Jonas Pederassi

Antennation and sexual performance of male digger wasps Sphex ingens Smith (Hymenoptera: Sphecidae)

ABSTRACT Antennation can play several roles in hymenopteran copulation, mainly in wasps. The digger wasp Sphex ingens Smith has a very peculiar sexual behaviour, in which forced copulation is a striking element. However, communication through antennation during the pre-copulation and copulation phases and the relationship between the sexual performance of males and the final result of copulation require further clarification. The sexual behaviour of wild populations of S. ingens was filmed during the breeding season in a site between the beaches Meros and Aventureiro, Ilha Grande, southeastern Brazil. We assessed antennation behaviour, courtship duration, sexual performance, and genital clasping. Only successful males had the genital clasping assessed. Evidence found so far points out that the successful males showed better sexual performance – that is, they antennated more in a shorter courtship duration. Also, genital clasping in successful males did not depend on antennation, courtship duration, or sexual performance. Our results shed light on some aspects of the sexual behaviour of wasps, as they explain part of the sexual selection mechanisms adopted by the species.

Acoustic niche partitioning in an anuran community from the municipality of Floriano, Piauí, Brazil

Vocalizations are an important trait for the identification of cryptic and/or closely related amphibian species. Different vocalizations also contribute to partitioning of the acoustic space by sympatric species. This study aimed to describe the advertisement calls of anurans in a pond of the municipality of Floriano, State of Piauí, Brazil, and infer the acoustic niche partitioning of amphibians. Euclidean distance was used in a cluster analysis approach to infer the acoustic similarities among species. Thirteen species were analysed: Boana raniceps, Dendropsophus nanus, D. rubicundulus , D. minutus, Leptodactylus fuscus, L. troglodytes, L. vastus, Pithecopus nordestinus , Physalaemus cuvieri, P. nattereri, Pleurodema diplolister, Proceratophrys cristiceps and Scinax ruber. From these, six showed more than 90% of acoustic overlap: P. nattereri , P. cuvieri, L. fuscus and L. vastus (Leptodactylidae); and, D. nanus and D. rubicundulus (Hylidae). Despite the acoustic similarities among these six species, the acoustic interference was reduced due to the small number of sympatric species and to distinct features on carrier frequency such as dominant frequency and the degree of modulation in the frequency. Environmental factors limit the periods and sites of reproduction respectively, which may maintain the low anuran diversity and consequently reduce acoustic overlap.

Predatory specialization in the wasp Sphex ingens for the capture of katydids

Sphex ingens is one of 30 species in the family Sphecidae that occur in the state of Rio de Janeiro. However, details of the behavior and sexual selection of natural populations of this wasp species have only recently been unveiled. In addition, the knowledge of its ecology is still poor. This is the first study on the feeding behavior interactions between S. ingens and prey captured to feed its larvae. Paralyzed prey were collected manually at the sites of wasp nests on Aventureiro Beach, Ilha Grande, Brazil during the provisioning activity of marked female S. ingens. All prey were preserved, their sex and sexual maturity were determined, and they were identified to the lowest possible taxonomic level. The body mass and size of the prey and female wasps were measured. Sphex ingens females captured only Pleminia vicina and Meroncidius sp. The body masses of wasps and katydids were positively correlated. The body mass of captured katydids was significantly dependent on the wasp’s wing length. Most of the prey were adult females, but the differences did not confirm possible preferences, as those values can be related to differences in the distribution and fluctuation in the population density of prey species and to the individual foraging strategies of female wasps. However, the predisposition to predatory specialization exhibited by S. ingens populations in Ilha Grande and elsewhere suggests that this interaction can be an important source of mortality for populations of pseudophylline katydid species.

Estimation of a closed population size of tadpoles in temporary pond

The practice of capture-recapture to estimate the diversity is well known to many animal groups, however this practice in the larval phase of anuran amphibians is incipient. We aimed at evaluating the Lincoln estimator, Venn diagram and Bayes theorem in the inference of population size of a larval phase anurocenose from lotic environment. The adherence of results was evaluated using the Kolmogorov-Smirnov test. The marking of tadpoles for later recapture and methods measurement was made with eosin methylene blue. When comparing the results of Lincoln-Petersen estimator corresponding to the Venn diagram and Bayes theorem, we detected percentage differences per sampling, i.e., the proportion of sampled anuran genera is kept among the three methods, although the values are numerically different. By submitting these results to the Kolmogorov-Smirnov test we have found no significant differences. Therefore, no matter the estimator, the measured value is adherent and estimates the total population. Together with the marking methodology, which did not change the behavior of tadpoles, the present study helps to fill the need of more studies on larval phase of amphibians in Brazil, especially in semi-arid northeast.