Age-related Variation in Snake Venom： Evidence from Two Snakes （Naja atra and Deinagkistrodon acutus） in Southeastern China

In this study we explored electrophoretic profiles, enzymatic activities and immunoreactivity of neonate and adult venoms from two snakes （Naja atra and Deinagkistrodon acutus） coexisting in southeastern China. Age-related variation in electrophoretic profiles was found in both species and proteolytic and fibrinogenolytic activity was higher in neonate than adult venoms. Neonate D. acutus venom had higher 5＇ nucleotidase, PLA2, hyaluronidase and gelatinolytie activity, but lower esterolytic activity, than adult venom. Neonate and adult D. acutus venoms showed identical phosphomonoesterase, LAO and fibrinolytic activities. Neonate N. atra venom had higher phosphomonoesterase and LAO activity, but lower 5＇ nucleotidase, PLA2, hyaluronidase and Ache activities than adult venom. Neonate and adult N. atra venoms showed similar gelatinolytic activity. Further, age-dependent immunoreactivity was found in both species, and cross-reactions between homologous venoms and antiserums were closely related to venom composition. We speculate that age-related variation in venom characteristics is possibly driven by evolutionary forces associated with ontogenetic shifts in dietary habits, competition and predation pressure.     

Predation on snakes of Argentina: Effects of coloration and ring pattern on coral and false coral snakes

The occurrence of coral snake coloration among unrelated venomous and non‐venomous snake species has often been explained in terms of warning coloration and mimicry. In Argentina, no field tests have been conducted to confirm this mimetic association between one venomous coral species (Micrurus phyrrocryptus, Elapidae) and two non‐venomous snake species with a similar color pattern (Lystrophis pulcher and Oxyrhopus rhombifer, Colubridae). The aims of this work were to test for the possible aposematic or cryptic function of the ring pattern and coloration of coral snakes and false coral snakes from central Argentina, and to analyse whether the pattern is effective throughout the year. Predation on snakes was estimated by using non‐toxic plasticine replicas of ringed venomous and non‐venomous snakes and unbanded green snakes placed along transects in their natural habitat during the dry and rainy season. Ringed color pattern was attacked by predators despite the background color. One of the replica types was attacked more than expected during the dry season, suggesting that both shape and width of rings may influence the choice by predators. The reaction of predators towards replicas that mimic snake species with ringed patterns is independent of the geographical region, and we can conclude that mimicry characteristics are quite general when the true models are present in the area.     

Post-translational modification accounts for the presence of varied forms of nerve growth factor in Australian elapid snake venoms

The Australian elapid snakes are amongst the most venomous snakes in the world, but much less is known about the overall venom composition in comparison to Asian and American snakes. We have used a combined approach of cDNA cloning and 2-DE with MS to identify nerve growth factor (NGF) in venoms of the Australian elapid snakes and demonstrate its neurite outgrowth activity. While a single 730 nucleotide ORF, coding for a 243 amino acid precursor protein was detected in all snakes, use of 2-DE identified NGF proteins with considerable variation in molecular size within and between the different snakes. The variation in size can be explained at least in part by N-linked glycosylation. It is possible that these modifications alter the stability, activity and other characteristics of the snake NGFs. Further characterisation is necessary to delineate the function of the individual NGF isoforms.     

The colouration of the venomous coral snakes (family Elapidae) and their mimics (families Aniliidae and Golubridae)

The bright coloured, highly venomous coral snakes, Leptomicrurus, Micrurus and Micruroides (family Elapidae) and a series of harmless or mildly toxic mimics form an important component of the snake fauna of the Americas. Coral snake patterns are defined as any dorsal pattern found in any species of venomous coral snake and/or any dorsal pattern containing a substantial amount of red, pink or orange distributed so as to resemble that of some species of venomous coral snake. The components of coral snake colouration are described and four principal dorsal patterns are recognized: unicolour, bicolour, tricolour and quadricolour. The tricolour patterns may be further clustered based on the number of black bands or rings separating the red ones as: monads, dyads, triads, tetrads or pentads. A detailed classification of all coral snake colour patterns is presented and each pattern is illustrated. The taxonomic distribution of these patterns is surveyed for mimics and the 56 species of highly venomous coral snakes. Among the latter, the most frequent encountered patterns are tricolour monads, tricolour triads and bicolour rings, in that order. No venomous coral snakes have a tricolour dyad, tricolour tetrad or quadricolour pattern. As many as 115 species of harmless or mildly toxic species, c. 18% of all American snakes, are regarded as coral snake mimics. The colouration and behavioural traits of venomous coral snakes combine to form a significant antipredator defence of an aposematic type. The mimics in turn receive protection from predators that innately or through learning avoid coral snake colour patterns. The precise resemblances in colouration between sympatric non-coral snakes and venomous coral snakes and the concordant geographic variation between the two strongly support this view. Batesian mimicry with the highly venomous coral snakes as the models and the other forms as the mimics is the favoured explanation for this situation. It is further concluded that a number of species in the genera Elaphe, Farancia, Nerodia and Thamnophis, although having red in their colouration, should not be included in the coral snake mimic guild.     

Bites by foreign venomous snakes in Britain.

In 1970-7 17 people in Britain were the victims of 32 bites by foreign venomous snakes. Crotalus atrox caused eight of these bites, Bitis arietans five, and the remaining 19 bites were caused by 12 different species. All the victims were bitten while handling the snake, and 24 bites were incurred by private individuals in their own homes. Poisoning was negligible in 17 of the 32 bites but life-threatening in at least two cases. Thus in the early stages snake bite may be unpredictable as a clinical problem. All victims of snake bite should be observed for at least 12 hours to assess the severity of poisoning and to ensure rational treatment. Local necrosis developed in six cases and resulted in prolonged illness in five of these cases; local incision was carried out and many have been a casual factor. Comprehensive stocks of antivenoms for treating bites by foreign venomous snakes are held by the National Health Services in Liverpool and London. Antivenom is indicated (a) for potentially serious systemic poisoning, as evidenced by hypotension, electrocardiographic changes, neurtrophilia, and acidosis (after viper or elapid bites), abnormal bleeding or non-clotting blood after viper bites; and ptosis or glossopharyngeal palsy after elapid bites; and (b) for bites from snakes whose venom causes local necrosis, to prevent or minimise this unpleasant complication. For effective antivenom treatment intravenous infusion is mandatory.     

Snake Species Discrimination by Wild Bonnet Macaques (Macaca radiata)

Wild bonnet macaques (Macaca radiata) were studied in southern India to assess their ability to discriminate non‐venomous, venomous and predatory snakes. Realistic snake models were presented to eight troops of bonnet macaques at feeding stations and their behavior was video‐recorded 3 min before and 3 min after snake exposure. Snakes presented were: (1) venomous Indian cobra (Naja naja) displaying an open hood with ‘eyespots’; (2) venomous common Indian krait (Bungarus caeruleus); (3) non‐venomous green keelback (Macropisthodan plumbicolor); (4) non‐venomous rat snake (Ptyas mucosus); and (5) Indian python (Python molurus) which preys on macaques. Latencies to detect and react to the snakes were evaluated to determine initial responsiveness. Longer‐term assessment was measured as the percentage of time individuals looked at the snakes and monitored the activity of nearby individuals before and after snake detection. All snake models engendered caution and maintenance of a safe distance. Alarm calling occurred only during python presentations. The cobra engendered a startle response or running in the largest percentage of individuals after its detection, whereas the rat snake and python elicited bipedal standing or ambulating to monitor the snakes. We also examined the influence of age on snake recognition. Juveniles and subadults looked at the cobra, krait, and python for a larger percentage of time than adults did; albeit, adults looked at the python substantially longer than at the other snakes. Age differences in behavior suggest that, with the exception of the python, repeated experience with snakes in the wild moderates excitability, consistent with the likely threat of envenomation.     

Feeding behavior and venom toxicity of coral snake Micrurus nigrocinctus (Serpentes: Elapidae) on its natural prey in captivity

The feeding behavior and venom toxicity of the coral snake Micrurus nigrocinctus (Serpentes: Elapidae) on its natural prey in captivity were investigated. Coral snakes searched for their prey (the colubrid snake Geophis godmani) in the cages. Once their preys were located, coral snakes stroke them with a rapid forward movement, biting predominantly in the anterior region of the body. In order to assess the role of venom in prey restraint and ingestion, a group of coral snakes was 'milked' in order to drastically reduce the venom content in their glands. Significant differences were observed between snakes with venom, i.e., 'nonmilked' snakes, and 'milked' snakes regarding their behavior after the bite. The former remained hold to the prey until paralysis was achieved, whereas the latter, in the absence of paralysis, moved their head towards the head of the prey and bit the skull to achieve prey immobilization by mechanical means. There were no significant differences in the time of ingestion between these two groups of coral snakes. Susceptibility to the lethal effect of coral snake venom greatly differed in four colubrid species; G. godmani showed the highest susceptibility, followed by Geophis brachycephalus, whereas Ninia psephota and Ninia maculata were highly resistant to this venom. In addition, the blood serum of N. maculata, but not that of G. brachycephalus, prolonged the time of death of mice injected with 2 LD(50)s of M. nigrocinctus venom, when venom and blood serum were incubated before testing. Subcutaneous injection of coral snake venom in G. godmani induced neurotoxicity and myotoxicity, without causing hemorrhage and without affecting heart and lungs. It is concluded that (a) M. nigrocinctus venom plays a role in prey immobilization, (b) venom induces neurotoxic and myotoxic effects in colubrid snakes which comprise part of their natural prey, and (c) some colubrid snakes of the genus Ninia present a conspicuous resistance to the toxic action of M. nigrocinctus venom.     

Snake venom proteins in hemostasis: new results

Biological features of venomous snakes as well as biochemical properties and actions of their venoms which serve for prey acquisition, indicate the vertebrates' haemostasis system as a vulnerable target for snake venom actions. Components exerting a specific, either stimulating or inactivating effect on basal membrane or endothelial cells of the vascular wall, on platelets, on almost every step of plasma coagulation or fibrinolysis respectively, have been isolated and purified from snake venoms. Snake venom proteins acting with a defined specificity on cellular or plasmatic components of the human haemostatic system are being used in coagulation and aggregation tests, in photometric assays in conjunction with chromogenic substrates as well as in immunological systems as biochemical tools for research and diagnostic purposes.     

Snake-venom resistance as a mammalian trophic adaptation: lessons from didelphid marsupials

Mammals that prey on venomous snakes include several opossums (Didelphidae), at least two hedgehogs (Erinaceidae), several mongooses (Herpestidae), several mustelids, and some skunks (Mephitidae). As a group, these taxa do not share any distinctive morphological traits. Instead, mammalian adaptations for ophiophagy seem to consist only in the ability to resist the toxic effects of snake venom. Molecular mechanisms of venom resistance (as indicated by biochemical research on opossums, mongooses, and hedgehogs) include toxin-neutralizing serum factors and adaptive changes in venom-targeted molecules. Of these, toxin-neutralizing serum factors have received the most research attention to date. All of the toxin-neutralizing serum proteins discovered so far in both opossums and mongooses are human α1B-glycoprotein homologs that inhibit either snake-venom metalloproteinases or phospholipase A(2) myotoxins. By contrast, adaptive changes in venom-targeted molecules have received far less attention. The best-documented examples include amino-acid substitutions in mongoose nicotinic acetylcholine receptor that inhibit binding by α-neurotoxins, and amino-acid substitutions in opossum von Willebrand factor (vWF) that are hypothesized to weaken the bond between vWF and coagulopathic C-type lectins. Although multiple mechanisms of venom resistance are known from some species, the proteomic complexity of most snake venoms suggests that the evolved biochemical defences of ophiophagous mammals are likely to be far more numerous than currently recognized. Whereas most previous research in this field has been motivated by the potential for medical applications, venom resistance in ophiophagous mammals is a complex adaptation that merits attention from comparative biologists. Unfortunately, evolutionary inference is currently limited by ignorance about many relevant facts that can only be provided by future research.     

Phenotypic integration in the feeding system of the eastern diamondback rattlesnake (Crotalus adamanteus)

Selection can vary geographically across environments and temporally over the lifetime of an individual. Unlike geographic contexts, where different selective regimes can act on different alleles, age‐specific selection is constrained to act on the same genome by altering age‐specific expression. Snake venoms are exceptional traits for studying ontogeny because toxin expression variation directly changes the phenotype; relative amounts of venom components determine, in part, venom efficacy. Phenotypic integration is the dependent relationship between different traits that collectively produce a complex phenotype and, in venomous snakes, may include traits as diverse as venom, head shape and fang length. We examined the feeding system of the eastern diamondback rattlesnake (Crotalus adamanteus) across environments and over the lifetime of individuals and used a genotype–phenotype map approach, protein expression data and morphological data to demonstrate that: (i) ontogenetic effects explained more of the variation in toxin expression variation than geographic effects, (ii) both juveniles and adults varied geographically, (iii) toxin expression variation was a result of directional selection and (iv) different venom phenotypes covaried with morphological traits also associated with feeding in temporal (ontogenetic) and geographic (functional) contexts. These data are the first to demonstrate, to our knowledge, phenotypic integration between multiple morphological characters and a biochemical phenotype across populations and age classes. We identified copy number variation as the mechanism driving the difference in the venom phenotype associated with these morphological differences, and the parallel mitochondrial, venom and morphological divergence between northern and southern clades suggests that each clade may warrant classification as a separate evolutionarily significant unit.     

Bothrops jararaca snakes produce several bothrojaracin isoforms following an individual pattern

More than one isoform of bothrojaracin (BJC), a potent and specific thrombin inhibitor isolated from Bothrops jararaca venom, has been found in individual venoms collected from adult snakes. Variations in snake venom composition have previously been associated with factors such as age, sex, geographic origin, season of the year and diet. In order to obtain further information concerning individual patterns of expression of BJC isoforms, we have analyzed five individual Bothrops jararaca snake venoms collected at the same time from adult female snakes from the same geographic region. As expected, crude venoms showed a similar migration pattern on SDS-PAGE. BJC was purified using a procedure which includes an affinity chromatography step (PPACK-thrombin Sepharose). A slight variation in the amount of BJC obtained from individual venom samples was noticed. Inhibition of thrombin-induced platelet aggregation as well as migration pattern on SDS-PAGE (under reducing and non-reducing conditions) and isoelectric focusing varied considerably among BJC samples from the five snakes. The amino-terminal sequences (residues 1–34) of individual BJC samples were compared with the sequence deduced from isolated cDNAs encoding α and β chains of BJC. A high degree of homology was detected, although some residues differed from one sample to other. Altogether, data confirmed the heterogeneity found for BJC purified from individual snakes. Thus, the results indicate that: (1) individual specimens of Bothrops jararaca have different patterns of BJC isoform expression; and (2) it seems that genetic factors, at least in part, determine the variability found in BJC production.     

The status of Pliocercus and Urotheca (Serpentes: Golubridae), with a review of included species of coral snake mimics

The generic name Urotheca Bibron, 1843 is revived for a group of Neotropical colubrid snakes diagnosed by a long, thickened but fragile tail and the presence of a specialized naked pocket on the asulcate surface of the hemipenial capitulum. Urotheca includes those species previously placed in the lateristriga group of the genus Rhadinaea and the coral snake mimics usually referred to the genus Pliocercus. The many names based upon the coral snake mimics are shown to represent two species at most: Urotheca elapoides, a bicolour (red and black) or tricolour (red, yellow and black) banded or ringed form found in Mexico and northern Central America and U. euryzona, which is usually bicolour (red, yellow or white and black) and ranges from Nicaragua to western Ecuador. Coloration in U. elapoides resembles closely that of sympatric species of venomous coral snakes. Local variation in coloration and a geographic trend in the colour of the light rings (usually red in the north, white to the south) in U. euryzona parallels similar colour variation in the sympatric venomous coral snake Micrurus mipartitus. These patterns of variation add strong support to the idea that the two species are mimics of the highly venomous coral snakes. Urotheca, including the non-mimetic species U. decipiens, U. fulmceps, U. guentheri, U. lateristriga, U. multilineata and U. pachyura, shares the characteristic of a very long and disproportionately thickened and fragile tail with the coral snake mimics of the distantly related genus Scapkiodontophis. Members of both genera have a very high proportion (about 50%) of the tails broken indicating a probable predator escape device. Breakage is intercentral, with a calcified cap developing over the tip of the distal surface of the new terminal vertebra unlike the situation in many lizards where there is an intracentral fracture septum and the tail is regenerated.     

舟山眼镜蛇毒抗肿瘤有效组分分离及其抑瘤作用研究初探

目的从舟山眼镜蛇(Naja atraCantor)蛇毒(snake venom,SV)中分离得蛇毒组分,探讨SV及其分离组分的LD50和抑制肿瘤的作用。方法采用凝胶柱层析方法从蛇毒中分离得到了前Ⅰ1、Ⅰ1、Ⅱ1、Ⅱ2、Ⅲ1、Ⅲ2及Ⅳ等7种组分。采用急性毒性实验、MTT法,研究SV及其7种SV分离组分的LD50和抑制肿瘤的作用。结果 SV经Sephadex G-50层析,可分离为前Ⅰ、Ⅰ、Ⅱ、Ⅲ及Ⅳ5个组分,根据峰面积大小排列:ⅢⅡⅠⅣ前Ⅰ。5个组分再经Sephadex G-25柱层析,可获得7个脱盐组分:前Ⅰ1、Ⅰ1、Ⅱ1、Ⅱ2、Ⅲ1、Ⅲ2及Ⅳ。通过急性毒性实验,明确Ⅳ的毒性最大,其次为Ⅲ2及Ⅲ1,三者的LD50值均低于SV;而Ⅰ1、Ⅱ1、Ⅱ2的毒性均小于SV,前Ⅰ1几乎无毒。SV组分Ⅲ2和Ⅳ的抑瘤作用最强,在高浓度(20μg/ml)时对实验中的2种人肿瘤细胞的抑制率均达到60%以上。结论从SV中分离得到了前Ⅰ1、Ⅰ1、Ⅱ1、Ⅱ2、Ⅲ1、Ⅲ2以及Ⅳ7种组分;组分Ⅳ毒性最强,依次为Ⅲ2Ⅲ1SVⅡ2Ⅱ1Ⅰ1前Ⅰ1;SV及其7种分离组分对2种人肿瘤细胞株(SGC-7901、A549)的生长抑制有一定的特异性,而不同的SV分离组分对同一肿瘤细胞抑制作用亦有差异。     

Coral snake mimicry: live snakes not avoided by a mammalian predator

The occurrence of coral snake coloration among unrelated venomous and non-venomous New World snake species has often been explained in terms of warning coloration and mimicry. The idea that snake predators would avoid coral snakes in nature seems widely established and is postulated in many discussions on coral snake mimicry. However, the few workers that have tested a potential aposematic function of the conspicuous colour pattern focused exclusively on behaviour of snake predators towards coloured abstract models. Here we report on behaviour of temporarily caged, wild coatis (Nasua narica) when confronted with co-occurring live snakes, among which were two species of venomous coral snakes. Five different types of responses have been observed, ranging from avoidance to predation, yet none of the coatis avoided either of the two coral snake species or other species resembling these. As in earlier studies coatis appeared to avoid coral snake models, our findings show that results from studies with abstract snake models cannot unconditionally serve as evidence for an aposematic function of coral snake coloration.     

Phylogeny-Based Comparative Analysis of Venom Proteome Variation in a Clade of Rattlesnakes (Sistrurus sp.)

A long-standing question in evolutionary studies of snake venoms is the extent to which phylogenetic divergence and diet can account for between-species differences in venom composition. Here we apply phylogeny-based comparative methods to address this question. We use data on venom variation generated using proteomic techniques for all members of a small clade of rattlesnakes (Sistrurus sp.) and two outgroups for which phylogenetic and diet information is available. We first complete the characterization of venom variation for all members of this clade with a “venomic” analysis of pooled venoms from two members of this genus, S. milarius streckeri and S. m. milarius. These venoms exhibit the same general classes of proteins as those found in other Sistrurus species but differ in their relative abundances of specific protein families. We then test whether there is significant phylogenetic signal in the relative abundances of major venom proteins across species and if diet (measured as percent mammals and lizards among all prey consumed) covaries with venom composition after phylogenetic divergence is accounted for. We found no evidence for significant phylogenetic signal in venom variation: K values for seven snake venom proteins and two composite venom variables [PC 1 and 2]) were all nonsignificant and lower (mean = 0.11+0.06 sd) than mean K values (>0.35) previously reported for a wide range of morphological, life history, physiological and behavioral traits from other species. Finally, analyses based on Phylogenetic Generalized Least Squares (PGLS) methods reveal that variation in abundance of some venom proteins, most strongly CRISP is significantly related to snake diet. Our results demonstrate that venom variation in these snakes is evolutionarily a highly labile trait even among very closely-related taxa and that natural selection acting through diet variation may play a role in molding the relative abundance of specific venom proteins.     

Variation in the diet of the viperine snake Natvix mama in relation to prey availability

The diet of the viperine snake was compared with food availability in the Ebro Delta, a wetland largely occupied by rice fields, in 1990 and 1991. Snake selection of prey type and size was studied seasonally and by snake group: males, females and immature snakes. Overall, feeding activity (percentage of individuals with prey and number of prey per stomach) increased with food availability. Diet analysis showed that viperine snakes mainly foraged on the green frog Rana perezi (adults and tadpoles) and the carp Cyprinus earpio. Conversely, viperine snakes rejected the mosquito fish Gambusia holbroki which is the most abundant species in autumn, when Natrix maura has a low feeding activity. Statistical comparisons between viperine snake diet and prey availability showed that males selected small carp, immature snakes selected tadpoles and, in spring, females selected frogs. The selection of small carp by males may reflect a sexual divergence of trophic niche related to sexual size dimorphism, as females are larger than males. As tadpoles are presumably easier to catch than fish, tadpole selection by immature individuals may reflect variance in capture abilities. In spring, the selection of frogs by females overlapped with vitellogenesis, suggesting that females compensate for the cost of reproduction by selecting green frogs, which have a greater biomass and higher energy content than fish. Carps eaten in spring were smaller than in summer. Moreover, in summer viperine snakes selected smaller carp than the available mean size. This divergent tendency between carp size selection and carp size availability reveals how seasonal diet shifts in prey size selection may be a response to an increase in prey size.     

粤西茂名地区毒蛇咬伤的流行病学特征研究

目的 探讨茂名地区毒蛇咬伤的流行病学特征.方法 收集2014～2019年我院收治的毒蛇咬伤患者1625例的临床资料,对毒蛇种类、性别、年龄、咬伤部位、咬伤地点、伤后就诊时间、住院时间进行统计分析.结果 茂名地区主要致伤毒蛇为竹叶青蛇和眼镜蛇;受伤患者以41～70岁男性多见;被咬伤部位主要为腕关节、踝关节以下;咬伤地点多...