Geographical and Interspecific Cranial Variation in Big-Eared Ground Squirrels (Spermophilus): A Multivariate Study

Abstract

Robinson, Jon William, and R. S. Hoffmann (Department of Systematics and Ecology and Museum of Natural History, University of Kansas, Lawrence, Kansas 66045) 1975. Geographical and interspecific cranial variation in big-eared ground squirrels (Spermophilus): a multivariate study. Syst. Zool. 24:79-88.-Interspecific and subspecific variation in cranial morphology of the big-eared ground squirrels (Spermophilus) was described and found to be related to patterns of chromosomal variation. The first discriminant function (DF) and first principal component (pc) were found to correspond roughly to the latitudinal location of the species. In this study, looking at the scatter plots of individuals on Pc's would not have helped one to find groups. Differences considered to be biologically meaningful were found between pairs: Spermophilus r. richardsonii and Spermophilus richardsonii aureus; Spermophilus columbianus columbianus and Spermophilus undulatus; and Spermophilus parryii kennicottii and Spermophilus parryii leucostictus. The S. richardsonii subspecies group was reorganized so the S. richardsonii is now a species distinct from the three subspecies S. elegans elegans, S. elegans aureus and S. elegans nevadensis. S. p. leucostictus and S. p. kennicottii, if only cranial morphology were considered, could be regarded as different species. [Ground squirrels; multivariate analysis; taxonomy; interspecific relationships; evolution; ecology; chromosomal variation.] The North American big-eared ground squirrels (Davis, 1939) presently include the species Spermophilus armatus, S. beldingi, S. brunneus, S. columbianus, S. richardsonii and S. undulattus. (Hall and Kelson, 1959; Fig. 1). North American and Eurasian populations of the arctic ground squirrel (S. undulatus) were considered conspecific by Heptner (1941) and Rausch (1953). However, Gromov et al. (1965) differentiated Middle Asian and western Siberian populations (S. undulatus) from those of eastern Siberia and North America (S. parryii), on morphological grounds, as did Nadler et al. (1973) on the basis of chromosomal and biochemical differences. They are herein considered distinct species. All named taxa of North American bigeared ground squirrels were studied, with the following exceptions. Spermophilus brunneus was not included in this study because insufficient specimens were available, as was also true of the subspecies S. columbianus ruficaudus. Only arctic populations of S. parryii were studied; S. p. kennicottii from northern Alaska, S. p. janensis and S. p. leucostictus from the Verkhoyansk and Chukotsk regions of northeastern Siberia. The latter two subspecies were lumped because they are geographioally very close and no study has shown there to be a significant difference between the two. Among the wide-ranging S. undulatus, only a sample from the Altai Mountains of the U.S.S.R. and Mongolia (S. u. eversmanni, S. u. stramineus) was used, due to availability of specimens. Distributions of these groups are mapped (Fig. 1). Some work had already been done on the ecological relationships of certain taxa (Durrant and Hansen, 1954; Turner, 1972) and their chromosomal morphology described (Nadler, 1966; Nadler, et al., 1971; Liapunova and Vorontsov, 1970). There has also been some alpha taxonomic work done on these squirrels (Howell, 1938; Davis, 1939; Heptner, 1941; Rausch, 1953; Gromov et al., 1965). In this study we describe interspecific variation present in this subset of the genus Spermophilus based on 36 skull characters using multivariate and univariate statistical methods of data analysis. This morphological vari-