A recent gibbon ape leukemia virus germline integration in a rodent from New Guinea.

Germline colonization by retroviruses results in the formation of endogenous retroviruses (ERVs). Most colonization's occurred millions of years ago. However, in the Australo-Papuan region (Australia and New Guinea), several recent germline colonization events have been discovered. The Wallace Line separates much of Southeast Asia from the Australo-Papuan region restricting faunal and pathogen dispersion. West of the Wallace Line, gibbon ape leukemia viruses (GALVs) have been isolated from captive gibbons. Two microbat species from China appear to have been infected naturally. East of Wallace's Line, the woolly monkey virus (a GALV) and the closely related koala retrovirus (KoRV) have been detected in eutherians and marsupials in the Australo-Papuan region, often vertically transmitted. The detected vertically transmitted GALV-like viruses in Australo-Papuan fauna compared to sporadic horizontal transmission in Southeast Asia and China suggest the GALV-KoRV clade originates in the former region and further models of early-stage genome colonization may be found. We screened 278 samples, seven bat and one rodent family endemic to the Australo-Papuan region and bat and rodent species found on both sides of the Wallace Line. We identified two rodents (Melomys) from Australia and Papua New Guinea and no bat species harboring GALV-like retroviruses. Melomys leucogaster from New Guinea harbored a genomically complete replication-competent retrovirus with a shared integration site among individuals. The integration was only present in some individuals of the species indicating this retrovirus is at the earliest stages of germline colonization of the Melomys genome, providing a new small wild mammal model of early-stage genome colonization.

Out of Southern East Asia of the Brown Rat Revealed by Large-Scale Genome Sequencing.

The geographic origin and migration of the brown rat (Rattus norvegicus) remain subjects of considerable debate. In this study, we sequenced whole genomes of 110 wild brown rats with a diverse world-wide representation. We reveal that brown rats migrated out of southern East Asia, rather than northern Asia as formerly suggested, into the Middle East and then to Europe and Africa, thousands of years ago. Comparison of genomes from different geographical populations reveals that many genes involved in the immune system experienced positive selection in the wild brown rat.

Phylogenetic analysis of the tree-kangaroos (Dendrolagus) reveals multiple divergent lineages within New Guinea.

Amongst the Australasian kangaroos and wallabies (Macropodidae) one anomalous genus, the tree-kangaroos, Dendrolagus, has secondarily returned to arboreality. Modern tree-kangaroos are confined to the wet tropical forests of north Queensland, Australia (2 species) and New Guinea (8 species). Due to their behavior, distribution and habitat most species are poorly known and our understanding of the evolutionary history and systematics of the genus is limited and controversial. We obtained tissue samples from 36 individual Dendrolagus including representatives from 14 of the 17 currently recognised or proposed subspecies and generated DNA sequence data from three mitochondrial (3116 bp) and five nuclear (4097 bp) loci. Phylogenetic analysis of these multi-locus data resolved long-standing questions regarding inter-relationships within Dendrolagus. The presence of a paraphyletic ancestral long-footed and derived monophyletic short-footed group was confirmed. Six major lineages were identified: one in Australia (D. lumholtzi, D. bennettianus) and five in New Guinea (D. inustus, D. ursinus, a Goodfellow's group, D. mbaiso and a Doria's group). Two major episodes of diversification within Dendrolagus were identified: the first during the late Miocene/early Pliocene associated with orogenic processes in New Guinea and the second mostly during the early Pleistocene associated with the intensification of climatic cycling. All sampled subspecies showed high levels of genetic divergence and currently recognized species within both the Doria's and Goodfellow's groups were paraphyletic indicating that adjustments to current taxonomy are warranted.

Sperm morphology of the Rattini - are the interspecific differences due to variation in intensity of intermale sperm competition?

It is widely accepted that in mammals a causal relationship exists between postcopulatory sexual selection and relative testes mass of the species concerned, but how much it determines sperm size and shape is debatable. Here we detailed for the largest murine rodent tribe, the Rattini, the interspecific differences in relative testes mass and sperm form. We found that residual testes mass correlates with sperm head apical hook length as well as its angle, together with tail length, and that within several lineages a few species have evolved highly divergent sperm morphology with a reduced or absent apical hook and shorter tail. Although most species have a relative testes mass of 1-4%, these derived sperm traits invariably co-occur in species with much smaller relative testes mass. We therefore suggest that high levels of intermale sperm competition maintain a sperm head with a long apical hook and long tail, whereas low levels of intermale sperm competition generally result in divergent sperm heads with a short or non-existent apical hook and shorter tail. We thus conclude that sexual selection is a major selective force in driving sperm head form and tail length in this large tribe of murine rodents.

Endogenous Gibbon Ape Leukemia Virus Identified in a Rodent (Melomys burtoni subsp.) from Wallacea (Indonesia).

UNLABELLED: Gibbon ape leukemia virus (GALV) and koala retrovirus (KoRV) most likely originated from a cross-species transmission of an ancestral retrovirus into koalas and gibbons via one or more intermediate as-yet-unknown hosts. A virus highly similar to GALV has been identified in an Australian native rodent (Melomys burtoni) after extensive screening of Australian wildlife. GALV-like viruses have also been discovered in several Southeast Asian species, although screening has not been extensive and viruses discovered to date are only distantly related to GALV. We therefore screened 26 Southeast Asian rodent species for KoRV- and GALV-like sequences, using hybridization capture and high-throughput sequencing, in the attempt to identify potential GALV and KoRV hosts. Only the individuals belonging to a newly discovered subspecies of Melomys burtoni from Indonesia were positive, yielding an endogenous provirus very closely related to a strain of GALV. The sequence of the critical receptor domain for GALV infection in the Indonesian M. burtoni subsp. was consistent with the susceptibility of the species to GALV infection. The second record of a GALV in M. burtoni provides further evidence that M. burtoni, and potentially other lineages within the widespread subfamily Murinae, may play a role in the spread of GALV-like viruses. The discovery of a GALV in the most western part of the Australo-Papuan distribution of M. burtoni, specifically in a transitional zone between Asia and Australia (Wallacea), may be relevant to the cross-species transmission to gibbons in Southeast Asia and broadens the known distribution of GALVs in wild rodents. IMPORTANCE: Gibbon ape leukemia virus (GALV) and the koala retrovirus (KoRV) are very closely related, yet their hosts neither are closely related nor overlap geographically. Direct cross-species infection between koalas and gibbons is unlikely. Therefore, GALV and KoRV may have arisen via a cross-species transfer from an intermediate host whose range overlaps those of both gibbons and koalas. Using hybridization capture and high-throughput sequencing, we have screened a wide range of rodent candidate hosts from Southeast Asia for KoRV- and GALV-like sequences. Only a Melomys burtoni subspecies from Wallacea (Indonesia) was positive for GALV. We report the genome sequence of this newly identified GALV, the critical domain for infection of its potential cellular receptor, and its phylogenetic relationships with the other previously characterized GALVs. We hypothesize that Melomys burtoni, and potentially related lineages with an Australo-Papuan distribution, may have played a key role in cross-species transmission to other taxa.

Hiding in plain sight: two new species of diminutive marsupial (Dasyuridae: Planigale) from the Pilbara, Australia.

Many of Australias smaller marsupial species have been taxonomically described in just the past 50 years, and the Dasyuridae, a speciose family of carnivores, is known to harbour many cryptic taxa. Evidence from molecular studies is being increasingly utilised to help revise species boundaries and focus taxonomic efforts, and research over the past two decades has identified several undescribed genetic lineages within the dasyurid genus Planigale. Here, we describe two new species, Planigale kendricki sp. nov. (formerly known as Planigale 1) and P. tealei sp. nov. (formerly known as Planigale sp. Mt Tom Price). The two new species have broadly overlapping distributions in the Pilbara region of Western Australia. The new species are genetically distinct from each other and from all other members of the genus, at both mitochondrial and nuclear loci, and morphologically, in both external and craniodental characters. The new species are found in regional sympatry within the Pilbara but occupy different habitat types at local scales. This work makes a start at resolving the cryptic diversity within Planigale at a time when small mammals are continuing to decline throughout Australia.

Recent and rapid speciation with limited morphological disparity in the genus Rattus.

Recent and rapid radiations provide rich material to examine the factors that drive speciation. Most recent and rapid radiations that have been well-characterized involve species that exhibit overt ecomorphological differences associated with clear partitioning of ecological niches in sympatry. The most diverse genus of rodents, Rattus (66 species), evolved fairly recently, but without overt ecomorphological divergence among species. We used multilocus molecular phylogenetic data and five fossil calibrations to estimate the tempo of diversification in Rattus, and their radiation on Australia and New Guinea (Sahul, 24 species). Based on our analyses, the genus Rattus originated at a date centered on the Pliocene-Pleistocene boundary (1.84-3.17 Ma) with a subsequent colonization of Sahul in the middle Pleistocene (0.85-1.28 Ma). Given these dates, the per lineage diversification rates in Rattus and Sahulian Rattus are among the highest reported for vertebrates (1.1-1.9 and 1.6-3.0 species per lineage per million years, respectively). Despite their rapid diversification, Rattus display little ecomorphological divergence among species and do not fit clearly into current models of adaptive radiations. Lineage through time plots and ancestral state reconstruction of ecological characters suggest that diversification of Sahulian Rattus was most rapid early on as they expanded into novel ecological conditions. However, rapid lineage accumulation occurred even when morphological disparity within lineages was low suggesting that future studies consider other phenotypes in the diversification of Rattus.

Diversity of Leptospira spp. in bats and rodents from Papua New Guinea.

Leptospirosis is the most common bacterial zoonosis globally. The pathogen, Leptospira spp., is primarily associated with rodent reservoirs. However, a wide range of other species has been implicated as reservoirs or dead-end hosts. We conducted a survey for Leptospira spp. in bats and rodents from Papua New Guinea. Kidney samples were collected from 97 pteropodid bats (five species), 37 insectivorous bats from four different families (six species) and 188 rodents (two species). Leptospires were detected in a high proportion of pteropodid bats, including Nyctimene cf. albiventer (35%), Macroglossus minimus (34%) and Rousettus amplexicaudatus (36%). Partial sequencing of the secY gene from rodent and bat leptospires showed host species clustering, with Leptospira interrogans and L. weilii detected in rodents and L. kirschneri and a potential novel species of Leptospira detected in bats. Further research is needed in Papua New Guinea and other locales in the Pacific region to gain a better understanding of the circulation dynamics of leptospires in reservoir species and the risks to public and veterinary health.

Origin of agouti-melanistic polymorphism in Wild Black Rats (Rattus rattus) inferred from Mc1r gene sequences.

We examined nucleotide changes that underlie coat color variation in Black Rats (the Rattus rattus species complex), which show polymorphism in dorsal fur color, including either grayish brown (agouti) or black (melanistic) forms. We examined the full coding sequence of a gene known to produce melanism in other vertebrates-melanocortin-1-receptor gene Mc1r (954 bp) -using samples of both R. rattus (with 2n = 38) and its close relative Asian Black Rat (R. tanezumi; 2n = 42). We used 61 specimens from Japan with karyotype-known individuals and four samples from Pakistan. We found 11 allele sequences and constructed a network tree that shows two distinct clusters, with allelic segregation according to karyotype and by inference, representing the two species. We found that a nucleotide substitution from G to A at site 280, producing an amino acid change from glutamic acid to lysine, was associated with the dominant trait of the melanistic form of the coat color in R. rattus. Notably, the derived SNP 280A was found in a single allele, with the ancestral SNP 280G present in seven alleles. By contrast, all three alleles for R. tanezumi retain the ancestral SNP 280G. These results suggest a possible recent origin of melanism in R. rattus.

Detection of recombinant haplotypes in wild mice (Mus musculus) provides new insights into the origin of Japanese mice.

Japanese house mice (Mus musculus molossinus) are thought to be a hybrid lineage derived from two prehistoric immigrants, the subspecies M. m. musculus of northern Eurasia and M. m. castaneus of South Asia. Mice of the western European subspecies M. m. domesticus have been detected in Japanese ports and airports only. We examined haplotype structuring of a 200 kb stretch on chromosome 8 for 59 mice from throughout Eurasia, determining short segments (approximately 370-600 bp) of eight nuclear genes (Fanca, Spire2, Tcf25, Mc1r, Tubb3, Def8, Afg3l1 and Dbndd1) which are intermittently arranged in this order. Where possible we identified the subspecies origin for individual gene alleles and then designated haplotypes for concatenated alleles. We recovered 11 haplotypes among 19 Japanese mice examined, identified either as 'intact' haplotypes derived from the subspecies musculus (57.9%), domesticus (7.9%), and castaneus (2.6%), or as 'recombinant' haplotypes (31.6%). We also detected recombinant haplotypes unique to Sakhalin. The complex nature of the recombinant haplotypes suggests ancient introduction of all three subspecies components into the peripheral part of Eurasia or complicated genomic admixture before the movement from source areas. 'Intact'domesticus and castaneus haplotypes in other Japanese wild mice imply ongoing stowaway introductions. The method has general utility for assessing the history of genetic admixture and for disclosing ongoing genetic contamination.

Mus lepidoides (Muridae, Rodentia) of central Burma is a distinct species of potentially great evolutionary and biogeographic significance.

Mus lepidoides of central Burma (Myanmar) was described 75 years ago but has since been dismissed as a regional variant of the Indian field mouse, M. booduga. DNA sequences of multiple mitochondrial and nuclear genes from recently collected specimens, combined with a fresh morphological reassessment, reaffirm the distinctiveness of M. lepidoides from M. booduga and from all other species of Mus. Mus lepidoides is so distinct in fact that it warrants placement in its own Species Group within subgenus Mus. Molecular and morphological assessments of phylogenetic affinities converge on the exciting possibility that M. lepidoides represents the previously elusive sibling taxon to the Mus musculus Species Group. If confirmed, this relationship would provide the previously missing connection between the main radiation of subgenus Mus in Southeast and South Asia, and the radiation of the M. musculus Species Group in western Asia and Europe. We speculate that a common ancestor of M. lepidoides and the M. musculus Species Group occupied a continuous but episodic tract of xeric habitat that linked central Burma with northern India at various times during the late Pliocene and Quaternary. Further molecular and cytogenetic studies on the phylogenetic position of M. lepidoides clearly represent a high priority in mouse research.

Isotopic evidence for initial coastal colonization and subsequent diversification in the human occupation of Wallacea.

The resource-poor, isolated islands of Wallacea have been considered a major adaptive obstacle for hominins expanding into Australasia. Archaeological evidence has hinted that coastal adaptations in Homo sapiens enabled rapid island dispersal and settlement; however, there has been no means to directly test this proposition. Here, we apply stable carbon and oxygen isotope analysis to human and faunal tooth enamel from six Late Pleistocene to Holocene archaeological sites across Wallacea. The results demonstrate that the earliest human forager found in the region c. 42,000 years ago made significant use of coastal resources prior to subsequent niche diversification shown for later individuals. We argue that our data provides clear insights into the huge adaptive flexibility of our species, including its ability to specialize in the use of varied environments, particularly in comparison to other hominin species known from Island Southeast Asia.

Comparative analysis of evolutionary modes in Mc1r coat color gene in wild mice and mustelids.

Sequences from ten species of Mus (Rodentia, Muridae) of the melanocortin-1 receptor (Mc1r) gene (945 bp), which plays a key role in coat color determination, were compared with an existing Mc1r dataset (ca. 498 bp) from 12 species of Mustela and Martes (Carnivora, Mustelidae). The dN/dS ratio (omega) was estimated at 0.19 for Mus and 0.35 for the mustelids, using a likelihood-based one-ratio model with empirical codon frequencies. Running the model with equal codon frequencies gave a dramatic increase in omega for the mustelids (1.02) but not for Mus (0.31), indicating stronger codon usage bias in Mc1r among mustelids. When omega was estimated with the free-ratio model, significantly accelerated rates of amino acid replacement (nearly 1 in omega) were seen in several regions of the Mus phylogeny, such as in the ancestral subgeneric lineages, possibly associated with ecological niche shifting. Our results suggest that both functional constraints on coat color variation and selective constraints on codon usage bias have participated in structuring Mc1r gene sequences. Furthermore, they suggest that these contrasting influences have acted differentially in Mus and the mustelid lineages, and also differentially during the course of evolution within the genus Mus.

Phylogeny and biogeography of African Murinae based on mitochondrial and nuclear gene sequences, with a new tribal classification of the subfamily.

BACKGROUND: Within the subfamily Murinae, African murines represent 25% of species biodiversity, making this group ideal for detailed studies of the patterns and timing of diversification of the African endemic fauna and its relationships with Asia. Here we report the results of phylogenetic analyses of the endemic African murines through a broad sampling of murine diversity from all their distribution area, based on the mitochondrial cytochrome b gene and the two nuclear gene fragments (IRBP exon 1 and GHR). RESULTS: A combined analysis of one mitochondrial and two nuclear gene sequences consistently identified and robustly supported ten primary lineages within Murinae. We propose to formalize a new tribal arrangement within the Murinae that reflects this phylogeny. The diverse African murine assemblage includes members of five of the ten tribes and clearly derives from multiple faunal exchanges between Africa and Eurasia. Molecular dating analyses using a relaxed Bayesian molecular clock put the first colonization of Africa around 11 Mya, which is consistent with the fossil record. The main period of African murine diversification occurred later following disruption of the migration route between Africa and Asia about 7-9 Mya. A second period of interchange, dating to around 5-6.5 Mya, saw the arrival in Africa of Mus (leading to the speciose endemic Nannomys), and explains the appearance of several distinctive African lineages in the late Miocene and Pliocene fossil record of Eurasia. CONCLUSION: Our molecular survey of Murinae, which includes the most complete sampling so far of African taxa, indicates that there were at least four separate radiations within the African region, as well as several phases of dispersal between Asia and Africa during the last 12 My. We also reconstruct the phylogenetic structure of the Murinae, and propose a new classification at tribal level for this traditionally problematic group.

A perspective for resolving the systematics of Rattus, the vertebrates with the most influence on human welfare.

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.

Bandicoot fossils and DNA elucidate lineage antiquity amongst xeric-adapted Australasian marsupials.

Bandicoots (Peramelemorphia) are a unique order of Australasian marsupials whose sparse fossil record has been used as prima facie evidence for climate change coincident faunal turnover. In particular, the hypothesized replacement of ancient rainforest-dwelling extinct lineages by antecedents of xeric-tolerant extant taxa during the late Miocene (~10 Ma) has been advocated as a broader pattern evident amongst other marsupial clades. Problematically, however, this is in persistent conflict with DNA phylogenies. We therefore determine the pattern and timing of bandicoot evolution using the first combined morphological + DNA sequence dataset of Peramelemorphia. In addition, we document a remarkably archaic new fossil peramelemorphian taxon that inhabited a latest Quaternary mosaic savannah-riparian forest ecosystem on the Aru Islands of Eastern Indonesia. Our phylogenetic analyses reveal that unsuspected dental homoplasy and the detrimental effects of missing data collectively obscure stem bandicoot relationships. Nevertheless, recalibrated molecular clocks and multiple ancestral area optimizations unanimously infer an early diversification of modern xeric-adapted forms. These probably originated during the late Palaeogene (30-40 Ma) alongside progenitors of other desert marsupials, and thus occupied seasonally dry heterogenous habitats long before the onset of late Neogene aridity.

Preliminary genetic characterization of two lineages of black rats (Rattus rattus sensu lato) in Japan, with evidence for introgression at several localities.

We conducted a pilot survey of genetic diversity among 37 karyotyped individuals of the black rat Rattus rattus (sensu lato) from six localities on the Japanese Islands, using complete gene sequences of mitochondrial cytochrome b (cyt b) and nuclear interphotoreceptor retinoid binding protein (IRBP). Our sampling included two previously documented karyotypic groups: 'Oceanian' with 2n = 38 and 'Asian' with 2n = 42. Cyt b sequences for most individuals clustered according to their karyotypic groups, with an average between-group divergence of 3.8%. One exception was that individuals from Kagoshima (Kyushu Island) showed 'Asian' karyotypes combined with a cyt b haplotype that differed by a single nucleotide substitution from the haplotype of the 'Oceanian' karyotypic group. Six IRBP haplotypes were identified. They belonged to three distinct IRBP lineages (I-III), with an average inter-lineage divergence of 1%. Among homozygous individuals, these lineages showed good association with the karyotypic groups: IRBP lineage I occurred only with 'Oceanian' karyotypes, while IRBP lineages II and III both occurred with 'Asian' karyotypes. Individuals from Kagoshima all possessed IRBP of 'Asian' lineages, despite the presence of an 'Oceanian' mitochondrial type. The Chichijima population (Ogasawara Islands) featured exclusively 'Asian' karyotypes and cyt b sequences, but various combinations of all three IRBP lineages. The Kagoshima and Chichijima populations thus provide strong evidence of viable hybridization and genetic introgression between the two karyotypic groups, but with variable genetic outcomes. Our results demonstrate the potential of combined analysis of karyotypes and mitochondrial and nuclear gene sequences to elucidate the complex dispersal and population history of the black rat.

Molecular and morphological assessment of Delma australis Kluge (Squamata: Pygopodidae), with a description of a new species from the biodiversity 'hotspot' of southwestern Western Australia.

The Australian pygopodid lizard genus Delma is characterised by morphologically conservative but genetically divergent lineages and species. An initial assessment of molecular and morphological variation in Delma australis Kluge, 1974 throughout its main distribution in Western and South Australia reveals at least two undescribed species that are presently included under this epithet. Here we describe the most distinctive and easily diagnosed taxon of these, D. hebesa sp. nov., from the proteaceous scrub and mallee heath on the south coast sandplains of southwestern Western Australia. We also foreshadow the need for an expanded genetic framework to assist in unequivocally diagnosing additional candidate species in D. australis, which is redescribed herein and shown to be monophyletic for those specimens sampled, albeit displaying geographic variation in a range of molecular and morphological characters. Delma hebesa sp. nov. differs from all other described Delma species, including regional populations of D. australis, by a combination of molecular genetic markers, colouration and scalation. Based on phylogenetic affinities and shared morphologies, a D. australis species-group is proposed to accommodate D. australis, D. torquata and the new species described herein. The addition of another new vertebrate species from southwestern Western Australia, recognised globally as a biodiversity 'hotspot', underlines our lack of understanding of genetic diversity and evolutionary histories in this biodiverse region.

Morphological diversity and evolution of the spermatozoon in the mouse-related clade of rodents.

Most species in the three highly speciose families of the mouse-related clade of rodents, the Muridae, Cricetidae, and Nesomyidae (superfamily Muroidea), have a highly complex sperm head in which there is an apical hook but there are few data available for the other related families of these rodents. In the current study, using light and electron microscopies, we investigated the structure of the spermatozoon in representative species of four other families within the mouse-related clade, the Dipodidae, Spalacidae, Pedetidae, and Heteromyidae, that diverged at or near the base of the muroid lineage. Our results indicate that a diverse array of sperm head shapes and tail lengths occurs but none of the species in the families Spalacidae, Dipodidae, or Pedetidae has a sperm head with an apical hook. By contrast, a rostrally extending apical hook is present in spermatozoa of members of the Family Heteromyidae which also invariably have comparatively long sperm tails. These findings suggest that the hook-shaped sperm head in the murid, cricetid, and nesomyid rodents evolved after divergence of this lineage from its common ancestor with the other families of the mouse-related clade, and that separate, and independent, convergent evolution of a similar sperm head form, and long sperm tail, occurred in the Heteromyidae.

Molecular genetic evidence for the place of origin of the Pacific rat, Rattus exulans.

Commensal plants and animals have long been used to track human migrations, with Rattus exulans (the Pacific rat) a common organism for reconstructing Polynesian dispersal in the Pacific. However, with no knowledge of the homeland of R. exulans, the place of origin of this human-commensal relationship is unknown. We conducted a mitochondrial DNA phylogeographic survey of R. exulans diversity across the potential natural range in mainland and Island Southeast Asia in order to establish the origin of this human-commensal dyad. We also conducted allozyme electrophoresis on samples from ISEA to obtain a perspective on patterns of genetic diversity in this critical region. Finally, we compared molecular genetic evidence with knowledge of prehistoric rodent faunas in mainland and ISEA. We find that ISEA populations of R. exulans contain the highest mtDNA lineage diversity including significant haplotype diversity not represented elsewhere in the species range. Within ISEA, the island of Flores in the Lesser Sunda group contains the highest diversity in ISEA (across all loci) and also has a deep fossil record of small mammals that appears to include R. exulans. Therefore, in addition to Flores harboring unusual diversity in the form of Homo floresiensis, dwarfed stegodons and giant rats, this island appears to be the homeland of R. exulans.