Submicroscopic morphology of the infrared receptor of pit vipers

Summary The fine structure of the infrared receptor membrane of pit vipers has been studied under the electronmicroscope. From the outer to the inner surfaces, within a total thickness of only 8 to 16 , the following seven layers were recognized: 1. Outer epithelium, 2. outer connective layer, 3. layer of vacuolar cells, 4. layer of nerve endings, 5. layer of nerve fibers, 6. inner connective layer, 7. inner epithelium.The nerve endings, which form a densely packed layer, represent the most prominent component of the sensory membrane. Their inner structure is remarkable because of the high mitochondrial concentration. The population density of these organoids is as great as virtually to occupy the entire ending. Almost half of the volume of the sensory membrane is thus made of compact masses of mitochondria.The structure of the myelinated nerve fibers entering the sensory membrane, was analyzed together with the stages of transformation into nerve endings.This study revealed that there is a special region of the nerve fiber in its transition toward the nerve ending where mitochondriogenesis is very active, permitting the analysis of the mechanism of formation of these cell organoids. Some physiological implications inferred from the particular structure of the sensory membrane are discussed. Special emphasis is put on the enormous mitochondrial concentration at the nerve endings. The hypothesis is advanced that these organoids might in some way be involved in the mechanism of transducing emperature changes into nerve impulses.This paper was supported by a grant of the Office of Scientific Research of the U.S. Air Force given to the Instituto de Anatomía General y Embriologia, Facultad de Ciencias Médicas, Universidad de Buenos Aires, Argentina.Postdoctoral fellow of the Instituto Nacional de Microbiología, Buenos Aires, Argentina.     

Mitochondriogenesis in nerve fibers of the infrared receptor membrane of pit vipers

Summary The myelinated nerve fibers that innervate the infrared receptor membrane of pit vipers were studied under the electronmicroseope. Along the course of the fiber, toward the nerve terminal, segments of the axon with an increasing concentration of mitochondria were found, and a special region was recognized where an active process of mitochondriogenesis seems to occur. In these regions the axon has varying amounts of mitochondria, is devoid of neuroprotofibrils, and the axoplasmic matrix is dense and contains numerous membranes, some of which can be traced as infoldings of the axolemma.The images observed have led to postulate tentatively a mechanism of mitochondrial formation, which would start with the infolding of the axolemma, would continue with the curving of two parallel membranes around a denser portion of axoplasmic matrix, the development of inner crests and the final closing of the membrane. In this mechanism both the axon membrane and the axoplasmic matrix would be involved.The possible electrochemical properties of mitochondrial membranes deriving from an excitable membrane are discussed in relation to the special receptive properties of these nerve fibers.This paper was supported by a grant of the Office of Scientific Research of the U.S. Air Force given to the Instituto de Anatomía General y Embriología, Facultad de Ciencias Médicas, Universidad de Buenos Aires, Argentina.Postdoctoral fellow of the Instituto Nacional de Microbiología, Buenos Aires, Argentina.     

Strike-induced chemosensory searching in old world vipers and new world pit vipers at San Diego Zoo

Rattlesnakes (Crotalus unicolor, C vegrandis) and Russell's vipers (Vipera russelli) at San Diego Zoo exhibited sustained high rates of tongue flicking after striking mice (Mus musculus) but not after seeing, smelling, and/or detecting thermal cues arising from mice. Called strike-induced chemosensory searching (SICS), this phenomenon contributes to poststrike trailing of envenomated prey. Because these zoo-raised snakes had always been offered dead rodents, and because these prey were usually ingested without first being struck, the present snakes had rarely exercised their innate predatory repertoire (ie, ambush tactics including striking, releasing, and trailing). Indeed, most specimens had never before struck a mouse and, hence, had never exhibited SICS. The occurrence of SICS in the present study clearly indicates that this important aspect of the predatory repertoire had not been degraded as a consequence of long-term captive husbandry.     

Prey envenomation does not improve digestive performance in Taiwanese pit vipers (Trimeresurus gracilis and T. stejnegeri stejnegeri)

It has been a common belief that snake venom may help in the digestion of its prey, although direct examples and supporting evidence have not been sufficient. To address this, the present study examined whether pre-injecting natural amounts of pit viper venom into experimental mice may accelerate their digestion by the snakes or gain energy benefit as compared to the control without the envenomation. Live adults of two Asian pit viper species Trimeresurus gracilis and T. stejnegeri stejnegeri, which inhabit the cold and warm environment respectively, were the subjects studied herein. A natural dose of 1.2 mg of each of the pit viper venom in phosphate-buffered saline (PBS) was injected into the mouse (about 10% of the snake mass) before it was being fed to the same species of vipers, while the pit vipers in control group were given mouse injected with sterile PBS. The snakes were kept at 14 °C or 24 °C, and parameters of gut passage time, costs of digestion, and/or digestive efficiency were measured. The results did not support the hypotheses that envenomation facilitates prey digestion. The venom in fact caused longer first defecation time and lower assimilation energy at 14 °C. Besides, the time to reach the oxygen consumption peak, and the first defecation time of T. s. stejnegeri were longer than that of T. gracilis.     

Defensive and infrared reception responses of true vipers, pitvipers, Azemiops and colubrids

It has been suggested that true vipers (Viperidae: Viperinae) possess the ability to detect temperature differences between objects despite the lack of an apparent infrared radiation sensor. We tested the ability to distinguish between heated and unheated targets in three species of pitvipers (Viperidae: Crotalinae), four species of true vipers, two species of colubrids (Colubridae: Natricinae, Colubrinae) and Azemiops feae (Viperidae: Azemiopinae). All species of pitvipers tested could distinguish between the warm and cool targets, while no tested species of true viper, colubrid or Azemiops demonstrated this ability. In addition, pitvipers exhibited behaviors that true vipers or Azemiops did not exhibit. Our results suggest that the tested species of true vipers, Azemiops and colubrids may not posses the ability to sense infrared radiation or do not use it in a defensive context, and suggest that some defensive behaviors are associated with the pit organ in pitvipers.     

Natural levels of colour polymorphism reduce performance of visual predators searching for camouflaged prey

Polymorphism, the coexistence of two or more variants within a population, has served as a classic model system to address questions about the evolution and maintenance of intraspecific variation. It has been hypothesized that a natural level of colour polymorphism may impair the search efficiency of visually orientated predators. To test this polymorphism protects hypothesis, we asked human participants to search for images of natural black, striped or grey Tetrix subulata grasshopper colour morphs presented against photographs of their natural habitat on computer screens. Fewer grasshoppers were detected when morphs were presented in mixed than in uniform sequences. All three morphs benefited to comparable degrees, in terms of reduced detection, from being presented in polymorphic sequences. Our findings demonstrate that natural levels of polymorphic variation can impede the efficiency of visually orientated predators and increase survival of prey. This protective effect supports the limited attention hypothesis, explains why predators develop ‘search images’, may account for the spread and establishment of novel colour variants, and contributes to maintenance of polymorphisms. © 2014 The Authors. Biological Journal of the Linnean Society published by John Wiley & Sons Ltd on behalf of The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112 , 546–555.     

Optimal pit site selection in antlion larvae: the relationship between prey availability and pit maintenance costs

Journal of Ethology - Traps are an efficient method of capturing prey for ambush predators, but trap building and maintenance are costly. We describe suitable hunting sites for pit-building antlion...     

Identification and functional analysis of a novel bradykinin inhibitory peptide in the venoms of New World Crotalinae pit vipers

A novel undecapeptide has been isolated and structurally characterized from the venoms of three species of New World pit vipers from the subfamily, Crotalinae. These include the Mexican moccasin (Agkistrodon bilineatus), the prairie rattlesnake (Crotalus viridis viridis), and the South American bushmaster (Lachesis muta). The peptide was purified from all three venoms using a combination of gel permeation chromatography and reverse-phase HPLC. Automated Edman degradation sequencing and MALDI-TOF mass spectrometry established its peptide primary structure as: Thr-Pro-Pro-Ala-Gly-Pro-Asp-Val-Gly-Pro-Arg-OH, with a non-protonated molecular mass of 1063.18 Da. A synthetic replicate of the peptide was found to be an antagonist of bradykinin action at the rat vascular B2 receptor. This is the first bradykinin inhibitory peptide isolated from snake venom. Database searching revealed the peptide to be highly structurally related (10/11 residues) with a domain residing between the bradykinin-potentiating peptide and C-type natriuretic peptide domains of a recently cloned precursor from tropical rattlesnake (Crotalus durissus terrificus) venom gland. BIP thus represents a novel biological entity from snake venom.     

Correlated evolution between coloration and ambush site in predators with visual prey lures

The evolution of a visual signal will be affected by signaler and receiver behavior, and by the physical properties of the environment where the signal is displayed. Crab spiders are typical sit‐and‐wait predators found in diverse ambush sites, such as tree bark, foliage, and flowers. Some of the flower‐dweller species present a UV⁺‐white visual lure that makes them conspicuous and attractive to their prey. We hypothesized that UV⁺‐white coloration was associated with the evolution of a flower‐dwelling habit. In addition, following up on results from a previous study we tested whether the UV⁺‐white coloration evolved predominantly in flower‐dwelling species occurring in Australia. We measured the reflectance of 1149 specimens from 66 species collected in Australia and Europe, reconstructed a crab spider phylogeny, and applied phylogenetic comparative methods to test our hypotheses. We found that the flower‐dwelling habit evolved independently multiple times, and that this trait was correlated with the evolution of the UV⁺‐white coloration. However, outside Australia non‐flower‐dwelling crab spiders also express a UV⁺‐white coloration. Therefore, UV⁺‐white reflectance is probably a recurring adaptation of some flower dwellers for attracting pollinators, although it may have other functions in non‐flower dwellers, such as camouflage.     

Snake venomics of the Lesser Antillean pit vipers Bothrops caribbaeus and Bothrops lanceolatus: correlation with toxicological activities and immunoreactivity of a heterologous antivenom

The venom proteomes of the snakes Bothrops caribbaeus and Bothrops lanceolatus, endemic to the Lesser Antillean islands of Saint Lucia and Martinique, respectively, were characterized by reverse-phase HPLC fractionation, followed by analysis of each chromatographic fraction by SDS-PAGE, N-terminal sequencing, MALDI-TOF mass fingerprinting, and collision-induced dissociation tandem mass spectrometry of tryptic peptides. The venoms contain proteins belonging to seven ( B. caribbaeus) and five ( B. lanceolatus) types of toxins. B. caribbaeus and B. lanceolatus venoms contain phospholipases A 2, serine proteinases, l-amino acid oxidases and zinc-dependent metalloproteinases, whereas a long disintegrin, DC-fragments and a CRISP molecule were present only in the venom of B. caribbaeus, and a C-type lectin-like molecule was characterized in the venom of B. lanceolatus. Compositional differences between venoms among closely related species from different geographic regions may be due to evolutionary environmental pressure acting on isolated populations. The venoms of these two species differed in the composition and the relative abundance of their component toxins, but they exhibited similar toxicological and enzymatic profiles in mice, characterized by lethal, hemorrhagic, edema-forming, phospholipase A 2 and proteolytic activities. The venoms of B. caribbaeus and B. lanceolatus are devoid of coagulant and defibrinogenating effects and induce only mild local myotoxicity in mice. The characteristic thrombotic effect described in human envenomings by these species was not reproduced in the mouse model. The toxicological profile observed is consistent with the abundance of metalloproteinases, PLA 2s and serine proteinases in the venoms. A polyvalent (Crotalinae) antivenom produced in Costa Rica was able to immunodeplete approximately 80% of the proteins from both B. caribbaeus and B. lanceolatus venoms, and was effective in neutralizing the lethal, hemorrhagic, phospholipase A 2 and proteolytic activities of these venoms.     

Exploring the proteomes of the venoms of the Peruvian pit vipers Bothrops atrox, B. barnetti and B. pictus

We report the comparative proteomic characterization of the venoms of Bothrops atrox, B. barnetti and B. pictus. The venoms were subjected to RP-HPLC and the resulting fractions analyzed by SDS-PAGE. The proteins were cut from the gels, digested with trypsin and identified via peptide mass fingerprint and manual sequencing of selected peptides by MALDI-TOF/TOF mass spectrometry. Around 20-25 proteins were identified belonging to only 6-7 protein families. Metalloproteinases of the classes P-I and P-III were the most abundant proteins in all venoms (58-74% based on peak area A214 nm), followed by phospholipases-A(2) (6.4-14%), disintegrins (3.2-9%) and serine proteinases (7-11%), and some of these proteins occurred in several isoforms. In contrast cysteine-rich secretory proteins and L-amino acid oxidases appeared only as single isoforms and were found only in B. atrox and B. barnetti. C-type lectins were also detected in all venoms but at low levels (~ 5%). Furthermore, the venoms contain variable numbers of peptides (<3 kDa) and non-protein compounds which were not considered in this work. The protein composition of the investigated Bothrops species is in agreement with their pharmacological and pathological effects.     

Ingested prey increase risks of visual predation in transparent Chaoborus larvae

Summary Transparency reduces the chances of detection of large planktonic animals by visual predators. An important constraint on the transparency of planktonic animals may be ingested food which could be seen through the body, thereby increasing the vulnerability of transparent zooplankton to visual predators. To test this hypothesis, we presented fed and un-fed Chaoborus larvae to juvenile coho salmon (Oncorhynchus kisutch). Overall, the presence of prey in the gut of Chaoborus increased their probability of capture by 68%. Predation risks due to the visibility of ingested food increased in proportion to meal size: larvae with nearly full gut were captured about three times faster on the average than larvae which had little food in their gut. Although Chaoborus larvae may be able to reduce this increased predation risk by migrating downward to low light levels, this behavior would reduce feeding opportunities by removing the larvae from surface waters where prey density is generally high. In this way, visual predators may limit the growth and the maximum size that can be achieved by transparent animals.     

Specific color sensitivities of prey and predator explain camouflage in different visual systems

In situations of aggressive mimicry, predators adapt their colorto that of the substrate on which they sit for hunting, a behaviorthat is presumed to hide them from prey as well as from theirown predators. Females of few crab-spider species encountersuch situations when lying on flowers to ambush pollinators.To evaluate the efficiency of spider camouflage on flowers,we measured by spectroradiometry adult female Thomisus onustusand marguerite daisies, Leucanthemum vulgare. We compared chromaticcontrast (color used for short-range detection) of each pairof spider and flower to detection thresholds computed in thevisual systems of both Hymenopteran prey and passerine birdpredator. We also computed achromatic contrast (brightness)used for long-range detection. In both visual systems, eachindividual spider was efficiently matching the precise colorof the flower center on which it was hunting. Being significantlydarker than flowers, crab-spiders could in theory be detectedat long range by either predator or prey using achromatic contrast.However, long-range detection is unlikely, owing to small spidersize. Spiders also generated significant chromatic and achromaticcontrasts to both Hymenoptera and bird when moving on flowerperiphery. Our study is the first to identify which photoreceptorsof both prey and predator are involved in camouflage. The analysissuggests more research on bird predation and vision to determineto which extent bird predators effectively constrain spidercrypsis.     

Deceptive color signaling in the night: a nocturnal predator attracts prey with visual lures

The role color signaling plays in the nocturnal condition ofthe terrestrial ecosystem is currently poorly understood. Ingeneral, arthropods active in the night are inconspicuouslycolored. However, in addition to inconspicuously colored dorsum,several genera of nocturnal orb spiders also have conspicuousventrum spots. In this study, we tested whether the inconspicuouslycolored dorsum functioned to reduce spiders‘ visibilityto diurnal predators while the spiders were perching on barkwith ventrum spots well concealed. We also evaluated when spiderssit on webs with conspicuous ventrum spots fully exposed, wouldthey serve as deceptive color signals to lure visually orientatednocturnal prey. We first quantified how diurnal hymenopteranpredators viewed the dorsum and nocturnal lepidopteran preyviewed the ventrum spots of nocturnal orb spiders Neoscona punctigeraby calculating color contrasts. The diurnal color contrast ofspiders’ dorsum when viewed by hymenopteran insects againstbark was lower than the discrimination threshold. However, thenocturnal color contrasts of spiders‘ ventrum spots whenviewed by moths were high. In the field, webs with N. punctigeraintercepted significantly more insects than those without. Whenthe color signal of ventrum spots was altered by paint, webs’prey interception rates decreased significantly. These resultsdemonstrate that even in the nocturnal condition certain terrestrialorganisms exhibit visual lures to attract prey.     

A model of the visual localization of prey by frog and toad

In this paper we demonstrate how prey localization can be acheived rapidly and accurately by coupling prey-selection and lens-accommodation processes within a feedback loop. Information derived from prey selection supplies a setpoint for accomodation. In turn, adjustment of the lens modifies the visual input and can alter the prey selection process. The natural feedback of this goal-seeking system automatically corrects for the problem of ambiguity in binocular matching.Although it is of general interest as a depth algorithm, we tie the model to the known anatomy, physiology and behavior of frogs and toads. Instead of building a global depth-map we propose that the goal of catching a prey leads a frog or toad to select a particular region of its visual world for special scrutiny. We suggest that the first step of the prey-catching sequence is to adjust the accommodative state of the lenses and thus lock the visual apparatus on to a stimulus. We identify brain regions that could provide the neural substrates necessary to support the model's various functional stages and present experiments, with a computer simulation, that compare its functioning to animal behavior.     

Snake venomics of the pit vipers Porthidium nasutum, Porthidium ophryomegas, and Cerrophidion godmani from Costa Rica: toxicological and taxonomical insights

Within the Neotropical pit vipers, a lineage of primarily Middle American snake species referred to as the “Porthidium group” includes the genera Atropoides, Cerrophidion, and Porthidium. In this study, the venom proteomes of Porthidium nasutum, P. ophryomegas, and Cerrophidion godmani from Costa Rica were analyzed, and correlated to their toxic and enzymatic activities. Their HPLC profiles revealed a higher similarity between the two Porthidium species than between these and C. godmani. Proteins belonging to nine (P. nasutum), eight (P. ophryomegas), and nine (C. godmani) families were identified by mass spectrometry or N-terminal sequencing. Final cataloging of proteins and their relative abundances confirmed the close relationship between venoms of P. nasutum and P. ophryomegas, departing from that of C. godmani. Since the latter species had been taxonomically classified as Porthidium godmani previously, our venomic analyses agree with its current generic status. Venoms of P. nasutum and P. ophryomegas, despite containing abundant metalloproteinases and serine proteinases, lack procoagulant activity on human plasma, in contrast to venom of C. godmani. The latter induced strong myotoxicity in mice, which correlates with its high proportion of phospholipases A₂, whereas venoms from the two Porthidium species, containing lower amounts of these enzymes, induced only mild muscle damage.     

Influence of prey body characteristics and performance on predator selection

At the time of settlement to the reef environment, coral reef fishes differ in a number of characteristics that may influence their survival during a predatory encounter. This study investigated the selective nature of predation by both a multi-species predator pool, and a single common predator (Pseudochromis fuscus), on the reef fish, Pomacentrus amboinensis. The study focused on the early post-settlement period of P. amboinensis, when mortality, and hence selection, is known to be highest. Correlations between nine different measures of body condition/performance were examined at the time of settlement, in order to elucidate the relationships between different traits. Single-predator (P. fuscus) choice trials were conducted in 57.4-l aquaria with respect to three different prey characteristics [standard length (SL), body weight and burst swimming speed], whilst multi-species trials were conducted on open patch reefs, manipulating prey body weight only. Relationships between the nine measures of condition/performance were generally poor, with the strongest correlations occurring between the morphological measures and within the performance measures. During aquaria trials, P. fuscus was found to be selective with respect to prey SL only, with larger individuals being selected significantly more often. Multi-species predator communities, however, were selective with respect to prey body weight, with heavier individuals being selected significantly more often than their lighter counterparts. Our results suggest that under controlled conditions, body length may be the most important prey characteristic influencing prey survival during predatory encounters with P. fuscus. In such cases, larger prey size may actually be a distinct disadvantage to survival. However, these relationships appear to be more complex under natural conditions, where the expression of prey characteristics, the selectivity fields of a number of different predators, their relative abundance, and the action of external environmental characteristics, may all influence which individuals survive.     

Foraging and breeding performance of Japanese cormorants in relation to prey type

Seabirds are high trophic predators in marine ecosystems and are sensitive to change in food supply and thus seabirds can be used as monitors of the marine environment. In order to study the foraging responses of Japanese cormorants Phalacrocorax filamentosus breeding at Teuri Island, Hokkaido to changes in fish availability, the diet was assessed from the regurgitations of parents and chicks, and diving behavior was measured by using time-depth recorders. Breeding performance (brood size, chick growth, breeding success) was monitored using conventional methods to study their breeding responses. Japanese cormorants changed the diet and foraging behavior over four summers. The birds fed mainly on epipelagic schooling fish when they were available and on demersal fish when pelagic fish availability was low. They tended to dive deeper and longer in a year when they fed mainly on demersal fish than the other years, reflecting the change in the depth distribution of prey fish. Chick growth rate did not differ among years, but fledging success was lower in the years of demersal fish as their meal delivery rate was low. When epipelagic schooling fish were considered scare, parents maintained chick growth by reducing brood size. High variability and unpredictability in pelagic fish abundance are key factors affecting the foraging and breeding performance of Japanese cormorants, which could potentially be used to monitor fish resources.