Oecomys Bicolor Research Articles

Testicular histomorphometric patterns and spermatogenesis dynamics of Oecomys bicolor tomes, 1860 (Rodentia: Cricetidae).

Although the order Rodentia does not present a high risk of extinction compared to mammals as a whole, several families demonstrate high levels of threat and/or data deficiency, therefore highlighting the need for targeted research and the application of ecological and reproductive data to the development of conservation actions. The order Rodentia, the largest among mammals, includes 9 families, and the family Cricetidae is the most diverse of the Brazilian rodents. In Brazil, 12 of the 16 genera of Oecomys are found. Oecomys bicolor is known in Brazil as the 'arboreal rat' and is, found in dry, deciduous and tropical forests. The mean body weight of Oecomys bicolor was 35.8 g and the gonadal, tubular and epithelial somatic indexes were, 0.53%, 0.47% and 0.37%, respectively. Seminiferous tubules volume density was 89.72% and the mitotic and meiotic indexes corresponded to 8.59 and 2.45 cells, respectively, and the yield of spermatogenesis was 23.83 cells. The intertubular compartment represented 10.28% of the testis parenchyma and around 5% of the interstitial space was occupied by Leydig cells, whose number per gram of testis was 11.10 × 107 cells. By evaluating the biometric and histomorphometric characteristics of the testis, there is evidence that this species has a high investment in reproduction. Due to the high contribution of the seminiferous epithelium and the intertubular compartment in this species, compared to the others of the same family, it is possible to infer that the species Oecomys bicolor has a promiscuous reproductive behaviour.

Diet of small mammals in semi‐deciduous forest fragments in Central Brazil

AbstractMarsupials and rodents are two of the most specious mammalian group, displaying a variety of diet and feeding habits. However, the knowledge about diet for several small mammal species is scant in the scientific literature, and most species are classified as insectivore–omnivore (marsupials), or frugivore–graminivore (rodents). In this study, we described diet composition based on digestive tract contents of 12 species of small mammals (7‐rodents and 5‐marsupials), in semi‐deciduous forest fragments of Central Brazil. We analysed 47 digestive tract contents belong to Calomys tener (10), Oecomys bicolor (10), Gracilinanus agilis (6), Marmosa murina (5), Rhipidomys macrurus (5), Calomys expulsus (2), Cryptonanus chacoensis (2), Monodelphis kunsi (2), Oecomys catherinae (2), Caluromys philander (1), Oligoryzomys mattogrossae (1) and Necromys lasiurus (1). We found parts of arthropods and fruits in the digestive tract of all species, with the exception of N. lasiurus, which contained only arthropods. The most representative arthropod taxa were Hymenoptera (present in 11 species), Coleoptera (9 spp.), Arachnida (7 spp.) and Isoptera (6 spp.). The seeds of Piperaceae (present in 3 small mammal species), Myrtaceae (2 spp.) and Poaceae (1 sp.) were also identified. This study reports the first records of diet composition for the marsupials C. chacoensis and M. murina, and rodents C. expulsus, C. tener, O. bicolor, O. catherinae and R. macrurus. Our findings contribute to understanding the diet composition and natural history of the Brazilian Savanna small mammals.

Litter size and reproductive condition of small mammals in southern Goiás, Brazil

Litter size and reproductive conditions are important in natural history. However, this information is scarce in scientific literature. Here, we presented litter size data for eight small mammal species (four marsupials and four rodents) and investigated the reproductive conditions of three small rodent species in the transition between the Atlantic Forest and Cerrado in central Brazil. We counted the number of young born, the number of embryos found in the uterus, and recorded the presence of well-developed teats and evident scrotum to evaluate the reproductive condition. The litter sizes ranged from one (Oecomys bicolor) to 11 (Gracilinanus agilis and Marmosa murina). We did not find evidence of reproductive seasonality. The pattern found here is similar to other studies carried out in different locations of South America.

The importance of sampling methods and landscape variation on explaining small mammal communities in a Neotropical ecotone region

Understanding the main patterns that affect biodiversity in local and biogeographic scale is central in ecological and conservation studies. Here, we investigated the trappability of small mammals by different methodologies in a fragmented landscape on Atlantic Forest-Cerrado ecotone, and compared the estimated richness and composition of this study community with small mammals surveyed in central Brazil phytogeographic domains. We compared the number of captures between trap type, trap position and the interaction between these variables using a generalized linear mixed model, and compare our findings with those from published data in a radius of 1000 km, using rarefaction and extrapolation methods. Pitfall traps were essential in capturing Monodelphis kunsi, Calomys tener and Oligoryzomys fornesi, whereas wire-cage traps were more efficient on capturing Didelphis albiventris. Calomys expulsus and D. albiventris were significantly more captured in traps on the ground, and Gracilinanus agilis, Marmosa murina, Oecomys bicolor, O. catherinae and Rhipidomys macrurus had more captures in traps on understory. The use of different trap types, mainly pitfall traps, as sampling the vertical strata of habitat, is a good strategy for achieving the completeness sampling of small mammals in the Neotropics. The relative lower small mammal richness in Atlantic Forest-Cerrado ecotone compared to other domains could be explained by the historical higher habitat loss reported for this ecotone zone; thus, we highlight the need of conservation efforts for the preservation of small mammals and else biota that inhabit such type of environment.

Intense genomic reorganization in the genus Oecomys (Rodentia, Sigmodontinae): comparison between DNA barcoding and mapping of repetitive elements in three species of the Brazilian Amazon.

Oecomys Thomas, 1906 is one of the most diverse and widely distributed genera within the tribe Oryzomyini. At least sixteen species in this genus have been described to date, but it is believed this genus contains undescribed species. Morphological, molecular and cytogenetic study has revealed an uncertain taxonomic status for several Oecomys species, suggesting the presence of a complex of species. The present work had the goal of contributing to the genetic characterization of the genus Oecomys in the Brazilian Amazon. Thirty specimens were collected from four locations in the Brazilian Amazon and three nominal species recognized: Oecomys auyantepui (Tate, 1939), Oecomys bicolor (Tomes, 1860) and Oecomys rutilus (Anthony, 1921). COI sequence analysis grouped Oecomys auyantepui, Oecomys bicolor and Oecomys rutilus specimens into one, three and two clades, respectively, which is consistent with their geographic distribution. Cytogenetic data for Oecomys auyantepui revealed the sympatric occurrence of two different diploid numbers, 2n=64/NFa=110 and 2n=66/NFa=114, suggesting polymorphism while Oecomys bicolor exhibited 2n=80/NFa=142 and Oecomys rutilus 2n=54/NFa=90. The distribution of constitutive heterochromatin followed a species-specific pattern. Interspecific variation was evident in the chromosomal location and number of 18S rDNA loci. However, not all loci showed signs of activity. All three species displayed a similar pattern for 5S rDNA, with only one pair carrying this locus. Interstitial telomeric sites were found only in Oecomys auyantepui. The data presented in this work reinforce intra- and interspecific variations observed in the diploid number of Oecomys species and indicate that chromosomal rearrangements have led to the appearance of different diploid numbers and karyotypic formulas.

Population dynamics and reproduction of Cricetid rodents in a deciduous forest of the Urucum Mountains, western Pantanal, Brazil

The population dynamics and reproduction of Cricetid rodents of the Urucum Mountains were analyzed in a region poorly known in terms of life history characteristics of mammals. Animals were obtained from a museum’s mammal collection, but were originally captured using pitfalls. Data collection was performed for five days every month in three areas, from December 2000 to September 2002. The most frequent species found were the rodents Akodon toba, Calomys callosus, Euryoryzomys nitidus, and Oecomys bicolor. These species were usually more abundant in the rainy season and in the beginning of the dry season. However, there were differences between young and adults for A. toba and E. nitidus, with both species showing a peak of young in the rainy season, followed by a posterior peak of adults in the early dry season. Thus, there was a correlation between the population variations of A. toba and C. callosus, and between E. nitidus and O. bicolor. The seasonal availability of resources should be influencing the reproduction rate as well as the occurrence of young in the populations, since the climatic seasons are well defined in the region. Calomys callosus showed the largest litter size and presence of sexual dimorphism in size and mass. The species showed mostly similar responses to climatic seasonality, but differed in attributes related to their specific life histories.Key words: reproductive effort, abundance, sexual dimorphism, sex ratio, small mammals, litter size, seasonality response, male reproductive condition.

Use of vertical space by small mammals in gallery forest and woodland savannah in south-western Brazil

AbstractWe examined the community composition and abundance of small mammals in the vertical strata of gallery forests and woodland savannahs in south-western Brazil. Captures were carried out during the winter and summer months of 2006/2007. Traps were set in three transect lines per habitat, with 10 capture stations on each line. Each station had three traps: on the ground, in the understorey (2–3 m in height), and in the canopy (8–10 m) in each physiognomy. With an effort of 3600 trap-nights, 11 species of small mammals were captured, which were distributed differently regarding the forest physiognomies and utilisation of vertical strata. The species showed a high degree of habitat segregation in the two physiognomies, with only the climbing-ratRhipidomys macrurusfound in both habitats. The correspondence analysis revealed thatCaluromys philanderoccurred mostly in the canopy;Cryptonanus agricolai,Marmosa murina, andOecomys bicolorin the understorey; andGracilinanus agilisandNectomys rattuson the ground. The utilisation of traps in different strata increased species richness in the Cerrado biome, showing that the small-mammal community is distributed along the vertical complexity of the forest and even in different physiognomies, enabling more species to coexist.

The parasitism of Ixodes luciae (Acari: Ixodidae) on marsupials and rodents in Peruvian Amazon

In this work the infestation with I. luciae on Didelphimorphia and Rodentia in different environments of Peruvian Amazon was studied. Didelphimorphia was represented by the family Didelphidae. Specimens belonging to Caluromys lanatus, Didelphis marsupialis, Marmosops sp.2, Metachirus nudicaudatus, Philander andersoni and Philander opossum were infested with adults I. luciae and one Micoureus sp. was infested with larvae. In Rodentia, the infestation with I. luciae nymphs was restricted to Hylaeamys perenensis, Hylaeamys yunganus and Oligoryzomys microtis, while one Oecomys bicolor (all Cricetidae) was infested with larvae of this species. The few larvae were found on rodents captured in primary forest. The only significant difference (P < 0.05) in prevalence of adult ticks on Didelphimorphia was between P. andersoni and M. nudicaudatus (chi-square distribution). Adult tick distribution was significant different in P. andersoni in comparison with M. nudicaudatus, P. opossum and D. marsupialis (Kruskal-Wallis test). No significant effect of month or environment was detected in relation to adult tick infestation on Didelphimorphia. The prevalence of nymphal infestation as well as tick distribution showed that H. perenensis and H. yunganus were significantly more prone to be infested with nymphs of I. luciae than O. microtis. Prevalence of nymph infestation was higher in primary and secondary forest than rural areas while abundance was higher in secondary forest when compared with rural areas (P < 0.05). Kruskal-Wallis test showed differences (P < 0.05) for nymphal infestation during December in relation to January, March, April and June. The natural cycle of I. luciae appeared to be continuous, bound to adult tick infestation on Philander and nymphal infestation on Hylaeamys in forested environs.

Variação morfológica de pegadas de roedores arborícolas e cursoriais do Cerrado

Considerando que os roedores possuem diversas formas de locomoção, o presente estudo apresenta e discute variações na forma das pegadas anteriores e posteriores de sete espécies [Akodon cursor (Winge, 1887), Necromys lasiurus (Lund, 1840), Oecomys bicolor (Tomes, 1860), Oecomys concolor (Wagner, 1845), Oligoryzomys nigripes (Olfers, 1818), Hylaeamys megacephalus (Fischer, 1814) e Rhipidomys macrurus (Gervais, 1855)], utilizando técnicas de morfometria geométrica e análises discriminantes. As variáveis de forma das pegadas foram relacionadas com a topologia filogenética e os modos de locomoção das espécies para verificar a influência de fatores históricos e ecológicos na morfologia das pegadas. A forma das pegadas dos roedores arborícolas (curtas e largas) foi claramente distinta dos cursoriais (estreitas e alongadas). As reclassificações das pegadas anteriores (Kappa = 0,72) e posteriores (Kappa = 0,88) das espécies foram consideradas substanciais e quase perfeitas, respectivamente. As pegadas posteriores discriminaram melhor as espécies além de indicarem os níveis de atividade arborícola e cursorial dos roedores. Efeitos alométricos foram observados nas análises das pegadas anteriores (13%) e posteriores (3%). O modo de locomoção explicou 90,3% da variação na forma nas pegadas dos roedores (p = 0,02), indicando convergência nos padrões morfológicos nas pegadas das espécies de roedores arborícolas e cursoriais.

Mammals, Volta Grande Environmental Unity, Triângulo Mineiro, states of Minas Gerais and São Paulo, Southeastern Brazil

The Volta Grande Environmental Unity represents one of the few remnants of Cerrado protected by a reserve in the Triângulo Mineiro region, municipalities of Conceição das Alagoas (19°55' S, 48°23' W) and Miguelópolis (20°12' S, 48°03' W), in the states of Minas Gerais and São Paulo, respectively. The mammalian fauna of this reserve was inventoried between 2003 and 2004 to generate estimates about taxonomic composition, richness, and abundance of species. A sampling effort of 832 trapping-nights resulted in 24 species recorded. Cumulative curves suggest that the overall inventory is not complete and that more species are likely to be registered. The majority of species recorded is widespread along the Cerrado, but include some noteworthy records of endangered species, such as the Giant anteater (Myrmecophaga tridactyla) and the Manned wolf (Chrysocyon brachyurus). The record of the arboreal cricetid rodent Oecomys bicolor represents a slight extension of the southeastern limit of its distribution.

Tick collections from the Peruvian Amazon, with new host records for species of Ixodes Latreille, 1795 (Acari: Ixodidae) and Ornithodoros Koch, 1844 (Acari: Argasidae)

Abstract Tick-infested bats, rodents and marsupials were captured along the Iquitos-Nauta highway, Loreto Department, in the Peruvian Amazon. The only ticks found on Chiroptera were members of the Ornithodoros hasei (Schulze, 1935) species group, collected from Noctilio albiventris Desmarest, 1818, Rhinophylla pumilio Peters, 1865 and Myotis albescens (E. Geoffroy, 1806). Rhinophylla pumilio is a new host and M. albescens was confirmed as a host for the O. hasei group. Among Rodentia, Oecomys bicolor (Tomes, 1860), Oligoryzomys microtis (Allen, 1916), Hylaeamys perenensis (Allen, 1901) and Hylaeamys yunganus (Thomas, 1902) were infested with larvae (O. bicolor) or nymphs (other three rodents) of Ixodes luciae Senevet, 1940; all are new hosts for I. luciae. Tick infestation was more diverse among the Didelphimorphia, where a nymph and larva of Amblyomma sp. were collected on Philander opossum (Linnaeus, 1758), a nymph of Amblyomma sp. on Caluromys lanatus (Olfers, 1818), and a larva of Ixodes pararicinus K...

Semideciduous Atlantic Forest mammals and the role of the Paraná River as a riverine barrier

The role of the Parana River as an effective barrier for mammalian dispersal was evaluated. Four species were analyzed based on their characteristics and distributions along river margins: Caluromys lanatus (Didelphimorphia), Hylaeamys megacephalus, Oecomys bicolor (Rodentia), and Alouatta caraya (Atelidae). Considering their characteristics of small body sizes, arboreal life styles (of most species), and distributions in both river margins, the Parana River is suggested to be a weak geographic barrier for mammal dispersal.

Population and Community Ecology of Small Mammals in a Gallery Forest of Central Brazil

Population ecology of small mammals was examined over a 14-month period in the tropical gallery forests of the cerrado of central Brazil. Mark-recapture techniques provided detailed information on age structure, population dynamics, biomass, and patterns of reproduction for six species of oryzomyine rodents ( Oecomys bicolor, Oecomys concolor, Oryzomys capito, Oligoryzomys eliurus, Rhipidomys mastacalis , and Nectomys squamipes ) and two species of marsupials ( Didelphis albiventris and Gracilinanus agilis ). Different species show distinctive patterns of population increase and reproductive activity, with some maintaining stable populations throughout the year and others having a boom-and-bust pattern. Those that show pronounced differences in population size at different times of the year generally reach their lowest population levels during the region's pronounced dry season. Among the smaller-bodied species, the great majority of mammalian biomass on the study area is contained in the rodents. If the larger-bodied species are included, however, the marsupials comprise most of the biomass. Most species did not appear to be long-lived. Only D. albiventris persisted on the grid for >12 months; the majority of species lasted <6 months. The tropical gallery forests of central Brazil support a small-mammalian fauna that is at least as rich and complex as any other tropical site that has been examined to date and may support higher densities than any other site heretofore examined.