Inter-individual variation and temperature-dependent antipredator behavior in the snake Tomodon dorsatus (Dipsadidae)

Study of defensive behavior of a venomous snake as a new approach to understand snakebite

Snakebites affect millions of people worldwide. The majority of research and management about snakebites focus on venom and antivenom, with less attention given to snake ecology. The fundamental factor in snakebites is the snakes' defensive biting behavior. Herein we examine the effects of environmental variables (temperature, time of day, and human stimulus) and biological variables (sex and body size) on the biting behavior of a medically significant pit viper species in Brazil, Bothrops jararaca (Viperidae), and associate it with the epidemiology of snakebites. Through experimental simulations of encounters between humans and snakes, we obtained behavioral models applicable to epidemiological situations in the State of São Paulo, Brazil. We found a significant overlap between behavioral, morphological, environmental, and epidemiological data. Variables that increase snakebites in epidemiological data also enhance the tendency of snakes to bite defensively, resulting in snakebites. We propose that snakebite incidents are influenced by environmental and morphological factors, affecting the behavior of snakes and the proportion of incidents. Thus, investigating behavior of snakes related to snakebite incidents is a valuable tool for a better understanding of the epidemiology of these events, helping the prediction and, thus, prevention of snakebites.

Fear-based aggression and its relationship to corticosterone responsiveness in three species of python

It has long been known that even closely related species can vary in their antipredator behavior, and in the last two decades there has been mounting interest in how these differences might relate to the hormonal stress response. We tested the relationship between fear-based aggression, a form of antipredator behavior, and plasma corticosterone levels in three species of python [Children's Python (Antaresia childreni), Ball Python (Python regius), Bismarck Ring Python (Bothrochilus boa)]. We recorded the amount of striking in response to perturbation before and after a controlled, stressful confinement. We also measured plasma corticosterone levels prior to confinement, after confinement, and after confinement plus an adrenocorticotropin hormone (ACTH) injection, the later to induce a maximal corticosterone response. We performed among species analyses using two mixed models, and we determined between individual variance within each species to estimate repeatability. Bismarck Ring Pythons struck more than either Ball Pythons or Children's Pythons, and Ball Pythons had a suppressed corticosterone response compared to Children's and Bismarck Ring Pythons. Thus, mean species fear-based aggression correlated with species level differences in corticosterone profile. We also found evidence suggesting behaviors are repeatable within individuals. Our results point to a need for further exploration of aggression, anti-predator behavior, and corticosterone profile.

Bites by Tomodon dorsatus (serpentes, dipsadidae): Clinical and epidemiological study of 86 cases

A total of 86 proven cases of Tomodon dorsatus bites admitted to Hospital Vital Brazil (HVB) of Butantan Institute, in São Paulo, Brazil, between 1945 and 2018, were retrospectively analyzed. The cases included were those in which the snake was brought to HVB and was correctly identified. Of the 86 cases of snake bites, it was possible to describe the sex of the snake in 52 cases; 31 (59.6%) snakes were male. Only 52 snakes out of 86 could be studied because of their preservation status. The length of snakes (snout-vent length) ranged from 180 to 770 mm. Of the 86 snakes, 72 could be distinguished as adults (n = 63, 87.5%) or juveniles (n = 9, 12.5%). Most bites occurred in the spring and summer seasons (n = 57, 66.3%) and during warmer periods of the day (n = 61, 72.6%), between 9 a.m. and 3 p.m. The mean (±standard deviation) age of the victims was 26.9 ± 17.2 years, and 60 (69.8%) were men. Approximately 90% of the patients sought medical care within 6 h after the bite. Both upper (n = 45, 52.3%) and lower (n = 37, 43.0%) limbs were the most frequently bitten, particularly the feet and hands (n = 54, 62.8%). The local clinical manifestations were pain (n = 55, 64.0%), transitory bleeding (n = 23, 26.7%), erythema (n = 22, 25.6%), edema (n = 14, 16.3%), paresthesia (n = 9, 10.5%), and ecchymosis (n = 3, 3.5%). Only 10 (11.6%) patients reported non-specific systemic symptoms characterized by transient dizziness or mild headache, and 21 (24.4%) patients showed no evidence of envenomation. A 20 min whole blood clotting test was performed in 31 (36.0%) patients on admission and all of them had coagulable blood. Supportive treatment was offered to 38 (44.2%) patients, namely, antiseptic (n = 20, 23.3%), antihistamines (n = 12, 14.0%), and analgesics (n = 9, 10.5%). Four (4.7%) patients were inappropriately treated with Bothrops antivenom before their admission to HVB. No sequelae or relevant complications were observed in patients, and the prognosis was benign. Therefore, although T. dorsatus bites can cause mild local symptomatology, it is important that health professionals know how to make the correct diagnosis to avoid unnecessary use of antivenom.

Beyond body size: muscle biochemistry and body shape explain ontogenetic variation of anti-predatory behaviour in the lizard Salvator merianae

Anti-predatory behaviour evolves under the strong action of natural selection because the success of individuals avoiding predation essentially defines their fitness. Choice of anti-predatory strategies is defined by prey characteristics as well as environmental temperature. An additional dimension often relegated in this multilevel equation is the ontogenetic component. In the tegu Salvator merianae, adults run away from predators at high temperatures but prefer fighting when it is cold, whereas juveniles exhibit the same flight strategy within a wide thermal range. Here, we integrate physiology and morphology to understand ontogenetic variation in the temperature-dependent shift of anti-predatory behaviour in these lizards. We compiled data for body shape and size, and quantified enzyme activity in hindlimb and head muscles, testing the hypothesis that morphophysiological models explain ontogenetic variation in behavioural associations. Our prediction is that juveniles exhibit body shape and muscle biochemistry that enhance flight strategies. We identified biochemical differences between muscles mainly in the LDH:CS ratio, whereby hindlimb muscles were more glycolytic than the jaw musculature. Juveniles, which often use evasive strategies to avoid predation, have more glycolytic hindlimb muscles and are much smaller when compared with adults 1-2 years old. Ontogenetic differences in body shape were identified but marginally contributed to behavioural variation between juvenile and adult tegus, and variation in anti-predatory behaviour in these lizards resides mainly in associations between body size and muscle biochemistry. Our results are discussed in the ecological context of predator avoidance by individuals differing in body size living at temperature-variable environments, where restrictions imposed by the cold could be compensated by specific phenotypes.

Crossing regimes of temperature dependence in animal movement

A pressing challenge in ecology is to understand the effects of changing global temperatures on food web structure and dynamics. The stability of these complex ecological networks largely depends on how predator-prey interactions may respond to temperature changes. Because predators and prey rely on their velocities to catch food or avoid being eaten, understanding how temperatures may affect animal movement is central to this quest. Despite our efforts, we still lack a mechanistic understanding of how the effect of temperature on metabolic processes scales up to animal movement and beyond. Here, we merge a biomechanical approach, the Metabolic Theory of Ecology and empirical data to show that animal movement displays multiple regimes of temperature dependence. We also show that crossing these regimes has important consequences for population dynamics and stability, which depend on the parameters controlling predator-prey interactions. We argue that this dependence upon interaction parameters may help explain why experimental work on the temperature dependence of interaction strengths has so far yielded conflicting results. More importantly, these changes in the temperature dependence of animal movement can have consequences that go well beyond ecological interactions and affect, for example, animal communication, mating, sensory detection, and any behavioral modality dependent on the movement of limbs. Finally, by not taking into account the changes in temperature dependence reported here we might not be able to properly forecast the impact of global warming on ecological processes and propose appropriate mitigation action when needed.