Volumen y Número: Nº 2

Notas sobre morfologia, distribuição geográfica, história natural e citogenética de Cryptonanus guahybae (Didelphimorphia: Didelphidae)

, , ,

Este trabalho apresenta dados sobre os aspectos sobre cariótipo, distribuição geográfica, habitats de ocorrência e morfometria de Cryptonanus guahybae (Tate, 1931), baseados em 15 espécimes tombados no Museu de Ciências Naturais da Universidade Luterana do Brasil. Os exemplares são procedentes das seguintes localidades do estado do Rio Grande do Sul: 1. Usina Hidrelétrica de Itá; 2. Derrubadas; 3. Estação Ecológica de Aracuri – Esmeralda (Planalto Meridional); 4. Tapes (Planície Costeira Interna); 5. Venâncio Aires (Depressão Central); e 6. Área de Proteção Ambiental da Lagoa Verde e entorno – Rio Grande (Planície Costeira Externa). Ampliamos a distribuição geográfica da espécie cerca de 250 km em direção norte e 100 km em direção sul, sendo os municípios de Derrubadas e Rio Grande, respectivamente, os novos limites norte e sul dessa distribuição. O registro no município de Derrubadas também expande cerca de 180 km em direção oeste o limite de distribuição geográfica de C. guahybae. A análise citogenética dos espécimes do Rio Grande revelou um número diplóide (2n) igual a 14 e de braços autossômicos (NF) igual a 24, sendo os pares 1, 2 e 3 submetacêntricos, o par 4 metacêntrico, os pares 5 e 6 subtelocêntricos, o cromossomo sexual X submetacêntrico e o Y acrocêntrico. O par 6 apresentou regiões organizadoras de nucléolo (Ag-RON) nos telômeros de seus braços curtos. Dados sobre os exemplares procedentes do município de Rio Grande indicam a ocorrência da espécie em matas de restinga, nos biótopos de interior e bordas de mata arenosa ciliar e interior, e clareiras de mata palustre, sendo efetuadas capturas no solo e no sub-bosque (altura = 0.5–1.55 m).

Notes on morphology, geographic distribution, natural history, and citogenetics of Cryptonanus guahybae (Didelphimorphia: Didelphidae). This article reports data on karyotype, geographic distribution, habitat occurrence and morphometry of Cryptonanus guahybae (Tate, 1931) based on 15 specimens deposited in the mammal collection of the Museu de Ciências Naturais of Universidade Luterana do Brasil. The specimens were recorded in the following localities in Rio Grande do Sul state: 1. Itá Hydroelectric Power Plant; 2. Derrubadas; 3. Aracuri Ecological Station – Esmeralda (Southern Plateau); 4. Tapes (Inner Coastal Plain); 5. Venâncio Aires (Central Depression) and 6. Lagoa Verde Reserve Area and surroundings – Rio Grande (External Coastal Plain). We amplified the extension of the species distribution ca. 100 km southwards and 250 km northwards, being the municipalities of Derrubadas and Rio Grande, respectively, the new northern and southern limits of its geographical range. Derrubadas municipality record also extends C. guahybae distribution ca. 180 km westwards. Cytogenetic analysis showed a diploid number of 2n = 14 and fundamental number FN = 24 with pairs 1, 2 and 3 being submetacentrics, pair 4 metacentric, pairs 5 and 6 subtelocentrics; while sexual chromosomes X and Y were a submetacentric and an acrocentric, respectively. Ag-NOR analysis showed a single region located in the short arms of pair 6. In relation to habitat occurrence, the specimens from Rio Grande municipality were recorded in restinga forest, occupying the inner or borderline of sandy riparian forest and inner and gaps of flooded forest. Individuals were trapped on the ground and in short trees (heights = 0.5–1.55 m).

Seasonal variation in foraging group size of crab-eating foxes and hoary foxes in the Cerrado Biome, Central Brazil

,

In regions with a pronounced dry season, such as the Cerrado Biome (Brazilian savannah), climate seasonality may affect food availability for canid species and, consequently, their foraging behavior. We investigated seasonal variation in foraging group size of crab-eating foxes (Cerdocyon thous) and hoary foxes (Lycalopex vetulus) in the Cerrado region for three consecutive years. Data were obtained by direct observations of foraging foxes during spotlight surveys. Both species were sighted foraging individually or in pairs with or without their juvenile offspring. However, crab-eating foxes foraged in pairs more frequently in the wet season and individually more frequently in the dry season whereas hoary foxes foraged mostly individually throughout the year. The higher frequency of solitary foragers in the dry season is possibly a response to the seasonal shortages in the availability of clumped and locally abundant food resources such as fruit and insects, important items in the diet of the crab-eating fox during the wet season. The absence of seasonal variation in foraging group size of the hoary fox may be related to its specialized food habits, since termites predominate in the diet of this species in both seasons.

Variação sazonal no tamanho de grupo de forrageio em cachorros-do-mato e raposas-do-campo no bioma Cerrado, Brasil central. Em regiões com uma estação seca pronunciada, como o Bioma Cerrado (savana brasileira), a sazonalidade climática pode afetar a disponibilidade de alimento para as espécies de canídeos e, conseqüentemente, seu comportamento de forrageio. Nós investigamos a variação sazonal no tamanho de grupo de forrageio de cachorros-do-mato (Cerdocyon thous) e raposas-do-campo (Lycalopex vetulus) na região do Cerrado por três anos consecutivos. Os dados foram obtidos através de observação direta em focagens noturnas dos animais forrageando. Ambas as espécies foram avistadas forrageando individualmente ou em pares com ou sem sua prole juvenil. Entretanto, os cachorros-do-mato foram vistos forrageando em pares mais freqüentemente na estação úmida e individualmente mais freqüentemente na estação seca ao passo que as raposas-do-campo forragearam principalmente individualmente durante todos os meses do ano. A maior freqüência de forrageadores solitários durante a estação seca é possivelmente uma resposta à diminuição sazonal na disponibilidade de recursos alimentares abundantes e com distribuição agregada como frutos e insetos, itens importantes na dieta do cachorro-do-mato durante a estação úmida. A ausência de variação sazonal no tamanho de grupo de forrageio na raposa-do-campo pode estar relacionada ao seu hábito alimentar especializado, uma vez que cupins predominam na dieta desta espécie em ambas as estações.

Morfometría de las paleocuevas de la «Fm.» Chapadmalal y su asignación a Actenomys (Rodentia), Paedotherium (Notoungulata) y otros mamíferos fósiles hospedantes

, ,

En la «Formación» Chapadmalal, aflorante en las barrancas que se extienden desde Mar del Plata a Miramar, se diferencian paleocuevas que han sido asignadas al roedor fósil Actenomys sp. (Rodentia, Caviomorpha). La asignación se basa en la elevada frecuencia de restos de Actenomys sp. hallados en estas bioestructuras y en su capacidad cavadora. Si bien es evidente que Actenomys sp. construía cuevas, y muchas de las paleocuevas le corresponden, no es la única especie coetánea que pudo haberlas construido. Se analizaron morfométricamente las paleocuevas aflorantes en las barrancas costeras de Mar del Plata – Miramar correspondientes a los Pisos/Edad Chapadmalalense y Marplatense y la identificación de los posibles constructores. Se seleccionaron las paleocuevas en sección transversal y se tomaron dos medidas estructurales, correspondientes al diámetro transverso y dorsoventral, con las que se construyó un índice estructural. Se registró el material fósil asociado a las mismas en los casos donde estaba expuesto. Los análisis estadísticos incluyeron distribución de frecuencias, correlaciones, análisis de residuales y diferencia de medias, en las medidas individuales y en el índice. Se identifican cuevas construidas por Actenomys sp., en estadios juveniles y adultos, y por Paedotherium sp. Se reconocen diferencias métricas entre las cuevas del Chapadmalalense y Marplatense, posiblemente asociadas a una diferencia en la abundancia relativa de Paedotherium sp. y Actenomys sp. Asimismo se refuerza la existencia de cuevas de Lagostomopsis sp. y se identifica la posible construcción, o uso oportunista, de las mismas por Eumysops sp., Dolicavia sp. y otros cávidos.

Morphometry of paleocaves at the Chapadmalal “Formation” assigned to fossorial rodent Actenomys sp. (Rodentia, Caviomorpha), Paedotherium (Notoungulata), and to other fossil mammals. Paleocaves assigned to fossorial rodent Actenomys sp. (Rodentia, Caviomorpha) are present at the Chapadmalal “Formation”, cropping out from Mar del Plata to Miramar. The assignation is based on the high frequency of fossil material of Actenomys sp. within the paleocaves and in the digging capacity recognized for the genera. Although it is evident that Actenomys sp. built caves and most of these correspond to the genera, it is not the only coetaneal mammal with the capacity of construction of these structures. Paleocaves of Chapadmalalan and Marplatan age were analyzed morphometrically and the generic assignation of their producers was evaluated. Paleocaves in transverse section were selected, its dorsoventral and lateromedial diameter was measured and used for calculating a structural index. The fossil material exposed in paleocaves was determined to a specific level in all possible cases. The statistical analyses performed include frequency distributions, correlations, residual analyses, and mean differences on individual measurements and on the index. Paleocaves constructed by Actenomys sp., in juvenile and adult stages, and by Paedotherium sp. are recognized. Metric difference between paleocaves of Chapadmalalan and Marplatan ages are recognized, in possible association with a different abundance of Paedotherium sp. and Actenomys sp. The presence of paleocaves of Lagostomopsis sp. is reinforced and is suggested the possible construction, or opportunistic use, of paleocaves by Eumysops sp., Dolicavia sp. and other Caviidae.

Evaluation of population parameters of coypu Myocastor coypus (Rodentia, Myocastoridae) during and outside the authorised hunting season in the floodplain of the Paraná River, Argentina

, , , ,

We studied a Myocastor coypus (Molina, 1782) population during the authorised hunting season (AHS) and outside the hunting season (OHS) in the floodplain of the Paraná River (Argentina), a representative area for this species within its original geographic range. The aims of this work were to describe and compare fluctuations in population parameters (relative abundance, sex ratio, age structure) and in the physical condition between these two periods. Additionally, we discussed the possible occurrence of simultaneous influence of environmental factors (particularly the hydroperiod) and hunting pressure on these parameters. The absolute density during the AHS was 2.78 individuals/ha. No differences in the trapping success index were found between AHS and OHS. Throughout the study period the sex ratio remained 1:1. Adults predominated at the beginning of the AHS. There was no predominance of any age class during the OHS. The physical condition index (PCI) decreased during the AHS for both sexes, while in OHS only for females increased in December. No differences were found in the PCI between AHS and OHS for both sexes. The hydroperiod of the Paraná River showed a decrease during AHS and more stable but lower values during OHS. We hypothesise that these results could be related to a compensatory favourable effect of the habitat conditions (particularly the hydrological regime) over the negative effect of hunting pressure.

Evaluación de parámetros poblacionales de Myocastor coypus (Rodentia, Myocastoridae) durante la temporada de caza autorizada y fuera de ella en la planicie aluvial del Río Paraná (Argentina). Se estudió una población silvestre de Myocastor coypus (Molina, 1782) dentro de la temporada de caza autorizada (TCA) y fuera de ella (FCA) en la planicie aluvial del Río Paraná (Argentina), un área representativa dentro de su rango original de distribución. Los objetivos de este estudio fueron describir y comparar las fluctuaciones observadas en algunos parámetros poblacionales (abundancia relativa, proporción de sexos, estructura de edades) y en la condición física entre ambos períodos, y discutir el posible efecto simultáneo de factores ambientales (hidroperíodo) y de la presión de caza sobre ellos. La densidad absoluta en TCA fue de 2.78 individuos/ha. No se observaron diferencias significativas entre TCA y FCA en los los índices de éxito de trampeo estimados. Durante todo el período estudiado la proporción de sexos fue 1: 1. Los adultos fueron la clase de edad predominante y estuvieron más representados al inicio que al final de la TCA. No predominó niguna clase de edad durante la FCA. El índice de condición física (ICF) decreció a lo largo de TCA para ambos sexos mientras que sólo las hembras alcanzaron un pico relativo en diciembre (FCA). No obstante, no existieron diferencias en IFC entre TCA y FCA. El hidroperíodo del Río Paraná mostró un decrecimiento durante la TCA mientras que en la FCA se observaron valores más bajos y estables. Los resultados observados podrían estar relacionados con un efecto compensatorio de las condiciones de hábitat (particularmente del régimen hidrológico) sobre el efecto negativo de la presión de caza.

Behavioral counter-strategies against infanticide in corn mouse females, Calomys musculinus

, ,

Based on the hypothesis that in C. musculinus both female territorial behavior and promiscuity are counter-strategies against infanticide by females and males respectively, our objective was to test the following predictions: (1) mother aggression deters infanticide by females; (2) previous matings prevent infanticide by males. We conducted 116 behavioral encounters between mothers and intruders to study the nest related behaviors. Mother-pups units (Mu) were grouped in three treatments in relation to the intruder feature: 55 Mu were placed with siring males, 27 Mu and 34 Mu were housed with non-siring males and reproductively active females, respectively. We also calculated offspring survival rate for each treatment. The nest related behaviors varied among the three groups tested. Mothers showed high rates of aggressive behavior towards females. In presence of siring males mothers remained calm inside the nest. When the intruders were non-siring males mothers exhibited high rates of nest defense behavior. The lowest survival rate was registered in presence of the non-siring males, while the highest rates were registered in presence of females or siring males. The absence of aggressiveness and the high rate of nest defense by mothers against siring and non-siring males respectively, would support that promiscuity acts as a counter-strategy against infanticide by males. Mother aggressive behavior against intruder females would show that female territoriality may be an effective way of pup protection.

Contraestrategias comportamentales contra el infanticidio en hembras de C. musculinus. Bajo la hipótesis de que la territorialidad intra-sexual y el apareamiento múltiple por parte de las hembras de C. musculinus actúan como contra-estrategias para evitar el infanticidio cometido por hembras y machos respectivamente, nuestro objetivo fue probar las siguientes predicciones: 1) la agresión de la madre impide el infanticidio por hembras, 2) los apareamientos previos previenen el infanticidio por parte de machos. Estudiamos comportamientos relacionados al nido en 116 unidades madre-cría (Mc) agrupadas en tres tratamientos en relación a las características del intruso: 55 Mc alojadas con los padres de las crías; 27 Mc y 34 Mc alojadas con machos sin experiencia sexual con la madre y con hembras reproductivas, respectivamente. En cada tratamiento se calcularon las tasas de sobrevida. Las madres fueron agresivas hacia las hembras. En presencia de los padres las madres permanecieron tranquilas en sus nidos. La menor tasa de sobrevida se registró en presencia del macho no padre; las mayores en presencia del padre y hembras reproductivas. La ausencia de agresividad y las altas tasas de defensa del nido exhibidas por las madres hacia los padres y los machos extraños respectivamente, apoyan la hipótesis que propone la promiscuidad como contraestrategia al infanticidio por machos. La respuesta altamente agresiva de las madres hacia las hembras intrusas sería una estrategia efectiva para la protección de sus crías.

Distribución de los armadillos (Xenarthra: Dasypodidae) en la provincia de Buenos Aires, Argentina

,

En este trabajo se analiza la distribución de las especies actuales de armadillos registradas en el territorio de la provincia de Buenos Aires. La información proviene de trabajos de campo, revisión bibliográfica y colecciones de museo. Se analizan aspectos temporales y espaciales. Se obtuvieron 401 registros georreferenciados para siete especies. Dasypus hybridus y Chaetophractus villosus son los armadillos más comunes y ampliamente distribuidos en la provincia. C. villosus parece estar siendo favorecida por las nuevas prácticas agrícolas y D. hybridus muestra una ampliación en el uso del hábitat. Para Zaedyus pichiy se registraron cambios en la distribución en la zona sureste de la provincia, cuya explicación más consensuada son los cambios en las condiciones climáticas. Para Chlamyphorus truncatus esta revisión dejó ver la necesidad de realizar estudios, ya que la zona en donde se distribuye está siendo intensamente degradada. La única especie actual extinta, Tolypeutes matacus, probablemente haya desaparecido por cambios climático-ambientales. Dasypus novemcinctus ha ingresando en la provincia hace pocos años, registrándose en la ecorregión Delta e Islas del Paraná. No se ha podido verificar la presencia de Euphractus sexcinctus, Cabassous tatouay y Dasypus septemcinctus. La historia de la distribución de los armadillos presentada en este trabajo sugiere que el registro producido durante los últimos años refleja cambios climático-ambientales. Así, el seguimiento de estos taxones permitirá observar e interpretar tendencias en lo que se refiere al uso y modificación del ambiente como así también en las condiciones de temperatura y precipitación, tan urgentes debido al cambio climático global.

Armadillos (Xenarthra: Dasypodidae) distribution in Buenos Aires province, Argentina. In this paper we analyze the distribution of extant armadillos species in the Buenos Aires province. The information comes from fieldwork, literature and collections. The analyses contain temporal and spatial aspects. We obtained 401 georeferenced records from seven species. Dasypus hybridus and Chaetophractus villosus are the most common and widely distributed armadillos. C. villosus appears to be facilitated by new agricultural practices and D. hybridus shows an increase in habitat use. A movement was registered for Zaedyus pichiy in the southeast of the province, which can be explained by changes in climate conditions. For Chlamyphorus truncatus this review shows the need for further studies since its distribution area is being intensely degraded. The only extinct species, Tolypeutes matacus, probably disappeared due to climatic and environmental changes. Dasypus novemcinctus appeared in the province few years ago, in the ecoregion Delta e Islas del Paraná. The presence of Euphractus sexcinctus, Cabassous tatouay and Dasypus septemcinctus has not been verified. The history of armadillo’s distribution presented in this paper reflects climate and environmental changes. We believe these are key taxa, and the monitoring of these species will allow us to observe and interpret trends related to the use and modification of the environment as well as the conditions of temperature and precipitation.