Pr-SNTX,a short-chain three-finger toxin from Papuan pigmy mulga snake,is an antagonist of muscle-type nicotinic acetylcholine receptor (α2βδε)

Three-finger toxins (3FTxs) are one of the major components in snake venoms. In this study, we isolated a cDNA encoding a short-chain 3FTx, Pr-SNTX, from Pseudechis rossignolii. The amino acid sequence of Pr-SNTX is nearly identical to that of its ortholog in Pseudechis australis. Pr-SNTX protein inhibited muscle-type (α₂βδε), but not neuronal α7 nicotinic acetylcholine receptor (nAChR) activity.     

Importance of fire in influencing the occurrence of snakes in an upland region of arid Australia

In arid Australia, changes to historic fire regimes may now produce more large‐scale wildfire events. The impacts of these fires on fauna communities are poorly known. We sought to test the impacts of fire on the occurrence of two arid‐zone snake species, the desert death adder (Acanthophis pyrrhus) and monk snake (Parasuta monachus), specialist inhabitants of hummock grassland and mulga shrubland, respectively. We also examined the influence of fire on the occurrence of a habitat generalist, the sympatric Stimson's python (Antaresia stimsoni). Under an Information‐Theoretic framework we modelled the occurrence of each species with a range of habitat variables, including fire history, using logistic regression. As predicted, the two habitat specialists were more likely to be encountered at locations that had a lower percentage of surrounding area burnt in the most recent wildfires (2002), while fire variables failed to predict the occurrence of the habitat generalist. Acanthophis pyrrhus, already predisposed to endangerment through a suite of life‐history characteristics, may be at increased risk through accidental and deliberate burning and fragmentation of old‐growth hummock grasslands. We stress the importance of prescribed burning and natural fire breaks in maintaining areas of old‐growth hummock grassland across the landscape.     

Insights into the adaptive significance of vertical pupil shape in snakes

Pupil shape in vertebrates ranges from circular to vertical, with multiple phylogenetic shifts in this trait. Our analyses challenge the widely held view that the vertical pupil evolved as an adaptation to enhance night vision. On functional grounds, a variable‐aperture vertical pupil (i) allows a nocturnal species to have a sensitive retina for night vision but avoid dazzle by day by adjusting pupil closure, and (ii) increases visual acuity by day, because a narrow vertical pupil can project a sharper image onto the retina in the horizontal plane. Detection of horizontal movement may be critical for predators that wait in ambush for moving prey, suggesting that foraging mode (ambush predation) as well as polyphasic activity may favour the evolution of vertical pupil shape. Camouflage (disruption of the circular outline of the eye) also may be beneficial for ambush predators. A comparative analysis in snakes reveals significant functional links between pupil shape and foraging mode, as well as between pupil shape and diel timing of activity. Similar associations between ambush predation and vertically slit pupils occur in lizards and mammals also, suggesting that foraging mode has exerted major selective forces on visual systems in vertebrates.     

Temperature-Induced Changes in the Number of Vesicles in the Free Nerve Endings of Temperature Neurons of the Snake

By observing ultrastructural changes under the electron microscope, we illustrated exocytosis and recycling of vesicles in the infrared receptor, a kind of free nerve ending in the pit organ of the crotaline snake, Trimeresurus flavoviridis. While maintaining the snake pit organs at stable temperatures of 15°C, 25°C, and 30°C, we fixed them by perfusion and then processed them for transmission electron microscopy. The largest number of clear and coated vesicles appeared in the terminals at the lowest temperature. The perimeter and area of a terminal were enlarged at 30°C, and “opening waves” on the plasma were prominently found at the highest temperature. We also observed coated vesicles that budded from the plasma membrane in the terminals. The configuration of mitochondria in the terminals was quantitatively different between lower and higher temperatures. The data suggest that exocytosis and endocytosis in these terminals operate in a manner similar to that observed in other cell types.     

墨旱莲对4种蝮蛇毒引起的炎症和出血的影响

目的探讨墨旱莲提取液对短尾蝮蛇毒、蛇岛蝮蛇毒、白眉蝮蛇毒及尖吻蝮蛇毒所致的炎症和出血的影响。方法应用短尾蝮蛇毒、蛇岛蝮蛇毒、白眉蝮蛇毒及尖吻蝮蛇毒所致大鼠足跖肿胀的致炎模型,观察墨旱莲提取液对蛇毒所致大鼠足跖肿胀的影响。墨旱莲提取液分别与不同蛇毒混合,给小鼠腹部皮下注射,观察其对蛇毒引起的小鼠皮下出血的影响。结果墨旱莲提取液15g／kg连续2次灌胃给药,对短尾蝮蛇毒、蛇岛蝮蛇毒、白眉蝮蛇毒或尖吻蝮蛇毒所致大鼠足跖肿胀的急性炎症造模和短尾蝮蛇毒棉球肉芽肿的慢性炎症造模(20g／kg)均有明显的抑制作用,对这些蛇毒引起的小鼠皮下出血也能明显抑制。结论墨旱莲提取液对短尾蝮蛇毒、蛇岛蝮蛇毒、白眉蝮蛇毒及尖吻蝮蛇毒引起的炎症和出血均有明显的抑制作用。     

Novel microsatellite loci identified from the Australian eastern small‐eyed snake (Elapidae: Rhinocephalus nigrescens) and cross species amplification in the related genus Suta

A total of 15 microsatellite primers pairs were developed for the Australian small‐eyed snake Rhinoplocephalus nigrescens. Five primers were used to screen 93 individuals of R. nigrescens and were also tested against eight species of the closely related genus Suta. Allelic diversity in R. nigrescens was high in three loci (12–27) and there was high heterozygosity (0.58–0.82). Observed heterozygosity did not deviate from Hardy–Weinberg expectations for the five loci tested. These primers will be useful in studies of population genetics and mating systems of small‐eyed snakes and related species.     

Do juvenile gape-limited predators compensate for their small size when feeding?

When juvenile and adult animals occur syntopically, juveniles are at a distinct performance disadvantage due to their absolutely small size. Yet, optimal foraging theory predicts that juvenile predators should feed efficiently in order to compete with adults for food, and to minimize their exposure to predators. Previous authors have suggested that one way for juvenile animals to accomplish these ecological tasks is by increasing their overall feeding performance relative to adults (compensation hypothesis). Nonetheless, only a handful of studies have tested whether juvenile animals have increased feeding performance (e.g. decreased ingestion and/or handling times relative to body size) compared with adults. We tested this hypothesis by examining the ontogeny of head dimensions and feeding performance (ingestion time and number of mandibular protractions) on fish prey for broad-banded water snakes Nerodia fasciata . Individuals were fed fish scaled in a 1:1 ratio to their head width. All head dimensions scaled with significant negative allometry versus body size, and thus smaller snakes had relatively larger heads for their body size compared with larger snakes. By contrast, most head variables (except head volume) exhibited positive allometry versus head length, demonstrating that larger snakes had larger head dimensions relative to head size compared with smaller snakes. In the performance trials, smaller snakes had worse feeding performances when feeding on similarly sized fish prey (relative to their head width) compared with larger snakes. Therefore, these data show that smaller water snakes do not compensate for their size through increased feeding performance.     

Feeding preferences in 2 disjunct populations of tiger snakes, Notechis scutatus (Elapidae)

Variations at both the genetic and phenotypic levels play animportant role in responses to food and food-related stimuli.Knowledge of such variations is crucial to understanding howpopulations adapt to changing environments. We investigatedthe dietary preferences of 2 tiger snake populations and comparedthe responses of diet-naive animals (laboratory-born neonates),diet-controlled animals (laboratory-reared juveniles), and naturaldiet–experienced animals (wild-caught adults) to visualand chemical cues from 6 prey types (mouse, skink, silver gull,chicken, shearwater, and frog). The mainland population inhabitsa swamp, feeds mostly on frogs, and suffers heavy predation.The second population inhabits a small nearby offshore islandwith no standing water (no frogs); feeds mostly on skinks, mice,and, as adults, silver gull chicks; and suffers no known predation.Although different prey are eaten in the 2 populations, adultwild-caught snakes from both populations showed a significantpreference for 3 types of prey (frog, mouse, and chick), irrespectiveof their natural diet. Neonates responded to all prey cues morethan they did to control stimuli in both populations. However,the island neonates showed significantly higher interest insilver gull chick stimuli (the main prey of the island adultsnakes) than did their mainland conspecifics. Laboratory-bredjuveniles displayed behavioral plasticity by significantly increasingtheir response to mice after being fed baby mice for 7 months.We conclude that genetic-based differences in food-related cuesare important in tiger snakes but that they are also capableof behavioral plasticity. Island adult and neonate snakes exhibitedresponses to prey types no longer consumed naturally (frog),suggesting that behavioral characters may have been retainedfor long periods under relaxed selection. Island neonates showeda strong interest in a novel prey item (silver gull). This resultcomplements previous work describing how island snakes havedeveloped the ability to swallow larger prey than usual, aswell as seemingly developing a taste for them.