Domingos de Jesus Rodrigues

Antiproliferative activity of Rhinella marina and Rhaebo guttatus venom extracts from Southern Amazon

The venom of amphibians is a fascinating source of active substances. In view of their medical importance and aiming to explore the amazing Brazilian biodiversity, we conducted bioprospecting of antiproliferative activity in extracts of Rhinella marina and Rhaebo guttatus toads occurring in the Southern Amazon of Mato Grosso, Brazil. LC-MS and HPLC analysis of the venom extracts of R. marina revealed four bufadienolides (telocinobufagin, marinobufagin, bufalin and resibufogenin. R. guttatus venom extracts contained only marinobufagin. First, R. marina and R. guttatus venom extracts were evaluated for cytotoxicity against tumor cell lines by the MTT assay. All extracts revealed cytotoxicity, where R. marina extracts were comparable to doxorubicin (IC₅₀ values ranging from 0.01 to 0.23 μg/mL). Only extracts of R. guttatus toad venom caused membrane disruption of human erythrocytes. The extracts were investigated for selective activity by determining their effect on stimulated human peripheral blood mononuclear cells (PBMC) with the Alamar Blue™ assay. The extracts were up to 80-fold more selective against leukemia cells when compared to dividing leukocytes. Aiming to confirm these antiproliferative effects, BrdU incorporation into DNA was measured in HL-60 treated cells with R. marina venom extracts. These extracts decreased BrdU incorporation at both concentrations tested. In summary, nine extracts of R. marina and R. guttatus venom showed pronounced lethal and discriminating effects on tumor lines, especially those from R. marina, highlighting toad parotoid gland secretions as a promising source for novel lead anticancer chemicals.

Temporary Pond Availability and Tadpole Species Composition in Central Amazonia

Abstract Habitat availability for larval development is one of the main factors affecting the distribution of anuran species. However, little is known about the spatial distribution of these habitats, and estimates of the number of available ponds for a given reserve size are not available in Amazonia. Temporary water bodies were surveyed in a 30-m strip around a 144-km system of trails in a terra firme tropical forest, and tadpoles were collected to evaluate differences in species composition between isolated and streamside ponds. More than 90% of the ponds were <150 m from a stream, and the tadpole species composition differed between isolated and streamside ponds. Isolated ponds were less common, but were, on average, more stable in time than streamside ponds. Despite the limited distribution of isolated forest ponds, species of frogs dependent on them were found throughout the reserve. The presence of both types of ponds is important for the maintenance of the local pond-breeding anuran community. This study shows that isolated and streamside forest ponds maintain a distinct assemblage of frogs, and isolated ponds are much less common, but are, on average, more predictable in time than streamside ponds.

Padrão reprodutivo de Elachistocleis bicolor (Anura, Microhylidae) na Serra da Bodoquena, Mato Grosso do Sul, Brasil

The reproductive pattern of Elachistocleis bicolor (Guerin Meneville, 1838) was studied at Serra da Bodoquena, from October 2000 to September 2001. Reproduction occurred in the wet season (October to April) and was correlated to high continuous pluviometric precipitation. The species presents sexual size dimorphism, with females larger than males. The number of mature eggs per ovary was 620 ± 251 (n=39) and mature eggs measured 1.15 ± 0.30 mm (n=40). Elachistocleis bicolor presented significant relations between snout-vent length and number of mature eggs (n=39; r2=0.25; p=0.001), individual weight and number of mature eggs (n=41, r2=0.30; p=0.002), snout-vent length and ovarian weight (n=35; r2=0.47; p<0.01), and individual weight and ovarian weight (n=36; r2=0.55; p<0.01). Weight and volume are better to study size-fecundity relationships than snout-vent length. The females invested 22.7 ± 6.3 % (n=35) of their weights in reproduction and the variance associated to this variable was high, related to the reproductive mode of the species.

Rapid assessment of fruit-color selection by birds using artificial fruits at local scale in Central Amazonia

Modeling clays have been used in several ecological experiments and have proved to be an important tool to variables control. The objective of our study was to determine if fruit color in isolated and grouped displays influences the fruit selection by birds in the field using artificial fruits. Data were collected in six plots distributed homogeneously in 3 km long trails with a minimum distance of 0.5 km. We used a paired experimental design to establish our experiments, so that all treatments were available to the local bird community in each plot. Overall, red was more pecked than brown and white. Isolated red and brown displays were significantly more pecked than others display. Even though our study was conducted in small spatial scales, artificial fruits appeared to be efficient in register fruit consumption attempts by bird. Although inconclusive about selective forces that sharp the dynamics of fruit color polymorphisms and choice by frugivorous birds, our findings corroborate recent studies wherein birds showed preferences by high- over low-contrast fruit signals.

Functional necrophilia: a profitable anuran reproductive strategy?

Explosive breeding is a common reproductive strategy, especially in anurans. In some cases of explosive breeding in anurans, intense aggressive interactions occur among males attempting to gain access to females, and for terrestrial species that mate in water, females may die by drowning during long mating struggles. Such occurrences are obviously detrimental to females, and may also cause a decrease in the reproductive success of males through depletion of energy without obtaining access to a live female. However, the males of the small Amazonian frog Rhinella proboscidea can promote the ejection of oocytes from the abdominal cavities of dead females and fertilize them. This behaviour can minimize losses to both partners during explosive reproduction events. The existence of such a “functional necrophile strategy” shows that there may be possible selection in favour of stronger and more persistent males in explosive breeders.

Amphibia, Anura, Microhylidae, Chiasmocleis avilapiresae Peloso and Sturaro, 2008 and Chiasmocleis bassleri Dunn, 1949: New Distribution records

This note reports the presence of Chiasmocleis bassleeri and C. avilapiresae in the north of Mato Grosso state. It extends the distribution of C. avilapiresae and C. bassleri 140 km from the nearest known locality (Aripuana, MT, Brazil) and 1170 and 1350 km from the type-locality (Floresta Nacional de Caxiuana, state of Para, Brazil and Rio Utoquinia to Rio Tapiche, Peru, respectively).

Predation of bat (Molossus molossus: Molossidae) by the centipede Scolopendra viridicornis (Scolopendridae) in Southern Amazonia

Centipedes are opportunistic carnivore predators, and large species can feed on a wide variety of vertebrates, including bats. The aim of this study was to report the third record of bat predation by centipedes worldwide, the first record in the Amazon region, while covering aspects of foraging, capture and handling of prey. We observed the occurence in a fortuitous encounter at Cristalino State Park, located in the Amazon region of the state of Mato Grosso, Brazil. The attack took place in a small wooden structure, at about three meters from the floor, and was observed for 20 minutes. During the observation, the centipede stung the neck and abdominal region of the bat several times, grabbing the prey with its 15 pairs of front legs while hanging from the ceiling with its hind legs. This type of observation suggests that vertebrates can be important preys for invertebrates such as giant centipedes, both for its nutritional composition and for the amount of energy available in a single prey.

Amphibia, Anura, Leptodactylidae, Leptodactylus paraensis Heyer, 2005: distribution extension, new state record, and geographic distribution map

This note reports the presence of Leptodactylus paraensis at the municipality of Claudia, state of Mato Grosso, central Brazil. This is the first recorded for this species in Mato Grosso.

Amblyomma tick species infesting amphibians and reptiles in the seasonally dry Amazon forest, with new host records for Amblyomma rotundatum (Acari: Ixodida: Ixodidae)

Abstract Our study yielded a list of ticks found on amphibians and reptiles at five sites within seasonally dry Amazon forest in Mato Grosso State, central Brazil, in addition to new host records for A. rotundatum. We collected 431 tick specimens: 79 larvae, 115 nymphs, 38 females, and 199 males belonging to A. humerale, A. rotundatum, and Amblyomma sp., on 39 anurans and 21 reptiles. The toads R. guttatus and R. margaritifera and the frog L. pentadactylus are new hosts for A. rotundatum.

Antiplasmodial and Cytotoxic Activities of Toad Venoms from Southern Amazon, Brazil

The drug-resistance of malaria parasites is the main problem in the disease control. The huge Brazilian biodiversity promotes the search for new compounds, where the animal kingdom is proving to be a promising source of bioactive compounds. The main objective of this study was to evaluate the antiplasmodial and cytotoxic activity of the compounds obtained from the toad venoms of Brazilian Amazon. Toad venoms were collected from the secretion of Rhinella marina and Rhaebo guttatus in Mato Grosso State, Brazil. The powder was extracted at room temperature, yielding 2 extracts (RG and RM) and a substance (‘1’) identified as a bufadienolide, named telocinobufagin. Growth inhibition, intraerythrocytic development, and parasite morphology were evaluated in culture by microscopic observations of Giemsa-stained thin blood films. Cytotoxicity was determined against HepG2 and BGM cells by MTT and neutral red assays. The 2 extracts and the pure substance (‘1’) tested were active against chloroquine-resistant Plasmodium falciparum strain, demonstrating lower IC50 values. In cytotoxic tests, the 2 extracts and substance ‘1’ showed pronounced lethal effects on chloroquine-resistant P. faciparum strain and low cytotoxic effect, highlighting toad parotoid gland secretions as a promising source of novel lead antiplasmodial compounds.