RESUMO

O eletrocardiograma (ECG) é um importante método diagnóstico, essencial para determinar o ritmo e o funcionamento elétrico do coração. Os gambás (D. albiventris) frequentemente são atendidos nos Centros de Triagem de Animais Silvestres (CETAS), contudo pouco se sabe sobre o sistema cardiovascular dessa espécie. Dessa forma, o objetivo foi estabelecer valores de referência dos parâmetros eletrocardiográficos dessa espécie. Foram utilizados 32 filhotes, considerados hígidos nos exames clínicos geral e específico. Avaliaram-se a frequência cardíaca, o ritmo, a morfologia, a amplitude e a duração das ondas P, o complexo QRS e T, a duração dos intervalos PR e QT e o segmento ST. A frequência cardíaca média foi de 214 batimentos por minuto (bpm), o ritmo sinusal mostrou-se normal e houve arritmia sinusal em 25% dos pacientes. O eixo médio foi de 40º(QRS)e 47º (P). A onda P apresentou morfologia positiva (81,3%) e negativa (18,7%), amplitude de 0,03mV (±0,01) e duração de 0,04s (±0,04). O complexo QRS apresentou morfologia QRS ou RS (31%) e duração de 0,05s (±0,06). A amplitude de Q foi de -0,04mV (±0,05), a de R foi 0,23mV (±0,16) e S -0,07mV (±0,08). Já a onda T apresentou morfologia variada, amplitude de 0,04mV (±0,04) e duração de 0,04s (±0,09). O intervalo PR obteve duração de 0,05s (±0,08), QT com intervalo entre 0,08 e 0,21 e o segmento ST médio de 0,05s (±0,02). Dessa forma, observou-se que foi possível realizar o ECG em gambás filhotes e que o sexo e o peso não influenciaram no traçado obtido. Os resultados diferiram de cães, gatos e de outras espécies de gambás.

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The establishment of parameters for tear production in different species is important for better understanding eye´s health and is one of the components of the ophthalmic semiological technique. Particularities derived from the anatomophysiology of non-domestic species induce the search for more reliable methodologies. The aim was to evaluate and compare tear production of white-eared opossum (Didelphis albiventris) and Brazilian common opossum (Didelphis aurita) by three different methods. Fifteen individuals of each species, juveniles, healthy, of both sexes, with 60 to 90 days of life, were physically restrained. Phenol red thread test (PRTT), endodontic absorbent paper point tear test (EAPPTT) and modified -Schirmer tear test (mSTT) were performed. PRTT was the most difficult to perform because of the wire malleability, while EAPPTT was more feasible for both species. The median ± semi-quartile range for PRTT were 19.79±2.61mm/15 "and 5.22±2.92mm/15", for EAPPTT were 16.25±1.82mm/min and 10.9±3.04mm/min, and for STTm were 0±1.63mm/min and 0±1.63mm/min for white-eared opossum and Brazilian common opossum respectively. There was no difference between the right and left eye neither sex. A significant difference was obtained for the same test to different species. No significant correlation was found between the tests for both species. The description of tear production parameters for juvenile white-eared opossum and Brazilian common opossum may be used as a tool, which will allow the early diagnosis of ocular diseases.(AU)

O estabelecimento do parâmetro de produção lacrimal nas diferentes espécies é importante para o entendimento da saúde do olho e é um dos componentes da semiotécnica oftálmica. Particularidades derivadas da anatomofisiologia das espécies não domésticas induzem a busca de metodologias que sejam mais fidedignas aos parâmetros. Objetivou-se com este estudo avaliar e comparar a produção lacrimal de gambás-de-orelha-branca (Didelphis albiventris) e gambás-de-orelha-preta (Didelphis aurita) por três diferentes métodos. Quinze indivíduos de cada espécie, juvenis, hígidos, de ambos os sexos, com 60 a 90 dias de vida, foram contidos fisicamente para realização do teste lacrimal do vermelho de fenol (TLVF), da ponta de papel absorvente estéril e do teste lacrimal de Schirmer modificado (TLSm). O TLVF foi o mais difícil de ser executado devido à maleabilidade do fio, enquanto a TEPA se mostrou mais exequível para ambas as espécies. A mediana ± intervalo semi-interquartil para o TLVF foi de 19,79±2,61mm/15" e 5,22±2,92mm/15", para a TEPA foram de 16,25±1,82mm/min e 10,93±3,04mm/min, e para o TLSm foram de 0±1,63mm/min e 0±1,63mm/min, para gambás-de-orelha-branca e gambás-de-orelha-preta, respectivamente. Não houve diferença entre o olho direito e esquerdo e nem quanto ao sexo. Obteve-se diferença significativa para um mesmo teste entre as espécies. Não foi encontrada correlação significativa entre os testes para ambas as espécies. A quantificação da porção aquosa da lágrima poderá auxiliar no diagnóstico precoce de doenças oculares nas espécies estudadas.(AU)

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RESUMO

The establishment of parameters for tear production in different species is important for better understanding eye´s health and is one of the components of the ophthalmic semiological technique. Particularities derived from the anatomophysiology of non-domestic species induce the search for more reliable methodologies. The aim was to evaluate and compare tear production of white-eared opossum (Didelphis albiventris) and Brazilian common opossum (Didelphis aurita) by three different methods. Fifteen individuals of each species, juveniles, healthy, of both sexes, with 60 to 90 days of life, were physically restrained. Phenol red thread test (PRTT), endodontic absorbent paper point tear test (EAPPTT) and modified -Schirmer tear test (mSTT) were performed. PRTT was the most difficult to perform because of the wire malleability, while EAPPTT was more feasible for both species. The median ± semi-quartile range for PRTT were 19.79±2.61mm/15 "and 5.22±2.92mm/15", for EAPPTT were 16.25±1.82mm/min and 10.9±3.04mm/min, and for STTm were 0±1.63mm/min and 0±1.63mm/min for white-eared opossum and Brazilian common opossum respectively. There was no difference between the right and left eye neither sex. A significant difference was obtained for the same test to different species. No significant correlation was found between the tests for both species. The description of tear production parameters for juvenile white-eared opossum and Brazilian common opossum may be used as a tool, which will allow the early diagnosis of ocular diseases.(AU)

O estabelecimento do parâmetro de produção lacrimal nas diferentes espécies é importante para o entendimento da saúde do olho e é um dos componentes da semiotécnica oftálmica. Particularidades derivadas da anatomofisiologia das espécies não domésticas induzem a busca de metodologias que sejam mais fidedignas aos parâmetros. Objetivou-se com este estudo avaliar e comparar a produção lacrimal de gambás-de-orelha-branca (Didelphis albiventris) e gambás-de-orelha-preta (Didelphis aurita) por três diferentes métodos. Quinze indivíduos de cada espécie, juvenis, hígidos, de ambos os sexos, com 60 a 90 dias de vida, foram contidos fisicamente para realização do teste lacrimal do vermelho de fenol (TLVF), da ponta de papel absorvente estéril e do teste lacrimal de Schirmer modificado (TLSm). O TLVF foi o mais difícil de ser executado devido à maleabilidade do fio, enquanto a TEPA se mostrou mais exequível para ambas as espécies. A mediana ± intervalo semi-interquartil para o TLVF foi de 19,79±2,61mm/15" e 5,22±2,92mm/15", para a TEPA foram de 16,25±1,82mm/min e 10,93±3,04mm/min, e para o TLSm foram de 0±1,63mm/min e 0±1,63mm/min, para gambás-de-orelha-branca e gambás-de-orelha-preta, respectivamente. Não houve diferença entre o olho direito e esquerdo e nem quanto ao sexo. Obteve-se diferença significativa para um mesmo teste entre as espécies. Não foi encontrada correlação significativa entre os testes para ambas as espécies. A quantificação da porção aquosa da lágrima poderá auxiliar no diagnóstico precoce de doenças oculares nas espécies estudadas.(AU)

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Mammalian torpor is a phenotype characterized by a controlled decline of metabolic rate, generally followed by a reduction in body temperature. During arousal from torpor, both metabolic rate and body temperature rapidly returns to resting levels. Metabolic rate reduction experienced by torpid animals is triggered by active suppression of mitochondrial respiration, which is rapidly reversed during rewarming process. In this study, we analyzed the changes in the maximal activity of key enzymes related to electron transport system (complexes I, III and IV) in six tissues of torpid, arousing and euthermic Chilean mouse-opossums (Thylamys elegans). We observed higher maximal activities of complexes I and IV during torpor in brain, heart and liver, the most metabolically active organs in mammals. On the contrary, higher enzymatic activities of complexes III were observed during torpor in kidneys and lungs. Moreover, skeletal muscle was the only tissue without significant differences among stages in all complexes evaluated, suggesting no modulation of oxidative capacities of electron transport system components in this thermogenic tissue. In overall, our data suggest that complexes I and IV activity plays a major role in initiation and maintenance of metabolic suppression during torpor in Chilean mouse-opossum, whereas improvement of oxidative capacities in complex III might be critical to sustain metabolic machinery in organs that remains metabolically active during torpor.

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Despite the singular morphology of the male genital system and the different reproductive strategies of marsupials, little emphasis has been given to the testis morphology and spermatogenic kinetics in this mammalian order. The present study aimed to investigate the testis function and the duration of spermatogenesis in the southeastern four-eyed opossum, Philander frenatus. Testes of six adult males were routinely processed for histological and stereological analyses. In order to determine the duration of spermatogenesis, intratesticular injections of tritiated thymidine were performed 1h, 13days and 21days before the sacrifice. Based on the development of the acrosomic system, ten stages of the seminiferous epithelium cycle were characterized. The mean body and testis weights for the P. frenatus were respectively 326±20g and 0.4±0.05g, providing a gonadosomatic index of 0.3±0.02%. The most advanced germ cell types labeled at 1h, 13days and 21days after thymidine injections were, respectively, preleptotene spermatocytes at stage IV, pachytene spermatocytes at stage IV and diplotene spermatocytes at stage IX. Based on the stages frequencies and the most advanced labeled germ cells, each spermatogenic cycle and the entire spermatogenic process lasted respectively 13.5±0.5 and 60.9±2.4days. When compared to the vast majority of eutherian mammals already investigated, these data indicate that the Philander frenatus presents a relatively long duration of spermatogenesis.

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The Patagonian opossum (Lestodelphys halli), the southernmost living marsupial, inhabits dry and open environments, mainly in the Patagonian steppe (between ~32 °S and ~49 °S). Its rich fossil record shows its occurrence further north in Central Argentina during the Quaternary. The paleoenvironmental meaning of the past distribution of L. halli has been mostly addressed in a subjective framework without an explicit connection with the climatic "space" currently occupied by this animal. Here, we assessed the potential distribution of this species and the changes occurred in its geographic range during late Pleistocene-Holocene times and linked the results obtained with conservation issues. To this end, we generated three potential distribution models with fossil records and three with current ones, using MaxEnt software. These models showed a decrease in the suitable habitat conditions for the species, highlighting a range shift from Central-Eastern to South-Western Argentina. Our results support that the presence of L. halli in the Pampean region during the Pleistocene-Holocene can be related to precipitation and temperature variables and that its current presence in Patagonia is more related to temperature and dominant soils. The models obtained suggest that the species has been experiencing a reduction in its geographic range since the middle Holocene, a process that is in accordance with a general increase in moisture and temperature in Central Argentina. Considering the findings of our work and the future scenario of global warming projected for Patagonia, we might expect a harsh impact on the distribution range of this opossum in the near future.

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The Didelphidae are considered solitary opossums with few social interactions, usually limited to mating-related or mother-pouch young interactions. Anecdotal reports suggest that additional interactions occur, including den sharing by a few individuals, usually siblings. Here, we report novel observations that indicate opossums are more social than previously thought. These include nest sharing by males and females of Marmosa paraguayana, Gracilinanus microtarsus and Marmosops incanus prior to the onset of the breeding season and without signs of sexual activity; this is taken to indicate early pair-bonding matching and cooperative nest building. We also recorded den sharing among recently weaned siblings of Didelphis aurita and Caluromys philander. In addition, we observed 13 individuals of Didelphis albiventris representing three age classes resting without agonistic interactions in a communal den. These are the first reports of gregarious behaviour involving so many individuals, which are either unrelated or represent siblings from at least two litters, already weaned, sharing the same den with three adults. Sociality in opossums is probably more complex than previously established, and field experimental designs combining the use of artificial nests with camera traps or telemetry may help to gauge the frequency and extent of these phenomena.

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The aggregation of parasites among hosts is associated with differential host exposure and susceptibility to parasites, which varies according to host gender, body size, reproductive status and environmental factors. We evaluated the role of these factors on infestation by Eimeria spp. (Eimeriidae) in the agile gracile mouse opossum (Gracilinanus agilis), a semelparous didelphid inhabiting neotropical savannahs. Eimeria spp. abundance and prevalence among G. agilis were associated with the breeding status of individuals and to a lesser extent to climatic season, with both sexes presenting higher Eimeria spp. burdens during late breeding/wet season. On the other hand, male-biased parasitism was restricted to dry/mating season. We suggest that male spatial organization and diet may account for increased parasite burdens within this sex, although future studies should evaluate the role of physiological differences associated with androgen hormones. Finally, a rapid increase in Eimeria spp. loads among females during the late breeding/wet season seems associated with seasonal changes in susceptibility, due to breeding costs related to semelparity, and exposure to infective propagules, while male-die off seems to explain maintenance of higher Eimeria spp. burdens within this sex in the same period.

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1. Much of the current understanding of ecological systems is based on theory that does not explicitly take into account individual variation within natural populations. However, individuals may show substantial variation in resource use. This variation in turn may be translated into topological properties of networks that depict interactions among individuals and the food resources they consume (individual-resource networks). 2. Different models derived from optimal diet theory (ODT) predict highly distinct patterns of trophic interactions at the individual level that should translate into distinct network topologies. As a consequence, individual-resource networks can be useful tools in revealing the incidence of different patterns of resource use by individuals and suggesting their mechanistic basis. 3. In the present study, using data from several dietary studies, we assembled individual-resource networks of 10 vertebrate species, previously reported to show interindividual diet variation, and used a network-based approach to investigate their structure. 4. We found significant nestedness, but no modularity, in all empirical networks, indicating that (i) these populations are composed of both opportunistic and selective individuals and (ii) the diets of the latter are ordered as predictable subsets of the diets of the more opportunistic individuals. 5. Nested patterns are a common feature of species networks, and our results extend its generality to trophic interactions at the individual level. This pattern is consistent with a recently proposed ODT model, in which individuals show similar rank preferences but differ in their acceptance rate for alternative resources. Our findings therefore suggest a common mechanism underlying interindividual variation in resource use in disparate taxa.

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