The karyotype of Microtus xanthognathus (Leach) is described, based on material from one female and one male vole. The diploid chromosomal number was found to be 54, and the fundamental number 62. The metacentric X-chromosome was of medium size and averaged 6.6% of the haploid complement. The designated Y-chromosome was near acrocentric. The specific distinction of M. xanthognathus and Microtus chrotorrhinus (Miller) was confirmed by the recognition of major differences in karyotype and differences in fundamental number. The distributional history of M. xanthognathus is briefly discussed

Rausch, Robert L.

Rausch, Virginia R.

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University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Faculty Publications from the Harold W. Manter Laboratory of Parasitology Parasitology, Harold W. Manter Laboratory of 6-1974 The Chromosomal Complement of the Yellow-Cheeked Vole Virginia R. Rausch Arctic Health Research Center Robert L. Rausch Arctic Health Research Center, rausch@u.washington.edu Follow this and additional works at: https://digitalcommons.unl.edu/parasitologyfacpubs  Part of the Parasitology Commons Rausch, Virginia R. and Rausch, Robert L., "The Chromosomal Complement of the Yellow-Cheeked Vole" (1974). Faculty Publications from the Harold W. Manter Laboratory of Parasitology. 528. https://digitalcommons.unl.edu/parasitologyfacpubs/528 This Article is brought to you for free and open access by the Parasitology, Harold W. Manter Laboratory of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Faculty Publications from the Harold W. Manter Laboratory of Parasitology by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. 267THE CHROMOSOMAL COMPLEMENT OF THEYELLOW·CHEEKED VOLEMicrotus xanthognathus (Leach)V. R. RAUSCH AND R. L. RAUSCHArctic Health Research Center, Center for Disease Control,Public Health Service, U.S. Dept. of HEW, Fairbanks, AlaskaThe karyotype of Microtus xanthognathlls (Leach) is described, based onmaterial from one female and one male vole. The diploid chromosomal numberwas found to be 54, and the fundamental number 62. The metacentric X-chromosome was of medium size and averaged 6.6% of the haploid complement.The designated Y-chromosome was near acrocentric. The specific distinction ofM. xanthogllathlls and Microtlls chrotorrhilllls (Miller) was confirmed by therecognition of major differences in karyotype and differences in fundamentalnumber. The distributional history of M. xallthognathus is briefly discussed.IntroductionThe yellow-cheeked vole, Microtus xanthognathus (Leach) is a biologicallylittle-known species occurring in boreal North America from west-central Alaska tothe western shore of Hudson Bay. The northern limits of its range in Canadacorrespond approximately to the timber-line. Within this extensive region, thevoles are generally considered to be rare, although they sometimes become numerouslocally. A morphologically similar vole, Microtus chrotorrhinus (Miller), has adisjunct distribution in eastern North America, from northern Labrador to the GreatLakes, and south in the Appalachian Mountains to North Carolina. Whether thesevoles differ only infraspeeifieally or represent distinct species has not been determined(d. Hall and Kelson, 1959, p. 741), although Guilday and Bender (960) identifiedremains of both voles in late Pleistocene deposits in Pennsylvania, and consideredthat their coeval association was indicative of specific distinction.During the spring of 1973, yellow-cheeked voles locally attained high densitiesin north-central Alaska, where we were able to obtain a series of animals. Thisprovided an opportunity to determine the chromosomal complement of M. xanthog-nathus and compare it with that of M. chrotorrhinus.Materials and MethodsKaryotypes were prepared from an adult female vole captured at Bettles Field,Alaska Oat 66°55'30" N, long 151°30'00" W), on about 25 May 1973, andfrom a subadult male caught at mile 28, Yukon Highway, Alaska (approx. lat.65°40' N, long. 149°07' W), on 21 June 1973. The animals were given 0.5 ml of0.05% Coleemid (Ciba) intraperitoneally, and after 1.5 h, bone marrow, spleen,and testes were collected for squash-preparations. Hypotonic treatment, fixation,and staining followed the method of Nadler and Block (1962). Dry ice was usedto make permanent mounts (Conger and Fairchild, 1953). The chromosomeswere photographed on Kodak high contrast copy film and enlarged. Arm-ratios weredetermined for all chromosomes in six cells from the male and three from the female(all from bone marrow), and for the metaeentrie-submetaeentrie elements and sex-chromosomes in an additional four male and seven female cells; total length onlyManuscript received November 20, 1973Can. J. Genet. Cytol. 16: 267-272. 1974.Rausch & Rausch in Canadian Journal of Genetics and Cytology (June 1974) 16(2).268 V. R. RAUSCH AND R. L. RAUSCHwas recorded for subtelocentric-acrocentrie autosomes in these latter cleven. Thechromosomes of one cell from each animal were used in the karyotypes, which wereassembled by grading the 52 autosomes by size and selecting pairs on the basis ofarm-ratios and morphologic characteristics.ResultsThe diploid chromosomal number for M. xanthognathus was found to bc 54,and the fundamental numbcr 62.Male: The karyotype of the male is shown in Fig. 1. Fifty-four chromo-somes were prcsent in 39 of 40 cells examined from bone marrow and testcs(spermatogonia). Among the 52 autosomes, three groups werc distinguished bycentromeric position, cxpressed here by arm-ratio: II submcdian, bordering onsubterminal, in the largest autosomes (pair I in thc karyotype), in which the rangeof arm-ratios was 2.61-4.40 (av 3.12); 21 subterminal to terminal in 46 autosomesof medium to small size (pairs 2-24), in which the arm-ratios ranged from 4.0 to~ 13.66; and 31 median in the smallest autosomes (pairs 25 and 26), in which theranges of arm-ratios were 1.26-1.88 (av 1.47) and 1.0-1.44 (av 1.16), respectively.In the second group, the ratios indicated that all were subtelocentrics or acrocentrics,but the small arms were minute and individually indistinct even when the chromo-somes were less contracted than those shown in Fig. 1. The consistent exceptionwas the acrocentric pair 2, with well defined arms; the range of arm-ratios in thispair was 6.11-8.69 (av 7.55). The arm-ratio of the X-chromosome ranged from1.01 to 1.34 (av 1.16). The Y-chromosome was one of a series of small-size sub-telocentrics-acrocentrics (arm-ratio range 4.0-7.80, av 5.04), but was not identifiedwith certainty; the chromosome so designated in the karyotype was selected by in-spection. In the preparations from testes, meiotic figures showed 26 autosomalbivalents and one sex-chromosome bivalent, the latter with an end-to-end relation-ship in some cells (Fig. 3).Female: The karyotype is shown in Fig. 2. Fifty-four chromosomes werecounted in 61 of 65 cells from bone marrow and spleen. As in the male, threeautosomal groups were distinguished: one pair of large submetacentrics (range ofarm-ratios 2.43-3.63, av 2.88); 23 pairs of subtelocentrics-acrocentrics (range ofarm-ratios 4.0 to ~ 13.33); and two pairs of very small metacentrics (range ofarm-ratios for pair 25,1.31-1.77, av 1.60, and for pair 26,1.09-1.31, av 1.20).In the X-chromosomes, the centromeres were median, and the range of arm-ratioswas 1.02-1.35 (av 1.15). The X-chromosome of M. xanthognathus was ofmedium size, and constituted al1 average of 6.6% (range 5.7-7.9%) of the haploidcomplement.DiscussionThe karyotype of M. chrotorrhinus was described by Meylan (1967), whofound the diploid number to be 60, and the fundamental number 64. With theexception of a single pair of small metacentrics, the autosomes were acrocentric.The sex-chromosomes, a submetacentric X and an acrocentric Y, werc much largerthan any of the autosomes. Meylan noted that the karyotype of M. chrotorrhinusresembles that of the palaearctic Microtus agresti,l' (Linnaeus) (2n = 50, FN =54), which also has giant sex-chromosomes.The karyotype of M. xanthognathus differs from that of M. chrotorrhinus innumber of chromosomes, in fundamental number, and in having sex-chromosomeswell within the range of size of the autosomes. The average lengths of theRausch & Rausch in Canadian Journal of Genetics and Cytology (June 1974) 16(2).CHROMOSOMES OF MICROTUS 269,c<••••(,c((rig•'"IIIIccII4-<o,...Ic~·C·. (\J. . C\IRausch & Rausch in Canadian Journal of Genetics and Cytology (June 1974) 16(2).270 V. R. RAUSCH AND R. L. RAUSCHc • rf 9C C•><C c ><, C,.....~0toj• Ca"-"'"C •'"(;;a'".....",'~<:;( 10;:C CoIi ~C 10;:c • '">-:~.....0'"C I a.;>,0;>,....• •oj::.::NoilC C ~,C C ,C- C~V <.\II'- CII I <.\II 10- co <.\IRausch & Rausch in Canadian Journal of Genetics and Cytology (June 1974) 16(2).CHROMOSOMES OF MICROTUS 271X-chromosome in our material were 3.S,u (female) and 4.2,u (male), and of theV-chromosome 1.9,u. The X-chromosome of M. chrotorrhinus was 8p (female)and 7. S,u (male), and the Y-chromosome, approximately 5p (Meylan, 1967). Theyellow-cheeked vole has in addition a pair of large submetacentric and a pair ofsmall metacentric autosomes not found in the other species. In chromosomalcharacteristics, M. xanthognathus does not seem to resemble closely any otherspecies of Microtus for which karyotypes have been defined.The pattern of the present geographic range of M. xanthognathus suggests thatthis vole spread from the Beringian Refugium during post-glacial time (d. Guthrie,1968). Its distribution resembles those in North America of Ciethrionomysrutiius (Pallas) and of Citellus parryi (Richardson), both holarctic species thatwere present in Beringia during the last (Wurm or Wisconsin) glaciation (Rausch,1963; Macpherson, 1965). Teeth indistinguishable from those of M. xanthog-nathus have been found in late Pleistocene deposits and in the basal portion of post-glacial deposits in central Alaska (Repenning et ai., 1964; Guthrie, 1968). Guildayand Bender (1960) reported a dehydrated specimen of possible Pleistocene age frompermanently frozen deposits in east-central Alaska.Guthrie (1968) noted that the absence of any counterpart of this vole inEurasia might be taken as support for the mgument that it spread into northwesternNorth America post-glacially from the south. Since M. xanthognathus occupies arestricted biotope, the lowland tundra in central Beringia would seem to have beenan ecological barrier to extension of its range westward during the last glacial period,but a further argument in support of its post-glacial immigration from the southFig. 3. Meiotic preparation from testis, M. xOllthognathus, 26 II + XY (arrow).Rausch & Rausch in Canadian Journal of Genetics and Cytology (June 1974) 16(2).272 V. R. RAUSCH AND R. L. RAUSCHmight be based upon the limited extent of taiga in Beringia during Wiirm time(Hopkins, 1972). In any case, if this vole became widely distributed during thelast (Eem or Sangamon) interglaciation, the glacial advances of Wiirm (Wisconsin)time might have left relict populations in Beringia and south of the continentalice-sheet, as is indicated in the case of varying lemmings, Dicrostonyx spp. (Mac-pherson, 1965; Rausch and Rausch, 1972). If unequivocal palaeontologicalevidence can confirm that M. xanthognathus was present in Beringia during the lastglacial period, it would be the first known instance of survival there of a late-Pleistocene immigrant of nearctic origin.During the period 1949-1973, in addition to those specimens from Bettles andthe Yukon Highway, we have obtained M. xanthognathus from Lake Minchumina,McGrath, and Fairbanks, in central Alaska. The record from Bettles represents asignificant extension northward of the known range of this vole in Alaska.AcknowledgementsWe should like to express our gratitude to the several persons whose interestmade this work possible. Dr. Leslie A. Viereck, Institute of Northern Forestry,U.S. Forest Service, Fairbanks, and Mr. John J. Burns, Alaska Department of Fishand Game, Fairbanks, provided information leading to the acquisition of the voles.Messrs. Jerry O. Wolff and Stephen D. West, Institute of Northern Forestry, and C.Davis Rhodes, Arctic Health Research Center, made special efforts to Jive-trapspecimens. Mr. Jerry Kocer, Bettles, contributed a live vole, and Mr. Gerald C.Kelley, Arctic Health Research Center, prepared the photographs.ReferencesConger, A. D., and Fairchild, L. M. 1953. A quick-freeze method for making smear slidespermanent. Stain Techno!. 28: 281-283.Guilday, 1. E., and Bender, M. S. 1960. Late Pleistocene records of the yellow-cheeked vole,Microtlls xallthognathlls (Leach). Ann. Carnegie Mus. 35: 315-330.Guthrie, R. D. 1968. Paleoecology of a late Pleistocene smal1 mammal community frominterior Alaska. Arctic 21: 223-244.Hall, E. R., and Kelson, K. R. 1959. The mammals of North America. Ronald Press, NewYork.Hopkins, D. M. 1972. The paleogeography and climatic history of Beringia during lateCenozoic time. lnternord No. 12: 121-150.Macphe'son, A. H. 1965. The origin of diversity in mammals of the Canadian arctic tundra.Syst. Zoo!' 14: 153-173.Meylan, A. 1967. Karyotype and giant sex chromosomes of M icrotlls chrotorrhilllls (Miller)(Mammalia: Rodentia). Can. 1. Genet. Cyto!. 9: 700-703.Nadler, C. F., and Block, M. H. 1962. The chromosomes of some North American chip-munks (Sciuridae) belonging to the genera Tamias and Eutamias. Chromosoma 13: 1-15.Rausch. R. L. 1963. A review of the distribution of holarctic Recent mammals. pp. 29-43ill Pacific Basin Biography (J. L. Gressitt, Ed.). Bishop Museum Press, Honolulu.Rausch, R. L., and Rausch, V. R. 1972. Observations on chromosomes of Dicrostollyxtorquatus stevclIsolli Nelson and chromosomal diversity in varying lemmings. Z. Sauge-tierk. 37: 372-384.Repenning, C. A., Hopkins, D. M., and Rubin, M. 1964. Tundra rodents in a late Pleistocenefauna from the Tofty Placer District, central Alaska. Arctic 17: 176-197.Rausch & Rausch in Canadian Journal of Genetics and Cytology (June 1974) 16(2).

The Chromosomal Complement of the Yellow-Cheeked Vole

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The Chromosomal Complement of the Yellow-Cheeked Vole

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