Idaho Ground Squirrel Research Articles

Taxonomy and Distribution of the Idaho Ground Squirrel, Spermophilus brunneus

Spermophilus brunneus was found in isolated meadows surrounded by coniferous forests in Adams and Valley counties, Idaho, and also further south at lower elevations in the relatively xeric foothills north of the Payette River in Gem, Payette, and Washington counties. Marked differences in pelage coloration related to soil color exist between the disjunct northern and southern populations. Univariate and multivariate analyses of external, cranial, baculum, and pelage characters revealed significant sexual dimorphism in external and cranial characters and also that northern and southern S. brunneus are well-differentiated taxa. The bacula are about as distinct as those of S. townsendii idahoensis are from S. washingtoni , suggesting that the two S. brunneus may be approaching species-level differentiation. A change in soils, vegetation, and topography, but no apparent biogeographic barrier, separates the two taxa. Southern S. brunneus is described herein as a new subspecies.

Mate guarding as paternity insurance in Idaho ground squirrels.

Following a copulation, males in many species of vertebrates (particularly birds) and invertebrates remain near the inseminated female and repel other suitors with displays or force. Guarding males must delay resumption of competitive mate searching, but they may insure their paternity by reducing possibilities for secondary matings and sperm competition. Among mammals, post-copulatory mate guarding has been reported in rodents, mongooses, ungulates and primates, including humans, but the effects of such behaviour on male reproductive success have not been determined genetically. I report here that mate guarding by male Idaho ground squirrels (Spermophilus brunneus) enhances a male's probability of paternity. Furthermore, an analysis based on game theory shows that mate guarding is an evolutionarily stable strategy for male S. brunneus, but not male Belding's ground squirrels (S. beldingi), which resume searching once copulation is completed.

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

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-

Chromosomes and giemsa-bands of the Idaho spotted ground squirrel,Spermophilus brunneus (Howell)

Хромосомы и Г-полосыSpermophilus brunneus изучалы. Хотя кариотипы сходние, и гомология между 13 из 18 парами аутосомов,S. brunneus отличается отS. townsendii mollis (2n=38) в других морфологических, меховых, и биохимических признаках; эти признаки соединяЯ;ютS. brunneus с болиьшеухей гууппой. Промежуточност признаков уS. brunneus предлагает что этот пеликтовый вид, немного расходящийся из ранного прародителя у подродаSpermophilus.