David J. Hafner

Historical and Ecological Biogeography of Nearctic Pikas (Lagomorpha: Ochotonidae)

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.

BASAL CLADES AND MOLECULAR SYSTEMATICS OF HETEROMYID RODENTS

Abstract 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.

Pikas and Permafrost: Post-Wisconsin Historical Zoogeography of Ochotona in the Southern Rocky Mountains, U.S.A.

Occurrence of pikas (Ochotona princeps) in the southern Rocky Mountains is closely tied to past and present distribution of alpine permafrost conditions, which produce and maintain appropriate talus-slope habitat. Estimates of full-Wisconsin elevational depression of alpine permafrost and vegetation zones support the existence of glacial-maximum dispersal corridors between currently isolated populations of O. princeps. Altithermal warming accounts for 66.7% of apparent post-Wisconsin extinctions of insular populations of pikas in the region. Populations at sites with altithermal refugia >100 km2 enjoyed high survivorship (93.8%) compared to smaller refugia (6.1–15.2%). Extant populations are located within 5 km of current alpine permafrost and within 20 km of the estimated altithermal occurrence of permafrost, indicating minor subsequent dispersal from a more restricted distribution of 6000 yr ago. Recolonization of sites within 20 km has been rare (≤7.8%). Depending on the time scale considered, pikas ar...

Cryptic Species in the Mexican Pocket Gopher Cratogeomys merriami

Abstract 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 México, México 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.

EVOLUTIONARY RELATIONSHIPS OF WHITE-FOOTED MICE (PEROMYSCUS ) ON ISLANDS IN THE SEA OF CORTEZ, MEXICO

Abstract Sixteen populations of Peromyscus on islands in the Sea of Cortéz (= 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.

Systematic Revision of Pocket Gophers of the Cratogeomys gymnurus Species Group

Abstract 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 Merriams (1895) species planiceps to represent members of this clade, which occurs in the Volcán 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.

Evolutionary Relationships of Pocket Gophers (Cratogeomys castanops Species Group) of the Mexican Altiplano

Abstract 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 ratio-transformed 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 Mayrán), and least effective in its western portion (Río Nazas), which should be geographically broadened to include the neighboring Río Aguanaval.

Historical biogeography of western peripheral isolates of the least shrew, Cryptotis parva

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.

Genetics of a Contact Zone between Three Chromosomal Forms of the Grasshopper Mouse (Genus Onychomys): A Reassessment

Chromosomal, genic, and morphologic data were used to reassess the specific status of Onychomys arenicola relative to O. torridus and O. leucogaster at a previously investigated zone of sympatry (Hinesley, 1979). Chromosomal analysis revealed one karyotypic variant in a sample of 28 individuals of all three taxa. This individual exhibited a fundamental number intermediate between O. torridus and O. arenicola based on non-differentially stained karyotypes, suggesting that it might be an F1 hybrid between the latter two taxa. However, estimates of hybridization between these two taxa based on standard karyotypic methods are unreliable, and the systematic status of O. arenicola cannot be determined using standard karyotypic techniques alone (Hinesley, 1979). Electrophoretic analysis of all three species from the zone of sympatry indicates a lack of genic introgression between the three taxa. The one chromosomal variant was genically indistinguishable from O. torridus . Genie, bacular, and cranial analyses support the specific status of O. arenicola , and indicate a closer phylogenetic relationship between O. leucogaster and O. arenicola , than between O. arenicola and its presumed sister taxon, O. torridus .

Cophylogeny on a Fine Scale: Geomydoecus Chewing Lice and Their Pocket Gopher Hosts, Pappogeomys bulleri

Abstract: Many species of pocket gophers and their ectoparasitic chewing lice have broadly congruent phylogenies, indicating a history of frequent codivergence. For a variety of reasons, phylogenies of codiverging hosts and parasites are expected to be less congruent for more recently diverged taxa. This study is the first of its scale in the pocket gopher and chewing louse system, with its focus entirely on comparisons among populations within a single species of host and 3 chewing louse species in the Geomydoecus bulleri species complex. We examined mitochondrial DNA from a total of 46 specimens of Geomydoecus lice collected from 11 populations of the pocket gopher host, Pappogeomys bulleri. We also examined nuclear DNA from a subset of these chewing lice. Louse phylogenies were compared with a published pocket gopher phylogeny. Contrary to expectations, we observed a statistically significant degree of parallel cladogenesis in these closely related hosts and their parasites. We also observed a higher rate of evolution in chewing louse lineages than in their corresponding pocket gopher hosts. In addition, we found that 1 louse species (Geomydoecus burti) may not be a valid species, that subspecies within G. bulleri are not reciprocally monophyletic, and that morphological and genetic evidence support recognition of a new species of louse, Geomydoecus pricei.