American Society of Mammalogists Taxonomic Status and Biogeography of the Southern Bog Lemming, Synaptomys cooperi, on the Central Great Plains Author(s): Gregory M. Wilson and Jerry R. Choate Source: Journal of Mammalogy, Vol. 78, No. 2 (May, 1997), pp. 444-458 Published by: American Society of Mammalogists Stable URL: http://www.jstor.org/stable/1382897 . Accessed: 11/08/2011 18:26 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. American Society of Mammalogists is collaborating with JSTOR to digitize, preserve and extend access to Journal of Mammalogy. http://www.jstor.org TAXONOMIC STATUS AND BIOGEOGRAPHY OF THE SOUTHERN BOG LEMMING, SYNAPTOMYS COOPERI, ON THE CENTRAL GREAT PLAINS GREGORY M. WILSON AND JERRY R. CHOATE Present address of GMW: Department of Zoology, 430 Life Sciences West, Oklahoma State University, Stillwater, OK 74078 Sternberg Museum of Natural History, Fort Hays State University, Hays, KS 67601 We assessed geographic and nongeographic variation among populations of the southern bog lemming (Synaptomys cooperi) in Arkansas, Iowa, Illinois, Kansas, Missouri, Nebraska, and South Dakota based on morphological data. Univariate and multivariate analyses of 15 cranial characters revealed no consistent sexual dimorphism. Geographic variation in cra- nial morphology of adults varied clinally, with individuals increasing in size from north to south and east to west. The largest individuals overall were from southwestern Kansas (S. c. paludis) and southwestern Nebraska (S. c. relictus), and the smallest individuals were from populations in eastern Illinois (S. c. gossii). We found only minor steps in clinal varia- tion of cranial morphology, which may be attributed to periodic or recent isolation. No individuals of S. c. paludis and S. c. relictus have been collected since 1946 and 1968, respectively, and these taxa may be extinct. Because of the paucity of specimens, taxo- nomic conclusions as to the intraspecific relationships of populations are speculative. We, therefore, recommend retention of the currently recognized subspecies S. c. gossii, S. c. paludis, and S. c. relictus until genetic characters can be analyzed. Key words: Synaptomys cooperi, cranial morphometrics, taxonomy, biogeography, Great Plains The southern bog lemming, Synaptomys Hibbard and Rinker (1942) named S. c. cooperi (Rodentia: Muridae, Arvicolinae- paludis from Meade County State Park Musser and Carleton, 1993), is endemic to (=Meade State Lake) in southwestern Kan- North America. It is an eastern species sas. In comparison with eight adult S. c. (Armstrong et al., 1986) that has a spotty gossii from eastern Kansas, many individu- distribution and often unpredictable occur- als had darker pelage and larger cranial and rence in the northeastern United States and external measurements. Additionally, in 10 southeastern Canada west to ca. 100'W on of the 19 skulls available for examination, the Great Plains (Hall, 1981; Linzey, 1983; two grooves, rather than the usual one, were Musser and Carleton, 1993). Two of the present on the anterior surface of the upper nominal subspecies that occur in the Great incisors. Plains Physiographic Province, S. c. palu- Jones (1954) caught one southern bog dis and S. c. relictus, are believed to be bio- lemming (that he initially assigned to the geographic relicts left behind when the subspecies S. c. gossii) at Rock Creek State range of the species retreated northward and Fish Hatchery in Dundy Co., southwestern eastward sometime after the Pleistocene. Nebraska, in 1952. After three additional These relict populations persisted where specimens were captured in 1956 at the marshes and artesian springs provided suit- same locality, Jones (1958) named the sub- able habitat (Hibbard and Rinker, 1942; species S. c. relictus. Most external and cra- Jones, 1958; Wetzel, 1955). nial characters of two specimens (an old Journal of Mammalogy, 78(2):444-458, 1997 444 May 1997 WILSONAND CHOATE-VARIATION IN TAXONOMYAND BIOGEOGRAPHY 445 adult female and an adult female) were in- and mixed-grass prairie in western Kansas termediate between S. c. paludis and S. c. and Nebraska (Kiichler, 1964) produced pe- gossii. He did not mention grooves on the riodic barriers to gene flow among popula- upper incisors. tions of S. cooperi on the Great Plains, thus In their taxonomic revisions of Synapto- enabling slight divergence of the isolated mys in North America, both Howell (1927) populations. and Wetzel (1955) showed that cranial size in S. cooperi varies clinally (as defined by MATERIALS AND METHODS and Ashlock, 1991) in the reverse of Mayr We examined 911 of S. Rule, with dimensions increas- specimens cooperi Bergmann's from Arkansas, Illinois, Iowa, Kansas, Minne- from north to south and from east to ing sota, Missouri, Nebraska, South Dakota, and west the Subse- throughout species' range. Wisconsin (Appendix I). Because S. cooperi, quent paleontological studies produced like many other arvicoline rodents, possesses similar findings (Guilday et al., 1978; hypsodont dentition (Miller, 1896; Semkin, Semken, 1984). Wetzel (1955:18) observed 1984), traditionalmethods used to estimate age that S. c. paludis was the largest subspecies of other muridrodents are inappropriate(Ander- in North America, being "distinctly larger son, 1959; Carleton, 1985; Phillips, 1969). We (by two standard errors) than S. c. gossii" assigned specimens to one of three age classes from eastern Kansas in characters other than based on criteria similar to those described by Carleton Choate and Williams (1978), "length of tail, length of maxillary toothrow, (1985), and Wetzel (1955), but we only used two age length of incisive foramen, and nasal classes because of small samples for juveniles. width." Wetzel (1955:18), thus, with agreed Adults of S. cooperi can be distinguishedeasily Hibbard and Rinker that S. c. (1942) palu- from subadultsby the fusion, or near fusion, of dis was a valid subspecies, albeit only a the interorbitalridges in the former and a wide "conservative or localized relic race" of the separation in the latter (Wetzel, 1955). We large prairie form, S. c. gossii, to the east. assigned specimensthat possessed many (butnot As Wetzel (1955:18) explained, "A grada- all) features of adults to the subadultage class, tion from Meade County to eastern Kansas thus ensuringthat the adultage class was "pure." would perhaps be observable could the geo- We selected 15 mensuralcharacters, as defined DeBlase and Martin Howell graphical gap be spanned by series of speci- by (1981), (1927), mens." Because S. c. relictus was described Wetzel (1955), and Wilson (1994), because of their taxonomic utility and repeatability;width to the review by Wetzel (1955), subsequent of incisors, width of nasal bone, of it has never been evaluated upper length taxonomically. nasal bone, length of rostrum (as described by In of S. c. in addition, populations gossii Hooper, 1952), breadthof rostrum,length of in- northcentral Kansas have been only recently cisive foramen, total length of toothrow,length discovered (Clark et al., 1986; Welker and of maxillary toothrow, zygomatic breadth, Choate, 1994) and did not exist or were un- breadthof braincase,mastoidal breadth, interor- known to Jones (1954, 1958) and Wetzel bital breadth, condylobasilar length, greatest (1955). length of skull, and palatofrontaldepth. We re- We used univariate and multivariate sta- corded measurementsto the nearest 0.01 mm with We did not record external tistical techniques to investigate both geo- digital calipers. and variation measurementsfrom labels of study skins because graphic nongeographic among these measurementsoften are unreliable. of S. cooperi on the Great populations We used the PC version (Release 6.03 Edition) Plains based on cranial data. morphological of the StatisticalAnalysis System (SAS Institute, we examined skulls for the Also, presence Inc., 1988a, 1988b) to analyze nongeographic of grooves on the upper incisors and as- and geographic variation within and among sessed differences among taxa in pelage samples (localities). We calculated percentage coloration. We hypothesized that the elimi- contributionto the total varianceby gender, age nation of marshy corridors across the short- (adult, subadult),gender-by-age interaction, and 446 JOURNALOF MAMMALOGY Vol. 78, No. 2 error categories from sums-of-squares estimates by Hall (1981), S. c. gossii is represented by (VARCOMP procedure), as described by Leamy samples A through K and sample N, S. c. palu- (1983) and Straney (1978), using all adults and dis by sample L, and S. c. relictus by sample M. subadults from all localities combined. We en- We used the UNIVARIATE procedure of SAS tered gender first and then age because gender to compute descriptive statistics for adult indi- is a fixed factor (Leamy, 1983). We used a one- viduals within each sample and a one-way way analysis of variance (ANOVA) to determine ANOVA to test for morphological variation if each of the 15 morphometric characters dif- among sample (locality) means. Tukey's stu- fered significantly (P 0.05) between subadult