Vol. 5, Nº 1

The aim of this work was to determine the diet and feeding preferences of Calomys venustus. Relative food availability was determined through seasonal vegetation censuses and the species present were recorded. Microhistological analysis of the stomach contents was used for the determination of the seasonal diet. A cafeteria test was used to study laboratory feeding preferences. It was determined that C. venustus is omnivorous, showing a tendency to folivory in spring and autumn and to granivory in summer. Furthermore, significant differences between the relative composition of leaves, seeds and arthropods in each season were observed. C. venustus did not consume those leaves that were abundant in the habitat, or consumed them in low proportions and showed a high preference for seed consumption under conditions of equal food availability.

Estudio de la dieta y preferencias alimentarias de Calomys venustus (Rodentia, Muridae). El objetivo de este estudio fue determinar la dieta y preferencias alimentarias de Calomys venustus. La disponibilidad alimentaria relativa se determinó a través de censos estacionales de vegetación, registrándose la cobertura de las especies presentes. La dieta se determinó estacionalmente por el método microhistológico sobre contenido estomacal, y para el estudio de preferencias alimentarias en laboratorio se utilizó el test de cafetería. C. venusutus tuvo un comportamiento alimentario omnívoro, tendiendo hacia la folivoría en primavera y otoño y hacia la granivoría en verano. Además, hubo diferencias significativas entre la composición relativa de hojas, semillas y artrópodos en cada estación. C. venustus no consumió aquellas hojas que fueron abundantes en el hábitat, o solo las consumió en bajas proporciones, y presentó una alta preferencia por semillas en el experimento de consumo bajo condiciones de igual disponibilidad alimentaria.

En la localidad de Cacheuta (Mendoza, Argentina), ubicada a 1237 m de altura sobre el nivel del mar, se estudiaron los ciclos reproductivos mediante cortes histológicos de gónadas en Ctenomys mendocinus. Se encontró que la actividad sexual probablemente comienza a mediados de invierno hasta comienzos de otoño donde se evidencia una notable regresión gonadal.

Histological study of gonads of Ctenomys mendocinus from Cacheuta (Mendoza, Argentina). The reproductive cycles of Ctenomys mendocinus specimens from Cacheuta (Mendoza, Argentina), at 1237 m above sea level, were studied using histological sections of gonads. Observations led to determine that the sexual activity of this species takes place from July through February–March, and that there is a noticeable period of gonadal regression in April and June.

Agonistic interactions and receptivity of females during mating encounters in the corn mouse (Calomys musculinus) were studied. Twenty-nine couples were observed for copulatory behavior during postpartum estrus; 14 of them were composed of males and females that had bred together at least once (familiar male group), and 15 were composed of a male and a female each with reproductive experience, but were unknown to each other (strange male group). No significant differences between the familiar male and the strange male group were found in either the mount latency or the intromission latency. The strange male group showed a trend to have higher mount and intromission frequencies, both at the first and the second ejaculatory series, although some of these differences did not reach statistical significance. Also, males in the strange male group showed significantly higher ejaculatory thrust frequencies, both at the first and the second ejaculatory series, than males in the familiar male group. The post-ejaculatory interval was significantly longer in the strange male group. The incidence of all agonistic behaviors other than a stereotyped kind of fighting that precedes copulation (“precopulatory fighting”) was higher in strange male group than in the familiar male group. In both groups, aggressive postures were more frequently seen in females than in males, and conversely, submissive postures were significantly more frequent in males than in females. Also, females in the strange male group made significantly more approaches than those in the familiar male group. Taken together, these findings suggest that C. musculinus is a non-monogamous species.

Este estudio resume el conocimiento sobre la abundancia y distribución de la población del elefante marino del sur, Mirounga leonina, actualizando la información publicada hasta 1990 con datos demográficos para el período 1991–1997 durante las dos etapas terrestres del ciclo anual (reproducción: septiembre–octubre y muda: diciembre–febrero). La información se obtuvo mediante censos aéreos y terrestres de la Península Valdés (PV) y áreas adyacentes. La agrupación de elefantes marinos de PV es la única en el mundo que se encuentra en incremento. La producción de crías aumentó el 41% entre 1982 y 1997, y el incremento fue lineal entre 1969 y 1997. En 1982 se censaron 7416 adultos reproductores en su mayoría distribuidos en 477 harenes; en 1997 el número de adultos fue 12572 repartidos en 492 harenes. La mediana del tamaño de los harenes aumentó de 11 a 16 hembras en el mismo período. El incremento poblacional se asoció a una variación en la distribución espacial de los animales en la costa. En 1982, el 42% de las hembras reprodujo en el sector SE de PV mientras que en 1997 lo hizo el 73%. El número de hembras adultas que mudan en PV se estimó en 11200 individuos para 1994. La distribución de animales fue similar durante la reproducción y la muda. El incremento en la producción de crías indica un aumento en el tamaño poblacional posiblemente asociado a factores que operan durante la etapa pelágica del ciclo anual.

Population status and distribution of southern elephant seals at Península Valdés, Argentina. Southern elephant seals, Mirounga leonina, breed and molt in Península Valdés (PV) along a 200 km stretch of coast. We conducted one aerial survey (1992) and three terrestrial surveys (1995 to 1997) of the entire population at the peak of the breeding season (first week of October) and compared results with similar data published for the period 1982–1990. During aerial survey, we photographed all harems and recorded solitary individuals by sex and age categories (breeding females, harem bulls, bachelor males, pups and weanlings). Females were counted from photographs and pup production was estimated based on the number of females plus weanling. During terrestrial surveys, all recorded individuals were categorized by sex and age. Pup production increased 41%, from 7455 in 1982 to 12106 in 1997. Growth was linear from 1969 (counts made by other authors) to 1997. Based on reported pup production for the species in the world, PV is the fourth largest southern elephant seal colony. At the peak of the breeding season of 1997 there were 24726 animals of both sexes ashore, including pups. The size of the population 1 year of age was estimated in 42371 individuals. There were 477 harems in 1982 and 492 in 1997; 99% of the females bred in harems. The range of distribution of elephant seals in Patagonia did not change, but the spatial distribution of births along the coastline of PV varied with the increase in numbers. In 1982, 58% of the births occurred in 106 km in the NE portion of the peninsula, versus 27% in 1997. In 1997, 73% of the females gave birth in 77 km along the SE coast. Only 1% of the adult population bred outside PV. We estimated the number and distribution of adult females during the molt conducting two aerial surveys when the maximum number of animals were ashore (last weeks of December 1993 and January 1994). Females made 40% and 95% of the molting population in each census, respectively. PV is apparently the only southern elephant seal colony in the world that is expanding. The increase in pup production could be the result of factors operating while the animals are at sea, where abundant food resources may be a crucial determinant of population trends.

Two years of extensive sampling in Paraguay, as well as the comparison of the newly collected material with specimens deposited in museums, revealed the presence of three previously unrecorded species of bats in Paraguay: Tonatia brasiliense, Chiroderma doriae, Natalus stramineus, and Histiotus macrotus. Additionally, exact localities documenting the presence of Diaemus youngi in Paraguay are documented for the first time. The sudden appearance and abundance of this species in Paraguay may be the result of increasing livestock activities in the area.

Importantes registros de murciélagos (Chiroptera) de Paraguay. Dos años de colecta intensiva de pequeños mamíferos en territorio paraguayo, así como la comparación del nuevo material con ejemplares de museo, ha permitido reconocer la presencia en Paraguay de tres especies de murciélagos no reportadas previamente: Tonatia brasiliense, Chiroderma doriae, Natalus stramineus e Histiotus macrotus. Asimismo, se documenta por primera vez de manera exacta la presencia de Diaemus youngi en Paraguay. La aparentemente súbita aparición y abundancia de esta especie en el Chaco paraguayo puede ser resultado del incremento en las actividades pecuarias en el área.

Se ha estimado la distribución original del jaguar (Panthera onca) desde el sur de Estados Unidos hasta el sur de Argentina. En Sudamérica actualmente ocupa el 65% del área de distribución original. En el 36% de esta, las poblaciones de jaguar se encuentran disminuidas. En el noroeste de Argentina, además del desarrollo de actividades económicas y escasas áreas protegidas, otro factor de amenaza es la caza ejercida por los ganaderos, al considerarlo el único o principal factor de la desaparición de ganado bovino. En este trabajo se actualiza el conocimiento sobre la distribución actual del jaguar en las provincias de Jujuy y Salta (en el extremo noroeste de Argentina), y se discute la relación entre su presencia y el desarrollo de ganadería extensiva. Se obtuvieron 196 registros de presencia de jaguar, a partir de 1990, a través de trabajos de campo (n = 119, 60.25%) y entrevistas (n = 77, 39.75%). Estos registros se clasificaron como i) avistajes de jaguares (en el 21.42% de los registros), ii) jaguares cazados (18.36%), iii) bovinos depredados (36.73%) y señales (18.36% huellas y fecas), y iv) ataques a humanos (5.10%). Se puede considerar que la distribución del jaguar en estas provincias se encuentra actualmente entre los 22° 50′ – 25° S y los 63° 50′ – 65° O. El 93.58% de los registros corresponden a zonas con ganadería extensiva. Se discute la posible relación entre la distribución del jaguar y el desarrollo de la ganadería extensiva.

Jaguar Panthera onca distribution in Jujuy and Salta provinces in northwestern Argentina. Originally, jaguar (Panthera onca) spread from the south of the United States to the south of Argentina. At present, this species occupies 65% of the original range in South America; and in 36% of this area its population has been reduced. In northwestern Argentina, in addition to economic activities and the scarcity of protected areas, the jaguar is threatened by hunting, since ranchers consider this animal the main factor of cattle destruction. This work shows the present distribution of jaguar in the provinces of Jujuy and Salta, in northwesthern Argentina, and also discusses the relationship between jaguar and the raising of cattle in an extensive way. One hundred and ninety six records of jaguar’s presence were obtained since 1990 from field works (n = 119, 60.25%) and interviews (n = 77, 39.75%). They were classified as: i) sightings of jaguars (21.42%), ii) killed jaguars (18.36%), iii) depredated cattle (36.73%), and tracks and feces (18.36%), and iv) attacks to humans (5.10%). The jaguar distribution in these provinces is between 22° 50′ – 25° S and 63° 50′ – 65° W. The 93.58% of these records belong to areas with extensive cattle raising. The relationship between extensive cattle rearing and jaguar distribution is analyzed.

Se estudió la variabilidad genética de individuos adultos de ambos sexos pertenecientes a dos especies de Platyrrhini. Se analizaron 16 muestras de sangre de Alouatta caraya (ACA) y 12 de Cebus apella paraguayanus (CAP). Se estudiaron 10 sistemas proteicos mediante electroforesis horizontal en geles de poliacrilamida. De 14 loci analizados en A. caraya, solo AMP y TF fueron polimórficos (P = 0.1429; = 0.0359); de los 13 loci estudiados en C. a. paraguayanus, solo ESD fue polimórfico (P = 0.0769; = 0.0062). La distancia genética entre ACA y CAP fue D = 0.5962. Los valores de H y D son discutidos respecto de otros previamente publicados para primates neotropicales.

Protein variability analysis for Alouatta caraya and Cebus apella (Primates: Platyrrhini). The genetic variability of adult individuals of both sexes belonging to two species of Platyrrhini was studied. Sixteen blood samples of Alouatta caraya (ACA) and 12 of Cebus apella paraguayanus (CAP) were analyzed. Ten protein systems were examined by horizontal polyacrilamide gel electrophoresis. Out of 14 loci scored in ACA, only AMP and TF were polymorphic (P = 0.1429; = 0.0359), whereas only ESD was polymorphic in 13 loci studied in CAP (P = 0.0769; = 0.0062). The genetic distance between ACA y CAP was D = 0.5962. Values of H and D are discussed with respect to previous published data on Neotropical primates.

Ulyses F.J. Pardiñas y Carlos A. Galliari | Comentario sobre el trabajo «Los mamíferos del Parque Biológico Sierra de San Javier, Tucumán, Argentina: observaciones sobre su sistemática y distribución». Capllonch et al., 1997 (Mastozoología Neotropical, 4:49–71)

Luciano J.M. De Santis, M.F. Tejedor y P.C. Straccia | Acerca de Lestodelphys halli (Marsupialia, Didelphidae): comentarios sobre la nueva información aportada por Birney et al. (1996)

Analía G. Autino | Contribución al conocimiento de la biología y sistemática de los murciélagos de las yungas de la Argentina y sus insectos ectoparásitos

Guillermo D’Elía | Posición filogenética y dinámica poblacional del roedor subterráneo Ctenomys rionegrensis

Andrea Lasserre | Calomys musculinus and Calomys laucha female and male gametes (Sigmodontinae): characteristics, development and interaction

Olga V. Suárez | Estrategias reproductivas y cuidado parental en Akodon azarae (Rodentia, Muridae)

Myriam R. Laconi | Mating systems in Calomys musculinus and Calomys laucha (Muridae; Sigmodontinae)