A syncytin-like endogenous retrovirus envelope gene of the guinea pig specifically expressed in the placenta junctional zone and conserved in Caviomorpha

Syncytins are genes of retroviral origin that have been co-opted by mammalian hosts for a function in placentation. Two such genes have already been identified in simians, as well as two distinct, unrelated ones in Muridae and a fifth in the rabbit. Here we searched for similar genes in the guinea pig, which belongs to the Caviomorpha lineage within the Hystricognathi suborder of rodents and displays a placental structural organization with several characteristic features comparable to those of the human organ, including deep trophoblast invasion of maternal tissues. An in silico search for envelope (env) genes with full coding capacity identified a candidate gene that showed specific expression in the placenta, as revealed by RT-qPCR using RNAs from a large panel of tissues. This gene belongs to an endogenous retroviral element present at a single-copy in the guinea pig genome, still displaying a retroviral organization - with a degenerate gag and pol, but an intact env gene. In situ hybridization of guinea pig placenta sections demonstrated specific expression at the level of the invasive trophoblast-containing junctional zone, as observed in humans for syncytin-1 and consistent with a role in invasion of the maternal uterine tissues. The identified gene displays a conserved open reading frame in the Caviomorpha, consistent with an entry date >30 million years, and sequence analyses showed purifying selection of the gene. Conclusively, despite the absence of a demonstrated fusogenic activity, it is likely that the identified env gene - that we named syncytin-like env-Cav1 - exerts a physiological function possibly related to trophoblast invasion, in the course of caviomorph placentation.

Structure of parasite component communities of didelphid marsupials: insights from a comparative study

The parasite fauna of the gray four-eyed opossum, Philander opossum (Linnaeus, 1758), and the common opossum, Didelphis marsupialis Linnaeus, 1758, in Camp du Tigre, French Guiana, is characterized. Nine species from the gastrointestinal system were recovered from both species, which shared 80% of their parasites. The parasite fauna comprised several monoxenous species (63%) and was dominated by Aspidodera raillieti Travassos, 1914, which exhibited high levels of prevalence and abundance in both communities. Only 2 species (Moennigia sp. and Spirura guianensis) had been recorded in other species of mammals. Both species richness and taxonomic composition at the level of component communities from this locality were compared against 11 communities present in the Virginia ( Didelphis virginiana ), white-bellied (Didelphis albiventris), and common opossum from Argentina, Brazil, Mexico, and the United States. Neither host phylogeny nor taxonomy accounted for statistical differences in species richness. There was no statistical difference among species richness values among the 9 localities studied. Taxonomic similarity was analyzed by means of the Jaccard's similarity index, including all, and only common species (occurring in prevalence >10%). The results suggest that sympatric species of marsupials share more species of parasites than parasite communities occurring in conspecific marsupials from different localities. As a consequence, taxonomic composition of these parasite communities varied depending on the locality. Probably, marsupials of the monophyletic Didelphini offer the same compatibility toward their parasites, by presenting them with similar habitats. Subtle differences in lifestyles of the marsupials may determine the chance of encounter between the symbionts and prevent some parasites from completing their life cycles. Further and more rigorous tests are necessary to determine the roles of encounter and compatibility filters, as well as the role of chance, in the structuring of parasite communities in marsupials.

Phylogeny and phylogeography of squirrel monkeys (genus Saimiri) based on cytochrome b genetic analysis

Squirrel monkeys (genus Saimiri) are distributed over a wide area encompassing the Amazon Basin: French Guiana, Suriname, and Guyana, together with Western Panama and Western Costa Rica. The genus Saimiri includes a complex of species and subspecies displaying considerable morphological variation. Taxonomic and systematic studies have identified, in this genus, one to seven species comprising up to 16 subspecies. The phylogenetic relationships between these taxa are poorly understood. Molecular markers have yielded a consistent framework for the systematics of Central and South American Saimiri, identifying four distinct clades: S. oerstedii, S. sciureus, S. boliviensis, and S. ustus. Here, we reconsider the phylogenetic and biogeographic history of Saimiri on the basis of mitochondrial (mtDNA) sequence data, focusing mostly on individuals originating from the Amazon Basin. We studied 32 monkeys with well-defined geographic origins and inferred the phylogenetic relationships between them on the basis of full-length cytochrome b gene nucleotide sequences. The high level of gene diversity observed (0.966) is consistent with the high level of behavioral and morphological variation observed across the geographic range of the genus: 20 mtDNA haplotypes were identified with a maximum divergence of 4.81% between S. b. boliviensis and S. ustus. In addition to confirming the existence of the four clades previously identified on the basis of molecular characters, we suggest several new lineages, including S. s. macrodon, S. s. albigena, S. s. cassiquiarensis, and S. s. collinsi. We also propose new patterns of dispersion and diversification for the genus Saimiri, and discuss the contribution of certain rivers and forest refuges to its structuring.

Dengue infection in neotropical forest mammals

In South America, dengue is the arbovirus-transmitted disease with the highest incidence. Unlike other arboviruses, wild mammals have no confirmed role in the cycle of dengue in the neotropics, although serological studies have suggested a possible secondary amplification cycle involving mammals other than nonhuman primates. In French Guiana, where all four serotypes (DENV-1, DENV-2, DENV-3, DENV-4) are present, the disease is endemic with outbreak events. To determine whether wild mammals can be infected by DENV, rodents, marsupials, and bats were captured over several periods, from 2001 to 2007, at two sites. The first location is a secondary forest surrounded by an urban area where dengue is endemic. The second location is a forest edge site where the disease has not yet emerged. A total of 10,000 trap-nights were performed and 616 mammals were captured. RNAs representing the four DENV serotypes were detected at both sites by reverse-transcriptase polymerase chain reaction in the livers and/or sera of 92 mammals belonging to 14 out of 32 species distributed among all the orders investigated: Rodentia (33 positive/146 tested), Marsupialia (40/318), and Chiroptera (19/152). Sequence analyses of a portion of the capsid and premembrane junction revealed that mammal strains of DENV-1, DENV-2, DENV-3, and DENV-4 had only 92.6%, 89%, 95%, and 95.8% identity, respectively, with strains circulating in the human population during the same periods. Regarding DENV-2, strains related (99% identity) to those responsible for an epidemic event in humans in French Guiana concurrent to the capture sessions were also evidenced, suggesting that wild mammals in edge habitats can be infected by circulating human strains. Our results demonstrate, for the first time, that neotropical wild mammals can be infected with dengue virus. The question of whether mammals maintain DENV in enzootic cycles and can play a role in its reemergence in human populations remains to be answered.

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.

Automated scanning for phylogenetically informative transposed elements in rodents

Transposed elements constitute an attractive, useful source of phylogenetic markers to elucidate the evolutionary history of their hosts. Frequent and successive amplifications over evolutionary time are important requirements for utilizing their presence or absence as landmarks of evolution. Although transposed elements are well distributed in rodent taxa, the generally high degree of genomic sequence divergence among species complicates our access to presence/absence data. With this in mind we developed a novel, high-throughput computational strategy, called CPAL (Conserved Presence/Absence Locus-finder), to identify genome-wide distributed, phylogenetically informative transposed elements flanked by highly conserved regions. From a total of 232 extracted chromosomal mouse loci we randomly selected 14 of these plus 2 others from previous test screens and attempted to amplify them via PCR in representative rodent species. All loci were amplifiable and ultimately contributed 31 phylogenetically informative markers distributed throughout the major groups of Rodentia.

Absence of leishmania in Guianan bats

Studying the ecology of Leishmania parasites is essential for understanding and controlling the epidemiology of the diseases they cause. Despite their abundance and diversity in neotropical forests, few studies have been conducted to investigate the potential involvement of Chiroptera in the Leishmania pathogenic complexes. However, phlebotomine sand flies are known to colonize the same anthropized habitat, are attracted to bats, and are able to transmit trypanosomatids. Thus, 216 bats representing 29 species were sampled in the field in different primary and secondary forests of French Guiana where human cutaneous leishmaniases have been reported, together with 62 non-volant mammals. A series of 411 tissue samples representing 47 mammalian species were cultured and screened for the presence of Leishmania spp. by a genus-specific polymerase chain reaction. All 278 individuals surveyed were negative. Thus, bats do not appear to be involved in the Leishmania parasitic cycles in the Guyanas.

Genetic analysis of the Saimiri breeding colony of the Pasteur Institute (French Guiana): development of a molecular typing method using a combination of nuclear and mitochondrial DNA markers

Saimiri (Cebidae) groups a complex of species and subspecies, which present a large morphological plasticity. Genetic analysis is complicated by the absence of consensus on classification criteria and the paucity of molecular tools available for the genus. As the squirrel monkey is widely used in biomedical research, breeding centers have been established, but the genetic make up and diversity of many of the existing colonies is unknown precluding a rationale breeding policy. To develop a genetic typing strategy for the Saimiri breeding colony of Pasteur Institute of French Guiana, we have used Cytochrome b, a mitochondrial marker, and nuclear microsatellites. Cytochrome b sequences from wild-caught Saimiri boliviensis, Saimiri sciureus sciureus and S. s. collinsi reference specimens and captive animals identified 11 haplotypes, grouped into three distinct clades. An estimate of genetic variability within each captive morphotype, and of the extent of molecular divergence between the Bolivian, Guyanese and Brazilian breeds was obtained from the analysis of three nuclear microsatellites. Taxon-specific microsatellites enabled typing of F0-F3 animals, but did not differentiate Brazilian from Guyanese animals. Three locus microsatellite analysis of a representative sample from each generation showed no trend for loss of heterozygosity, and identified hybrid animals between Bolivian and the two others sub-species. These data provide novel evidence for taxonomic classification and a rationale strategy to further type the whole colony.

The Sahara as a vicariant agent, and the role of Miocene climatic events, in the diversification of the mammalian order Macroscelidea (elephant shrews)

Although the Sahara is a major geographical feature of the African continent, its role in the diversification of animal species is not well understood. We present here a molecular phylogeny for members of the endemic African mammalian order Macroscelidea (elephant shrews) with molecular-clock calculations; this molecular phylogeny provides convincing evidence that the genus Elephantulus is diphyletic. Elephantulus rozeti, the only elephant shrew species that resides north of the Sahara, is the sister group of a species from a different genus (Petrodromus tetradactylus), which resides just south of the Sahara. The split between these taxa coincided with major Miocene climatic events, which triggered the cooling and aridification of midlatitude continental regions, and a shift in the Sahara from a tropical to an arid environment. Thus, the North African distribution of E. rozeti is not the result of dispersion from an eastern species of the genus, but instead the result of a vicariant event involving the formation of the Sahara. The splitting events involved with most Elephantulus species in our analysis appear to coincide with these climatic events. This coincidence suggests that the environmental consequences associated with this period played an important role in the radiation of this order of mammals. The strongly supported phylogeny provides compelling evidence for a complex history of mosaic evolution, including pronounced bradytelic morphological evolution in some lineages, accelerated morphological evolution in others, and a remarkably slow rate of evolution of the male reproductive structure.

Napoleon Bonaparte and the fate of an Amazonian rat: new data on the taxonomy of Mesomys hispidus (Rodentia: Echimyidae)

The spiny rat Mesomys hispidus is one of many South American rodents that lack adequate taxonomic definition. The few sampled populations of this broadly distributed trans-Amazonian arboreal rat have come from widely separated regions and are typically highly divergent. The holotype was described in 1817 by A.-G. Desmarest, after Napoleon's army brought it to Paris following the plunder of Lisbon in 1808; however, the locality of origin has remained unknown. Here we examine the taxonomic status of this species by direct comparison of 50 extant individuals with the holotype at the morphometric and genetic levels, the latter based on 331 bp of the mitochondrial cytochrome b gene retrieved from a small skin fragment of the holotype with ancient DNA technology. Extensive sequence divergence is present among samples of M. hispidus collected from throughout its range, from French Guiana across Amazonia to Bolivia and Peru, with at least seven mitochondrial clades recognized (average divergence of 7.7% Kimura 2-parameter distance). Sequence from the holotype is, however, only weakly divergent from those of recent samples from French Guiana. Moreover, the holotype clusters with greater that 99% posterior probability with samples from this part of Amazonia in a discriminant analysis based on 22 cranial and dental measurements. Thus, we suggest that the holotype was originally obtained in eastern Amazonia north of the Amazon River, most likely in the Brazilian state of Amapá. Despite the high level of sequence diversity and marked morphological differences in size across the range of M. hispidus, we continue to regard this assemblage as a single species until additional samples and analyses suggest otherwise.

Rodent phylogeny and a timescale for the evolution of Glires: evidence from an extensive taxon sampling using three nuclear genes

Rodentia is the largest order of placental mammals, with approximately 2,050 species divided into 28 families. It is also one of the most controversial with respect to its monophyly, relationships between families, and divergence dates. Here, we have analyzed and compared the performance of three nuclear genes (von Willebrand Factor, interphotoreceptor retinoid-binding protein, and Alpha 2B adrenergic receptor) for a large taxonomic sampling, covering the whole rodent and placental diversity. The phylogenetic results significantly support rodent monophyly, the association of Rodentia with Lagomorpha (the Glires clade), and a Glires + Euarchonta (Primates, Dermoptera, and Scandentia) clade. The resolution of relationships among rodents is also greatly improved. The currently recognized families are divided here into seven well-defined clades (Anomaluromorpha, Castoridae, Ctenohystrica, Geomyoidea, Gliridae, Myodonta, and Sciuroidea) that can be grouped into three major clades: Ctenohystrica, Gliridae + Sciuroidea, and a mouse-related clade (Anomaluromorpha, Castoridae + Geomyoidea, and Myodonta). Molecular datings based on these three genes suggest that the rodent radiation took place at the transition between Paleocene and Eocene. The divergence between rodents and lagomorphs is placed just at the K-T boundary and the first splits among placentals in the Late Cretaceous. Our results thus tend to reconcile molecular and morphological-paleontological insights.

Evolutionary history of the most speciose mammals: molecular phylogeny of muroid rodents

Phylogenetic relationships between 32 species of rodents representing 14 subfamilies of Muridae and four subfamilies of Dipodidae were studied using sequences of the nuclear protein-coding genes Lecithin Cholesterol Acyl Transferase (LCAT) and von Willebrand Factor (vWF). An examination of some evolutionary properties of each data matrix indicates that the two genes are rather complementary, with lower rates of nonsynonymous substitutions for LCAT. Both markers exhibit a wide range of GC3 percentages (55%-89%), with several taxa above 70% GC3 for vWF, which indicates that those exonic regions might belong to the richest class of isochores. The primary sequence data apparently harbor few saturations, except for transitions on third codon positions for vWF, as indicated by comparisons of observed and expected pairwise values of substitutions. Phylogenetic trees based on 1,962 nucleotidic sites from the two genes indicate that the 14 Muridae subfamilies are organized into five major lineages. An early isolation leads to the clade uniting the fossorial Spalacinae and semifossorial Rhizomyinae with a strong robustness. The second lineage includes a series of African taxa representing nesomyines, dendromurines, cricetomyines, and the sole living member of mystromyines. The third one comprises only the mouselike hamster CALOMYSCUS: The fourth clade represents the cricetines, myospalacines, sigmodontines, and arvicolines, whereas the fifth one comprises four "traditional" subfamilies (Gerbillinae, Murinae, Otomyinae, and Acomyinae). Within these groups, we confirm the monophyly of almost all studied subfamilies, namely, Spalacinae, Rhizomyinae, Nesomyinae, Cricetomyinae, Arvicolinae, Sigmodontinae, Cricetinae, Gerbillinae, Acomyinae, and Murinae. Finally, we present evidence that the sister group of Acomyinae is Gerbillinae, and we confirm a nested position of Myospalacinae within Cricetinae and Otomyinae within Murinae. From a biogeographical point of view, the five main lineages spread and radiated from Asia with different degrees of success: the first three groups are now represented by a limited number of species and genera localized in some regions, whereas the last two groups radiated in a large variety of species and genera dispersed all over the world.

Protein sequence signatures support the African clade of mammals

DNA sequence evidence supports a superordinal clade of mammals that comprises elephants, sea cows, hyraxes, aardvarks, elephant shrews, golden moles, and tenrecs, which all have their origins in Africa, and therefore are dubbed Afrotheria. Morphologically, this appears an unlikely assemblage, which challenges-by including golden moles and tenrecs-the monophyly of the order Lipotyphla (Insectivora). We here identify in three proteins unique combinations of apomorphous amino acid replacements that support this clade. The statistical support for such "sequence signatures" as unambiguous synapomorphic evidence for the naturalness of the Afrotherian clade is reported. Using likelihood, combinatorial, and Bayesian methods we show that the posterior probability of the mammalian tree containing the Afrotherian clade is effectively 1.0, based on conservative assumptions. Presenting sequence data for another African insectivore, the otter shrew Micropotamogale lamottei, we demonstrate that such signatures are diagnostic for including newly investigated species in the Afrotheria. Sequence signatures provide "protein-morphological" synapomorphies that may aid in visualizing monophyletic groupings.

Molecular evidence of an African Phiomorpha-South American Caviomorpha clade and support for Hystricognathi based on the complete mitochondrial genome of the cane rat (Thryonomys swinderianus)

The complete mitochondrial genome of an African cane rat, Thryonomys swinderianus (Rodentia, Hystricognathi), was included in a phylogenetic analysis along with 4 rodents, 14 additional eutherians, and 3 noneutherian outgroups. Monophyly of the suborder Hystricognathi, represented by the cane rat and the South American guinea pig, Cavia porcellus, was strongly supported by maximum-parsimony, neighbor-joining, and maximum-likelihood methods. The molecular-based estimate of the divergence time of Old and New World Hystricognathi (approximately 85 million years before present, MYBP) is consistent with an hypothesis of vicariance divergence due to the rifting of the African and South American continents 86-100 MYBP. Monophyly of Rodentia or the superordinal clade Glires (Rodentia and Lagomorpha) were not supported.

Molecular characterization and mitochondrial sequence variation in two sympatric species of Proechimys (Rodentia: Echimyidae) in French Guiana

Variations in mitochondrial DNA characters were used to characterize two morphologically similar and sympatric species of Neotropical terrestrial rodents of the genus Proechimys (Mammalia: Echimyidae). We sequenced both cytochrome b (1140pb) and part of the control region (445pb) from four individuals of P. cuvieri and five of P. cayennensis from French Guiana, which allowed us to depict intra- and inter-specific patterns of variation. The phylogenetic relationships between the nine sequences evidence the monophyly of each species, and illustrate that more polymorphism might exist within P. cuvieri than within P. cayennensis. By developing species-specific primers to amplify a fragment of the cytochrome b gene, we were able to identify 50 individuals of Proechimys spp. caught in two localities of French Guiana. In both sites of primary rainforests, we showed that the two species live in syntopy, and this observation emphasizes the need to document ecological differences which should exist in order to diminish inter-specific competition.

Diversity and phylogenetic implications of CsCl profiles from rodent DNAs

Buoyant density profiles of high-molecular-weight DNAs sedimented in CsCl gradients, i.e., compositional distributions of 50- to 100-kb genomic fragments, have revealed a clear difference between the murids so far studied and most other mammals, including other rodents. Sequence analyses have revealed other, related, compositional differences between murids and nonmurids. In the present study, we obtained CsCl profiles of 17 rodent species representing 13 families. The modal buoyant densities obtained for rodents span the full range of values observed in other eutherians. More remarkably, the skewness (asymmetry, mean - modal buoyant density) of the rodent profiles extends to values well below those of other eutherians. Scatterplots of these and related CsCl profile parameters show groups of rodent families that agree largely with established rodent taxonomy, in particular with the monophyly of the Geomyoidea superfamily and the position of the Dipodidae family within the Myomorpha. In contrast, while confirming and extending previously reported differences between the profiles of Myomorpha and those of other rodents, the CsCl data question a traditional hypothesis positing Gliridae within Myomorpha, as does the recently sequenced mitochondrial genome of dormouse. Analysis of CsCl profiles is presented here as a rapid, robust method for exploring rodent and other vertebrate systematics.

The bushlike radiation of muroid rodents is exemplified by the molecular phylogeny of the LCAT nuclear gene

Phylogenetic relationships among 40 extant species of rodents, with an emphasis on the taxonomic sampling of Muridae and Dipodidae, were studied using sequences of the nuclear protein-coding gene LCAT (lecithin cholesterol acyl transferase). Analysis of 804 bp from the exonic regions of LCAT confirmed many traditional groupings in and around Muridae. A strong support was found for the families Muridae (represented by 29 species) and Dipodidae (5 species). Compared with Sciuridae, Gliridae, and Caviomorpha, the Dipodidae family appeared the closest relative of Muridae, confirming the suprafamilial Myodonta concept. Within the speciose family Muridae, the first branching leads to the fossorial Spalacinae and semifossorial Rhyzomyinae. The remaining components of Muridae appear as a polytomy from which are issued Sigmodontinae, Calomyscinae, Arvicolinae, Cricetinae, Mystromyinae, Nesomyinae, and some Dendromurinae (Steatomys and Dendromus). This phylogeny is interpreted as the result of a bushlike radiation at the end of the early Miocene, leading to emergence of most living subfamilies. The separation between three additional taxa, Murinae, Gerbillinae, and "Acomyinae" (which comprises the genera Acomys, Deomys, Uranomys, and Lophuromys), has occurred more recently from a common ancestor issued from the main basal radiation. As previously shown by other molecular studies, the vlei rats, Otomyinae, are nested within Old World Murinae. In the same way, the zokors, Myospalacinae, appear strongly nested within the hamsters, Cricetinae. Finally, we propose a sister group relationship between Malagasy Nesomyinae and south African Mystromyinae.