Janet K. Braun

Invasion facilitates hybridization with introgression in the Rattus rattus species complex

Biological invasions result in novel species interactions, which can have significant evolutionary impacts on both native and invading taxa. One evolutionary concern with invasions is hybridization among lineages that were previously isolated, but make secondary contact in their invaded range(s). Black rats, consisting of several morphologically very similar but genetically distinct taxa that collectively have invaded six continents, are arguably the most successful mammalian invaders on the planet. We used mitochondrial cytochrome b sequences, two nuclear gene sequences (Atp5a1 and DHFR) and nine microsatellite loci to examine the distribution of three invasive black rat lineages (Rattus tanezumi, Rattus rattus I and R. rattus IV) in the United States and Asia and to determine the extent of hybridization among these taxa. Our analyses revealed two mitochondrial lineages that have spread to multiple continents, including a previously undiscovered population of R. tanezumi in the south‐eastern United States, whereas the third lineage (R. rattus IV) appears to be confined to Southeast Asia. Analyses of nuclear DNA (both sequences and microsatellites) suggested significant hybridization is occurring among R. tanezumi and R. rattus I in the United States and also suggest hybridization between R. tanezumi and R. rattus IV in Asia, although further sampling of the latter species pair in Asia is required. Furthermore, microsatellite analyses suggest unidirectional introgression from both R. rattus I and R. rattus IV into R. tanezumi. Within the United States, introgression appears to be occurring to such a pronounced extent that we were unable to detect any nuclear genetic signal for R. tanezumi, and a similar pattern was detected in Asia.

How Desert Rodents Overcome Halophytic Plant Defenses

onvergent evolution among desert rodents has received a great deal of attention in recent years, with research centering on the question of how phylogenetically unrelated species evolving on different continents have developed similar morphological, behavioral, ecological, or physiological characteristics in response to similar selective pressures posed by the desert environment (Mares 1975, 1993a, 1993b, Schluter and Ricklefs 1993). The heat and aridity of deserts pose severe challenges for both plants and animals. Deserts generally support reduced levels of plant biomass compared with more mesic habitats (Hadley and Szarek 1981, Rosenzweig

PHYLOGENETIC AND BIOGEOGRAPHIC RELATIONSHIPS OF MOUSE OPOSSUMS THYLAMYS (DIDELPHIMORPHIA, DIDELPHIDAE) IN SOUTHERN SOUTH AMERICA

Abstract Phylogenetic relationships among 51 individuals of South American mouse opossums (Thylamys) were examined by using nucleotide sequence data from the mitochondrial cytochrome-b gene. Parsimony, likelihood, Bayesian, and genetic distance analyses revealed several distinct clades. T. macrurus (subtropical forest of eastern Paraguay) was strongly differentiated from all other species. T. venustus (Yungas forest on eastern slopes of the Andes of Bolivia and Argentina) separated into 2 strongly supported clades, providing support for recognition of 2 species, T. venustus and T. cinderella, but not supporting the distinctness of T. sponsorius. T. tatei (central coast of Peru) was sufficiently different from T. elegans (Matorral of Chile) to support species recognition. The dichotomy between northern (Chile and Bolivia) and southern (Argentina) clades of T. pallidior suggested the presence of 2 subspecies. High levels of DNA sequence variation indicated substantial genetic differentiation among and between clades, and combined with the phylogenetic analyses provide support for the systematic conclusions. Estimates of times since divergence suggest a radiation beginning in the Miocene and continuing through the Pliocene and correspond with changes in climate, vegetation, and geology that occurred during these times.

A New Genus and Species of Phyllotine Rodent (Rodentia: Muridae: Sigmodontinae: Phyllotini) from South America

A new genus of phyllotine rodent is described. One species from northwestern San Luis Province and southeastern San Juan Province, Argentina is included. This new genus is compared with species of Eligmodontia, Calomys, Andalgalomys , and Graomys . External, cranial, and dental characters indicate that the new genus is most closely related to Calomys and Eligmodontia . The new genus may be distinguished using both quantitative and qualitative characters. The discovery of a new genus of Sigmodontine rodent specialized for desert environments in Argentina is the second in 15 years and underscores the need for further faunal work in arid areas of South America.

Comparative phylogeography of invasive Rattus rattus and Rattus norvegicus in the U.S. reveals distinct colonization histories and dispersal

Invasive Rattus are arguably the most costly and destructive invasive species on the planet, but little is known concerning their invasion history and population structure in the U.S. We utilized both nuclear microsatellites and mitochondrial DNA sequences (mtDNA) to compare the colonization history, patterns of gene flow, and levels of genetic diversity of Rattus rattus and R. norvegicus in the U.S. Analyses of mtDNA suggest R. rattus is characterized by a single rapid expansion into the U.S. from one or two very closely related mtDNA lineages or geographic sources. For R. norvegicus, mtDNA analyses suggest at least four invasions distinct in space and/or time have occurred to establish its distribution in the U.S. Microsatellite analyses suggest for R. rattus that dispersal is characterized by an isolation-by-distance pattern, suggesting a relatively low frequency of long distance dispersal, and low levels of establishment for novel propagules. In contrast, microsatellite analyses of R. norvegicus suggest high frequencies of long distance dispersal and essentially panmixia among nearly all sampled populations, as well as a high frequency of novel propagules entering at the east and west coasts and assimilating into established populations. We discuss these results in the context of invasive Rattus management in the U.S. and their implications for invasive species in general, as well as the implications for managing the spread of rat-borne pathogens.

Phylogenetic Relationships of South American Grass Mice of the Akodon varius Group (Rodentia, Cricetidae, Sigmodontinae) in South America

Abstract Phylogenetic relationships among individuals of 9 taxa of the Akodon varius group of sigmodontine (tribe Akodontini) rodents from Argentina, Bolivia, and Paraguay were examined using nucleotide sequence data from the entire 1,140 base pairs of the mitochondrial cytochrome-b gene to clarify the evolutionary relationships among lineages. Two individuals of A. iniscatus were included to test proposed relationships with the A. varius group. Maximum-parsimony, minimum-evolution, maximum-likelihood (TVM+I+G), and Bayesian analyses revealed 2 major clades, 1 composed of Yungas Forest taxa and 1 of non-Yungas (lowlands) taxa, and 8 well-supported terminal clades. The Yungas Forest clade includes A. glaucinus, A. simulator, A. tartareus, and A. varius, which are recognized as distinct species. A. iniscatus was the most basal taxon in the lowlands clade containing A. dayi, A. toba, and A. dolores. Results support the proposed conspecificity of A. dolores and A. molinae, and the relationship within the A. varius group, which had not been clearly defined, is clarified. A. dayi and A. toba were found to be more closely related to A. dolores than to the Yungas Forest clade with which they historically have been associated. A low level of percent sequence divergence between A. toba and A. dolores suggests the need for a closer examination of this relationship, as does the high level of within-clade percent sequence divergence for A. dayi.

SYSTEMATICS OF THE ABROCOMA CINEREA SPECIES COMPLEX (RODENTIA: ABROCOMIDAE), WITH A DESCRIPTION OF A NEW SPECIES OF ABROCOMA

Abstract The genus Abrocoma (family Abrocomidae) is distributed from southern Peru and northern Chile to Bolivia and then southward to the west-central region of Mendoza Province, Argentina. The systematics of the genus is poorly known. Ten taxa were originally described but later synonymized into 2 species. Five taxa were included in Abrocoma cinerea and 5 in A. bennetti. A 3rd species, A. boliviensis, was described in 1990, and a new genus and species, Cuscomys ashaninka, were described in 1999. We reevaluate the systematics of the A. cinerea species complex, with emphasis on Argentine specimens, using cranial, dental, and external morphology. A new species of Abrocoma from Mendoza Province, Argentina, is described. Karyotypic information is presented. Behavior, habitat, and natural history are also discussed.

A new species of Akodon (Muridae: Sigmodontinae) from Northwestern Argentina.

A new species of Akodon is described using cranial, dental, and external morphology and morphometric data. The new species inhabits an isolated, ecotonal, montane forest-grassland area in central Tucuman Province, Argentina. This species, which appears to be closely related to A. puer caenosus , is here included in the boliviensis group of akodont rodents. Comparisons are made with A. spegazzinii and A. puer caenosus , which are found in the general area and are of similar body size and general morphology.

A new species of phyllotine rodent, genus Andalgalomys (Muridae : Sigmodontinae), from Argentina

A new species of Andalgalomys is described from the Monte Desert-Chacoan thorn-scrub region of Argentina. This genus previously was known in Argentina only near Andalgala, Catamarca Province, from a single isolated valley; specimens of the new species are the first documentation of the genus outside the province. Specimens from localities in Catamarca and San Luis provinces are reported. The distribution of the genus is extended southward ca. 500 km. The diploid number of chromosomes is 60.

Molecular systematic revision of tree bats (Lasiurini): doubling the native mammals of the Hawaiian Islands

This study reports the phylogenetic relationships of 13 species of lasiurine bats using 4 loci from mitochondrial and Y-chromosomal DNA. Our results support a sister taxon relationship between the red and hoary bats, with the yellow bats being more distantly related. Several taxonomic revisions are suggested based on the results of this study. We support the recognition of 3 separate genera: Lasiurus (red bats), Dasypterus (yellow bats), and Aeorestes (hoary bats, including A. egregius which groups more closely to the hoary bats than its traditional placement with the red bats). We recognize L. frantzii as a distinct species and recognize L. blossevillii salinae as a subspecies rather than species. We elevate 3 previously recognized subspecies of A. cinereus to specific status. The phylogeography of the endangered Hawaiian hoary bat is studied in detail, and hoary bats are found to have undergone multiple invasions of the Hawaiian Islands from North America over its evolutionary history. We also report the presence of 2 species of Aeorestes on the Hawaiian Islands where only one previously had been known.