Arturo I. Kehr

Species affinity and infracommunity ordination of helminths of Leptodactylus chaquensis (Anura: Leptodactylidae) in two contrasting environments from Northeastern Argentina

One hundred seventy-two frogs (Leptodactylus chaquensis) were collected from November 2002 to November 2003, in agricultural (n = 132) and nonagricultural (n = 40) areas. Both sites are near the city of Corrientes, Argentina. The main goals of this study were as follows: (1) to determine the helminth parasite community in agricultural and nonagricultural habitats; (2) to analyze the relationships between helminth parasites and site of infection, frog body size, and gender; (3) to identify and examine covariation and association of helminth communities; and (4) to determine the mean richness and diversity of parasite communities. The helminth compound community of this amphibian species consisted of 24 species: 19 in agricultural habitats and 18 in nonagricultural habitats. The mean richness, mean diversity, and evenness of helminths were significantly different between the habitats (P < 0.05). The body size of the host was the important factor in determining parasite richness. Both habitats exhibited differences in community ordination. The helminth species in the 2 habitats exhibited the same interspecific relationships, although differences were observed in the intensity of infection.

Coexistence of helminth species in Lysapsus limellus (Anura: Pseudidae) from an Argentinean subtropical area: influence of biotic and abiotic factors

Abstract. The need for studies on helminth communities of South American amphibians was addressed by examining changes in composition and population dynamics of the helminth component and infracommunities in the frog Lysapsus limellus Cope, 1862, from 1994 to 1996. Two pond types were considered, one permanent and one semipermanent. The main goals of this study were (1) to investigate the relationships between pond type, season, study time, frog body size, and frog sex and the presence-absence and counts of helminth parasite species in the frog host, L. limellus, and (2) to examine the co-occurrence of the different parasite species in the frog host in terms of the structure, assembly, and dynamics of the helminth infracommunity. Parasite presence and absence were analyzed using logistic regression and parasite counts were analyzed using log-linear modeling. To examine the association between parasite species, a principal components analysis was carried out on the correlation matrix for the counts. The pattern of co-occurrences was also examined through a randomization test. The main results were as follows: (1) five parasite species were found in the infracommunity; (2) the pond type and the host size class were the principal factors related to the presence and absence of parasites for the three dominant species, while the year of study and the host sex were only important for one of the species; (3) for the parasite counts, many more factors were significant, with body size class and pond type always important factors for the three core species of the infracommunity, with season, year of study, and sex also sometimes important, and (4) strong associations were observed between some helminth species of the host from the permanent pond, but the same species did not co-occur in frogs in the semipermanent pond. The life histories of the five species can be considered as opportunistic or r strategists.

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.

NICHE SPECIFICITY OF TWO GLYPTHELMINS (TREMATODA) CONGENERS INFECTING LEPTODACTYLUS CHAQUENSIS (ANURA: LEPTODACTYLIDAE) FROM ARGENTINA

Abstract Sixty-five specimens of the frog Leptodactylus chaquensis were infected by 2 Glypthelmins species (Glypthelmins repandum: 41%, and Glypthelmins palmipedis: 38%) in the small intestine. This study was designed to determine the site specificity of both species along the length of the small intestine by analyzing the distribution, niche overlap, morphological characteristics, and population dynamics. The location of G. palmipedis is very restricted, with the core infection site in the anterior small intestine. In contrast, G. repandum can be characterized as having an expanded niche within the small intestine. In single infections and with different intensities, individuals of both parasitic species showed preference for the anterior small intestine. In concurrent infections and with different intensities, the distribution of G. palmipedis did not change when G. repandum was present; however, displacement of G. repandum toward the middle of the small intestine was observed. Glypthelmins species used the same microhabitat and presumably the same food resource and were generally found to overlap more than expected by chance. This finding suggests the possibility of different feeding mechanisms given by differences in their pharynx size by 37%. Also, the coexistence of these could be associated with the differentiation of realized niches.

Helminth community structure in the Argentinean bufonid Melanophryniscus klappenbachi: importance of habitat use and season

The goal of this study was to evaluate the relative influence of terrestrial habits, season, and host body size on the species richness and abundance of helminth parasites in the toad Melanophryniscus klappenbachi, for which a greater abundance of nematode parasites was expected. A total of 90 toads were collected in the Chaco Province, Argentina. The helminth community found in infected toads included 17 taxa and was dominated particularly by larval parasites. Contrary to our expectations, nematode species showed lower values of infection parameters. Infected toads harbored a maximum of seven species, and the mean helminth richness was 3.16u2009±u20091.66 species per infected toads. Season played a significant effect on determining the species richness and abundance of the parasite infracommunity. Similarly, the prevalence of infection of several helminth species (8/47xa0%) varied greatly over time. Host body size was the main factor in determining the infrapopulation structure of helminth parasites. Species richness was significantly and negatively correlated with host body size. Strong associations were observed mainly between larvae of some species. The transmission strategies of parasites suggest that this bufonid acquires infections through direct contact with larval parasites from aquatic and terrestrial habitats and by ingestion of infective larvae. The characteristic of the host tegument, such as the presence of alkaloids, could significantly contribute to the low occurrence of infection by skin-penetrating nematodes. Results also showed that diets and mobility of the host and the local microhabitat conditions play an important role in parasitic infections of toads.

The effect of chemical signal of predatory fish and water bug on the morphology and development of Elachistocleis bicolor tadpoles (Anura: Microhylidae)

Changes in environmental conditions can induce organisms to alter their morphology, behavior and life history. Predation is an important factor in many aquatic communities and can strongly select for anti-predator responses. In the present work, we examined the responses in morphology, growth rate and development rate of Elachistocleis bicolor tadpoles raised in the presence of chemical cues from two different predators: a water bug (Belostoma elongatum) and a fish (Moenkausia dichroura). The experiment was performed in microcosm conditions. The experimental design consisted of three treatments: chemical cues from fish, cues from water bugs and a control group. Each treatment was replicated 30 times. Each container held a single larva. The main results were: (1) there were significant differences in body depth between the predator treatments (fish vs. water bug) and between the control group and the water bug treatment, (2) there were significant differences in tail depth between predator treatments (fish vs. water bug) and between the control group and the fish treatment, (3) there were no significant differences in the growth rate and developmental rate among the treatments. Our results suggest that the presence of predaceous fish and water bugs cause different effects on tadpole morphology. In the presence of water bugs, tadpoles decreased body depth, whereas in the presence of fish tadpoles increased tail depth. These responses could be related to the way in which predators capture their prey. Predator chemical cues did not have any detectable effect on the growth rate and development rate of E. bicolor tadpoles.

Spatial distribution, temporal variation and specificity of microhabitat of Tropisternus species (Coleoptera: Hydrophilidae) in permanent ponds.

The spatial distribution and temporal variation of 11 species of Tropisternus were analyzed in two permanent ponds located in the province of Corrientes, Argentina. Samples were collected every 15xa0days, between October 2010 and March 2011. The species recorded were Tropisternus collaris (Fabricius), Tropisternus ovalis Castelnau, Tropisternus laevis (Sturm), Tropisternus lateralis limbatus (Brullé), Tropisternus longispina Fernández & Bachmann, Tropisternus carinispina Orchymont, Tropisternus bourmeisteri Fernández & Bachmann, Tropisternus apicipalpis (Chevrolat), Tropisternus dilatatus Bruch, Tropisternus obesus Bruch, and Tropisternus ignoratus Knisch. The first four were present in higher proportions than the remaining during most of the study period. The spatial distribution of individuals was mostly related to the homogeneity or heterogeneity of the ecosystem in relation to microhabitats with aquatic vegetation: In ponds with different microhabitats, individuals were mainly aggregated, whereas in ponds with homogenous features, individuals were randomly distributed. However, when species were analyzed individually, the spatial distribution and the use of microhabitat by each species were different with respect to preference and behavior.

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.

Population parameters of two water scavenger beetles: Derallus angustus Sharp, 1882 and Enochrus vulgaris (Steinheil, 1869) (Coleoptera: Hydrophilidae) in permanent ponds: spatial distribution and microhabitat preference

The spatial distribution, temporal variation, and microhabitat preference of two populations of aquatic Coleoptera were analysed in permanent ponds located in the province of Corrientes, Argentina. Samples were collected every 15 days, between October 2010 and October 2011. The dispersion index and distribution models (Poisson Series, positive binomial and negative binomial) were used to evaluate the spatial distribution. For the evaluation of the microhabitat preference we used non-parametric Kruskal–Wallis test and then the Dunn test with the Bonferroni’s correction. In the test of the use of different microhabitats, we used a K proportion test and, when significant, a two proportion Z test was applied between pairs of microhabitats. The species analysed were the hydrophilids Derallus angustus Sharp and Enochrus vulgaris (Steinheil). The results indicate that the spatial distribution of individuals was mostly related to the homogeneity or heterogeneity of the ecosystem. However, when species were analysed individually, the spatial distribution and the use of microhabitat by each of them were different with respect to preference and behaviour. The macrophytes also play a role in the dynamics of these species, as they favour or limit the abundance by modifying the structure thereof.

A preliminary study of aquatic Coleoptera in temporary ponds and the ecological variables influencing their richness and diversity

Water beetles possess a wide variety of ecological attributes that allow them to occupy a wide range of aquatic habitats. Temporary ponds are environments that experience recurrent drought periods that may differ in duration; each pond is further characterized by a particular fauna, and by the size of the population that can be supported. The richness (S) and diversity (H) of water beetles collected in temporary ponds in Corrientes province were analyzed. Rarefaction was used to avoid estimation bias and to use comparative methodology. Pearson correlations were calculated using water temperature, depth, surface (m²), diversity (Shannon & Wiener) and richness. A total of 660 individuals, including 42 species, 22 genera and 7 families were recorded. The greatest percentage of species belonged to the family Hydrophilidae (45%) followed by Dytiscidae (32%) and Noteridae (15%), while the remaining families represent less than 10% of the total species. The Kruskal- Wallis tests did not find significant differences in diversity and richness between the temporary ponds analyzed. The most correlated variables in different ponds were diversity and hydroperiod, surface and depth