MORPHOLOGICAL DIFFERENTIATION IN THE WHITE-EARED OPOSSUM GROUP (DIDELPHIDAE: DIDELPHIS)

The lumbosacral plexus in two Didelphis species (Didelphidae, Didelphimorphia): origin and nerve distribution

Morphological studies provide knowledge that allow us to understand how animals interact with the natural environment or the captivity. The goal of this study was to describe the origin and antimeric distribution of lumbosacral plexus nerves in Didelphis aurita and D. albiventris. Fourteen adult cadavers of D. aurita, seven males and seven females, and 13 adult cadavers of D. albiventris, nine males and four females were used. The specimens were sexed, identified, fixed and dissected until the origins of the lumbosacral plexus nerves were exposed. Data were represented as absolute frequency and simple percentage. The lumbosacral plexuses derived a trunk for the femoral and obturator nerves from the ventral branches of L3-L4 (75%) in D. aurita, and in D. albiventris the femoral nerve of L3-L4 (73.1%) and the obturator nerve of L3-L4 (61.5%). In both species, formation of a lumbosacral trunk derived from L5-L6-S1 occurred in 78.6% of D. aurita and 61.5% of D. albiventris. The origin and distribution of lumbosacral plexus nerves of the studied species present similarities with domestic and wild eutherian mammals.

Molecular diversity of Sarcocystis spp. in opossums (Didelphis spp.) from Southeastern and Midwestern Brazil

South American opossums (Didelphis spp.) are definitive hosts of Sarcocystis neurona, Sarcocystis speeri, Sarcocystis lindsayi and Sarcocystis falcatula. In Brazil, diverse studies have demonstrated a high frequency of Sarcocystis falcatula-like in sporocysts derived from opossums, and high genetic diversity has been observed in surface antigen-encoding genes (SAGs). In this study, genetic diversity of Sarcocystis spp. derived from Didelphis albiventris and Didelphis aurita from the cities of Campo Grande and São Paulo, was accessed by sequencing SAG2, SAG3, SAG4, the first internal transcribed spacer (ITS-1) and cytochrome c oxidase subunit I (cox1). Molecular identification was performed for 16 DNA samples obtained from sporocyst or culture-derived merozoites. The ITS-1, cox1, and SAG3 fragments were cloned, whereas SAG2 and SAG4 were sequenced directly from PCR products. Four alleles variants were found for SAG2, 13 for SAG3 and seven for SAG4, from which four, 13 and four, respectively, were novel. Twenty-seven allele variants were found for ITS-1, all phylogenetically related to S. falcatula-like previously described in Brazil. Sarcocystis sp. phylogenetically related to Sarcocystis rileyi was evidenced by cox1 in three opossums. Further studies are needed to clarify the role of Didelphis spp. as definitive hosts of Sarcocystis spp. other than that previous described.

Insularity and Aridity as Drivers of Mandibular Disparity in Thylamys elegans (Waterhouse, 1839) from Populations of the Atacama Desert, Chile

Island ecosystems differ in several elements from mainland ecosystems and may induce variations related to natural selection and patterns of adaptation in most aspects of the biology of an organism. Thylamys elegans (Waterhouse, 1839) is a marsupial endemic to Chile, distributed from Loa River to Concepción. Historically, three subspecies have been described: Thylamys elegans elegans, Thylamys elegans coquimbensis and Thylamys elegans soricinus. For this research, two morphometric approaches and a biomechanical model were used to compare the mandible shapes and biomechanics between two Chilean mouse opossum populations belonging to different subspecies: one from the coastal desert of Chile (T. e. coquimbensis) and the other from the central inland region (T. e. elegans). Additionally, mandibles of insular populations found in the Reserva Nacional Pinguino de Humboldt (RNPH)), from which the subspecies association is unknown, were also included. The results showed that insular populations have differences in mandibular shapes, sizes and biomechanical characteristics compared to continental populations, which may be related to environmental variables like aridity and vegetation cover, prey type, insularity effects and/or the founder effect on micromammals, apart from vicariance hypotheses and other selective pressures.

Occipital condyle width (OCW) is a highly accurate predictor of body mass in therian mammals

BACKGROUND

Body mass estimation is of paramount importance for paleobiological studies, as body size influences numerous other biological parameters. In mammals, body mass has been traditionally estimated using regression equations based on measurements of the dentition or limb bones, but for many species teeth are unreliable estimators of body mass and postcranial elements are unknown. This issue is exemplified in several groups of extinct mammals that have disproportionately large heads relative to their body size and for which postcranial remains are rare. In these taxa, previous authors have noted that the occiput is unusually small relative to the skull, suggesting that occiput dimensions may be a more accurate predictor of body mass.

RESULTS

The relationship between occipital condyle width (OCW) and body mass was tested using a large dataset (2127 specimens and 404 species) of mammals with associated in vivo body mass. OCW was found to be a strong predictor of body mass across therian mammals, with regression models of Mammalia as a whole producing error values (~ 31.1% error) comparable to within-order regression equations of other skeletal variables in previous studies. Some clades (e.g., monotremes, lagomorphs) exhibited specialized occiput morphology but followed the same allometric relationship as the majority of mammals. Compared to two traditional metrics of body mass estimation, skull length, and head-body length, OCW outperformed both in terms of model accuracy.

CONCLUSIONS

OCW-based regression models provide an alternative method of estimating body mass to traditional craniodental and postcranial metrics and are highly accurate despite the broad taxonomic scope of the dataset. Because OCW accurately predicts body mass in most therian mammals, it can be used to estimate body mass in taxa with no close living analogues without concerns of insufficient phylogenetic bracketing or extrapolating beyond the bounds of the data. This, in turn, provides a robust method for estimating body mass in groups for which body mass estimation has previously been problematic (e.g., "creodonts" and other extinct Paleogene mammals).

Sarcocystis neurona and related Sarcocystis spp. shed by opossums (Didelphis spp.) in South America

Protozoan parasites of the genus Sarcocystis are obligatory heteroxenous cyst-forming coccidia that infect a wide variety of animals and encompass approximately 200 described species. At least four Sarcocystis spp. (S. falcatula, S. neurona, S. lindsayi and S. speeri) use opossums (Didelphis spp.) as definitive hosts, and two of them, S. neurona and S. falcatula, are known to cause disease in horses and birds, respectively. Opossums are restricted to the Americas, but their distribution in the Americas is heterogeneous. Five Didelphis spp. are distributed in South America (D. aurita, D. albiventris, D. marsupialis, D. imperfecta and D. pernigra) whereas just one opossum species (D. virginiana) is found in North America. Studies conducted in the last decades show that Sarcocystis spp., derived from South American Didelphis spp., have biological and genetic differences in relation to Sarcocystis spp. shed by the North American opossum D. virginiana. The aim of this review was to address the peculiar scenario of Sarcocystis species shed by South American opossums, with a special focus on diagnosis, epidemiology, and animal infections, as well as the genetic characteristics of these parasites.

Identification and characterization of repetitive DNA in the genus Didelphis Linnaeus, 1758 (Didelphimorphia, Didelphidae) and the use of satellite DNAs as phylogenetic markers

Didelphis species have been shown to exhibit very conservative karyotypes, which mainly differ in their constitutive heterochromatin, known to be mostly composed by repetitive DNAs. In this study, we used genome skimming data combined with computational pipelines to identify the most abundant repetitive DNA families of Lutreolina crassicaudata and all six Didelphis species. We found that transposable elements (TEs), particularly LINE-1, endogenous retroviruses, and SINEs, are the most abundant mobile elements in the studied species. Despite overall similar TE proportions, we report that species of the D. albiventris group consistently present a less diverse TE composition and smaller proportions of LINEs and LTRs in their genomes than other studied species. We also identified four new putative satDNAs (sat206, sat907, sat1430 and sat2324) in the genomes of Didelphis species, which show differences in abundance and nucleotide composition. Phylogenies based on satDNA sequences showed well supported relationships at the species (sat1430) and groups of species (sat206) level, recovering topologies congruent with previous studies. Our study is one of the first attempts to present a characterization of the most abundant families of repetitive DNAs of Lutreolina and Didelphis species providing insights into the repetitive DNA composition in the genome landscape of American marsupials.

Trypanosomatid species in Didelphis albiventris from urban forest fragments

Urbanization results in loss of natural habitats and, consequently, reduction of richness and abundance of specialist to the detriment of generalist species. We hypothesized that a greater richness of trypanosomatid in Didelphis albiventris would be found in fragments of urban forests in Campo Grande, Mato Grosso do Sul, Brazil, that presented a larger richness of small mammals. We used parasitological, molecular, and serological methods to detect Trypanosoma spp. infection in D. albiventris (n = 43) from forest fragments. PCR was performed with primers specific for 18S rDNA, 24Sα rDNA, mini-chromosome satellites, and mini-exon genes. IFAT was used to detect anti-Trypanosoma cruzi IgG. All hemoculture was negative. We detected trypanosomatid DNA in blood of 35% of opossum. Two opossums were seropositive for T. cruzi. The trypanosomatid species number infecting D. albiventris was higher in the areas with greater abundance, rather than richness of small mammals. We found D. albiventris parasitized by T. cruzi in single and co-infections with Leishmania spp., recently described molecular operational taxonomic unit (MOTU) named DID, and Trypanosoma lainsoni. We concluded that (i) trypanosome richness may be determined by small mammal abundance, (ii) D. albiventris confirmed to be bio-accumulators of trypanosomatids, and (iii) T. lainsoni demonstrated a higher host range than described up to the present.

'Candidatus Mycoplasma haemoalbiventris', a novel hemoplasma species in white-eared opossums (Didelphis albiventris) from Brazil

Opossums of the genus Didelphis are considered synanthropic animals due to their close contact with human beings. Previously, two species of hemotropic mycoplasmas (hemoplasmas) have been detected in opossums: 'Candidatus Mycoplasma haemodidelphidis' in the North American opossum (Didelphis virginiana) and a potentially novel hemotropic Mycoplasma sp. in the white-eared opossums (Didelphis albiventris) from Brazil. Accordingly, the aims of this study were as follows: (a) to determine the prevalence of hemotropic Mycoplasma spp. in free-ranging opossums, (b) to characterize molecularly the hemotropic Mycoplasma sp. infecting opossums and (c) to determine factors associated with hemoplasma infection in opossums from Canoinhas municipality, Santa Catarina State, southern Brazil. For this purpose, 50 white-eared opossums (33 captured and 17 road-killed animals) were evaluated by a pan-hemoplasma PCR assay based on 16S rRNA. Six out of 50 (12%; 95% CI: 5.6%-23.8%) opossums were infested by Ctenocephalides felis fleas. Twenty out of 50 (40%; 95% CI: 26.41%-54.82%) opossums tested positive for hemotropic Mycoplasma sp. by PCR. Sequencing and phylogenetic analysis of the 16S and 23S rRNA gene fragments confirmed that animals were infected by a potentially novel hemotropic Mycoplasma sp. previously reported in white-eared opossums from Brazil. No significant association was found between gender (p = .7759), trap area (p = .0887) or presence of fleas (p = .3811) and positivity for hemoplasmas. The potentially novel hemoplasma species seems to be highly prevalent in white-eared opossums from the states of Paraná, Santa Catarina and Mato Grosso do Sul. Based on the phylogenetic analyses of the 16S rRNA and 23S rRNA genes along with epidemiological data, the name 'Candidatus Mycoplasma haemoalbiventris' is proposed for this novel organism.

Detection of Hemotropic Mycoplasma sp. in white-eared opossums (Didelphis albiventris) from Southern Brazil

Opossums are marsupials from the New World of the genus Didelphis and known as synanthropic animals due to their proximity with human beings. To date, 'Candidatus Mycoplasma haemodidelphis' has been solely found infecting the North American opossum (Didelphis virginiana). Accordingly, the aim of this study was to screen eight white-eared opossums (Didelphis albiventris) from a public park in Maringa city, Paraná State, southern Brazil, for hemoplasma infection. Blood samples were taken from caudal venipuncture, and DNA was extracted and further screened by a pan-hemoplasma PCR assay. Seven out of eight (87.50%; CI 95%: 47.35-99.68%) white-eared opossums were positive for Mycoplasma spp. Sequencing of the 16S rRNA fragment showed 98,97% identity with 'Ca. M. haemodidelphis' detected in the USA. Three out of eight (37.50%; CI 95%: 8.52-75.51%) white-eared opossums were infested by Amblyomma dubitatum ticks. This is the first report on detection of a potentially novel hemotropic Mycoplasma sp. infecting opossums from South America.

Landscape use by two opossums is shaped by habitat preferences rather than by competitive interactions

Given the phylogenetic proximity and similar morphology of opossums (Didelphis spp.), they are good models to study factors that facilitate or impede coexistence of syntopic species and to better understand how landscape changes affect species distributions and habitat use. For this purpose, we used single-species and two-species occupancy models using records of D. albiventris, considered the dominant species, and D. aurita from a camera-trap survey conducted in an agricultural and conservation landscape in the Atlantic Forest of Argentina. We evaluated which factors determined the probability of species occurrence: habitat preferences or interspecific relationships. We also estimated the overlap in daily activity patterns between species, and evaluated changes in D. aurita activity in response to the occupancy probability of D. albiventris. Didelphis aurita had higher occupancy probabilities in the continuous native forest, whereas D. albiventris had higher occupancy probabilities in fragmented forests with less complex and more open vegetation structure, and greater proximity to buildings. Both opossums were almost absent in pine plantations. Results of the co-occurrence models and the overlap in diel activity suggest that D. aurita is not avoiding D. albiventris. Occurrences of these two opossums most probably reflect different adaptations by each species to different habitats, and competitive interactions seem to play a minor role in shaping their current distributions. Didelphis albiventris may be replacing D. aurita mainly as a result of changing environmental conditions, which become unfavorable to the latter but promote the creation of new habitat for the former.

On the identity of Didelphis marsupialis Linnaeus 1758

Given the confusion ensuing from a recent study suggesting that the name Didelphis marsupialis should be applied to white-eared opossums instead of the traditional view that it represents a black-eared opossum, we reviewed all the sources employed by Linnaeus to describe D. marsupialis and examined photographs of the putative type specimen, comparing them with specimens of black- and white-eared Didelphis. We conclude that the type specimen presents characters that would allow us to diagnose it as a black-eared opossum species. We believe that the proposed nomenclatural changes not only are unjustified but also disrupt the stability advocated by the International Commission on Zoological Nomenclature (ICZN).

Rapid assessment of nonvolant mammals in seven sites in the northern State of Pará, Brazil: a forgotten part of the Guiana Region

The Guiana Center of Endemism (GCE) extends across Guyana, Suriname, French Guiana, north of the Amazon River and east of the Negro River in Brazil, and Venezuela to the south of the Orinoco River. Regarding diversity of nonvolant mammals, the Brazilian part of this center is less studied, especially the area corresponding to the north of the State of Pará. Seven field trips lasting 12–15 days each were conducted in five conservation units in northern Pará, in order to assess the nonvolant mammalian fauna. Small mammals were captured using conventional and pitfall traps. Medium-sized and large mammals were recorded through direct observations on diurnal transect censuses, collections, camera traps, indirect evidence, and in some cases, interviews. We recorded 60 species distributed in nine orders. Among other contributions, a recently described species of

Which Factors Determine Spatial Segregation in the South American Opossums (Didelphis aurita and D. albiventris)? An Ecological Niche Modelling and Geometric Morphometrics Approach

Didelphis albiventris and D. aurita are Neotropical marsupials that share a unique evolutionary history and both are largely distributed throughout South America, being primarily allopatric throughout their ranges. In the Araucaria moist forest of Southern Brazil these species are sympatric and they might potentially compete having similar ecology. For this reason, they are ideal biological models to address questions about ecological character displacement and how closely related species might share their geographic space. Little is known about how two morphologically similar species of marsupials may affect each other through competition, if by competitive exclusion and competitive release. We combined ecological niche modeling and geometric morphometrics to explore the possible effects of competition on their distributional ranges and skull morphology. Ecological niche modeling was used to predict their potential distribution and this method enabled us to identify a case of biotic exclusion where the habit generalist D. albiventris is excluded by the presence of the specialist D. aurita. The morphometric analyses show that a degree of shape discrimination occurs between the species, strengthened by allometric differences, which possibly allowed them to occupy marginally different feeding niches supplemented by behavioral shift in contact areas. Overlap in skull morphology is shown between sympatric and allopatric specimens and a significant, but weak, shift in shape occurs only in D. aurita in sympatric areas. This could be a residual evidence of a higher past competition between both species, when contact zones were possibly larger than today. Therefore, the specialist D. aurita acts a biotic barrier to D. albiventris when niche diversity is not available for coexistence. On the other hand, when there is niche diversification (e.g. habitat mosaic), both species are capable to coexist with a minimal competitive effect on the morphology of D. aurita.

Natural infection of Didelphis aurita (Mammalia: Marsupialia) with Leishmania infantum in Brazil

Background

The opossum Didelphis have been considered as natural hosts of Leishmania parasites in the New World, suggesting an important role in the epidemiology of Visceral Leishmaniasis (VL). Among six extant species that belong to the genus Didelphis, only two (D. marsupialis and D. albiventris), have been mentioned as natural hosts of Leishmania infantum in Brazil and Colombia. In the present paper, it is reported for the first time, the observation of intracellular parasites (amastigotes) in tissues of Didelphis aurita naturally infected with Leishmania infantum in Brazil. We also discuss some aspects associated to the relationship between L. infantum and the geographical distribution of some species of the genus Didelphis.

Methods

The opossums studied were caught by wire traps (Tomahawk) in Barra de Guaratiba, a peri-urban area in Rio de Janeiro. The opossums were killed with an overdose of Thiopental sodium.At necropsy, macroscopic alterations were examined and samples from liver, spleen, lymph nodes, ear, abdominal skin, scent glands and bone marrow were collected for parasitological and molecular diagnoses.

Results

Forty-eight opossums were captured in an AVL endemic region, 30 being caught in a mangrove area and eighteen animals in a forest area near to some residential-yards. Among the thirty opossums trapped in the mangrove area, all of them were negative by both imprint and sera samples assayed on Dipstick Tests, that is a test based on a combination of protein-A colloidal gold conjugate and rk39 Leishmania antigen to detect anti-Leishmania antibody in serum or plasma. At the macroscopic examination one out of eighteen opossums, caught close to the forest, presented alterations compatible with spleen hypertrophy and three were positive by Dipstick Tests (16.6%) and presented amastigotes in the spleen and in one of them, the parasites were also observed in a submandibular lymph node. Leishmania infantum infections were confirmed through dot blot hybridization using a L. infantum-specific biotinylated probe.

Conclusions

In the present paper we present the first report of amastigotes in the tissues of Didelphis aurita (Mammalia: Marsupialia) naturally infected with Leishmania infantum. We also attempt to claim the particular role of some opossum species as hosts of Leishmania infantum, contributing at least in part on the description of potential sylvatic reservoirs.

Skull modularity in neotropical marsupials and monkeys: size variation and evolutionary constraint and flexibility

An organism is built through a series of contingent factors, yet it is determined by historical, physical, and developmental constraints. A constraint should not be understood as an absolute obstacle to evolution, as it may also generate new possibilities for evolutionary change. Modularity is, in this context, an important way of organizing biological information and has been recognized as a central concept in evolutionary biology bridging on developmental, genetics, morphological, biochemical, and physiological studies. In this article, we explore how modularity affects the evolution of a complex system in two mammalian lineages by analyzing correlation, variance/covariance, and residual matrices (without size variation). We use the multivariate response to selection equation to simulate the behavior of Eutheria and Metharia skulls in terms of their evolutionary flexibility and constraints. We relate these results to classical approaches based on morphological integration tests based on functional/developmental hypotheses. Eutherians (Neotropical primates) showed smaller magnitudes of integration compared with Metatheria (didelphids) and also skull modules more clearly delimited. Didelphids showed higher magnitudes of integration and their modularity is strongly influenced by within-groups size variation to a degree that evolutionary responses are basically aligned with size variation. Primates still have a good portion of the total variation based on size; however, their enhanced modularization allows a broader spectrum of responses, more similar to the selection gradients applied (enhanced flexibility). Without size variation, both groups become much more similar in terms of modularity patterns and magnitudes and, consequently, in their evolutionary flexibility.

A genetically diverse but distinct North American population of Sarcocystis neurona includes an overrepresented clone described by 12 microsatellite alleles

The population genetics and systematics of most coccidians remain poorly defined despite their impact on human and veterinary health. Non-recombinant parasite clones characterized by distinct transmission and pathogenesis traits persist in the coccidian Toxoplasma gondii despite opportunities for sexual recombination. In order to determine whether this may be generally true for tissue-cyst forming coccidia, and to address evolutionary and taxonomic problems within the genus Sarcocystis, we characterized polymorphic microsatellite markers in Sarcocystis neurona, the major causative agent of equine protozoal myeloencephalitis (EPM). Bayesian statistical modeling, phylogenetic reconstruction based on genotypic chord distances, and analyses of linkage disequilibrium were employed to examine the population structure within S. neurona and closely related Sarcocystis falcatula isolates from North and South America. North American S. neurona were clearly differentiated from those of South America and also from isolates of S. falcatula. Although S. neurona is characterized by substantial allelic and genotypic diversity typical of interbreeding populations, one genotype occurs with significantly excessive frequency; thus, some degree of asexual propagation of S. neurona clones may naturally occur. Finally, S. neurona isolated from disparate North American localities and diverse hosts (opossums, a Southern sea otter, and horses) comprise a single genetic population. Isolates associated with clinical neurological disease bear no obvious distinction as measured by these presumably neutral genetic markers.