Of marsupials and men: "Backdoor" dihydrotestosterone synthesis in male sexual differentiation

Following development of the fetal bipotential gonad into a testis, male genital differentiation requires testicular androgens. Fetal Leydig cells produce testosterone that is converted to dihydrotestosterone in genital skin, resulting in labio-scrotal fusion. An alternative 'backdoor' pathway of dihydrotestosterone synthesis that bypasses testosterone has been described in marsupials, but its relevance to human biology has been uncertain. The classic and backdoor pathways share many enzymes, but a 3α-reductase, AKR1C2, is unique to the backdoor pathway. Human AKR1C2 mutations cause disordered sexual differentiation, lending weight to the idea that both pathways are required for normal human male genital development. These observations indicate that fetal dihydrotestosterone acts both as a hormone and as a paracrine factor, substantially revising the classic paradigm for fetal male sexual development.

Genera mammalium: Monotremata, Marsupialia.

At head of title: Junta para Ampliación de Estudios é Investigaciones Científicas./ Museo Nacional de Ciencias Naturales.

Speciation of Antechinus stuartii and A. subtropicus (Marsupialia : Dasyuridae) in eastern Australia: molecular and morphological evidence

This paper evaluates the systematic status of the Antechinus populations of northern New South Wales and southern Queensland, using a combined morphological and molecular (allozymes and mitochondrial DNA) approach. Analysis of the d-loop section of the mitochondrial DNA control region revealed two highly supported clades within A. stuartii sensu lato that were sympatric in the Border Ranges of northern New South Wales. However, genetic distances between these clades were small ( approximately 3%), indicating that time of divergence was probably relatively recent. Allozyme electrophoresis also showed very small differences between clades/ species. Analyses of cranial and dental characters showed that the members of each of these clades differed morphologically and that the clades corresponded to A. stuartii and the recently described A. subtropicus. The combined results support the species status of A. stuartii and A. subtropicus, and suggest that speciation was likely a result of a recent vicariant event.

The status of hollow-bearing trees required for the conservation of arboreal marsupials in the dry sclerophyll forests of south-east Queensland, Australia

At 38 sites in the dry sclerophyll forests of south-east Queensland, Australia, hollow-bearing trees were studied to determine the effects of past forestry practices on their density, size and spatial distribution. The density of hollow-bearing trees was reduced at sites that had been altered by poisoning and ringbarking of unmerchantable trees. This was especially the case for living hollow-bearing trees that were now at densities too low to support the full range of arboreal marsupials. Although there are presently enough hollow-bearing stags (i.e., dead hollow-bearing trees) to provide additional denning and nesting opportunities, the standing life of these hollow-bearing stags is lower than the living counterparts which means denning and nesting sites may be limited in the near future. The mean diameter at breast height (DBH) of hollow-bearing stags was significantly less than that of living hollow-bearing trees. This indicated that many large hollow-bearing stags may have a shorter standing life than smaller hollow-bearing stags. Hollow-bearing trees appear to be randomly distributed throughout the forest in both silviculturally treated and untreated areas. This finding is at odds with the suggestion by some forest managers that hollow-bearing trees should have a clumped distribution in dry sclerophyll forests of south-east Queensland.

Cone topography and spectral sensitivity in two potentially trichromatic marsupials, the quokka (Setonix brachyurus) and quenda (Isoodon obesulus)

The potential for trichromacy in mammals, thought to be unique to primates, was recently discovered in two Australian marsupials. Whether the presence of three cone types, sensitive to short- (SWS), medium-(MWS) and long-(LWS) wavelengths, occurs across all marsupials remains unknown. Here, we have investigated the presence, distribution and spectral sensitivity of cone types in two further species, the quokka (Setonix brachyurus) and quenda (Isoodon obesulus). Immunohistochemistry revealed that SWS cones in the quokka are concentrated in dorso-temporal retina, while in the quenda, two peaks were identified in naso-ventral and dorso-temporal retina. In both species, MWS/LWS cone spatial distributions matched those of retinal ganglion cells. Microspectrophotometry (MSP) confirmed that MWS and LWS cones are spectrally distinct, with mean wavelengths of maximum absorbance at 502 and 538 nm in the quokka, and at 509 and 551 nm, in the quenda. Although small SWS cone outer segments precluded MSP measurements, molecular analysis identified substitutions at key sites, accounting for a spectral shift from ultraviolet in the quenda to violet in the quokka. The presence of three cone types, along with previous findings in the fat-tailed dunnart and honey possum, suggests that three spectrally distinct cone types are a feature spanning the marsupials.

Early pregnancy factor in marsupials

Maternal recognition of pregnancy in marsupials occurs in more subtle ways than it does in eutherians. For instance, unlike in eutherians, the plasma progesterone profiles of pregnant and non-pregnant animals are similar during the luteal phase. It is typically during the brief luteal phase that both gestation and parturition occur in marsupials. Yet histological and physiological changes have been documented between gravid and non-gravid uteri in certain monovular marsupials and between pregnant and non-pregnant animals in polyovular marsupials. Early pregnancy factor (EPF), a 10.8-kDa serum protein known to be homologous to chaperonin 10, is associated with maternal immunosuppression, embryonic development and pregnancy in eutherian mammals. It has been reported in two Australian marsupials: the dasyurid Sminthopsis macroura and the phalangerid Trichosurus vulpecula. This paper documents its occurrence in the New World didelphid Monodelphis domestica. EPF is detectable by rosette inhibition assay in the peripheral circulation of pregnant but not of non-pregnant or pseudopregnant animals. Our work focuses on the embryo–maternal signalling role of EPF during pregnancy. Because progesterone-driven changes are similar in pregnant and non-pregnant marsupials, these animals are an excellent laboratory model in which to investigate the role of EPF in orchestrating the physiological changes necessary to sustain pregnancy.

Mamíferos não voadores (Mammalia) da Estação Ecológica Serra Geral do Tocantins

A comunidade de mamíferos terrestres foi amostrada em três localidades (1-Mateiros, TO; 2- Rio da Conceição, TO e 3- Formosa do Rio Preto, BA) no interior da Estação Ecológica Serra Geral do Tocantins. Para o registro dos marsupiais e pequenos roedores foram utilizadas armadilhas convencionais (5.396 armadilhas.noite) e armadilhas de queda (5.300 pitfalls.noite) nas diferentes fitofisionomias encontradas, entre elas: campo úmido, campo limpo, campo sujo, campo cerrado, cerrado sensu stricto, cerrado com afloramentos rochosos, mata de galeria e mata de galeria úmida. No caso dos mamíferos de médio e grande porte, foram obtidos registros casuais através de observação direta e evidências indiretas (rastros, fezes, crânios e carcaças de animais encontrados mortos). Foram amostradas 24 espécies de pequenos mamíferos e 17 espécies de mamíferos de médio e grande porte, totalizando 41 espécies para a região. Considerando-se os pequenos mamíferos, a comunidade foi representada por várias espécies raras e de abundância intermediária, e poucas espécies muito abundantes. Os roedores cricetídeos dominaram tanto em número de espécies (14) quanto em abundância (50% da comunidade). As espécies se distribuíram, basicamente, em dois tipos de fisionomias: um grupo esteve restrito aos ambientes florestais, e outro às formações abertas, demonstrando a grande seletividade de hábitats e a importância de se amostrar o mosaico de hábitats presente na região para uma melhor caracterização da diversidade deste grupo de mamíferos. Em termos biogeográficos, a fauna de pequenos mamíferos amostrada apresentou certa sobreposição com a fauna da Caatinga e da Amazônia, evidenciando a importância destes domínios para a composição de espécies das comunidades que habitam a porção norte do Cerrado, além da presença de espécies endêmicas e de distribuição geográfica restrita ao norte do domínio, caracterizando uma comunidade distinta de outras regiões do Cerrado. Em relação aos mamíferos de médio e grande porte, a presença de um elevado número de espécies ameaçadas de extinção (10) também ressalta a importância da preservação desta região.

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.

Random X Inactivation and Extensive Mosaicism in Human Placenta Revealed by Analysis of Allele-Specific Gene Expression along the X Chromosome

Imprinted inactivation of the paternal X chromosome in marsupials is the primordial mechanism of dosage compensation for X-linked genes between females and males in Therians. In Eutherian mammals, X chromosome inactivation (XCI) evolved into a random process in cells from the embryo proper, where either the maternal or paternal X can be inactivated. However, species like mouse and bovine maintained imprinted XCI exclusively in extraembryonic tissues. The existence of imprinted XCI in humans remains controversial, with studies based on the analyses of only one or two X-linked genes in different extraembryonic tissues. Here we readdress this issue in human term placenta by performing a robust analysis of allele-specific expression of 22 X-linked genes, including XIST, using 27 SNPs in transcribed regions. We show that XCI is random in human placenta, and that this organ is arranged in relatively large patches of cells with either maternal or paternal inactive X. In addition, this analysis indicated heterogeneous maintenance of gene silencing along the inactive X, which combined with the extensive mosaicism found in placenta, can explain the lack of agreement among previous studies. Our results illustrate the differences of XCI mechanism between humans and mice, and highlight the importance of addressing the issue of imprinted XCI in other species in order to understand the evolution of dosage compensation in placental mammals.

Glossocercus chelodinae (MacCallum, 1921) n. comb. (Cestoda : Dilepididae) from freshwater turtles in Australia and a redefinition of the genus Bancroftiella Johnston, 1911

Glossocercus chelodinae (MacCallum, 1921) n. comb. is redescribed from fresh material recovered from the intestine of an Australian freshwater turtle, Chelodina expansa. G. chelodinae can be distinguished from all other species of the genus by the shape of its rostellar hooks. it is suggested that this species has colonised fish-eating turtles from fish-eating birds. The morphological relationships among Parvitaenia, Bancroftiella and Glossocercus are discussed. The diagnosis of Bancroftiella is amended and marsupials are eliminated as hosts. Bancroftiella sudarikovi Spasskii & Yurpalova, 1970 becomes a synonym of Glossocercus glandularis (Fuhrmann, 1905); only B. tennis Johnston, 1911, the type-species, and B. ardeae Johnston, 1911 remain in the genus.

Morphology of the thyroid in coastal and noncoastal populations of the koala (Phascolarctos cinereus) in Queensland

The gross morphology, histology, and ultrastructure of the thyroid gland of the koala, Phascolarctos cinereus, is described. Generally, the glands were found to contain large-diameter follicles in association with an epithelium of low height. Morphometric analysis demonstrated a high relative thyroid weight (0.3 +/- 0.2 g/kg) for koalas compared with the 0.07-0.24 g/kg typical of eutherian mammals and 0.03-0.1 g/kg found in other marsupials. The relative thyroid weight of glands (0.33 +/- 0.21 g/kg) from the coastal population (less than 28 km from the coastline) was found to be significantly higher (ANOVA: P = 0.007, significant at the 1% level) than that for glands (0.21 +/- 0.11 g/kg) of noncoastal koalas (greater than 28 km from the coastline). Follicle size was positively correlated (at the 0.1% level) with relative thyroid weight in the overall koala sample. The presence of C cells, occurring singly in the epithelial layer, was demonstrated in electron micrographs. Structural features such as low epithelial height, large follicle length and width, and large intercellular spaces in association with low concentrations of free TS (3.3 +/- 2.1 pM) and free T-3 (1.4 +/- 0.9 pM) as reported previously (Lawson et al., 1996) are consistent with an unusually low level of glandular activity in the koala thyroid even though iodine concentrations in the thyroid gland [4.7 +/- 1.6 mg/g (dry weight)] as well as leaf [0.8 +/- 0.3 mu g (dry weight)] and soil samples [3.8 mu g/g (dry weight)] from the koalas' habitat appear unremarkable. (C) 1998 Academic Press.