pp. 83-87

Authors: Jessica Fletcher, Anita Malhotra & Wolfgang Wüster

Abstract: Predators exploiting chemically defended prey are generally resistant to prey toxins. However, toxin resistance usually incurs a fitness cost and is therefore often lost when no longer needed. Bufonid toads are a frequently abundant food resource, but chemically defended by a group of cardiotonic steroids, bufadienolides. Bufophagous predators have evolved a specific and near-universal mechanism of resistance to these toxins, consisting of two amino acid substitutions in the Na+/K+-ATPase H1–H2 extracellular domain. The dynamics of loss or retention of this adaptation in secondarily non-bufophagous lineages remain inadequately understood. Here we explore this topic by showing that the piscivorous banded water cobra [i]Naja annulata[/i] retains the bufadienolide-resistant genotype of the otherwise toad-eating cobra clade. This confirms a trend for secondarily non-toad-eating snakes to retain bufadienolide resistance.

Keywords: Antipredator adaptation, cardiotonic steroid, cardiac glycoside, evolution, piscivory

pp. 76-82

Authors: Matheus Marques Bitencourt & Gleomar Fabiano Maschio

Abstract: Brazil has the largest diversity of crocodilians in the world, with six species present in the country. Considered as opportunistic generalist predators, these animals occupy the top of the food chain in river ecosystems. Anthropic actions result in an impact both on habitats and on the behaviour of the crocodilians, in addition to facilitating the encounter between humans and crocodilian species. In this study, we evaluated the characteristics of alligator incidents on humans in Brazil during the years 2000–2022. We used online platforms for scientific articles and news, collecting information about the victims, the species involved, and the locality of occurrence. We found 86 records of incidents, of which 18 resulted in the victim's death. The Amazon biome encompass the highest number of incidents, and the black caiman [i]Melanosuchus niger[/i] was the species involved most. Most incidents (n = 35) occurred with people who were fishing or on boats. Considering the size of the country's population, alligator incidents on humans in Brazil can be considered rare, but they should not be overlooked. The advancement of activities that degrade the environment, causing imbalances, can cause an increase in the likelihood of encounters and, consequently, incidents, which usually generates critical medical problems and negative consequences for the populations of these animals.

Keywords: Alligator, attack, bite, Caiman, [i]Melanosuchus[/i]

pp. 68-75

Author: Jesús A. Rivas

Abstract: The maximum size that snakes can reach has been a matter of long held debate until the discovery of [i]Titanoboa cerrejonensis[/i] (Boidae). It was an aquatic predator that lived 60–58 million years ago in what is currently eastern Colombia, occupying tropical swamps. It was calculated to measure 12.82 metres and it was speculated that it grew so much due to a warmer planetary weather. Its life history and ecology are speculated to be very similar to that of current day anacondas. Using data from a long-term study involving hundreds of green anacondas [i]Eunectes murinus[/i], this study makes inferences about aspects of the natural history of [i]T. cerrejonensis[/i] that perhaps will not be easily available by studying the fossil record. Drawing parallels with anaconda's biology, I estimate that a non-breeding female [i]T. cerrejonensis[/i] weighed approximately 1,232 kg, and 1,465 kg when pregnant. It would have started breeding at 480 cm SVL, weighing 95 kg. New-born [i]Titanoboa[/i] were between 181 and 215 cm. Its average meal was estimated to be 505 kg, with a potential maximum of 1,799 kg. I estimate that [i]Titanoboa[/i] had a growth rate of 0.046 mm/day compared with 0.036 in anacondas; which does not support the notion that it grew more due to a warmer planet. Although the results are largely speculative, they help give a better idea of what the life of an extinct snake was like.

Keywords: Gigantism, prey size, reproductive biology, life history, palaeothermometer, giant snake, allometry, palaeoecology

pp. 58-67

Authors: Geane Rodrigues de Souza, Tainã Lucas Andreani, Seixas Rezende Oliveira, Bruno Barros Bittar, Marco Antônio Guimarães & Alessandro Ribeiro Morais

Abstract:  The vocalisations of anurans are one of their principal forms of communication and are mainly used for specific recognition involving the attraction of reproductive mates and territorial defense. In this study, we analysed the advertisement calls of 101 individuals from a population of [i]Scinax fuscomarginatus[/i] sampled in the type locality of [i]S. pusillus[/i] (currently under the synonymy of [i]S. fuscomarginatus[/i]). Specifically, we investigated acoustic variation at several levels: intraindividual, interindividual, throughout the night, and across six breeding seasons by analysing temporal and spectral parameters. We identified that all parameters of the advertisement call can be used for individual recognition, with the maximum frequency having the greatest potential. We then observed that all other acoustic parameters were influenced by the predictor variables, with the exception of maximum frequency. The air temperature negatively influenced call duration, number of pulses, dominant frequency and minimum frequency; while it positively influenced pulse rate and call rate during the breeding season. Furthermore, with the exception of call duration and pulse rate, the other acoustic parameters varied significantly across the different nocturnal periods. This study provides data on the variation in [i]S. fuscomarginatus[/i] acoustic features. Besides, we also discuss the implications of individual recognition. Studies that consider different sources of variation for the same population of a given species are uncommon, but of paramount importance for understanding the behavioural dynamics of the population.

Keywords: advertisement call, behaviour, individual recognition, sexual-selection