The effects of temperature on the defensive strikes of rattlesnakes

Unpredictable aggressive defence of the venomous snake, Crotalus ravus, towards predators and humans

Antipredation behaviour is of high importance for the survival of prey animals, but it is also vital for the predator to understand the antipredator behaviour of potentially dangerous prey. Venomous snakes are particularly dangerous for their predators and humans, as a defensive bite may result in death. Here, we studied the behavioural response of the Mexican pigmy rattlesnake Crotalus ravus to the approach of simulated predators (birds and fox) and human, contrasting this to their predatory behaviour. Results showed that C. ravus defensive behaviour depended on the predator and was more aggressive towards humans. Mostly, for each type of behaviour the approach distance at first occurrence was similar among trials with different predators and reduced from freezing>rattling>escape>bite. However, we did not find clear behavioural patterns. In bird and fox trials, snakes always rattled or escaped before biting, however warning signals were not always displayed before biting and bite frequency was high in human trials, suggesting that this snake is dangerous for humans. Our results demonstrate that these snakes are flexible in their response to potential threats, but that the approach distance that elicits specific behaviours is mostly fixed.

Yawning and Its Temperature-Dependent Modulation in Leopard Geckos

Yawning is a stereotyped behavior widely observed in vertebrates, serving as an adaptation to the environment. Previous research has highlighted the correlations between yawning and physiological arousal or temperature regulation. However, the majority of those studies have primarily focused on endothermic animals. Thus far, the function of yawning in ectothermic animals remains unclear. In this study, we observed the behavior of leopard geckos, Eublepharis macularius, ectothermic reptiles, over a period of 3 days under constant ambient temperatures of 25°C, 30°C, or 35°C. By investigating the relationship between temperature, spontaneous yawning, and activity levels, we found that yawning frequency is affected by ambient temperature, and also observed a significant increase in post-yawning activity particularly under the 30°C and 35°C conditions. Furthermore, a near 24-hour periodicity in yawning was detected under all temperature conditions. These results align with previous studies conducted on endothermic animals, suggesting the conservation of primitive functions of yawning across vertebrate species.

Hooding cobras can get ahead of other snakes in the ability to evoke human fear

Fear of snakes is common not only in humans but also in other primates. Consequently, snakes are salient stimuli associated with prioritized attention, early detection and emotional significance. This has been interpreted as an adaptive evolutionary response of the primate brain to a risk of envenoming by a hidden snake. However, the struggle between mammals and snakes is not one-sided. Humans and carnivores regularly kill snakes, and thus snakes develop deterring defensive behaviour that may directly evoke enhanced fear. Here, we show that snakes depicted in threatening posture evoked on average more fear than those in resting posture. Significantly, African (Somali) and European (Czech) respondents considerably agreed on the relative fear elicited by various snakes. Nonetheless, not all defensive postures are equally efficient. Threatening cobras were perceived as top fear-evoking stimuli, even though most of them are not considered very frightening in resting posture. This effect can be attributed to their conspicuous hooding posture which evolved into an efficient warning signal for mammalian predators. Our result demonstrates that cobras are more effective than other snakes in the ability to evoke human fear by a simple behavioural display-hooding. This can be primarily explained by the behavioural evolution of cobras which successfully exploited pre-existing cognitive mechanisms of mammals. Whether human ancestors cohabiting with deadly venomous cobras further improved their fear response to hooding is uncertain, but likely.

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.

Functional diversity of snake locomotor behaviors: A review of the biological literature for bioinspiration

Organismal solutions to natural challenges can spark creative engineering applications. However, most engineers are not experts in organismal biology, creating a potential barrier to maximally effective bioinspired design. In this review, we aim to reduce that barrier with respect to a group of organisms that hold particular promise for a variety of applications: snakes. Representing >10% of tetrapod vertebrates, snakes inhabit nearly every imaginable terrestrial environment, moving with ease under many conditions that would thwart other animals. To do so, they employ over a dozen different types of locomotion (perhaps well over). Lacking limbs, they have evolved axial musculoskeletal features that enable their vast functional diversity, which can vary across species. Different species also have various skin features that provide numerous functional benefits, including frictional anisotropy or isotropy (as their locomotor habits demand), waterproofing, dirt shedding, antimicrobial properties, structural colors, and wear resistance. Snakes clearly have much to offer to the fields of robotics and materials science. We aim for this review to increase knowledge of snake functional diversity by facilitating access to the relevant literature.

Blood python (Python brongersmai) strike kinematics and forces are robust to variations in substrate geometry

Snake strikes are some of the most rapid accelerations in terrestrial vertebrates. Generating rapid body accelerations requires high ground reaction forces, but on flat surfaces snakes must rely on static friction to prevent slip. We hypothesize that snakes may be able to take advantage of structures in the environment to prevent their body from slipping, potentially allowing them to generate faster and more forceful strikes. To test this hypothesis, we captured high-speed video and forces from defensive strikes of juvenile blood pythons (Python brongersmai) on a platform that was either open on all sides or with two adjacent walls opposite the direction of the strike. Contrary to our predictions, snakes maintained high performance on open platforms by imparting rearward momentum to the posterior body and tail. This compensatory behavior increases robustness to changes in their strike conditions and could allow them to exploit variable environments.

Effect of Temperature on the Plasticity of Peripheral Hearing Sensitivity to Airborne Sound in the Male Red-Eared Slider Trachemys scripta elegans

Chelonians are considered the least vocally active group of extant reptiles and known as “low-frequency specialists” with a hearing range of <1.0 kHz. As they are ectothermic organisms, most of their physiological and metabolic processes are affected by temperature, which may include the auditory system responses. To investigate the influence of temperature on turtle hearing, Trachemys scripta elegans was chosen to measure the peripheral hearing sensitivity at 10, 20, 30, and 40°C (close to the upper limit of heat resistance) using the auditory brainstem response (ABR) test. An increase in temperature (from 10 to 30°C) resulted in improved hearing sensitivity (a wider hearing sensitivity bandwidth, lower threshold, and shorter latency) in T. scripta elegans. At 40°C, the hearing sensitivity bandwidth continued to increase and the latency further shortened, but the threshold sensitivity reduced in the intermediate frequency range (0.5–0.8 kHz), increased in the high-frequency range (1.0–1.3 kHz), and did not significantly change in the low-frequency range (0.2–0.4 kHz) compared to that at 30°C. Our results suggest that although the hearing range of turtles is confined to lower frequencies than that in other animal groups, turtle hearing showed exceptional thermal regulation ability, especially when the temperature was close to the upper limit of heat resistance. Temperature increases that are sensitive to high frequencies imply that the males turtles’ auditory system adapts to a high-frequency sound environment in the context of global warming. Our study is expected to spur further research on the high-temperature plasticity of hearing sensitivity in diverse taxa or in the same group with different temperature ranges. Moreover, it facilitates forecasting the adaptive evolution of the auditory system to global warming.

Bites by Xenodon merremii (Wagler, 1824) and Xenodon neuwiedii (Günther, 1863) (Dipsadidae: Xenodontini) in São Paulo, Brazil: a retrospective observational study of 163 cases

Despite the biological relevance and abundance of non-front-fanged colubroid snakes, little is known about their medical significance. Here, we describe the clinical, epidemiological, and biological aspects of bites by two colubroid species. We retrospectively analyzed cases of Xenodon merremii and Xenodon neuwiedii bites in which the offending snake was clearly identified. Analyses included variables related to the snake and the patient, including demographic data, clinical findings, and treatments. Of the 163 cases, 123 were bites by X. merremii and 40 by X. neuwiedii. Most bites occurred in spring and summer, predominantly during the daytime. Most offending snakes were female. Bites by X. merremii juveniles were more frequent in autumn than in other seasons, whereas those by X. neuwiedii adults were in the summer. Hands and feet were the most frequently affected regions, with no significant difference between upper and lower limbs bitten by either X. merremii or X. neuwiedii. The main clinical findings were pain, transitory bleeding, erythema, and local edema. Local edema was proportionally more frequent with X. neuwiedii bites than with X. merremii bites. No patient had extensive edema or systemic envenomation. A significant association between the snout-vent-length and transitory bleeding in bites by X. merremii, but not in those by X. neuwiedii, was identified. Whole blood clotting tests were normal in all tested patients (62 cases). Sixteen patients were incorrectly treated with anti-Bothrops antivenom. In conclusion, most accidents caused by X. merremii and X. neuwiedii present mild local symptomatology. These snakes can be mistaken for lance-headed vipers, and some bites present symptoms that resemble mild bites by Bothrops sp. Physicians should be aware of X. merremii and X. neuwiedii bites to avoid unnecessary patient distress and overprescription of antivenom.

Thermal robustness of biomechanical processes

Temperature influences many physiological processes that govern life as a result of the thermal sensitivity of chemical reactions. The repeated evolution of endothermy and widespread behavioral thermoregulation in animals highlight the importance of elevating tissue temperature to increase the rate of chemical processes. Yet, movement performance that is robust to changes in body temperature has been observed in numerous species. This thermally robust performance appears exceptional in light of the well-documented effects of temperature on muscle contractile properties, including shortening velocity, force, power and work. Here, we propose that the thermal robustness of movements in which mechanical processes replace or augment chemical processes is a general feature of any organismal system, spanning kingdoms. The use of recoiling elastic structures to power movement in place of direct muscle shortening is one of the most thoroughly studied mechanical processes; using these studies as a basis, we outline an analytical framework for detecting thermal robustness, relying on the comparison of temperature coefficients (Q ₁₀ values) between chemical and mechanical processes. We then highlight other biomechanical systems in which thermally robust performance that arises from mechanical processes may be identified using this framework. Studying diverse movements in the context of temperature will both reveal mechanisms underlying performance and allow the prediction of changes in performance in response to a changing thermal environment, thus deepening our understanding of the thermal ecology of many organisms.

The Effects of Temperature on the Kinematics of Rattlesnake Predatory Strikes in Both Captive and Field Environments

The outcomes of predator-prey interactions between endotherms and ectotherms can be heavily influenced by environmental temperature, owing to the difference in how body temperature affects locomotor performance. However, as elastic energy storage mechanisms can allow ectotherms to maintain high levels of performance at cooler body temperatures, detailed analyses of kinematics are necessary to fully understand how changes in temperature might alter endotherm-ectotherm predator-prey interactions. Viperid snakes are widely distributed ectothermic mesopredators that interact with endotherms both as predator and prey. Although there are numerous studies on the kinematics of viper strikes, surprisingly few have analyzed how this rapid movement is affected by temperature. Here we studied the effects of temperature on the predatory strike performance of rattlesnakes (Crotalus spp.), abundant new world vipers, using both field and captive experimental contexts. We found that the effects of temperature on predatory strike performance are limited, with warmer snakes achieving slightly higher maximum strike acceleration, but similar maximum velocity. Our results suggest that, unlike defensive strikes to predators, rattlesnakes may not attempt to maximize strike speed when attacking prey, and thus the outcomes of predatory strikes may not be heavily influenced by changes in temperature.