16. Seminarios - Presentación de artículos (17/10)

An austral anuran assemblage in the Neotropics: seasonal occurrence correlated with photoperiod.

The study describes habitat use and temporal occurrence of calling males for an austral anuran assemblage in the Neotropics, southern Brazil. Three study sites (S1 – a permanent river and a stream, S2 – a dam and backwater, S3 – two permanent ponds periodically connected) were sampled between August 2005 and July 2006. The site S3 presented the richest and most diverse assemblage and habitat use within studied sites, and was partitioned by species groups. Richness and abundance of calling males for overall assemblage were seasonal, concentrated in spring and summer and correlated with photoperiod. Temperature, rainfall and air humidity were not correlated with the richness and abundance of calling males. Photoperiod also explained the calling seasons when species were analyzed individually. Habitat use and temporal occurrence were complementary in the partitioning of breeding resources, explaining species coexistence.

Ecology of Hypsiboas albopunctatus (Anura: Hylidae) in a Neotropical Savanna

Although the treefrog Hypsiboas albopunctatus (Spix, 1824) (Anura: Hylidae) is abundant in South America, especially in regions of open vegetation in Brazil, information regarding its natural history is still scarce. This study describes its ecology including aspects of microhabitat use, population dynamics, diet, and reproduction in the Cerrado biome of central Brazil. We used model selection to test hypotheses of variation in survival and recapture rates as a function of differences in sex, seasonality, and climatic variables. We also tested hypotheses regarding sexual dimorphism. This species uses mainly herbaceous vegetation and bushes along margins of the ponds. Apparent survival, estimated using the Cormack-Jolly-Seber mark-recapture model, was higher for males than females and was negatively correlated with rainfall. Recapture probability was influenced by seasonality, presenting higher values in the wet season. This highlights the influence of weather, especially seasonal rainfall, on the population dynamics of anurans occurring in tropical savannas. The analysis of previously preserved individuals showed strong sexual dimorphism in body size and shape, with females being larger than males. Female body size positively correlated with clutch volume. Hypsiboas albopunctatus seems to have a generalist diet, consuming primarily Coleoptera, Aranae, and Orthoptera (assuming accidental vegetal ingestion). Prey size was positively correlated with anuran head size. Hypsiboas albopunctatus seems to be a generalist, as demonstrated by its continuous activity and reproduction, generalist diet, and habitat use, presenting some breeding adaptations to enhance offspring size, such as sexual size dimorphism related to clutch volume in females.

Effect of traffic noise on Scinax nasicus advertisement call (Amphibia, Anura)

Increased anthropogenic-made sounds such as traffic noises contribute to acoustic pollution, which produces deleterious effect on song vertebrates. We compared the advertisement call of Scinax nasicus (Cope, 1862) males in natural (as a reference or control, Site A) and Sites affected by traffic noises (Site B). Call structure was recorded and it was amplified in sonograms (software Raven Pro 1.5). Seven variables were measured on its advertisement call: duration (s), number of notes, number of pulses per note, maximum and minimum frequency (kHz), dominant frequency (kHz) and amplitude (dB). In addition, at each Site the background noise (the fundamental frequency, F0 and amplitude, dB) was measured. The amplitude of background noise reached higher values (68.02 dB) in Site B, while in Site A was lower (34.81 dB). Thus, the F0 in Site A was 6.28 kHz and in Site B it was 4.15 kHz. Frog call in noisy environment (Site B) were characterized by lesser duration (s) and number of pulses per note, higher maximum and dominant frequencies (kHz), lower minimum frequencies, and amplitude (dB) when compared with control environment (Site A). Our study highlights, that S. nasicus males shift their vocal structure in traffic noisy ponds, mainly by vocal “adjust” of their frequencies and amplitude to counteract masking effect. Finally, acoustic monitoring of anurans on noise environments should be considering the spatial, temporal and spectral overlap between noise and species-specific acoustic behaviour.

Human attitudes as threats in amphibians: the case of the Ornate Horned Frog (Ceratophrys ornata)

We analyzed the characteristics of the human-animal conflict coming from the attitudes that local communities have toward Ceratophrys ornata, focusing on two threats: aversion and pet trade. Surveys conducted in Argentina, Brazil and Uruguay (n = 194) showed a strong aversion to this species (45% of respondents), causing the death of at least 364 individuals. This aversion was strongly linked to symbolism and folklore beliefs, and also influenced by gender and education level. Pet trade interviews (n = 30) showed that 77% of the specimens kept in captivity were wild-caught (≈178 individuals). The killing of specimens based on aversion might have impacts at local level, especially in populations occurring in recent urbanized areas. Our results also revealed that capture of specimens for pet trade is an ongoing process. Due to the context of illegality in which trade occurs, it is highly challenging to determine/predict the extent of impacts.

Dietary sequestration of defensive steroids in nuchal glands of the Asian snake Rhabdophis tigrinus

The Asian snake Rhabdophis tigrinus possesses specialized defensive glands on its neck that contain steroidal toxins known as bufadienolides. We hypothesized that R. tigrinus does not synthesize these defensive steroids but instead sequesters the toxins from toads it consumes as prey. To test this hypothesis, we conducted chemical analyses on the glandular fluid from snakes collected in toad-free and toad-present localities. We also performed feeding experiments in which hatchling R. tigrinus were reared on controlled diets that either included or lacked toads. We demonstrate that the cardiotonic steroids in the nuchal glands of R. tigrinus are obtained from dietary toads. We further show that mothers containing high levels of bufadienolides can provision their offspring with toxins. Hatchlings had bufadienolides in their nuchal glands only if they were fed toads or were born to a dam with high concentrations of these compounds. Because geographic patterns in the availability of toxic prey are reflected in the chemical composition of the glandular fluid, snakes in toad-free regions are left undefended by steroidal toxins. Our findings confirm that the sequestration of dietary toxins underlies geographic variation in antipredatory behavior in this species and provide a unique example of sequestered defensive compounds in a specialized vertebrate structure.

Experimental evidence for predator learning and Müllerian mimicry in Peruvian poison frogs (Ranitomeya, Dendrobatidae)

The evolution of mimicry is one of the most powerful examples of evolution driven by natural selection; however it is rare in non-insect taxa and thus is understudied. Ranitomeya imitator underwent a ‘mimetic radiation’ and now mimics three congeneric model species (R. fantastica, R. summersi, and two morphs of R. variabilis), creating geographically distinct populations of the species, including four allopatric mimetic morphs. These complexes are thought to represent a case of Müllerian mimicry, but no prior empirical studies on learned avoidance by predators support this claim. In this study we used young chickens (Gallus domesticus) as naıve predators to determine if a comimetic morph of R. imitator and R. variabilis contribute to reciprocal learned avoidance by predators—a key component of Mullerian mimicry. Chickens exposed to either stimulus species demonstrated reciprocal learned avoidance; thus our results indicate that this complex functions as a Müllerian mimicry system. This study provides novel empirical evidence supporting predictions of the Müllerian mimicry hypothesis in anurans. Our study shows no difference between learned avoidance in stimuli frogs and a ‘novel’ morph of R. imitator that differed in both color and pattern, indicating that learned avoidance by predators may be generalized in this system. Generalized learning provides a plausible mechanism for the maintenance of both polytypic mimicry and the maintenance of intrapopulation phenotypic heterogeneity.

Nesting lizards (Bassiana duperreyi) compensate partly, but not completely, for climate change.

Species in which ambient temperatures directly determine offspring sex may be at particular risk as global climates change. Whether or not climate change affects sex ratio depends upon the effectiveness of buffering mechanisms that link ambient regimes to actual nest temperatures. For example, females may simply lay nests earlier in the season, or in more shaded areas, such that incubation thermal regimes are unchanged despite massive ambient fluctuation. Based on eight years of monitoring nests over a 10-year period in the field at an alpine site in southeastern Australia, we show that, even though lizards (Bassiana duperreyi, Scincidae) have adjusted both nest depth and seasonal timing of oviposition in response to rising ambient temperatures, they have been unable to compensate entirely for climate change. That inability stems from the fact that the seasonal progression of soil temperatures, and thus, the degree to which thermal regimes at the time of laying predict subsequent conditions during incubation, also has shifted with climate change. As a result, mean incubation temperatures in natural nests now have crossed the thermal threshold at which incubation temperature directly affects offspring sex in this population.

Diet of the Nile Crocodile (Crocodylus niloticus) in the Okavango Delta, Botswana

The analysis of stomach contents can shed light on patterns of prey availability and foraging habits of a predator; however, recent studies have shown the potential bias in dietary studies resulting from differential digestion rates of various prey items. The stomachs of 286 Nile Crocodiles (17–166 cm snout–vent length) were lavaged over a two-year period. Taking prey residence times into account, the contents were examined for prey eaten within 24 h. Crocodylus niloticus has a similar ontogenetic shift in diet to that of other crocodilians. Yearlings consumed primarily aquatic insecta and arachnida. As crocodile size increased (juveniles), the diet became more diverse including crustacea, amphibia, and fish. The largest size class (subadults) consumed primarily fish. Yearlings fed consistently throughout the year; however a higher proportion of empty stomachs occurred within the juvenile and subadult size classes during the winter months. Seven species of nematodes were found within the stomachs, four of which represent new geographic records.

Developments in amphibian parental care research: history, present advances, and future perspectives.

Despite rising interest among scientists for over two centuries, parental care behavior has not been as thoroughly studied in amphibians as it has in other taxa. The first reports of amphibian parental care date from the early 18th century, when Maria Sibylla Merian went on a field expedition in Suriname and reported frog metamorphs emerging from their mother’s dorsal skin. Reports of this and other parental behaviors in amphibians remained descriptive for decades, often as side notes during expeditions with another purpose. However, since the 1980s, experimental approaches have proliferated, providing detailed knowledge about the adaptive value of observed behaviors. Today, we recognize more than 30 types of parental care in amphibians, but most studies focus on just a few families and have favored anurans over urodeles and caecilians. Here, we provide a synthesis of the last three centuries of parental care research in the three orders comprising the amphibians. We draw attention to the progress from the very first descriptions to the most recent experimental studies, and highlight the importance of natural history observations as a source of new hypotheses and necessary context to interpret experimental findings. We encourage amphibian parental care researchers to diversify their study systems to allow for a more comprehensive perspective of the behaviors that amphibians exhibit. Finally, we uncover knowledge gaps and suggest new avenues of research using a variety of disciplines and approaches that will allow us to better understand the function and evolution of parental care behaviors in this diverse group of animals.

Natural history predicts patterns of thermal vulnerability in amphibians from the Atlantic Rainforest of Brazil

In the Brazilian Atlantic Rainforest (AF), amphibians (625 species) face habitat degradation leading to stressful thermal conditions that constrain animal activity (e.g., foraging and reproduction). Data on thermal ecology for these species are still scarce. We tested the hypothesis that environmental occupation affects the thermal tolerance of amphibian species more than their phylogenetic relationships. We evaluated patterns of thermal tolerance of 47 amphibian species by assessing critical thermal maxima and warming tolerances, relating these variables with ecological covariates (e.g., adult macro-and microhabitat and site of larval development). We used mean and maximum environmental temperature, ecological covariates, and morphological measurements in the phylogenetic generalized least squares model selection to evaluate which traits better predict thermal tolerance. We did not recover phylogenetic signal under a Brownian model; our results point to a strong association between critical thermal maxima and habitat and development site. Forest species were less tolerant to warm temperatures than open area or generalist species. Species with larvae that develop in lentic environment were more tolerant than those in lotic ones. Thus, species inhabiting forest microclimates are more vulnerable to the synergistic effect of habitat loss and climate change. We use radar charts as a quick evaluation tool for thermal risk diagnoses using aspects of natural history as axes.