M. Raymond Lee

Chromosomal Variation in Certain Populations of Peromyscus boylii and Its Systematic Implications

The karyotype of Peromyscus boylii attwateri is contrasted with that of P. b. boylii, P. b. rowleyi , and P. b. utahensis . The latter three taxa have identical karyotypes. Chromosomal and morphological evidence indicate that attwateri is specifically separated from the boylii-rowleyi-utahensis assemblage. Limited samples from Mexican populations of P. boylii imply that current taxonomic alignments in this species require reevaluation. The karyotype of Peromyscus difficilis comanche is described and it appears to be identical to that of Peromyscus truei truei and unlike those of northern populations of P. difficilis .

Karyotypes of Eight Species of Mexican Rodents (Muridae)

Karyotypes of six species of murid rodents from Mexico are reported for the first time, including: Nyctomys sumichrasti, Peromyscus hylocetes, Peromyscus perfulvus, Peromyscus banderanus, Baiomys musculus , and Neotoma goldmani . The chromosomes of some species clearly suggest affinities within the appropriate taxa. Identity of the sex chromosomes and an apparent automosomal polymorphism are shown for Neotoma alleni . The karyotype of Microtus mexicanus from western Mexico is polymorphic for two pairs of chromosomes and, more importantly, differs significantly from that of presumed M. mexicanus occurring north of Mexico.

Robertsonian Polymorphism in the Cotton Rat, Sigmodon Fulviventer

Karyotypes of 28 fulvous-bellied cotton rats, Sigmodon fulviventer, from Arizona and New Mexico were analyzed. Intrapopulational variation in diploid numbers of 30, 29, and 28 was found. This polymorphism is ascribed to Robertsonian changes: centric fusion or fission involving two pairs of acrocentric autosomes or one pair of metacentric autosomes, respectively. Possible mechanisms are discussed for the origin of this polymorphism and its evolutionary significance. The relatively high frequency of each diploid type is contrasted with the condition in certain other species of mammals. Tentative remarks concerning chromosomal relationships among four kinds of Sigmodon are presented.

Albumin Evolution in Peromyscus and Sigmodon

Phylogenetic relationships among certain cricetine rodents are examined using the quantitative micro-complement fixation technique. Antibodies against purified albumin from five species of Peromyscus , one species of Sigmodon , and one microtine rodent were used. In addition, serum from nine species of Peromyscus, Ochrotomys nuttalli , and fifteen subspecies and species of Sigmodon were examined. The fourteen species of Peromyscus represent three subgenera. Some, but not all of the results are inconsistent with current classification. The lineages leading to Peromsycus and Sigmodon are estimated to have diverged about 22 million years ago, whereas cricetines and microtines last shared a common ancestor some 40 million years ago.

Revision of The Pocket Mice, Perognathus Penicillatus

The species Perognathus penicillatus is revised taxonomically. Eight subspecies are recognized and characterized. The subspecies P. penicillatus minimus is here referred to Perognathus intermedius . The type locality of P. p. penicillatus is redesignated. Age-variation, secondary sexual variation, and individual variation within the species are summarized. Intraspecific differentiation, clinal variation, and the importance of geographical barriers are discussed.

The Chromosomes of Sigmodon ochrognathus and S. fulviventer Suggest a Realignment of Sigmodon Species Groups

The G- and C-banded karyotypes of Sigmodon ochrognathus (2n = 52) and S. fulviventer (2n = 28, 29, 30) are presented and compared to S. hispidus (2n = 52), which we regard as representative of the ancestral chromosomal type. Sigmodon ochrognathus differs from S. hispidus only by the addition of heterochromatic short arms on eight pairs of chromosomes. Sigmodon fulviventer possesses three unique chromosomes and lacks homologous counterparts for ten chromosomes found in S. hispidus . The available cytogenetic and immunological evidence suggests that S. fulviventer represents an evolutionary lineage well removed from all other North American species. We propose that S. hispidus, S. leucotis, S. alleni, S. ochrognathus, S. arizonae , and S. mascotensis comprise a species group and that S. fulviventer should be recognized as a separate monotypic species group.

Revision of the Desert Cottontail, Sylvilagus Audubonii, in the Southwest

Individual, secondary sexual and geographic variations are analyzed in Sylvilagus audubonii in the Southwest. Ways of distinguishing this species from both S. floridanus and S. nuttallii in this region are presented. A method of selecting homogeneity in age of specimens is suggested. Individual variation appears to be average and secondary sexual variation probably unimportant in most characters. Cranial and external characters are most useful in studying geographic variation while color, except in one subspecies, is of little significance. The geographic location of character shifts in 12 characters is shown graphically. Those shifts showing a high degree of concordancy form the primary basis for subspecific boundaries. Four subspecies of S. audubonii ( warreni, arizonae, minor and goldmani ) are recognized, and the name cedrophilus is placed in synonymy. Strong local variation occurring in certain subspecies is described. The Mogollon Plateau is shown to have been a most important geographic feature affecting the differentiation within this species in Arizona.

Karyotypic Variation in the Pocket Mice Perognathus amplus and P. longimembris

We studied the karyotypic variation of Perognathus amplus and P. longimembris in Arizona and adjacent Nevada and Utah. We extend the distribution of previously known fundamental-number (FN) variants. C-banded karyotypes showed that the FN variants do not result from addition or deletion of heterochromatic arms. We hypothesize that karyotypic evolution in these pocket mice proceeded in three directions from a presumed ancestral FN = 88 karyotype shared by both species. In both P. longimembris and P. amplus , parallel decreases in FN led to low-FN populations. In P. amplus , a separate lineage is characterized by increasing FN. The short-term cell-culture technique we used was superior to in vivo-colchicine, hypotonic methods for the production of chromosome spreads from pocket mice.

Cleaning Mammalian Skulls with Ammonium Hydroxide

The procedure for cleaning mammalian skulls with ammonium- hydroxide is given. Suitable for medium-sized rodents and marsupial or small but robust skulls, the process involves soaking the skull in concentrated ammonium-hydroxide for 24 hours and then boiling it in concentrated ammonium-hydroxide for 1 to 4 hours. Soft parts may be washed away and other tissue may be mechanically removed. Screens are useful for collecting separated bones and teeth.

Taxonomic Review of Cottontails, Sylvilagus floridanus and Sylvilagus nuttaliii, in Arizona

In Arizona, the two cottontails Sylvilagus floridanus and Sylvilagus nuttallii inhabit montane and submontane terrain. In this region they exhibit considerable morphological convergence and often have been confused. However, we have found several characters which will satisfactorily distinguish the two. Additional material now available together with that already present in various collections has enabled us to present a critical appraisal of the characteristics and geo- graphic occurrence here of the subspecies of S. floridanus and S. nut- tallii. A new subspecies of S. floridanus is described. S. nuttallii pinetis is redefined since previous descriptions were based on specimens of both S. nuttallii and S. floridanus. One specimen is discussed which may be a hybrid between the two species. A taxonomic review of cottontails of the species Sylvilagus flori- danus and Sylvilagus nuttallai in Arizona is called for in view of the confusion that has long existed in distinguishing these two species. Nelson (1909:199) in his revision of the rabbits of North America regarded certain specimens from the Hualpai Mountains and from near Prescott as Sylvilagus nuttallii and used them in his characteri- zation of the subspecies S. n. pinetis (Allen). Some 40 years later, Hall and Kelson (1951:54) regarded these same specimens as being Sylvilagus floridanus holzneri (Mearns). Certain specimens in some