Marmosa Research Articles

Thylamys pallidior (Didelphimorphia: Didelphidae)

Abstract Thylamys pallidior (O. Thomas, 1902) is a didelphid marsupial commonly called the white-bellied fat-tailed mouse opossum. A small mouse opossum, with tricolored pelage and a white venter, it has a seasonally incrassated tail, where fat deposits, primarily at the tail base, function in food storage. It is the most widely distributed species in the genus occurring from southwestern Peru and northern Chile southward along the eastern slopes of the Andes to southern Argentina. This species is found primarily in arid and semiarid habitats at elevations from sea level to about 4,500 m. It is not of special conservation status but may be uncommon in some areas.

Nested diets: a novel pattern of individual-level resource use

Many generalist populations may actually be composed of relatively specialist individuals. This ‘individual specialization’ may have important ecological and evolutionary implications. Although this phenomenon has been documented in more than one hundred taxa, it is still unclear how individuals within a population actually partition resources. Here we applied several methods based on network theory to investigate the intrapopulation patterns of resource use in the gracile mouse opossum Gracilinanus microtarsus. We found evidence of significant individual specialization in this species and that the diets of specialists are nested within the diets of generalists. This novel pattern is consistent with a recently proposed model of optimal foraging and implies strong asymmetry in the interactions among individuals of a population.

Monophyly of marsupial intraerythrocytic apicomplexan parasites from South America and Australia

Intraerythrocytic parasites (Apicomplexa: Sarcocystidae) of the South American mouse opossum (Thylamys elegans) from Chile, South America, and of the yellow-bellied glider (Petaurus australis) from Australia were found to be monophyletic using SSU rDNA and partial LSU rDNA sequences. Phylogenetic reconstruction placed both species within the family Sarcocystidae. These intraerythrocytic parasites of marsupials represent an as yet unnamed genus predicted to have bisporocystic oocysts and tetrazoic sporocysts, which is a characteristic feature of all members of the family Sarcocystidae. These results show that erythrocytic parasites share a common ancestor and suggest co-evolution with their vertebrate host.

Delineating geographic boundaries of the woolly mouse opossums, Micoureus demerarae and Micoureus paraguayanus (Didelphimorphia: Didelphidae)

This paper reports on molecular classification of the woolly mouse opossum, Micoureus spp., in the southeastern Atlantic Forest in Brazil, a hotspot of critically threatened biodiversity. Phylogenetic analysis and character-based diagnosis were done using DNA sequences from the mitochondrial cytochrome b gene and cytochrome c oxidase subunit I genes, and exon 6 of the nuclear dentine matrix protein 1 gene (DMP1). Although the nuclear DMP1 gene showed insufficient genetic variation for species diagnosis, the mtDNA analyses resulted in the robust grouping of samples of the M. paraguayanus/M. demerarae complex into three clades with distinct DNA sequence diagnostics for the species units in this study. The results support the species status of M. paraguayanus (Tate in Am Mus Novit 493: 1–13, 1931), which has a geographic distribution in the Atlantic Forest from the North and Northeast of Minas Gerais state in Brazil, going south along the coastal region of Brazil, to Paraguay and Argentina. Evidence of the boundary for this species and the provided diagnostics should facilitate and improve accuracy of studies that have been done in critical threatened fragments of the Atlantic Forest, especially in Minas Gerais and Bahia states, Brazil.

Ocorrência de Giardia, Cryptosporidium e microsporídios em animais silvestres em área de desmatamento no Estado de São Paulo, Brasil

A ocorrência de Giardia, Cryptosporidium e microsporídios foi investigada por meio da análise de 98 amostras fecais de animais silvestres capturados em uma área de desmatamento para a construção das barragens de Paraitinga e Biritiba, localizadas nos Municípios de Mogi das Cruzes, Salesópolis e Biritiba-Mirim, no Estado de São Paulo. As amostras foram obtidas de 46 roedores, 21 marsupiais, 16 sapos, nove morcegos, três primatas e três lagartos. As técnicas de centrífugo-flutuação com sulfato de zinco, de Kinyoun e a coloração de Gram-Chromotrope foram utilizadas, respectivamente, para a pesquisa de Giardia, de Cryptosporidium e de microsporídios. O total de animais parasitados por um dos protozoários investigados foi de 17,35% (17/98). Cistos de Giardia foram encontrados em amostras fecais de dois pequenos roedores da espécie Coendou villosus (ouriço-cacheiro). Os três animais positivos para Cryptosporidium foram roedores das espécies Akodon montensis, Thaptomys nigrita (ambos conhecidos como ratos do mato) e Sciurus aestuans (serelepe ou caxinguelê). Esporos de microsporídios foram encontrados nas fezes de 12 animais, sendo seis roedores das espécies Oligoryzomys sp.(um), Akodon montensis (três) e Coendou villosus (dois), três marsupiais pertencentes às espécies Didelphis aurita (dois) e Marmosops incanus (um) e três morcegos da espécie Diphylla ecaudata. Este é o primeiro relato de microsporidiose em animais silvestres no Brasil. A presente investigação enfatiza a importância de animais silvestres, particularmente pequenos mamíferos, como potenciais fontes de infecção desses protozoários para outras populações animais, incluindo o homem, em áreas de desmatamento.

Phylogenetic Analyses of Postcranial Skeletal Morphology in Didelphid Marsupials

In this study I provide a phylogenetic hypothesis for didelphid Marsupials including a suite of 114 postcranial characters. The postcranial evidence was cladistically analyzed separately and concatenated with a nonmolecular data set previously published (71 cranio-dental-external characters). A combined analysis was done including published IRBP (interphotoreceptor retinoid binding protein, 1158 bp), DMP-1 (dentin matrix protein 1, 1176 bp), and RAG-1 (recombinase-activating gene, 2790 bp) sequences to the nonmolecular data set. In order to compare and evaluate the influence of the inclusion of postcranial morphology to previous hypotheses, the taxon sampling of didelphine ingroup was almost similar to the one used in recent series of papers on didelphid phylogeny. The postcranial information includes 48 characters from the axial skeleton, 37 from the anterior limb, and 29 from the posterior limb. I present anatomical descriptions for each postcranial character, adding details of different conditions observed among didelphine ingroup, as well as some functional implications. Different hypotheses that are discussed as polymorphic characters are alternatively treated as composite entries (CO) and transformation series (TS) in morphological and combined analyses. Different codings of polymorphic postcranial characters produce topologies that in general are not contradictory. The principal difference is the loss of resolution of trees in TS analysis, compared to CO analysis in postcranial evidence, whereas the support values were in general low in both codings. The topology obtained from postcranial evidence supported some already recovered relationships, such as the monophyly of the large opossums (Didelphis, Philander, Chironectes, Lutreolina, and Metachirus), and several polytypic groups such as Didelphis, Monodelphis, Marmosops, Thylamys, Micoureus, and Philander. Additionally, the intermediate position of Hyladelphys between calorumyines and didelphines is kept in CO analysis. The inclusion of the postcranial data set to previous nonmolecular evidence causes little incongruence, although some modifications in the topology and support values were detected. The effect of different codings of polymorphic characters was similar respect to the postcranial-only data set. In this case, the topology obtained with CO analysis was also notably better resolved than TS analysis. Similarly to the postcranial-only analysis, the topologies obtained in the total morphological evidence applying the two kinds of codings are highly congruent, but the TS treatment seemed not to contribute to retention of more phylogenetic information, since the CO analysis was better resolved. The relationships obtained adding the postcranial evidence to published combined data set (i.e., morphology, IRBP, DMP-1, and RAG-1 sequences) were mostly better resolved and supported in the CO coding than the morphological analyses, although the TS coding causes loss of resolution in the strict consensus. In this sense, some strong differences on deep branch topology can be detected depending on the treatment applied to polymorphic entries and partitioned analyses (e.g., phylogenetic condition of the mouse opossums, nodes C and B). Including the postcranial evidence in the total data set, I also recovered the intermediate position of Hyladelphys, but never the distantly related clades recently recovered by the inclusion of RAG-1 sequences (clades B I in Gruber, K.F., R.S. Voss, and S.A. Jansa. 2007. Base-compositional heterogeneity in the RAG1 locus among didelphid marsupials: implications for phylogenetic inference and the evolution of GC content. Systematic Biology 56: 1–14). However, the position of Metachirus nudicaudatus and Tlacuatzin canescens is highly affected. Excluding the last gene, the partitioned combined analysis considering postcranial evidence was highly congruent with previous IRBP, morphology, and combined topologies, especially in the TS analysis, w

Metabolic, Ventilatory, and Hygric Physiology of the Gracile Mouse Opossum (Gracilinanus agilis)

We present the first complete study of basic laboratory-measured physiological variables (metabolism, thermoregulation, evaporative water loss, and ventilation) for a South American marsupial, the gracile mouse opossum (Gracilinanus agilis). Body temperature (T(b)) was thermolabile below thermoneutrality (T(b) = 33.5 degrees C), but a substantial gradient between T(b) and ambient temperature (T(a)) was sustained even at T(a) = 12 degrees C (T(b) = 30.6 degrees C). Basal metabolic rate of 1.00 mL O2 g(-1) h(-1) at T(a) = 30 degrees C conformed to the general allometric relationship for marsupials, as did wet thermal conductance (5.7 mL O2 g(-1) h(-1) degrees C(-1)). Respiratory rate, tidal volume, and minute volume at thermoneutrality matched metabolic demand such that O2 extraction was 12.4%, and ventilation increased in proportion to metabolic rate at low T(a). Ventilatory accommodation of increased metabolic rate at low T(a) was by an increase in respiratory rate rather than by tidal volume or O2 extraction. Evaporative water loss at the lower limit of thermoneutrality conformed to that of other marsupials. Relative water economy was negative at thermoneutrality but positive below T(a) = 12 degrees C. Interestingly, the Neotropical gracile mouse opossums have a more positive water economy at low T(a) than an Australian arid-zone marsupial, perhaps reflecting seasonal variation in water availability for the mouse opossum. Torpor occurred at low T(a), with spontaneous arousal when T(b) > 20 degrees C. Torpor resulted in absolute energy and water savings but lower relative water economy. We found no evidence that gracile mouse opossums differ physiologically from other marsupials, despite their Neotropical distribution, sympatry with placental mammals, and long period of separation from Australian marsupials.

Rediscovery and redescription of Marmosa (Stegomarmosa) andersoni Pine (Mammalia: Didelphimorphia: Didelphidae), an endemic Peruvian mouse opossum, with a reassessment of its affinities

Rediscovery and redescription of Marmosa (Stegomarmosa) andersoni Pine (Mammalia: Didelphimorphia: Didelphidae), an endemic Peruvian mouse opossum, with a reassessment of its affinities

A Sarcocystid Misidentified as Hepatozoon didelphydis: Molecular Data from a Parasitic Infection in the Blood of the Southern Mouse Opossum (Thylamys elegans) from Chile

The blood of 21 adult South American mouse opossums (Thylamys elegans) captured from April through August of 2005 in central Chile was examined for parasites. Light microscopic analysis of blood smears initially suggested that a highly pleomorphic Hepatozoon species typical of American opossums was infecting erythrocytes. Unexpectedly, amplification by PCR and sequencing of a DNA fragment of the small subunit rDNA combined with phylogenetic analyses indicated that the parasite is not a member of the suborder Adeleorina, which includes the Haemogregarina and Hepatozoon species, but that it is a clearly distinct member of the suborder Eimeriorina, which includes the cyst-forming family Sarcocystidae. Therefore, a reclassification of this unusual intraerythrocytic apicomplexan will require additional life cycle, microscopic, and molecular analyses.

The Mexican mouse opossum ( Marmosa mexicana) as a flower visitor at a neotropical palm

The Mexican mouse opossum ( Marmosa mexicana) as a flower visitor at a neotropical palm

Endoparasites of Fat-Tailed Mouse Opossums (Thylamys: Didelphidae) from Northwestern Argentina and Southern Bolivia, with the Description of a New Species of Tapeworm

The parasite fauna of 2 species of fat-tailed mouse opossums from northwestern Argentina is herein presented. Five species of helminths were found, i.e., Pterygodermatites kozeki, Hoineffia simplispicula, Oligacanthorhynchus sp., and a new species of tapeworm, Mathevotaenia sanmartini n. sp. (Cyclophyllidea: Anoplocephalidae). The new species is characterized by a calyciform scolex, relatively few testes (32), and a long cirrus sac; it occurs in fat-tailed mouse opossums at localities above 4,000 m. Those characters make it different from 6 species known to occur in marsupials from the New World, and from other species occurring in armadillos and bats. Didelphoxyuris thylamisis, H. simplicispicula, and Oligacanthorhynchus sp. appear to occur in marmosas from the Yungas region. In contrast, both P. kozeki and M. sanmartini n. sp. appear to occur exclusively in the Puna.

Genomic evidence for a large-Z effect

The 'large-X effect' suggests that sex chromosomes play a disproportionate role in adaptive evolution. Theoretical work indicates that this effect may be most pronounced in genetic systems with female heterogamety under both good-genes and Fisher's runaway models of sexual selection (males ZZ, females ZW). Here, I use a comparative genomic approach (alignments of several thousands of chicken-zebra finch-human-mouse-opossum orthologues) to show that avian Z-linked genes are highly overrepresented among those bird-mammalian orthologues that show evidence of accelerated rate of functional evolution in birds relative to mammals; the data suggest a twofold excess of such genes on the Z chromosome. A reciprocal analysis of genes accelerated in mammals found no evidence for an excess of X-linkage. This would be compatible with theoretical expectations for differential selection on sex-linked genes under male and female heterogamety, although the power in this case was not sufficient to statistically show that 'large-Z' was more pronounced than 'large-X'. Accelerated Z-linked genes include a variety of functional categories and are characterized by higher non-synonymous to synonymous substitution rate ratios than both accelerated autosomal and non-accelerated genes. This points at a genomic 'large-Z effect', which is widespread and of general significance for adaptive divergence in birds.

Selection, diversity and evolutionary patterns of the MHC class II DAB in free-ranging Neotropical marsupials

BackgroundResearch on the genetic architecture and diversity of the MHC has focused mainly on eutherian mammals, birds and fish. So far, studies on model marsupials used in laboratory investigations indicated very little or even no variation in MHC class II genes. However, natural levels of diversity and selection are unknown in marsupials as studies on wild populations are virtually absent. We used two endemic South American mouse opossums, Gracilinanus microtarsus and Marmosops incanus, to investigate characteristic features of MHC selection. This study is the first investigation of MHC selection in free-ranging Neotropical marsupials. In addition, the evolutionary history of MHC lineages within the group of marsupials was examined.ResultsG. microtarsus showed extensive levels of MHC diversity within and among individuals as 47 MHC-DAB alleles and high levels of sequence divergence were detected at a minimum of four loci. Positively selected codon sites were identified, of which most were congruent with human antigen binding sites. The diversity in M. incanus was rather low with only eight observed alleles at presumably two loci. However, these alleles also revealed high sequence divergence. Again, positive selection was identified on specific codon sites, all congruent with human ABS and with positively selected sites observed in G. microtarsus. In a phylogenetic comparison alleles of M. incanus interspersed widely within alleles of G. microtarsus with four alleles being present in both species.ConclusionOur investigations revealed extensive MHC class II polymorphism in a natural marsupial population, contrary to previous assumptions. Furthermore, our study confirms for the first time in marsupials the presence of three characteristic features common at MHC loci of eutherian mammals, birds and fish: large allelic sequence divergence, positive selection on specific sites and trans-specific polymorphism.

Rediscovery and redescription of Marmosa (Stegomarmosa) andersoni Pine (Mammalia: Didelphimorphia: Didelphidae), an endemic Peruvian mouse opossum, with a reassessment of its affinities

Mouse opossums of the genus Marmosa Gray (Didelphidae) represent a complex of taxa with poorly understood affinities. Species now placed within this genus are mostly the leftovers from previous taxonomic arrangements. Even the most recent and complete revisions have not fully resolved the relationships among Marmosa and the many taxa previously included in Marmosa or listed as synonyms of it. Herein, we review and discuss one of these taxa, Stegomarmosa, based on new specimens that significantly increase our knowledge of the morphological diversification of the group. Until recently, this genus/subgenus has been known only from a single specimen taken more than 50 years ago in southeastern Peru. In 1997-1998, six additional specimens were collected at two little-separated localities almost 200 km NW of the type locality. We include a detailed diagnosis of the genus-group Stegomarmosa and its type species, M. andersoni, and update the distribution for and provide new information on the natural history of the latter. We also discuss published claims, concerning geographic range, that may be inaccurate and misleading. Finally, we scored the morphological characters used in the most recent phylogenetic analyses of the didelphids, in order to explore the affinities of M. andersoni and to determine the distinctiveness of the taxon Stegomarmosa.

PERMANENT GENETIC RESOURCES: Characterization of eight microsatellite loci in the woolly mouse opossum, Micoureus paraguayanus, isolated from Micoureus demerarae

Eight novel microsatellite markers were isolated from the woolly mouse opossum from the Amazon Forest in Peru, Micoureus demerarae, using a partial genomic DNA library and an enrichment protocol. These loci were polymorphic in M. demerarae and Micoureus paraguayanus populations from the Atlantic Forest in Brazil with the number of alleles ranging from two to 23. Those eight loci plus another five already described for M. paraguayanus will allow for the evaluation of genetic diversity of populations from the 'Rio Doce' Park, one of the last Atlantic Forest fragments in Minas Gerais state, Brazil.

Bayesian Capture-Recapture Analysis: An Application in Modeling Semelparity of a Neotropical Didelphid Marsupial

We develop a series of Bayesian statistical models for estimating survival of a neotropic didelphid marsupial, the Brazilian gracile mouse opossum (Gracilinanus microtarsus). These models are based on the Cormack–Jolly–Seber model (Cormack, 1964; Jolly 1965; Seber 1965) with both survival and recapture rates expressed as a function of covariates using a logit link. The proposed models allow taking into account heterogeneity in capture probability caused by the existence of different groups of individuals in the population. The models were applied to two cohorts (Cohort, 2000, 2001) with the first one including 14 and the second one 15 sampling occasions. The best models for each of the cohorts indicate that G. microtarsus is best described as partially semelparous, a condition in which mortality after the first mating is high but graded over time, with a fraction of males surviving for a second breeding season (Boonstra, 2005).

Allometry, Antilog Transformations, and the Perils of Prediction on the Original Scale

Previous article No AccessErratumAllometry, Antilog Transformations, and the Perils of Prediction on the Original ScaleJack P. Hayes, and J. Scott Shonkwiler Jack P. HayesPhysiological and Biochemical Zoology 79:665–674 (2006) Search for more articles by this author , and J. Scott ShonkwilerPhysiological and Biochemical Zoology 79:665–674 (2006) Search for more articles by this author Physiological and Biochemical Zoology 79:665–674 (2006)Original articleAllometry, Antilog Transformations, and the Perils of Prediction on the Original ScalePDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by Physiological and Biochemical Zoology Volume 80, Number 5September/October 2007 Sponsored by Division of Comparative Physiology and Biochemistry, Society for Integrative and Comparative Biology Article DOIhttps://doi.org/10.1086/520866 Views: 9Total views on this site Citations: 12Citations are reported from Crossref © 2007 by The University of Chicago. All rights reserved.PDF download Crossref reports the following articles citing this article:J. M. Barker, C. E. Cooper, P. C. Withers, and S. C. Nicol Reexamining Echidna Physiology: The Big Picture for Tachyglossus aculeatus acanthion, Physiological and Biochemical Zoology 89, no.33 (Apr 2016): 169–181.https://doi.org/10.1086/686716Hannah Pusey, Christine E. Cooper, Philip C. Withers Metabolic, hygric and ventilatory physiology of the red-tailed phascogale (Phascogale calura; Marsupialia, Dasyuridae): Adaptations to aridity or arboreality?, Mammalian Biology 78, no.66 (Nov 2013): 397–405.https://doi.org/10.1016/j.mambio.2012.11.008Justine M. Barker, Christine E. Cooper, Philip C. Withers, Ariovaldo P. Cruz-Neto Thermoregulation by an Australian murine rodent, the ash-grey mouse (Pseudomys albocinereus), Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology 163, no.3-43-4 (Nov 2012): 336–342.https://doi.org/10.1016/j.cbpa.2012.07.011Philip C. Withers, Christine E. Cooper, Roberto F. Nespolo Evaporative water loss, relative water economy and evaporative partitioning of a heterothermic marsupial, the monito del monte ( Dromiciops gliroides ), Journal of Experimental Biology 215, no.1616 (Aug 2012): 2806–2813.https://doi.org/10.1242/jeb.070433A.J. Munn, C.E. Cooper, B. Russell, T.J. Dawson, S.R. McLeod, S.K. Maloney Energy and water use by invasive goats (Capra hircus) in an Australian rangeland, and a caution against using broad-scale allometry to predict species-specific requirements, Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology 161, no.22 (Feb 2012): 216–229.https://doi.org/10.1016/j.cbpa.2011.10.027Christine E. Cooper, Philip C. Withers Comparative physiology of Australian quolls (Dasyurus; Marsupialia), Journal of Comparative Physiology B 180, no.66 (Mar 2010): 857–868.https://doi.org/10.1007/s00360-010-0452-3C. E. Cooper, P. C. Withers, A. P. Cruz-Neto Metabolic, ventilatory, and hygric physiology of a South American marsupial, the long-furred woolly mouse opossum, Journal of Mammalogy 91, no.11 (Feb 2010): 1–10.https://doi.org/10.1644/09-MAMM-A-138R.1S. Schmidt, P.C. Withers, C.E. Cooper Metabolic, ventilatory and hygric physiology of the chuditch (Dasyurus geoffroii; Marsupialia, Dasyuridae), Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology 154, no.11 (Sep 2009): 92–97.https://doi.org/10.1016/j.cbpa.2009.05.002Christine Elizabeth Cooper, Ariovaldo P. Cruz-Neto Metabolic, hygric and ventilatory physiology of a hypermetabolic marsupial, the honey possum (Tarsipes rostratus), Journal of Comparative Physiology B 179, no.66 (Apr 2009): 773–781.https://doi.org/10.1007/s00360-009-0358-0Philip C. Withers, Christine E. Cooper Thermal, metabolic, hygric and ventilatory physiology of the sandhill dunnart (Sminthopsis psammophila; Marsupialia, Dasyuridae), Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology 153, no.33 (Jul 2009): 317–323.https://doi.org/10.1016/j.cbpa.2009.03.006P. C. Withers, C. E. Cooper Thermal, Metabolic, and Hygric Physiology of the Little Red Kaluta, Dasykaluta rosamondae (Dasyuromorphia: Dasyuridae), Journal of Mammalogy 90, no.33 (Jun 2009): 752–760.https://doi.org/10.1644/08-MAMM-A-286R.1C. E. Cooper, P. C. Withers, and A. P. Cruz‐Neto Metabolic, Ventilatory, and Hygric Physiology of the Gracile Mouse Opossum (Gracilinanus agilis) C. E. Cooper, P. C. Withers, and A. P. Cruz‐Neto, Physiological and Biochemical Zoology 82, no.22 (Jul 2015): 153–162.https://doi.org/10.1086/595967Related articlesAllometry, Antilog Transformations, and the Perils of Prediction on the Original Scale19 Jul 2015Physiological and Biochemical Zoology

22.P3. Reproductive energetics in gracile mouse opossum: Lean mass and basal metabolic rate effects in males and females

22.P3. Reproductive energetics in gracile mouse opossum: Lean mass and basal metabolic rate effects in males and females

Demographic consequences of population subdivision on the long-furred woolly mouse opossum (Micoureus paraguayanus) from the Atlantic Forest

Habitat destruction and fragmentation severely affected the Atlantic Forest. Formerly contiguous populations may become subdivided into a larger number of smaller populations, threatening their long-term persistence. The computer package VORTEX was used to simulate the consequences of habitat fragmentation and population subdivision on Micoureus paraguayanus, an endemic arboreal marsupial of the Atlantic Forest. Scenarios simulated hypothetical populations of 100 and 2000 animals being partitioned into 1–10 populations, linked by varying rates of inter-patch dispersal, and also evaluated male-biased dispersal. Results demonstrated that a single population was more stable than an ensemble of populations of equal size, irrespective of dispersal rate. Small populations (10–20 individuals) exhibited high instability due to demographic stochasticity, and were characterized by high rates of extinction, smaller values for metapopulation growth and larger fluctuations in population size and growth rate. Dispersal effects on metapopulation persistence were related to the size of the populations and to the sexes that were capable of dispersing. Male-biased dispersal had no noticeable effects on metapopulation extinction dynamics, whereas scenarios modelling dispersal by both sexes positively affected metapopulation dynamics through higher growth rates, smaller fluctuations in growth rate, larger final metapopulation sizes and lower probabilities of extinction. The present study highlights the complex relationships between metapopulation size, population subdivision, habitat fragmentation, rate of inter-patch dispersal and sex-biased dispersal and indicates the importance of gaining a better understanding of dispersal and its interactions with correlations between disturbance events.

The occurrence of the mouse opossum Marmosops ocellatus (Marsupialia, Didelphidae) in western Brazil

The aim of this report is to furnish a new record on the south-eastern distributional limits of a small marsupial, Marmosops ocellatus (formerly M. dorothea), in midwestern Brazil and update its geographic distribution in this country. The new locality where the species was registered is the Urucum mountains, in the vicinity of the Santa Cruz hill (coordinates: 191120S,571340W), Corumba municipality, Mato Grosso do Sul state (MS), centralwestern Brazil (Fig. 1). Urucum is covered mainly by semideciduous forests (IBGE 1992; Pott et al. 2000), and is near the Paraguay River, at its right margin. The species was trapped in pitfalls (108 l) at three different mountainous altitudes (200, 500 and 800m), during monthly surveys during 2001 and 2002 (July–June). During these surveys, 15 individuals of M. ocellatus were trapped in the study site, one at 200m, seven at 500m and seven at 800m. Seven individuals were males and eight were females. Their body mass averaged 38.3 g for adult males (range: 31.0–51.0; N=4) and 26.2 g for adult females (range: 23.0–30.0; N=5), revealing an apparent sexual dimorphism. The specimens were deposited in the Museu de Zoologia da Universidade de Sao Paulo (MZUSP 32877) and in the Mammal Collection of the Federal University of Santa Maria