Snake Body Size Research Articles

Diet variations across remote populations of a widely distributed snake species, the Asp viper (Vipera aspis aspis, Linnaeus, 1758)

Abstract Documenting intra-specific diet variations among remote populations, thus across different habitats, is important to address evolutionary (e.g., phenotypic plasticity) and conservation issues (e.g., capacity to adapt to changing prey availability). We compared the diet of different populations of Asp vipers (Vipera aspis aspis; Linnaeus, 1758) living in contrasted habitats of France and Switzerland. We sampled 1680 individuals in five geographical areas, broadly encompassing the distribution range of the species (West to East and North to South): Group 1 = Western Central France; Group 2 = Central France; Group 3 = West France; Group 4 = South France, and Group 5 = Switzerland. We compared mean total body size (TL) of snakes and their diet. We found strong similarities among the groups with a predominance of micromammals in the diet. In mountainous area (Group 5), however, snakes included a substantial number of reptiles and fed occasionally on amphibians and birds. The diet varied ontogenetically (juveniles often consuming lizards, adults heavily feeding on mammals) and sexually (females tending to feed more extensively on mammals). Overall, our results suggest that Asp vipers maintain a diet largely based on micromammals (mostly voles), at least across their continental distribution range.

Mercury bioaccumulation and Hepatozoon spp. infections in two syntopic watersnakes in South Carolina.

Mercury (Hg) is a ubiquitous environmental contaminant known to bioaccumulate in biota and biomagnify in food webs. Parasites occur in nearly every ecosystem and often interact in complex ways with other stressors that their hosts experience. Hepatozoon spp. are intraerythrocytic parasites common in snakes. The Florida green watersnake (Nerodia floridana) and the banded watersnake (Nerodia fasciata) occur syntopically in certain aquatic habitats in the Southeastern United States. The purpose of this study was to investigate relationships among total mercury (THg) concentrations, body size, species, habitat type and prevalence and parasitemia of Hepatozoon spp. infections in snakes. In the present study, we sampled N. floridana and N. fasciata from former nuclear cooling reservoirs and isolated wetlands of the Savannah River Site in South Carolina. We used snake tail clips to quantify THg and collected blood samples for hemoparasite counts. Our results indicate a significant, positive relationship between THg and snake body size in N. floridana and N. fasciata in both habitats. Average THg was significantly higher for N. fasciata compared to N. floridana in bays (0.22 ± 0.02 and 0.08 ± 0.006 mg/kg, respectively; p < 0.01), but not in reservoirs (0.17 ± 0.02 and 0.17 ± 0.03 mg/kg, respectively; p = 0.29). Sex did not appear to be related to THg concentration or Hepatozoon spp. infections in either species. We found no association between Hg and Hepatozoon spp. prevalence or parasitemia; however, our results suggest that species and habitat type play a role in susceptibility to Hepatozoon spp. infection.

Intraspecific Variation in Diet Composition and Morphology of Yucatecan Cantils (Agkistrodon russeolus Gloyd 1972 [Serpentes: Viperidae

Detailed studies on the natural history of snakes are essential for ecological hypothesis-driven research and effective conservation. Herein, we studied the diet composition and morphology of Yucatecan Cantils (Agkistrodon russeolus Gloyd 1972 [Serpentes: Viperidae]), an understudied viperid species endemic to the Yucatán Peninsula. We collected data from live free-ranging snakes; freshly road-killed snakes and snakes deliberately killed by local villagers; and museum specimens and literature sources. We compared their age classes, sexes, and color morphs. Data came from snakes from Yucatán, Quintana Roo, and Campeche in Mexico, and two records were from northern Belize, comprising most of the species' distribution range. Examination of 76 individuals resulted in 77 prey items from 68 snakes. Results indicated that A. russeolus is a generalist-opportunistic predator that feeds on a wide variety of vertebrates, but primarily on lizards and small mammals and less frequently on birds, snakes, and anurans. Geographic patterns in the diet and morphology of A. russeolus were evident: snakes from the coastal region were smaller in body size and less heavy bodied and with a heavily lizard-based diet, whereas snakes from both dry and moist forest regions were larger and heavier and their diet was primarily mammal based. We did not detect differences in diet composition among age classes because lizards and mammals were eaten at all stages of life, but an “ontogenetic telescope” was evident; that is, the importance of mammals increases with snake body size and the spectrum of prey types consumed also broadens. Males had longer tails than females, and females were light colored more often than males, but other morphological characteristics were similar between the sexes. The sexes and color morphs did not differ in diet composition. We did not detect dietary composition variations between seasons, and our data indicate that this species can feed year-round opportunistically. Because of increasing environmental pressures within its range, studies are urgently needed to elucidate other critical aspects of the ecology of this viperid species.

Multimale breeding aggregations by “many-friends” snakes: courtship behaviours by Malagasy Pseudoxyrhophiine snakes, Dromicodryas bernieri and D. quadrilineatus, and their sexual size dimorphism

When several male snakes dispute over one female in the breeding season, two major male-male rivalries are known to occur: male-male combat and multimale breeding aggregation. The roles of male body size and the degree of sexual size dimorphism are different between these rivalries. We report field observations of mating behaviour including a multimale breeding aggregation of pseudoxyrhophiins, Dromicodryas bernieri and D. quadrilineatus, in northwestern Madagascar, which have a local name, “Maro longo”, meaning “many friends”. To examine the relationships between sexual size dimorphism and mating strategies of males, we also analysed the body size of the two species of Dromicodryas and two other pseudoxyrhophiins, Leioheterodon madagascariensis and L. modestus, which are known to exhibit the male-male combat. Our data obtained during a long-term field study showed that D. bernieri and D. quadrilineatus have female-biased sexual size dimorphism, whereas L. madagascariensis and L. modestus have male-biased sexual size dimorphism. This result conforms to the general tendency of the relationship between body size and male-male rivalry in snakes.

Measuring Annual Variation in Reproductive Output Reveals a Key Role of Maternal Body Condition in Determining the Size of Eggs in Snakes.

Simple SummaryWe measured female reproductive traits of a colubrid snake (Lycodon rufozonatus) from Zhejiang, East China in four years (1999, 2010, 2011, and 2014). After removing the influence of female size, postpartum body mass was greater in 2010 than in 2014, clutch mass was greater in 2010 than in 2011 and 2014, and egg size was greater in 2010 than in the other three years. Egg size was positively related to postpartum body condition in each year. Females laid larger eggs in 2010 than in other three years after removing the influence of maternal size and body condition. Our study does not follow the prediction that reproductive females with different amounts of resources to invest should give priority to adjusting the number rather than size of offspring.Long-term studies are especially suited for disentangling the effects of extrinsic and intrinsic factors on both total reproductive investment and reproductive allocation in offspring number versus offspring size. Female reproductive traits of the red-banded wolf snake (Lycodon rufozonatus) from Zhejiang, East China were studied in four years between 1999 and 2014. Egg-laying dates overall extended from late June to late July, and varied among years. Postpartum body mass, clutch size, clutch mass, and egg size were positively related to female size (snout vent length, SVL) in each year. Postpartum body mass, clutch mass, and egg size differed among years after accounting for female SVL, whereas clutch size did not. Setting female SVL at the same level, postpartum body mass was greater in 2010 than in 2014, clutch mass was greater in 2010 than in 2011 and 2014, and egg size was greater in 2010 than in the other three years. Females did not trade off egg size against number. Egg size was positively related to postpartum body condition in each year. Females laid larger eggs in 2010 than in other three years after removing the influence of maternal body condition. Our study provides evidence for the traditional view that reproductive output is highly linked to maternal body size in snakes, but not following Smith and Fretwell’s (1974) classic prediction that females with different amounts of resources to invest in reproduction should give priority to adjusting the number rather than size of their offspring. Maternal body size and condition both are important sources of variation in egg size, but factors other than these two variables may also affect the size of eggs produced by female L. rufozonatus.

Mercury and Radiocesium Accumulation and Associations With Sublethal Endpoints in the Florida Green Watersnake (Nerodia floridana).

Mercury (Hg) and radiocesium (137 Cs) are well-known environmental contaminants with the potential to impact the health of humans and wildlife. Snakes have several characteristics conducive to studying environmental contamination but have rarely been included in the monitoring of polluted sites. We investigated the bioaccumulation of Hg and 137 Cs and associations with sublethal effects (standard metabolic rate [SMR] and hemoparasite infections) in Florida green watersnakes (Nerodia floridana). We captured 78 snakes from three former nuclear cooling reservoirs on the US Department of Energy's Savannah River Site in South Carolina (USA). For captured snakes, we (1) determined whole-body 137 Cs, (2) quantified total Hg (THg) using snake tail clips, (3) conducted hemoparasite counts, and (4) measured the SMR. We used multiple regression models to determine associations among snake body size, capture location, sex, tail THg, whole-body 137 Cs, Hepatozoon spp. prevalence and parasitemia, and SMR. Average whole-body 137 Cs (0.23 ± 0.08 Becquerels [Bq]/g; range: 0.00-1.02 Bq/g) was correlated with snake body size and differed significantly by capture site (Pond B: 0.67 ± 0.05 Bq/g; Par Pond: 0.10 ± 0.02 Bq/g; Pond 2: 0.03 ± 0.02 Bq/g). Tail THg (0.33 ± 0.03 mg/kg dry wt; range: 0.16-2.10 mg/kg) was significantly correlated with snake body size but did not differ by capture site. We found no clear relationship between SMR and contaminant burdens. However, models indicated that the prevalence of Hepatozoon spp. in snakes was inversely related to increasing whole-body 137 Cs burdens. Our results indicate the bioaccumulation of Hg and 137 Cs in N. floridana and further demonstrate the utility of aquatic snakes as bioindicators. Our results also suggest a decrease in Hepatozoon spp. prevalence related to increased burdens of 137 Cs. Although the results are intriguing, further research is needed to understand the dynamics between 137 Cs and Hepatozoon spp. infections in semiaquatic snakes. Environ Toxicol Chem 2022;41:758-770. © 2022 SETAC.

Sex- and size-dependent accumulation of Dechlorane Plus flame retardant in a wild frog-eating snake Amphiesma stolata

Despite several studies having addressed the bioaccumulation of Dechlorane Plus (DP) flame retardant in wildlife, there is still a dearth of information for reptiles in general and for snakes in particular. Here, we report the residue levels and trophic transfer of syn-, anti-, and anti-Cl11-DP in a frog-eating snake—namely, the striped keelback snake Amphiesma stolata—from a DP hotspot in South China. The concentrations of syn-, anti-, and anti-Cl11-DP in A. stolata ranged from 1.06–21.2, 2.13–21.5, and 0.16–10.6 ng/g lipid weight, respectively, with significantly higher levels in males compared with females. Statistical analysis showed that the concentrations of these chemicals were negatively correlated with body sizes (length and mass) of the snake. The fractional abundance of anti-DP (fanti) did not significantly differ either between the sexes or between A. stolata and its diet (i.e., frogs). However, fanti showed positive correlations with the snake's body size and negative correlations with ∑DP concentrations (summed concentrations of syn- and anti-DP), indicating that body size and DP residue levels are important factors influencing DP isomeric profiles in these snakes. Biomagnification factors estimated based on the relationship between A. stolata and frogs were 0.49 ± 0.01 (mean ± SE), 0.44 ± 0.09, and 1.79 ± 0.54 for syn-, anti-, and anti-Cl11-DP, respectively, suggesting trophic dilution of syn- and anti-DP and a mild biomagnification of anti-Cl11-DP from frogs to snakes.

Repeated dietary shifts in elapid snakes (Squamata: Elapidae) revealed by ancestral state reconstruction

Abstract Identifying the traits of ancestral organisms can reveal patterns and drivers of organismal diversification. Unfortunately, reconstructing complex multistate traits (such as diet) remains challenging. Adopting a ‘reconstruct, then aggregate’ approach in a maximum likelihood framework, we reconstructed ancestral diets for 298 species of elapid snakes. We tested whether different prey types were correlated with one another, tested for one-way contingency between prey type pairs, and examined the relationship between snake body size and dietary composition. We demonstrate that the evolution of diet was characterized by niche conservation punctuated by repeated dietary shifts. The ancestor of elapids most likely fed on reptiles and possibly amphibians, with deviations from this ancestral diet occurring repeatedly due to shifts into marine environments and changes in body size. Moreover, we demonstrate important patterns of prey use, including one-way dependency—most obviously the inclusion of eggs being dependent on a diet that already included the producers of those eggs. Despite imperfect dietary data, our approach produced a robust overview of dietary evolution. Given the paucity of natural history information for many organisms, our approach has the potential to increase the number of lineages to which ancestral state reconstructions of multistate traits can be robustly applied.

Adaptive foraging strategy of an insular snake (Lycodon semicarinatus, Colubridae) feeding on patchily distributed nests of sea turtles

Abstract Foraging tactics of predators generally include two major modes, active searching and ambushing. A colubrid snake, Lycodon semicarinatus, is a typical example of a predator, which uses both tactics to forage on sea turtles on islands of the Kerama Group in the Central Ryukyu Archipelago, Japan. To investigate factors that determine the foraging mode of this snake, we conducted a four-year field survey on its foraging behaviour on sea turtles on another island, Okinawa Island. We found that the snake performs only active searching at our study site. Snakes visited a small area exactly above the nest of sea turtles and attempted to burrow a tunnel to feed on eggs and hatchlings in the sand. Tunnels leading from the surface of the beach to the inside of the nest were formed only by large snakes. Many other snakes used the already made tunnels to capture eggs and hatchlings in the nest. When the snakes caught a hatchling, they brought the hatchling away into the nearby bush area without swallowing it above the nest (taking-away behaviour). When snakes failed to find food on a nest, they terminated the intensive search above the nest in approximately 5 minutes irrespective of snake body size, season, and the condition of the nest. Subsequently, they left the nest and resumed extensive searching for other nests. Our findings showed that L. semicarinatus has a different foraging strategy depending on populations. Two environmental traits, diversity of available prey animals other than sea turtles and characteristics of sand that beaches consist of, were considered as factors that might cause the difference in the foraging strategy. The fine sand of our study site enables snakes to form a sturdy tunnel in nests. We presume that such an environment facilitates the use of active searching by the snakes to find the nest with tunnels suitable for exploitation. The taking-away behaviour may be effective to reduce excessive contact with other conspecifics under the situation that the nest with tunnels attracts many visitors. Furthermore, the observation that the snake left the nest site after a consistent duration of unprofitable searching supports the giving-up time rule, which has been predicted by a theoretical model concerning the optimal time for predators to leave a patch.

Brain Allometry Across Macroevolutionary Scales in Squamates Suggests a Conserved Pattern in Snakes

Despite historical interest in brain size evolution in vertebrates, few studies have assessed variation in brain size in squamate reptiles such as snakes and lizards. Here, we analyzed the pattern of brain allometry at macroevolutionary scale in snakes and lizards, using body mass and snout vent length as measures of body size. We also assessed potential energetic trade-offs associated with relative brain size changes in Crotalinae vipers. Body mass showed a conserved pattern of brain allometry across taxa of snakes, but not in lizards. Body length favored changes of brain allometry in both snakes and lizards, but less variability was observed in snakes. Moreover, we did not find evidence for trade-offs between brain size and the size of other organs in Crotalinae. Thus, despite the contribution of body elongation to changes in relative brain size in squamate reptiles, snakes present low variation in brain allometry across taxa. Although the mechanisms driving this conserved pattern are unknown, we hypothesize that the snake body plan plays an important role in balancing the energetic demands of brain and body size increase at macroevolutionary scales. We encourage future research on the evolution of brain and body size in snakes to test this hypothesis.

Cretaceous Blind Snake from Brazil Fills Major Gap in Snake Evolution

SummaryBlind snakes (Scolecophidia) are minute cryptic snakes that diverged at the base of the evolutionary radiation of modern snakes. They have a scant fossil record, which dates back to the Upper Paleocene-Lower Eocene (∼56 Ma); this late appearance conflicts with molecular evidence, which suggests a much older origin for the group (during the Mesozoic: 160–125 Ma). Here we report a typhlopoid blind snake from the Late Cretaceous of Brazil, Boipeba tayasuensis gen. et sp. nov, which extends the scolecophidian fossil record into the Mesozoic and reduces the fossil gap predicted by molecular data. The new species is estimated to have been over 1 m long, much larger than typical modern scolecophidians (<30 cm). This finding sheds light on the early evolution of blind snakes, supports the hypothesis of a Gondwanan origin for the Typhlopoidea, and indicates that early scolecophidians had large body size, and only later underwent miniaturization.

Melanism, body size, and sex ratio in snakes\u2014new data on the grass snake (Natrix natrix) and synthesis

It is postulated that melanism in ectotherms is adaptive by enhancing thermoregulation, subsequent resource acquisition, and growth. Such effects may differ between the sexes as a result of the differential costs of self-maintenance and reproduction, but empirical support for the sex-specific consequences of melanism remains inconsistent. We studied the effects of melanism on body size and sex ratio in a population of the European grass snake (Natrix natrix) in SE Poland and also carried out a systematic review of the literature on the consequences of melanism in terrestrial snakes. Melanistic grass snakes of both sexes appeared to be smaller than the typical phenotype, which indicates higher predation pressure and minimal thermal benefits for black individuals. A female-biased sex ratio was observed in the typical phenotype, but not in melanistic snakes, suggesting that the costs for females and/or benefits for males are higher in melanistic individuals. In conjunction with earlier studies, our data indicate that the consequences of melanism may be related to the reproductive mode of species. In viviparous species, melanism tends to improve growth and/or body size and is more frequent in females, whereas the opposite holds for oviparous snakes. Further studies on melanism should examine a wider array of species with different reproductive strategies and traits beyond the usual thermal benefits.

Snakes and the Eternal City: variation in community metrics, body size and population density of snakes in contrasted landscapes of suburban Rome (Italy)

Reports of global declines in animal populations are now numerous and also include snakes, a group of animals now widely regarded as bio indicators. A prerequisite for any conservation management plan to protect or restore snake populations requires a data base that provides insight into population composition and changes. However, snakes are well known to be particularly difficult to quantitatively sample due to their secretive and elusive nature, and hence accumulating an adequate database for analysis requires long-term field studies that involve intensive searches. Populations of four snake species, Zamensis longissimus, Natrix helvetica, Vipera aspis and Hierophis viridiflavus living in two suburban areas of Rome with different extents of habitat alteration (deforestation), Vejo, a less altered site, and Tor Bella Monaca, a high altered site, have been monitored, but with interruptions since 1995. The results indicated that H. viridiflavus was the commonest species at both sites. Male bias was found in all four species but especially in Z. longissimus and V. aspis with detection of juveniles greatest in H. viridiflavus and N. helvetica. Snout to vent lengths (SVL) of H. viridiflavus and Z. longissimus, which were present at both sites, were greater at the less degraded habitat of the two study localities. Community metrics indicated that the degraded habitat had lower species richness, evenness, Shannon and Simpson diversity indices, but a higher dominance index. Recapture frequencies of snakes recaptured either once or multiple times were in general greater at Vejo. The highest population densities were found in H. viridiflavus, followed by V. aspis and N. helvetica, which were similar. However, long term trends in densities show declines in V. aspis and N. helvetica between 1995 and 2019. Population densities were in good agreement with density estimates found in previous studies of snakes in more natural habitats.

Niche partitioning within a population of sea snakes is constrained by ambient thermal homogeneity and small prey size

AbstractIn many populations of terrestrial snakes, the phenotype of an individual (e.g. body size, sex, colour) affects its habitat use. One cause for that link is gape limitation, which can result in larger snakes eating prey that are found in different habitats. A second factor involves thermoregulatory opportunities, whereby individuals select habitats based upon thermal conditions. These ideas predict minimal intraspecific variation in habitat use in a species that eats small prey and lives in a thermally uniform habitat, such as the sea snake Emydocephalus annulatus, which feeds on tiny fish eggs and lives in inshore coral reefs. To test that prediction, we gathered data on water depths and substrate attributes for 1475 sightings of 128 free-ranging E. annulatus in a bay near Noumea, New Caledonia. Habitat selection varied among individuals, but with a preference for coral-dominated substrates. The body size and reproductive state of a snake affected its detectability in deep water, but overall habitat use was not linked to snake body size, colour morph, sex or pregnancy. A lack of ontogenetic shifts in habitat use allows extreme philopatry in E. annulatus, thereby reducing gene flow among populations and, potentially, delaying recolonization after local extirpation events.

A Quantitative Analysis of Micrurus Coral Snakes Reveals Unexpected Variation in Stereotyped Anti-Predator Displays Within a Mimicry System.

SynopsisWarning signals in chemically defended organisms are critical components of predator–prey interactions, often requiring multiple coordinated display components for effective communication. When threatened by a predator, venomous coral snakes (genus Micrurus) display a vigorous, non-locomotory thrashing behavior that has previously been qualitatively described. Given the high contrast and colorful banding patterns of these snakes, this thrashing display is hypothesized to be a key component of a complex aposematic signal under strong stabilizing selection across species in a mimicry system. By experimentally testing snake response across simulated predator cues, we analyzed variation in the presence and expression of a thrashing display across five species of South American coral snakes. Although the major features of the thrash display were conserved across species, we found that predator cue type, snake body size, and species identity predict significant inter- and intraspecific variation in the propensity to perform a display, the duration of thrashing, and the curvature of snake bodies. We also found an interaction between curve magnitude and body location that clearly shows which parts of the display vary most across individuals and species. Our results suggest that contrary to the assumption that all Micrurus species and individuals perform the same display, a high degree of variation exists despite presumably strong selection to conserve a common signal. This quantitative behavioral characterization presents a new framework for analyzing the non-locomotory motions displayed by snakes in a broader ecological context, especially for signaling systems with complex interaction across multiple modalities.

Correlates of snake entanglement in erosion control blankets

ABSTRACTIn road construction projects across the United States, erosion control methods (e.g., erosion control blankets [ECBs]), are mandated to stimulate seedbed regeneration and prevent soil loss. Previous reports have suggested that snakes are vulnerable to entanglement in ECBs. We conducted a literature review, field surveys, and an entanglement experiment to examine what factors increase a snake's risk of ECB entanglement. Our literature review produced reports of 175 reptiles entangled in mesh products, 89.1% of which were snakes, with 43.6% of snake entanglements occurring in erosion control products. During our field surveys, we found 10 entangled snakes (n = 2 alive; n = 8 dead). From our experiment, we found that ECBs that contain fixed‐intersection, small‐diameter mesh consisting of polypropylene were significantly more likely to entangle snakes compared with ECBs with larger diameter polypropylene mesh or ECBs that have woven mesh made of natural fibers. Snake body size was also associated with entanglement; for every 1‐mm increase in body circumference, the probability of entanglement increased 4%. These results can help construct a predictive framework to determine those species and individuals that are most vulnerable to entanglement. © 2019 The Wildlife Society.

Antipredation behavior covaries with body size in Neotropical snakes

Abstract The use of defensive behaviors to avoid predation increases the likelihood of survival. Snake species have evolved numerous and diverse antipredatory behaviors to fit a variety of natural histories. Understanding how snakes react to simulated predation events can help us understand their ecology. I conducted behavioral trials on 11 colubrid and dipsadid species ( individuals) in the Republic of Panama to examine patterns of antipredation behavior. The level of aggression and number of antipredatory behaviors exhibited during simulated predation was positively correlated with body size. To complement these results, data from previously published studies were used to assess these patterns with a larger sample of Neotropical colubrids and dipsadids ( species). Indeed, the level of aggression and number of antipredatory behaviors known for each species was positively correlated with body size. However, the positive association between the number of antipredatory behaviors known for a species and body size was driven largely by colubrids and not dipsadids. Larger snakes may be more intimidating to potential predators, therefore making aggressive defensive behaviors more likely to be successful. Larger snakes also may encounter a higher diversity of predators and may benefit from the ability to choose from a suite of defensive behaviors specific to certain contexts. Although this study suggests two interesting patterns in the defensive behaviors of Neotropical colubrids and dipsadids, comparative studies of the interactions between snakes and their predators are needed to better understand the pressures driving variation in snake antipredation behavior.

Trophic specialization drives morphological evolution in sea snakes.

Viviparous sea snakes are the most rapidly speciating reptiles known, yet the ecological factors underlying this radiation are poorly understood. Here, we reconstructed dated trees for 75% of sea snake species and quantified body shape (forebody relative to hindbody girth), maximum body length and trophic diversity to examine how dietary specialization has influenced morphological diversification in this rapid radiation. We show that sea snake body shape and size are strongly correlated with the proportion of burrowing prey in the diet. Specialist predators of burrowing eels have convergently evolved a ‘microcephalic’ morphotype with dramatically reduced forebody relative to hindbody girth and intermediate body length. By comparison, snakes that predominantly feed on burrowing gobies are generally short-bodied and small-headed, but there is no evidence of convergent evolution. The eel specialists also exhibit faster rates of size and shape evolution compared to all other sea snakes, including those that feed on gobies. Our results suggest that trophic specialization to particular burrowing prey (eels) has invoked strong selective pressures that manifest as predictable and rapid morphological changes. Further studies are needed to examine the genetic and developmental mechanisms underlying these dramatic morphological changes and assess their role in sea snake speciation.

Behavioral thermal tolerances of free-ranging rattlesnakes (Crotalus oreganus) during the summer foraging season

Increasing temperature due to climate change is one of the greatest challenges for wildlife worldwide. Behavioral data on free-ranging individuals is necessary to determine at what temperatures animals modify activity as this would determine their capacity to continue to move, forage, and mate under altered thermal regimes. In particular, high temperatures could limit available surface activity time and time spent on fitness-related activities. Conversely, performance, such as feeding rate, can increase with temperature potentially having positive fitness effects. Here, we examine how the hunting behaviors of free-ranging Northern Pacific Rattlesnakes (Crotalus oreganus) associate with air temperature and body temperature. We continuously recorded snakes in the field using videography, capturing behaviors rarely considered in past studies such as movements in and out of refuge and strikes on prey. We found that as mean daily air temperature increased, hunting activity and the likelihood of hunting at night decreased, while the number of movements and distance moved per day increased. Snakes typically retreated to refuge before body temperatures reached 31°C. Body temperatures of snakes hunting on the surface were lower compared to temperatures of non-hunting snakes in refuge in the morning, while this relationship was inverted in the afternoon. Snake body size influenced the disparity of these temperatures. Finally, strike initiation and success occurred across a wide range of body temperatures, indicating hunting performance may not be strongly constrained by temperature. These results on the temperatures at which free-ranging rattlesnakes exhibit fitness-related behaviors could be valuable for understanding their vulnerabilities to future climates.

Venom yield and its relationship with body size and fang separation of pit vipers from Argentina

The amount of venom that a snake can inject is related to its body size. The body size is related to head size and to the distance between fangs. To correlate snake body size, distance between fangs and distance between puncture wounds with the venom yield (and consequently with the venom dose potentially injected in a single snakebite), we studied these variables in two species of public health importance in South America, Bothrops (Rhinocerophis) alternatus, and Crotalus durissus terrificus. In all cases a positive correlation was observed between body length, fang separation distance, distance between puncture wounds and venom yield, with a regression coefficient over 0.5 for Bothrops alternatus and over 0.6 for Crotalus durissus terrificus in all cases, being the relation distance between punctures wounds and venom yield of 0.54 and 0.69 respectively. The difference between fang separation and puncture separation was never greater than 30%, with a mean difference around 13%. The strong relationships between body size, fang separation and venom yield may be useful for planning potential venom production in serpentariums. In addition, because puncture mark separation gives an approximate idea of the size of the snake, this provides a rough idea of the size of the snake that produced a bite and the potential amount of venom that could have been injected.