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Historically, a large number of taxonomic forms has been recognized within Nearctic pikas (Lagomorpha: Ochotonidae; Ochotona), including up to 13 species and 37 subspecies. After 1965, 2 species and 37 forms have been recognized: the monotypic O. collaris of Alaska, British Columbia, Yukon, and Northwest Territories, and O. princeps, with 36 subspecies spread throughout western Canada and the western United States. The 36 subspecies of O. princeps have been distinguished by subtle differences, particularly in pelage coloration and body size, within the highly fragmented distribution of the species on isolated 'islands' of cool, rocky habitat. However, molecular phylogenetic studies (allozyme electrophoresis and sequencing of both mitochondrial and nuclear genomes) indicate the existence of 5 phylogenetic lineages within O. princeps. The cohesiveness of each lineage has been reinforced during glacial stages by introgressive hybridization among currently isolated populations within each lineage. In contrast, the low level of cranial variation and lack of consistent differentiation in cranial characters, pelage coloration, or body size among the 5 lineages indicates idiosyncratic interlocality variation due to high inbreeding within highly isolated populations, genetic drift, and possibly selection for common traits. Examination of allozymic, morphological, and nuclear DNA data indicates previous introgressive hybridization among several of the lineages, probably associated with contact during the Last Glacial Maximum. Herein we characterize morphometric variation between and among O. collaris (n = 164) and O. princeps (n = 1,999) and revise the subspecific taxonomy of O. princeps to 5 subspecies based on molecular phylogenetic lineages, at least 3 of which are known to possess a unique dialect in the short call: O.p. princeps (Northern Rocky Mountains), O. p. fenisex (Coast Mountains and Cascade Range), O. p. saxatilis (Southern Rocky Mountains), O. p. schisticeps (Sierra Nevada and Great Basin), and O. p. uinta (Uinta Mountains and Wasatch Range of central Utah). These 5 subspecies represent evolutionarily meaningful units for consideration of possible management applications if populations of O. princeps are imperiled by human activities. DOI: 10.1644/09-MAMM-A-277.1. Key words: alloz ymes, mitochondrial DNA, morphology, nuclear DNA, Ochotona collaris, Ochotona princeps, pika, subspecies, systematics, taxonomy

Once encompassing as many as 9 species of pocket gophers spread across most of the Mexican Altiplano, the genus Pappogeomys is now restricted to a single species, P. bulleri, occupying the mountains, tablelands, and coastal plains near the western end of the Trans-Mexican Volcanic Belt in west-central Mexico. Herein, we review the taxonomic history of Pappogeomys and examine relationships among populations of P. bulleri from throughout the geographic range of the species based on analyses of nonpreferentially stained karyotypes and mitochondrial and nuclear sequence data. Results of these analyses are concordant and reveal 3 major clades of P. bulleri that are separated by major physiographic features of the region, including the Sierra Madre del Sur and drainages of the Rio Grande de Santiago, Rio Ameca, Rio Ayuquila, and Rio Armeria. We reduce the number of subspecies of P. bulleri from 9 to 5 valid forms and provide a revised synonymy of the species. Key words: chromosomes, mitochondrial DNA, nuclear DNA, Pappogeomys, pocket gophers, systematics

The Southern Coahuila Filter-Barrier (SCFB) effectively subdivides the mammalian fauna of the Mesa del Norte, the northern and most extensive section of the Mexican Altiplano. Pocket gophers of the genus Cratogeomys north and south of this filter-barrier have been informally recognized as 2 distinct species, C. castanops and C. goldmani, respectively. Support for species recognition derives from early morphological comparisons and recent chromosomal and ectoparasite studies. Contradictory conclusions based on the only comprehensive morphometric study have prevented formal recognition of C. goldmani. A morphometric reevaluation based on ratiotransformed data reveals that the previous analysis was unduly biased by size, an ecophenotypically plastic character. When this factor is removed, morphometric variation is fully concordant with chromosomal diploid number and sequence data of mitochondrial and nuclear DNA. We provide synonymies and descriptions for C. goldmani apart from C. castanops, and revise the number of subspecies from a total of 26 to 2 subspecies in each species. The SCFB is most effective in its central portion (Desierto Mayran), and least effective in its western portion (Rio Nazas), which should be geographically broadened to include the neighboring Rio Aguanaval. Key words: chromosomes, Cratogeomys, filter-barrier, mitochondrial DNA, morphology, nuclear DNA, pocket gophers, systematics

The New World rodent family Heteromyidae shows a marvelous array of ecomorphological types, from bipedal, arid-adapted forms to scansorial, tropical-adapted forms. Although recent studies have resolved most of the phylogenetic relationships among heteromyids at the shallower taxonomic levels, fundamental questions at the deeper taxonomic levels remain unresolved. This study relies on DNA sequence information from 3 relatively slowly evolving mitochondrial genes, cytochrome c oxidase subunit I, 12S, and 16S, to examine basal patterns of phylogenesis in the Heteromyidae. Because slowly evolving mitochondrial genes evolve and coalesce more rapidly than most nuclear genes, they may be superior to nuclear genes for resolving short, basal branches. Our molecular data (2,381 base pairs for the 3-gene data set) affirm the monophyly of the family and resolve the major basal clades in the family. Alternative phylogenetic hypotheses of subfamilial relationships are examined statistically and the Perognathinae and Heteromyinae are found to represent sister clades relative to the Dipodomyinae. The 3 traditional subfamilial groupings are supported; the controversial placement of Microdipodops as a sister clade to Dipodomys in the Dipodomyinae is affirmed, Perognathus and Chaetodipus are distinct sister clades within the Perognathinae, and species of Liomys and Heteromys form the resolved clade Heteromyinae. However, Liomys is found to be paraphyletic relative to Heteromys and, given that this finding corroborates earlier studies, we present a formal taxonomy of Heteromys wherein we place Liomys in synonymy. Semiparametric and parametric methods are used to estimate divergence times from our molecular data and a chronogram of the Heteromyidae, calibrated by the oldest known fossils of Dipodomys and Perognathus, is presented. Our time estimates reveal subfamilial differentiation in the early Miocene (22.3-21.8 million years ago) and pose testable times of divergence for the basal heteromyid nodes. With the basal heteromyid clades resolved and cladogenic events positioned in a time framework, we review the major geological and paleoecological events of the Oligocene and Miocene associated with the early historical biogeography of the family. Key words: Chaetodipus, Dipodomys, Heteromyidae, Heteromys, historical biogeography, Liomys, Microdipodops, mitochondrial DNA, Perognathus, phylogenetics

A study of chromosomal variation in the Mexican pocket gopher Cratogeomys merriami revealed differences in diploid number that correspond to 3 major genetic and morphological clades within the species. Each of these 3 clades is diagnosable based on multiple characters, including chromosomal diploid number, quantitative and qualitative morphological characters, and mitochondrial DNA. Accordingly, we restrict the name C. merriami (Thomas) to include only pocket gophers of this genus from the states of Mexico, Mexico D.F., northern Morelos, and west-central Puebla. We resurrect the species name C. fulvescens Merriam to represent members of this genus from southern Tlaxcala, east-central Puebla, and parts of west-central Veracruz. Finally, we resurrect the species name C. perotensis Merriam to represent members of this genus from southern Hidalgo, northern Tlaxcala, north-central Puebla, and parts of west-central Veracruz. Based on the observation that differences in diploid number usually signal reproductive isolation between populations of pocket gophers, we hypothesize that C. merriami, C. fulvescens, and C. perotensis are reproductively incompatible. We provide synonymies and descriptions for these 3 species, along with a key to the C. castanops species group to which these species belong. Key words: chromosomes, Cratogeomys, mitochondrial DNA, morphology, nuclear DNA, pocket gophers, systematics

The genus Cratogeomys, particularly members of the Cratogeomys gymnurus species group, account for much of the high species diversity of pocket gophers in the Trans-Mexican Volcanic Belt. Recent molecular studies of this species group have shown strong discordance between genetically defined clades and current species taxonomy. Accordingly, we investigated relationships among the 5 species in the C. gymnurus species group using mitochondrial and nuclear DNA, chromosomes, and morphological characters. Although quantitative morphometrics provided little discrimination among species or clades within this group, the molecular data sets were consistent in identifying 5 allopatric clades, none of which corresponded to any of the 5 currently recognized species. Four of these 5 genetically defined clades lack clear diagnosability, and so are grouped into the single polytypic species, C. fumosus. The fifth clade is diagnosable based on multiple characters, including nuclear genotype, chromosomal diploid number, parasite fauna, and qualitative morphological characters. Accordingly, we resurrect Merriam's (1895) species planiceps to represent members of this clade, which occurs in the Volcan de Toluca and Valle de Bravo regions of central Mexico. Based on the observation that differences in diploid number usually signal reproductive isolation between populations of pocket gophers, we hypothesize that C. fumosus and C. planiceps are reproductively incompatible. We provide synonymies and descriptions for these 2 species, along with a key to this species group, which is now called the C. fumosus species group. Key words: chromosomes, Cratogeomys, mitochondrial DNA, morphology, nuclear DNA, pocket gophers, systematics

Restriction-site data for mitochondrial DNA were used to test the isolation-by-distance model of genetic variation in two species of Central American pocket gophers, Orthogeomys cherriei and O. underwoodi. Maximum-likelihood and parsimony analyses yielded trees with topologies concordant with predictions based on physiography. Relationships within O. cherriei reveal probable effects of a partial geographic barrier in the form of the Cordillera de Tilaran in northcentral Costa Rica. The phylogenetic tree for O. underwoodi branches in a ladder-like fashion from south to north suggesting the absence of obstructions to gene flow. Results of Mantel tests indicated that variation of mtDNA within O. cherriei is not consistent with a hypothesis of isolation-by-distance, whereas variation within O. underwoodi shows a statistically significant association with geographic distance. Estimates of intraspecific sequence divergence indicate that the present distributions of these two species resulted from climatic shifts in the Pleistocene. Key words: Orthogeomys, Rodentia, mtDNA, phylogeography, Central America

The least shrew, Cryptotis parva, has expanded its distribution westward during the past 20-30 years in response to increased irrigation and a simultaneous trend toward more mesic climate. The species is recolonizing regions that it invaded coincident with increased summer precipitation during the late Wisconsinan (13,000 years ago) before being forced to the south and east during the establishment of modern desert-scrub vegetation 4,000 years ago. Allozymic patterns among three recently discovered peripheral populations of Cryptotis parva in eastern New Mexico compared to a population from within the continuous range of the species in Texas indicate that two populations probably resulted from recent dispersal from the east, while a third may represent a relict of late Wisconsinan and alti-thermal intervals. This population, at Bitter Lake along the Pecos River Valley, is isolated from eastern populations by an elevated, arid plateau and from southern populations along the Pecos River by 600 km; it has a unique allozymic complement and it resembles the southern subspecies (C. p. berlandieri) in cranial morphology. Range maps of species of mammals must be viewed with caution, particularly at their distributional limits, in light of recent documentation of substantial range shifts (up to 450 km) over periods of 2-3 decades. Key words: Cryptotis parva, biogeography, mammalian distributions, Great Plains, genetics

Allozymic patterns among populations of Ochotona princeps indicate a pre-Wisconsin (>120,000 years ago) divergence of four major genetic units in the western United States (northern Rocky Mountains, southern Rocky Mountains, Cascade Range, and Sierra Nevada). Pikas initially spread south along cordilleran dispersal corridors during a pre-Wisconsin glacial stage, and were fragmented into isolated montane refugia during a subsequent interglacial. Range re-expansion during the Wisconsin allowed secondary contact of genetic units, while montane glaciers, pluvial lakes, and glacial lakes limited secondary contact in some areas. Low genetic variation in all examined populations of O. princeps is due to: the metapopulation structure of pikas, dictated by the fragmented nature of a narrowly defined habitat and maintained by low vagility and high philopatry; accelerated loss in small or isolated habitat patches; accelerated loss in summer-drought regions; and, in the Cascade Range genetic unit, derivation of current populations from a genetically depauperate source population. Key words: biogeography, genetics, Ochotona princeps, metapopulation, Ochotonidae, Nearctic

Paleoenvironmental implications of Wisconsinan mammalian faunas of the Edwards Plateau in central Texas are reevaluated following reassignment of fossil jumping mice (Zapus) from Schulze Cave to the eastern species, Zapus hudsonius. In contrast to previous interpretations, influences of western alpine-meadow associations are viewed as minor, represented by only one species, Sorex vagrans. Instead, the fauna was heavily influenced by eastern mesic-adapted species that retreated north and east during post-Wisconsinan desiccation of the region.

Genetic intergradation between Spermophilus mohavensis and S. tereticandus, estimated from cranial morphometrics, is restricted to known and purported sites of hybridization. The boundary between the two species coincides with the Wisconsinan distribution of pluvial lakes and river systems, which isolated a cooler, more mesic refugium of Mojave Desert flora and fauna during pluvial maxima. A continuous barrier was last present 10,000 years ago, but disappeared at least 6,000 years ago. Subsequent range expansion of either species across this previous barrier has been limited to 30 km, or an average of [less than or equal to] 5 m/year. Persistence of the initial contact zone may result from low vagility of both species, incorporation of rare immigrants through introgressive hybridization, competition, or a combination of these factors. Key words: Spermophilus, Xerospermophilus, morphology, contact zone, Mojave Desert, A common boundary exists between Spermophilus mohavensis and S. tereticaudus (Mojave ground squirrels), both of the subgenus Xerospermophilus. This contact boundary is in a small, isolated desert refugium in northwestern Mojave Desert. No large degree of genetic intergradation either at or near the contact zone is indicated from cranial morphometrics. Longevity of species contact boundary is attributed to low vagility, incorporation of rare immigrants from the alternate species via introgressive hybridization and competition, or a combination of these factors.

Sixteen populations of Peromyscus on islands in the Sea of Cortez (= Gulf of California), Mexico, were compared with 9 mainland species of Peromyscus based on sequence data for a 699-base-pair fragment of the mitochondrial DNA (mtDNA) COIII gene. An unrooted neighbor-joining tree based on corrected pairwise estimates of sequence divergence among variable mtDNA haplotypes indicated a recent (late Pleistocene) origin from a source on the adjacent mainland for 10 island forms representing P. boylii, P. crinitus, P. eremicus, P. eva, P. fraterculus, and P. maniculatus. Five other populations did not seem to be derived from species currently on the nearest mainland, suggesting overwater dispersal or distributional changes on the mainland after drowning of land-bridge connections. One population, possibly of more ancient origin, on Isla Cerralvo near the Baja California peninsula, probably originated via trans-Gulf rafting from the Sonoran mainland. Based on these results, 4 insular species (P. stephani, P. interparietalis, P. caniceps, and P. dickeyi) should be considered subspecies of P. boylii, P. eremicus, P. fraterculus, and P. merriami, respectively. The emergent view of evolutionary relationships within the subgenus Haplomylomys in the region reflects pre-Pleistocene phylogeographic events on the mainland surrounding the Gulf and a more recent origin of island populations. Key words: Haplomylomys, island biogeography, mitochondrial DNA, Peromyscus, Sea of Cortez