Rodrigo Cajade

Introduction of the American Bullfrog Lithobates catesbeianus (Anura: Ranidae) in Natural and Modified Environments: An Increasing Conservation Problem in Argentina

ABSTRACT. Several previous studies have established that the introduction of the American bullfrog, Lithobates catesbeianus, produces negative effects on native communities. Herein, the American bullfrog is reported for the first time in the province of Buenos Aires, Argentina in the locality of 9 de Julio. The stomach contents of the collected specimens were examined and the reproduction of the species was also confirmed at the study area. A total of 85.7% (n = 30) of the analyzed stomachs contained prey items, and eleven of these were identified. The prey items belonged mostly to coleopterans (50%) and vertebrates (11%). The pathogen Batrachochytrium dendrobatidis was not found on skin samples examined. The installation of Lithobates catesbeianus breeding facilities contributes to the incidental release of this species. A tightening of rules in the regulation of aquaculture activities and the use of control programs for naturalized populations are necessary to address the increasing dispersion of the species in Argentina and potential ecological problems.

Growth-Mark Formation and Chronology of Two Neotropical Anuran Species

Abstract In amphibians from tropical or subtropical regions well-expressed growth marks in bone could be expected because of the existence of strong dry/wet seasons, but little evidence is available. Additionally, temporal patterns of growth-mark formation may be a function of genetic and environmental factors. We used skeletochronology and a laboratory experiment to tease apart both causal sources, establishing direct correspondence between an observed pattern of bone growth and the actual age of Ceratophrys cranwelli and Dermatonotus muelleri from the subtropical Argentinean Chaco. Also, we describe the growth by application of the von Bertalanffy model. Growth rates decreased in both species, tending to reach asymptotic values at age 8–10 months after metamorphosis. Both species clearly exhibited haematoxylinophilic lines of arrested growth (LAG) after one year growing in captivity. These results reinforce the hypothesis that in subtropical climates the LAG formation is ultimately caused by a general intrinsic (genetic) control.

Reproductive biology of Argenteohyla siemersi pederseni Williams and Bosso, 1994 (Anura: Hylidae) in northeastern Argentina

The present study describes the reproductive biology of Argenteohyla siemersi pederseni in a modified “quebracho” forest of Schinopsis balansae in northeastern Argentina. Observations were made between January 2007 and March 2009 at El Perichón, Corrientes Province, Argentina. Argenteohyla s. pederseni bred once per year over a 3-day period in a semi-permanent pond during the first spring rains in mid-September. Males called while floating on the water surface. The advertisement call was short and repeated at regular intervals in relatively fast succession, forming groups of multiple calls. Aggressive calls were evoked in two different agonistic interactions. Eggs were black, laid in three-dimensional arrangements interspersed within the submerged vegetation. Egg number per clutch ranged from 2638 to 8987. Tadpole redescription shows many differences and similarities with previous descriptions. The reproductive biology of A. s. pederseni has several similarities with another pond-dwelling casque-headed frog species.

Age, body size and growth pattern of Argenteohyla siemersi pederseni (Anura: Hylidae) in northeastern Argentina

In this study we analysed the body size, age structure, age at maturity, longevity and growth pattern of Argenteohyla siemersi pederseni in north-eastern Argentina using skeletochronological methods. Body size was sexually dimorphic; females were significantly larger and heavier than males, regardless of age. As A. s. pederseni is an explosive breeder with only one reproductive episode per year, we assumed that each Line of Arrested Growth (LAG) observed was equivalent to one period of decreasing growth, LAGs reflecting a direct estimation of individual age. The minimum number of LAGs counted was two for males and three for females, but there was no sexual difference in longevity. The von Bertalanffys growth coefficients (K) were higher in males than in females for both size and body mass. Females had a lower growth rate than males, took longer to reach the minimum maturation size, and were older and larger at reproduction.

TROPHIC AND MICROHABITAT NICHE OVERLAP IN TWO SYMPATRIC DENDROBATIDS FROM LA SELVA, COSTA RICA

A B S T R A C T. — We studied the trophic ecology of Dendrobates auratus and Oophaga pumilio in La Selva Biological Station, Costa Rica. At this site, both dendrobatids are sympatric due to the introduction and naturalization of D. auratus in the last 24 years. Diets of both dendrobatids were recorded by the analysed stomach flushing technique. Microhabitats uses were defined as the site where each individual was captured. The influence of microhabitat on diets was evaluated by the dietary (prey proportions and volume) and microhabitat overlaps using Pianka’s (Ojk) overlap index calculated with EcoSim software. Diets of both dendrobatids were principally characterized by the preference of hymenopterans (ants), acarines and collembolans, resulted in a high overlapping in prey proportions and prey volume. However, diets overlaps were not significant, suggesting the absence of negative feeding interactions. Microhabitat use was low overlapped and also not significant, suggesting a differentiation on the use of spatial resource. The absence of negative feeding interactions between Dendrobates auratus and Oophaga pumilio could be due to segregation in microhabitat use and possible by the abundance of trophic resource in the area. The great large volumes of formicids and acarines in the diet of this dendrobatids are in agreement with the hypothesis of these arthropods as a dietary source of alkaloids.

Amphibia, Anura, Microhylidae, Elachistocleis skotogaster : map of geographic distribution, distribution extension, and new altitudinal records

The genus Elachistocleis is a neotropical group of small sized microhylid frogs, which is represented by two species in Argentina: Elachistocleis bicolor (Guerin-Meneville, 1838) and E. skotogaster Lavilla, Vaira and Ferrari, 2003. E. skotogaster was only known for the type locality Los Toldos, Santa Victoria department, Salta, 1100 m (Lavilla et al. 2003; Lavilla 2004), however, specimens from Bolivia with spotted bellies that are currently attributed to Elachistocleis ovalis might pertain to E. skotogaster (Lavilla 2004).

Depredación de Erythrolamprus poecilogyrus (Serpentes: Dypsadidae) por Lethocerus annulipes (Heteroptera: Belostomatidae)

Se da a conocer el primer registro de depredacion en la serpiente Erythrolamprus poecilogyrus por parte de la chinche de agua gigante Lethocerus annulipes .