Sicista subtilis Pallas 1773
Creators: name: Don E. Wilson
name: Russell A. Mittermeier
name: Thomas E. Lacher, Jr
Publisher: name: Lynx Edicions
Year: 2017
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Mammalia
Rodentia
Dipodidae
Sicista
Sicista subtilis

description: 12.
Southern Birch Mouse
Sicista subtilis
French: Siciste des steppes / German: Steppenbirkenmaus / Spanish: Raton listado meridional
Other common names: Pale Birch Mouse (vaga), Severtzov's Birch Mice (severtzovi), Siberian Birch Mouse (sibirica)
Taxonomy. Mus subtilis Pallas, 1773,
on road from Zverinogolovskoye to Kurgan, on Tobol River near Kaminskaya Kur’ya (suburb), Kurgan Oblast, Russia.
Steppe Species Group. Sicista subtilis has long been treated as a polytypic species with an expansive distribution. Five subspecies have been recognized and are distinguished by pelage color (severtzouvi, vag, and sibirica), karyotype (loriger), and male reproductive anatomy (#rizona), as summarized by L. Méhely in 1913, S. I. Ognev in 1935 and 1948, and V. E. Sokolov and colleagues in 1986. B. S. Vinogradov in 1937 noted that differences in pelage color are not sufficient to separate geographical forms because of intermediately colored mice.
Based on polymorphic karyotype and chromosome morphology, Yu. M. Kovalskaya and colleagues in 2011 suggested that five separate species of Sicista are represented in south-western Russian plain: S. loriger (2n = 26), west (on right bank) of Donets River; S. severtzovi (2n = 26), east and north (on left bank) of Don River, and west (on right bank) of Khopyor River (but specimens with 2n = 26 were also detected on left bank of Khopyor River); S. subtilis (2n = 24), both sides of Volga River, widely distributed east to north-western China; Sicista species 1 (2n = 22-26), east (on left bank) of Khopyor and Don rivers but west (right bank) of Volga River; and Sicista species 2 (2n = 16-22) between Donets and Don rivers. Independent evidence analyzed by T. Cserkész and colleagues in 2016 led them to conclude that S. severtzovi and S. subtilis were conspecific, and they recognized this taxon only at subspecific level, not as a separate valid species as was originally described by Ognev in 1935. Kovalskaya and colleagues and Cserkész and colleagues hypothesized that the large amount of chromosomal variation present within subspecies severtzovi may have resulted from multiple isolation-reticulation events triggered by continual changes in courses of large rivers (e.g. Volga and Don) in the southern Russian plain, Pleistocene glaciation events, or ancient hybridization events. Nevertheless, such rapid chromosomal evolution and large amount ofvariation are unusual within a single mammalian species. According to the biogeographical hypothesis of Kovalskaya and colleagues, together with transgressions by the Caspian Sea, climatic influences favored shift of the ancestral population of S. subtilis on left bank of Volga River from where it has spread eastward and reached its current extensive distribution. European populations of S. subtilis (sensu lato) are well studied, but fewer data are available for Asian populations. Subspecies vaga and sibirica, as far as it is known, differ from other subtilis forms only in pelage color. Subspecies vaga dwelling in sand steppes and semi-deserts is pale; sibirica living in cold steppesis darker. They also differ in the arrangement of the eighth, ninth and tenth pair of autosomes, as reported by V. E. Sokolov and colleagues in 1986. Results from analysis of cytochromeb sequences showed no significant genetic divergence between vaga and other trans-Volga subtilis populations; this suggested that vaga might best be treated as a synonym of nominate subtilis. Resulting neighbor-joining phylogenetic tree also showed that all individuals captured along Volga River and from Volga east to Altai Mountains formed one clade. Five subspecies recognized.
Subspecies and Distribution.
S.s.subtilisPallas,1773—bothsidesofVolgaRiverinEuropeanRussiaEthroughKazakhstanandSSiberiatoObRiverandWAltaiMts.
S.s.cimlanicaKovalskayaetal.,2000—knownexclusivelyfromTsimlyanskSandsnearDonRiver,SWRussia.
S.s.severtzoviOgnev,1935—fromtheleftbankoftheDonetsRiverEtotherightbankoftheVolgaRiverinEUkraine(Lugansk)andSWEuropeanRussia(Kursk,Belgorod,andVoronezhregions).
S.s.sibiricaOgnev,1935—foreststeppesofSSiberiaincludingmid-Altai,MinusinskDepression,STuva,andSIrkutskinRussia.
S. s. vaga Pallas, 1779 — W Kazakhstan from the vicinity of the left bank of Volga River E probably to Semey (East Kazakhstan Region), and possibly into NW China (N Xinjiang).
Descriptive notes. Head—body 60-5-72 mm, tail 745-82 mm, ear 9-5-13-3 mm, hindfoot 14-5-16-5 mm; weight 6-2—12 g. Pelage colors of Southern Birch Mice vary according to age and location. Mid-dorsalstripe bordered by two narrow bright beige stripes on both sides is noticeable and characteristic; brighter stripes are often bordered by darker lines resulting in one distinct stripe and two lateral diffused dark stripes on either side. There are three main pelage variations that historically have been identified as distinct subspecies, but this conception is outdated. Nominate subtilis has the basic form, with grayish brown to yellowish dorsum and grayish white venter; three dark medial stripes are typical but are not always present. Ognev in 1935 noted that dorsum of paler variation, sometimes called the “Pale Birch Mouse” (S. s. vaga), is rather grayish with pale yellow tinge and without diffused lateral dark stripes. Cserkész and colleagues in 2016 captured vaga in the Emba Valley, Kazakhstan, with “typical subtilis color” (visible beige stripes alongside black dorsal stripe and diffused lateral dark stripes). The third variation, the “Siberian Birch Mouse” (S. s. sibirica), has broader mid-dorsal stripe and distinct dark lateral stripes; dorsum is dark gray, with yellow-rusty overtone, resembling that of “Severtzov’s Birch Mice” (S. s. severtzovi). Hindfoot is long, c.23% of head-body length. Tail is ¢.100 —135% of head-body length. Condylobasal lengths are 17-3-18-5 mm, zygomatic breadths are 8:4-9-8 mm, interorbital breadths are 3-8-3-9 mm, and lengths of upper tooth rows are 2:8-3-2 mm. Glans penisis cylindrical and covered with small spines and is characterized by single penile spike (1-2 mm). Diploid numbers are 2n = 18-24, with several distinctive karyotypic forms. External and cranial measurements were taken from specimens captured in the Orenburg region, Russia, published by G. I. Shenbrot and colleagues in 1995 and 2008.
Habitat. Undisturbed, or relatively undisturbed, open habitats such as forest steppe, moist mesophilous grasslands, dry sandy steppe, and semi-desert at elevations up to c.1000 m. The Southern Birch Mouse is eurytopic but with a particular affinity for habitats with tall cover and well-developed herbaceous vegetation; however, it is also found in semi-deserts, primarily in sandy steppes with meadowsweet (Spiraea, Rosaceae) shrubs. Until the 1960s, Southern Birch Mice might have inhabited agricultural fields but now possibly avoid areas of intense agricultural activity. A. A. Tsvetkova and colleagues in 2008 and Tsvetkova and M. L. Oparin in 2016 reported that birch mice occupy fallow fields and margins of active fields but densities in undisturbed steppes were much greater. In 2016, Cserkész and colleagues captured individuals in somewhat disturbed habitats in Russia that showed evidence of light to moderate grazing by livestock but had vegetation cover of more than 60%. They also captured subspecies severtzovi in Ukraine and Russia in typical sand dune steppes with 40-70% cover, dominated by Koeleria (Poaceae), Artemisia (Asteraceae), and Euphorbia (Euphorbiaceae) with bare surfaces covered by mosses and lichens. Most individuals were trapped close to Cytisus (Fabaceae) shrubs. The same authors trapped severtzovi in Yamskaya Steppe (Belogorye Nature Reserve), Belgorod region, Russia, which was a humid mesophilous grassland with steppe floral elements and dominated by tall grass species (e.g. Poa angustifolia, Poaceae); vegetation cover was 100%.
Food and Feeding. Diet of the Southern Birch Mouse consists of insects and other invertebrates (noctuids, caterpillars, locusts, and small spiders), seeds, bulbs, succulent fruits, rhizomes,leaves, and stems. According to A. G. Voronov in 1951, Southern Birch Mice in the Naurzum Nature Reserve, Kazakhstan, ate cereal crops or grains and wild grasses, in particular basal bulbs of meadow-grass (Poa bulbosa vivipara) and mammoth lyme grass (Leymus racemosus), both Poaceae; tulips (Tulipa biflora, Tulipa sp., Liliaceae) bulbs, fruits, and seeds; and white goosefoot (Chenopodium album, C. acuminatum), Russian pigweed (Axyris amaranthoides), and Oriental bugseed (Corispermum orientale), all Amaranthaceae. They feed on flowers and seeds of Acacia, various Astragalus, alfalfa, peas and other species of Fabaceae, and species of Asteraceae, such as asters, sunflowers, and saw-wort (Saussurea amara).
Breeding. Reproduction of the Southern Birch Mouse begins shortly after emerging from hibernation, usually toward the end of May and beginning ofJune, depending on environmental factors, sex, and age of individuals. One litter is produced per year, with 2-8 young. Gestation lasts 25-30 days.
Activity patterns. Southern Birch Mice are nocturnal and crepuscular and sometimes active during the day based on many daytime observations. In captivity, Voronov noted two active periods: main one beginning at dusk and the other before dawn. They were more active during the day if inadequate food was provided; under such conditions in the wild, Southern Birch Mice are likely more easily captured. This higher prey potential is suggested by high numbers of Southern Birch Mice in owl pellets and stomach contents of birds of prey (harriers and kestrels) compared with those of other nocturnal rodents. While sleeping, the Southern Birch Mouse lies on its side or sits on its hindfeet, with its tail wrapped around its body. Body temperature is reduced, and in some cases, torpid individuals are unresponsive. This sleeping pose and ability to enter daily torpor are also typical for other species of Sicista. Voronov noted that captive individuals were less active by the end of September, and in October-November, they slept almost the entire day and only occasionally left the nest to obtain food. In the wild, Southern Birch Mice hibernate c¢.6-7 months of the year, usually from late September until the beginning of April in southern Ural and in October-May in the steppe region of Kazakhstan, according to V. E. Flint in 1960.
Movements, Home range and Social organization. Southern Birch Mice are agile and scamper about by moving with small jumps. They easily climb vertical stalks and use their tails to help balance. They use burrows of other rodents and other shelters such as holes among stones and tree roots. Captive Southern Birch Mice have been observed living in family groups rather peacefully, sleeping in the same nest together even though individuals differed in temperament. Social relationships might exist in wild populations of Southern Birch Mice as was presumed for the Tian Shan Birch Mouse (S. tianshanica) by A. A. Sludskiy and colleagues in 1977.
Status and Conservation. Classified as Least Concern on The IUCN Red List. Severtzov’s Birch Mouse was treated as a full species and classified as Least Concern on The IUCN Red List. Under optimal conditions and habitats, Southern Birch Mice can reach high densities and be the dominant member of small mammal communities. Distribution covers an expansive area containing unused or modestly used pastures or cultivated lands and unproductive regions such as sand and shrub steppes of Russia and Kazakhstan where only local factors such as small-scale development, utilization, and fires threaten populations. Intensive agricultural practices such as overgrazing, mechanical mowing, and cutting or plowing of grasslands can render favorable habitats such as meadows, grasslands, and fallow fields inhospitable.
Bibliography. Baskevich (2016), Cserkész (2007), Cserkész, Flop et al. (2017), Cserkész, Rusin & Sramko (2016), Cserkész, Takacs et al. (2016), Flint (1960), Holden & Musser (2005), Kovalskaya & Fedorovich (1997), Kovalskaya, Aniskin et al. (2011), Kovalskaya, Tikhonov et al. (2000), Krystufek, Zagorodnyuk & Amori (2008), Méhely (1913), Ognev (1935, 1948), Shenbrot et al. (1995, 2008), Sludskiy et al. (1977), Sokolov et al. (1986b), Tsvetkova (2008), Tsvetkova & Oparin (2016), Tsvetkova et al. (2008), Vinogradov (1937), Voronov (1951).
description: Published as part of Don E. Wilson, Russell A. Mittermeier & Thomas E. Lacher, Jr, 2017, Sminthidae, pp. 9-48 in Handbook of the Mammals of the World – Volume 7 Rodents II, Barcelona :Lynx Edicions on pages 45-46, DOI: 10.5281/zenodo.6603557