. the proximal edge of the nasal bones is straight, without straddle-type split at the back and is not elongated beyond the postnasal sutures, so it corresponds to S. zemni.The same conclusion is true for the samples from Zaporizhia.Another character (PNS) in the samples from Krortytsia and Zaporizhia is also similar to S. zemni: sutures form almost a straight line, which is slightly curved forwards (i.e.towards the nose) as a wide arc.In the samples from Eastern Ukraine, which are typical S. microphthalmus, the line of nasal sutures is straight or slightly curved backwards, and the proximal edge of the nasal bones without a straddle-type split, and they usually not elongated beyond the postnasal sutures.Hence, mole-rats from Khortytsia and Zaporizhia (left bank) are similar to S. zemni.
Auditory pore (DAP).In diagnoses of S. zemni and S. microphthalmus presented by V. Topachevsky (1969), essential differences between the species were given according to the absolute and relative (in comparison with М 1 ) size of the auditory pore.We have studied the variability of this character in our samples and we have found that samples of S. zemni from different parts of their range, including Khortytsia and Zaporizhia, are characterized by noticeably larger auditory pores.However, the reliability of this character is insignificant because of overlapping of the samples (fig.2).It is also noticeable that the pore in S. microphthalmus not only smaller, but also rounded (round-shaped), while in S. zemni it is often elongated, elliptic.Features of the occipital part.The temporal bones (character SIP, see tab. 1) in the mole-rat from Khortytsia are flattened laterally, just as in S. zemni.Three other diagnostic features for the pair zemni/microphthalmus were not described previously: 1) occipital crest (COE): in S. zemni and in the sample from Khortytsia the squamous part of the occipital bone is smooth, without a clear crest, while in S. microphthalmus there is a well-developed crest (crista occipitalis externa), extending from the top of the nuchal crest to the middle of the squamous part of the occipital bone; 2) shape of the foramen magnum (SGH): in S. zemni and in the sample from Khortytsia it is trapezoidal, extended upwards, its upper contour is rounded (in S. microphthalmus its lateral margins are parallel; the top line with inflection due to which the hole resembles a pentagon); 3) lateral occipital lines (LLS): on the squamous part of the occipital bone in S. zemni as well as in the sample from Khortytsia are almost collateral, diverging towards the nuchal crest (crista nuchae) under a slight angle (15-25 о ), but in S. microphthalmus these lines diverge under a greater angle, ca.40-60 о .

Comparison of samples and diagnostically valuable characters
The analysis of the complex of characters has showed that the mole-rats from Khortytsia and Zaporizhia (left bank) are identical to S. zemni.The described characters are stable and do not show significant geographical variation.Age-related peculiarities have little contribution into the general variability and do not affect significantly the accuracy of species identification.The individual variability of characters is essential, and for species identification we should consider a wide set of characters.Special importance should be given for two groups of cranial characters: (1) postnasal sutures and relative size of the nasal bones, and (2) morphological structures of the occipital area.In some cases, photos of the skull may be sufficient to identify the material.Spalax microphthalmus from Eastern Ukraine significantly differ from all other examined mole-rat samples which, as it turned out, belong to S. zemni (Khortytsia, right-bank parts of Zaporizhia and Dnipropetrovsk, also Kirovohrad, Mykolaiv, Ivano-Frankivsk and Lviv regions (including a type specimen of S. polonicus).

Biogeographic interpretations
The island mole-rat settlement on Khortytsia is obviously ancient.We have no information about artificial resettlement of the species onto the island, therefore, we recognize that the settlement has been formed naturally.Although mole-rats are able to swim (own data), such behavior is not common for them.Therefore, emergence of island populations is possible only via separation of placore parts from the main banks inhabited by mole-rats.The history of formation of Khortytsia shows signs of its shift from the left to the right bank.But this history might be more complicated considering the possibility of repeated changes of the riverbed in the region of Rapids.
We have a number of facts of obvious transitions of the ranges of strictly terrestrial vertebrate species through the Dnipro exactly in the region of the Dnipro Rapids near Zaporizhia (Zaporizhia Rapids).There are three clear examples of such transition: a settlement of the northern mole vole Ellobius talpinus (Коробченко та ін., 2014) and the great jerboa Allactaga major (Селюніна, 2008) in the Right-bank Middle Dnipro region, which are distributed mainly on the steppes eastwards from the Dnipro (i.e. in the Left-bank areas).In contrary, Lacerta viridis demonstrates a transition to the Left-Bank area, while its main range is located in the Right-bank area (Таращук, 1959).Contours of this lizard's range are very similar to Spalax zemni (see tab. 2).(Таращук, 1959; own data) a small segment of the range in the region of Dnipro Rapids the main range is westwards from the Dnipro; the species crossed the river in the region of Rapids The issue of historic hydrography of the Lower Dnipro and its connection with distribution ranges of animals was repeatedly discussed both in the relation to the terrestrial fauna (Підоплічко, 1936; Цемш, 1941; Загороднюк, 1999) and to hydrobionts (Афанасьев, 2014).The dynamics of the watercourse also affected the distribution of subterranean rodents, including mole-voles (Коробченко та ін., 2014).Based on the distribution of the Podolian mole-rat (Spalax zemni) in the old wider understanding of its taxonomic scope (i.e.including S. arenarius), I. Tsemsh (1941) andE. Reshetnyk (1941) recognized that the species1 crossed the Lower Dnirpo to the left bank, which suggests the changes of its range, as well as of changes of the Dnipro's course.Tsemsh wrote about it directly, while Reshetnyk avoided discussions about the boundaries of ranges.Discussing the issues of impermeability of the Dnipro in relation to dispersal of steppe species and giving examples of such distribution patterns on both banks (marmot, jerboa, pika, ground squirrels), I. Pidoplichko (1936) did not mention mole-rats at all.Despite this, the Dnipro river is a clear biogeographical coordinate in distribution of a number of steppe mammalians, in particular three mole-rat species (Загороднюк 1999).The studied material allows suggesting that in some cases "transitions" of mole-rats occurred across the riverbed.The Podolian mole-rat shows a biogeographical analogy with Lacerta viridis (fig.6).Moreover, the range of the European green lizard "crosses" the Dnipro to the left bank in the region of Zaporizhia Rapids and possibly the same applies to the Podolian mole-rat2 .We assume that S. zemni may occur in the Left-Bank Dnipro region, but the lack of morphological materials does not allow stating about it confidently.It is an important detail that species which crossed (according to our reconstruction) the Dnipro from east are absent on the islands, but the species which crossed the river from west are present on the islands and some adjacent left-bank areas.
Our analysis allows stating that mole-rat settlements on Khortytsia are evolutionary related to populations occurring on the right-bank steppe.We suggest the possibility of finding samples of Spalax zemni in the Left-bank Dnipro region.
the work collection of N. Lebedieva, Zaporizhia University); Podolian mole-rat: • 12 samples of S. zemni, collected in the Mykolaiv reg.(Shyrokyi Lan military training ground) by K. Redinov in 07.2005 in nests of raptors and passed to the authors, now preserved in NMNH (only 2 complete skulls in the series, the rest represents isolated mandibles); • 2 samples of S. zemni from the collection of L. Mehely, collected in Yavoriv dist.("Janow" = Ivano-Frankove), Lviv reg. in 1870 («№ 262, typus discriptionis») 2 and in Galych dist.(Kasova Hora), Ivano-Frankivsk reg. in 05.1937 (№ 630); • a series of S. zemni collected by E. Reshetnyk in 1937-1938, 10 mole-rat skulls from different districts of Right-Bank Ukraine (Mykolaiv, Dnipropetrovsk, Odessa regions), preserved in the collection of the Paleontological Department of NMNH (Коробченко, 2014); E a s t e r n mo l e -r a t : • comparative collection of S. microphthalmus amassed by the authors in 2007-2014, about 46 mole-rat skulls from different districts of Left-Bank Ukraine, mainly from the Luhansk reg.(samples of different periods collected by the authors or handed to them by colleagues), partly from the Donetsk reg.(samples from nests of Buteo rufinus, passed by D. Pylypenko).