Frederick B. Stangl

The Third Lower Premolar of the Cottontail, Genus Sylvilagus, and Its Value in the Discrimination of Three Species

-The enamel pattern of the third lower premolar of Sylvilagus is derived from its Blancan ancestor, Nekrolagus. The posterobuccal re-entrant of Nekrolagus is short and a fossettid lies opposite it. In Sylvilagus, the fossettid joins the re-entrant to form a broad reentrant. The enamel at the tooth base consists only of thin radial enamel. Ameloblasts above the tooth base deposit additional lamellar enamel to the basal radial enamel at the anterior and posterior ends of the tooth and at the anterior wall of the posterobuccal re-entrant. At the occlusal surface these areas consist of enamel thicker than that of the rest of the pattern. A small area of the occlusal surface of Nekrolagus fossettid shows tangential enamel. Two types of cementum are distinguished, and herein named. Deeper re-entrants and the Nekrolagus fossettid are filled with structural cementum but the outer surfaces are covered with coating cementum. The anterior wall of the posterobuccal re-entrant of p3 is without crenulations or simple in S. nuttallii and usually so in S. fioridanus. Sylvilagus audubonii usually has the anterior wall of the re-entrant moderately to strongly crenulated. Crenulation of the anterobuccal re-entrant wall does not separate species of cottontails in all cases but is helpful in separation of species where only isolated teeth are available and in mixtures of species as in some cave deposits.

Immunoelectrophoretic Relationships among Four Species of Woodrats (Cricetidae: Neotoma)

Immunological relationships among four species of woodrats (Neotoma floridana, Neotoma micropus, Neotoma albigula, and Neotoma mexicana) are cladistically analyzed, using a Peromyscus outgroup. Within this group, N. micropus and N. floridana comprise an antigenically derived sister group, while N. mexicana retains the most primitive antigenic composition. Neotoma albigula is intermediate but appears more closely related to the N. micropus-N. floridana clade. These results are concordant with a consensus series of relationships proposed on the basis of morphology, karyology, and other biochemical data sets. This agreement supports the potential utility of immunoelectrophoresis as a systematic tool. Evolutionary relationships within the genus Neotoma have been investigated using a variety of morphological (Goldman, 1910; Burt and Barkalow, 1942; Hooper, 1960; Carleton, 1980), biochemical (Birney, 1973; Zimmerman and Nejtek, 1975, 1977), and cytogenetic (Birney, 1973; Mascarello and Hsu, 1976; Koop et al., 1985) techniques. Of particular interest have been four closely related and widely available species of woodrats from the southcentral and southeastern United States. Neotoma micropus is a species of the southern Great Plains, whose range interfaces to the east with Neotoma floridana of the southeastern deciduous woodlands. The western range of N. micropus overlaps broadly with that of Neotoma albigula, and to a lesser extent, with the range of Neotoma mexicana. Immunoelectrophoresis has not been widely employed as a systematic tool in mammalogy. Earlier applications (Birney, 1973; Baranov et al., 1976, 1978) have demonstrated the utility of the technique in characterizing levels of genetic variation for specific proteins (e.g., lipoproteins, esterases) but afforded no systematic resolution. More recent studies, using tissue homogenates (e.g., blood, liver) to generate antisera, have proven a useful tool in reconstructing evolutionary relationships of an array of Old World fruit bat genera (Haiduk, 1983) and between closely related species of prairie dogs (McCullough, 1987). The present study assesses immunoelectrophoretic relationships of N. micropus, N. floridana, N. albigula, and N. mexicana, whose interrelationships have been relatively well ascertained by a variety of independent studies. Therefore, this study also provides an ideal test of the further utility of immunoelectrophoresis as a systematic

Multilocus analyses indicate a mosaic distribution of hybrid populations in ground squirrels (genus Ictidomys)

DNA sequence data from mitochondrial cytochrome-b (Cytb) and Y-linked structural maintenance of chromosomes (SmcY) genes were combined with 478 nuclear loci obtained from amplified fragment length polymorphisms (AFLP) to assess the extent of hybridization and genetic spatial structure of populations in two hybridizing species of ground squirrel (Ictidomys parvidens and Ictidomys tridecemlineatus). Based on AFLP analyses of 134 individuals from 28 populations, 10 populations were identified that possessed hybrid individuals. Overall estimates of FST values revealed strong support for population structure in the Cytb data set; however, analyses of the SmcY gene and the AFLP data indicated ongoing gene flow between species. Pairwise FST comparisons of populations were not significant for the SmcY gene; although they were significant for the Cytb gene, indicating that these populations were structured and that gene flow was minimal. Therefore, gene flow between I. parvidens and I. tridecemlineatus appeared to be restricted to populations that exhibited hybridization. In addition, the fragmented nature of the geographic landscape suggested limited gene flow between populations. As a result, the distributional pattern of interspersed parental and hybrid populations were compatible with a mosaic hybrid zone model. Because ground squirrels display female philopatry and male-biased dispersal, the ecology of these species is compatible with this hypothesis.

Spatial and Temporal Distribution of the Polymorphism for Tail-Tip Albinism in the Hispid Pocket Mouse, Chaetodipus hispidus (Rodentia: Heteromyidae)

-A survey of almost 1000 study skins of Chaetodipus hispidus from Oklahoma and Texas indicates that ca. 7% of all individuals are marked by tail-tip albinism, and that the character is about equally distributed by sex and nominal subspecies. No significant frequency differences were noted among the eight major habitats represented in the study area, although the three pooled habitats which comprise the interior grasslands of the Southern Plains support a significandly higher incidence of the partial albinism than the peripheral, more sparsely populated regions (remaining pooled habitats). Data from a single Texas county, spanning four decades, indicate that local populations undergo repeated fluctuations, which account for the observed erratic microgeographic (by county) distribution of the character. As with previous studies which have used partial albinism data as genetic indicators for past events and current population structure, we propose that surveys of mammal collections for examples of partial albinism could prove useful in the design of population genetic studies. The possible roles of selection and stochastic events in producing and maintaining the observed distribution patterns are discussed.

Pathology of an Unusual Lumbar Condition in a Young Black Bear (Ursus amercanus) from the Big Bend Region of Trans-Pecos Texas

ABSTRACT. The skeleton of a young American black bear (Ursus americanus) possessing asymmetrical distortions of the 5 caudalmost lumbar neural spines was recovered from west Texas. We attribute this abnormality, presumed to be congenital, to the absence or atrophy of the right multifidus muscle straddling L3 and to the series of compensatory muscle adjustments required to maintain spinal alignment. This finding may have important management implications for black bears in Texas, given the possibility that our specimen originates from a partially isolated population.

First Record of Sigmodon fulviventer in Texas: Natural History and Cytogenetic Observations

The discovery of a population of Sigmodon fulviventer along the western flanks of the Davis Mountains, Jeff Davis Co., Texas, represents a new record for the species from Texas, and extends the known range of the tawny-bellied cotton rat in the United States eastward > 100 km (Hall, 1981). Because the status of this isolated population is unknown, it seems advisable to detail varied aspects of the biology of this species (history and origin of the population, habitat, interspecific interactions, reproduction, cytogenetic variation) at the eastern extreme of its range in the United States.

Supernumerary Hind Foot on a Specimen of the Texas Mouse, Peromyscus attwateri (Rodentia: Cricetidae)

pear to have been shredded in the past. The first specimen is 105 cm tall, with 15 stems 2 to 19 mm in diameter at base. The second specimen is 68 cm tall, with 23 stems 1 to 7 mm in diameter. The third specimen is 70 cm tall, with three stems 3 to 16 mm in diameter. Despite past abuse, all three specimens appear healthy and are producing flowers. Although the area has been disturbed, it supports a diversity of woody plant species. Dominant species include Prosopis glandulosa Torr. (honey mesquite), Pithecellobium ebano (Berl.) C. H. Muller (Texas ebony), Zanthoxylum fagara (L.) Sarg. (colima), Celtis pallida Torr. (granjeno), and Karwinskia humboldtiana (R. et S.) Zucc. (coyotillo). Several other species that occur in Mexico and reach the northern limit of their