Although it is generally accepted that introduced small mammals have detrimental effects on island ecology, our understanding of these effects is frequently limited by incomplete knowledge of small mammal distribution, density, and biomass. Such information is especially critical in the Mariana Islands, where small mammal density is inversely related to effectiveness of Brown Tree Snake (Boiga irregularis) control tools, such as mouse-attractant traps. We used mark-recapture sampling to determine introduced small mammal distribution, density, and biomass in the major habitats of Guam, Rota, Saipan, and Tinian, including grassland, Leucaena forest, and native limestone forest. Of the five species captured, Rattus diardii (sensu Robins et al. 2007) was most common across habitats and islands. In contrast, Mus musculus was rarely captured at forested sites, Suncus murinus was not captured on Rota, and R. exulans and R. norvegicus captures were uncommon. Modeling indicated that neophobia, island, sex, reproductive status, and rain amount influenced R. diardii capture probability, whereas time, island, and capture heterogeneity influenced S. murinus and M. musculus capture probability. Density and biomass were much greater on Rota, Saipan, and Tinian than on Guam, most likely a result of Brown Tree Snake predation pressure on the latter island. Rattus diardii and M. musculus density and biomass were greatest in grassland, whereas S. murinus density and biomass were greatest in Leucaena forest. The high densities documented during this research suggest that introduced small mammals (especially R. diardii) are impacting abundance and diversity of the native fauna and flora of the Mariana Islands. Further, Brown Tree Snake control and management tools that rely on mouse attractants will be less effective on Rota, Saipan, and Tinian than on Guam. If the Brown Tree Snake becomes established on these islands, high-density introduced small mammal populations will likely facilitate and support a high-density Brown Tree Snake population, even as native species are reduced or extirpated.

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The murid rodent genus Rattus Fischer 1803 contains several species that are responsible for massive loss of crops and food, extinction of other species and the spread of zoonotic diseases to humans, as well as a laboratory species used to answer important questions in physiology, immunology, pharmacology, toxicology, nutrition, behaviour and learning. Despite the well-known significant impacts of Rattus, a definitive evolutionary based systematic framework for the genus is not yet available. The past 75 years have seen more dramatic changes in membership of Rattus than in almost any other genus of mammals. In fact, the Rattus genus has been a receptacle for any generalised Old World murine that lacked morphological specialisation and at one point, has included more than 560 species and/or subspecies, spread across Eurasia, Africa and the Australo-Papuan region. The dissolution of Rattus is ongoing as many of its constituent species and many genera of Rattini remain unsampled in any molecular study. To address this sampling limitation, we sequenced the mitochondrial cytochrome b (cytb) gene and examined phylogenetic relationships using both Bayesian and Maximum Likelihood algorithms for an expanded set of taxa within Rattus and among closely related genera. Here we place previously unsampled taxa in a phylogenetic context for the first time, including R. burrus, R. hoogerwerfi, R. lugens, and R. mindorensis within the Asian Rattus group, R. facetus within the Australo-Papuan Rattus radiation, and the undescribed ‘Bisa Rat’ described by Flannery as sister to the recently described genus Halmaheramys. We also present an exploratory foray into the wider topic of Rattus phylogenetics and propose that a reorganisation of the Rattus genus should require that it be a monophyletic group, include at least the type species R. norvegicus and R. rattus (plus their close allies); and exclude the Bandicota/Nesokia clade and other such specialised genera.

The occurrence of black fur, or melanism, in many mammalian species is known to be linked to DNA sequence variation in the agouti signaling protein (Asip) gene, which is a major determinant of eumelanin and pheomelanin pigments in coat color. We investigated 38 agouti (i.e., banded wildtype) and four melanistic Rattus rattus species complex (RrC) lineage II specimens from Okinawa Island, Ryukyu Islands, Japan, for genetic variation in three exons and associated flanking regions in the Asip gene. On Okinawa, a predicted loss-of-function mutation caused by a cysteine to serine amino acid change at p.124C>S (c.370T>A) in the highly conserved functional domain of Asip was found in melanistic rats, but was absent in agouti specimens, suggesting that the p.124C>S mutation is responsible for the observed melanism. Phylogeographic analysis found that Asip sequences from Okinawan RrC lineage II, including both agouti and melanistic specimens, differed from: 1) both agouti and melanistic RrC lineage I from Otaru, Hokkaido, Japan, and 2) agouti RrC lineages I and II from South Australia. This suggests the possibility of in-situ mutation of the Asip gene, either within the RrC lineage II population on Okinawa or in an unsampled RrC lineage II population with biogeographic links to Okinawa, although incomplete lineage sorting could not be ruled out.

Regions of Iran, Afghanistan, Pakistan and northwestern India have been proposed as the place of origin of Mus musculus castaneus. But despite the fact that Pakistan encompasses an important part of its range, M. m. castaneus populations in Pakistan have not been the subject of intensive genetic and biogeographic studies, except for a very small number of samples included in past studies. We studied genetic variation in M. m. castaneus (CAS) from northern Punjab Province, Pakistan, by using cytochrome b (Cytb) analysis in a sample of 98 individuals. Median-joining network revealed four well differentiated CAS sub-lineages coexisting within a small geographical region; these had previously been thought to have largely non-overlapping geographic distributions. Moreover, haplotypes from Pakistan occupied a central position in the network and all identified global haplotypes were also present in Pakistan. All identified CAS sub-lineages proved to be highly diverse on the basis of haplotype and nucleotide diversity indices. Tajima's D test and Fu's Fs tests of neutrality suggest recent population expansions in all sub-lineages. Expansion times were estimated as 21,760-134,930, 10,800-64,400 and 4950-30,665 ybp using substitution rates of 2.5%, 5% and 11%, respectively. Our results support the hypothesis that northern Punjab Province in Pakistan is the most likely source area for M. m. castaneus, and that the CAS sub-lineages in this region have undergone rapid population expansion events at different time periods, which appear to have benefitted from human-mediated transport, although one of them clearly predates the establishment of human settlements in this region.