Molecular systematics and evolution of Regina and the thamnophiine snakes.

Snakes of the tribe Thamnophiini represent an ecologically important component of the herpetofauna in a range of habitats across North America. Thamnophiines are the best-studied colubrids, yet little is known of their systematic relationships. A molecular phylogenetic study of 32 thamnophiine species using three complete mitochondrial genes (cytochrome b, NADH dehydrogenase subunit 2, and 12S ribosomal DNA) recovered a well-supported phylogeny with three major clades: a garter snake group, a water snake group, and a novel semifossorial group. The historically contentious genus Regina, which contains the crayfish-eating snakes, is polyphyletic. The phylogeographic pattern of Thamnophis is consistent with an hypothesis of at least one invasion of northern North America from Mexico.     

Influence of the venom delivery system on intraoral prey transport in snakes

We compared intraoral prey transport in venomous snake species from four families (two atractaspidids, nine elapids, three colubrids, 44 viperids) with that in eight non-venomous colubrid species, most feeding on similar mammalian prey. The morphology of the venom delivery system suggests that intraoral prey transport performance should be slightly decreased in atractaspidids, unmodified in most elapids and venomous colubrids, and increased or unmodified in vipers, as compared to that in non-venomous colubrid snakes. Our measurements of relative intraoral prey transport performance show that differences among families do not match expectations based on morphology or past studies. Decreased performance in Atractaspis results from reduction and loss of teeth on the medial palatal elements and dentaries, but affects only early phases of ingestion. Although joint and bone features of elapids and colubrids are similar, intraoral prey transport performance is significantly lower in elapids than in colubrids. Predicted enhancement of intraoral prey transport performance in vipers as compared to colubrids was not borne out by measurements, presumably because palatopterygoid movement during intraoral prey transport is reduced in many viper species to limit fang erection. Absence of significant performance differences between colubrids and viperids might suggest that evolution of the viperid venom delivery system was subject to little selection pressure from intraoral prey transport. Another possibility is that there are trade-offs between intraoral prey transport and strike performance in vipers related to relative skull mass and jaw fragility. Immobilizing prey prior to intraoral transport places less demand on transport performance in vipers. In this model, the conservative kinesis and greater robustness of the colubrid palate has greater potential for transporting live prey with less risk of injury.     

Signal evolution in prey recognition systems

In this paper a graphical model first developed in the context of kin recognition is adapted to the study of signalling in predator-prey systems. Antipredation strategies are envisioned as points along a signal-to-noise (S/N) axis, with concealing (low S/N) and conspicuous (high S/N) strategies being placed at opposite sides of this axis. Optimal prey recognition systems should find a trade-off between acceptance errors (going after a background cue as if it were a prey) and rejection errors (not going after a prey as if it were background noise). The model also predicts the types of cues the predator should use in opposite sides of the S/N axis.     

Sexual dimorphism in snakes: different reproductive roles favour different body plans

Because snakes have a highly simplified morphology, and many species have a wide (and broadly overlapping) range of adult body sizes within each sex, they offer an excellent opportunity to compare body composition of males and females. Evolutionary theory predicts that particular body components should be differentially enlarged in the two sexes. For example, we might expect the reproductive success of females to be enhanced by enlargement of organ systems involved in the processing and storage of energy (e.g. alimentary tract, liver, fat stores) whereas males would benefit from the enlargement of systems important for mate-searching, male–male combat and sperm competition (e.g. larger mass of skeletal muscles, tail, and kidneys). Dissection of 243 specimens of three snake species (117 Vipera aspis, 43 Elaphe longissima, 83 Coluber viridflavus) broadly supported these predictions. Strong sex differences were apparent in relative sizes (masses) of all the non-gonadal body components that we weighed. For example, males consistently had more musculature (relative to body length) than did conspecific females. Dimorphism in relative muscle mass is likely to be one of the most fundamental and widespread morphological differences between males and females in the Animal Kingdom.     

Energetic and physiological correlates of prey handling and ingestion in lizards and snakes

In this review, we summarize the energetic and physiological correlates of prey handling and ingestion in lizards and snakes. There were marked differences in the magnitude of aerobic metabolism during prey handling and ingestion between these two groups, although they show a similar pattern of variation as a function of relative prey mass. For lizards, the magnitude of aerobic metabolism during prey handling and ingestion also varied as a function of morphological specializations for a particular habitat, prey type, and behavior. For snakes, interspecific differences in aerobic metabolism during prey handling seem to be correlated with adaptations for prey capture (venom injection vs. constriction). During ingestion by snakes, differences in aerobic metabolism might be due to differences in cranial morphology, although allometric effects might be a potentially confounded effect. Anaerobic metabolism is used for prey handling and ingestion, but its relative contribution to total ATP production seems to be more pronounced in snakes than in lizards. The energetic costs of prey handling and ingestion are trivial for both groups and cannot be used to predict patterns of prey-size selection. For lizards, it seems that morphological and ecological factors set the constraints on prey handling and ingestion. For snakes, besides these two factors, the capacity of the cardio-respiratory system may also be an important factor constraining the capacity for prey handling and ingestion.     

Mechanisms of prey selection by predaceous stoneflies: roles of prey morphology,behavior and predator hunger

Summary Laboratory feeding experiments using Hesperoperla pacifica (Banks), Perlidae, and Megarcys signata (Hagen), Perlodidae, as predators and Baetis tricaudatus Dodds and Ephemerella altana Allen as prey indicate a strong effect of prey morphology and mobility and predator hunger on prey selection by stoneflies. Knowledge of both dietary composition and feeding behavior was necessary to fully understand prey selection by these stoneflies.Fasted stoneflies presented with live prey ate more E. altana while satiated stoneflies ate approximately equal numbers of the two mayfly species. This pattern of dietary composition was the result of a reduction of attack frequency on the slower swimming E. altana with predator satiation and a continued high attack rate on B. tricaudatus regardless of recent feeding history. In contrast, fasted H. pacifica fed fresh frozen mayflies ate more B. tricaudatus indicating the importance of differences in prey mobility in controlling dietary composition.The high degree of similarity in patterns of feeding and mechanisms underlying those patterns for H. pacifica and M. signata suggest that they may be using similar rules for choosing mayfly prey and we suggest that mayfly prey are ranked by stoneflies on the basis of handling times. A general mechanistic model for stoneflies feeding on mayflies is presented and discussed.     

Allometry and selection in a novel predator–prey system: Australian snakes and the invading cane toad

Because many organismal traits vary with body size, interactions between species can be affected by the respective body sizes of the participants. We focus on a novel predator–prey system involving an introduced, highly toxic anuran (the cane toad, Bufo marinus ) and native Australian snakes. The chance of a snake dying after ingesting a toad depends on the size of the snake and the size of the toad, and ultimately reflects the effect of four allometries: (1) physiological tolerance (the rate that physiological tolerance to toad toxin changes with snake size); (2) swallowing ability (the rate that maximal ingestible toad size (i.e. snake head size) increases with snake body size); (3) prey size (the rate that prey size taken by snakes increases with snake head size) and (4) toad toxicity (the rate that toxicity increases with toad size). We measured these allometries, and combined them to estimate the rate at which a snake's resistance changes with toad toxicity. The parotoid glands (and thus, toxicity) of toads increased disproportionately with toad size (i.e. relative to body size, larger toads were more toxic) but simultaneously, head size relative to body size (and thus, maximal ingestible prey size relative to predator size) declined with increasing body size in snakes. Thus, these two allometries tended to cancel each other out. Physiological tolerance to toxins did not vary with snake body size. The end result was that across snake species, mean adult body size did not affect vulnerability. Within species, however, smaller predators were more vulnerable, because the intraspecific rate of decrease in relative head size of snakes was steeper than the rate of increase in toxicity of toads. Thus, toad invasion may cause disproportionate mortality of juvenile snakes, and adults of the sex with smaller mean adult body sizes.     

Fatal attraction: adaptations to prey on native frogs imperil snakes after invasion of toxic toads

Adaptations that enhance fitness in one situation can become liabilities if circumstances change. In tropical Australia, native snake species are vulnerable to the invasion of toxic cane toads. Death adders (Acanthophis praelongus) are ambush foragers that (i) attract vertebrate prey by caudal luring and (ii) handle anuran prey by killing the frog then waiting until the frog''s chemical defences degrade before ingesting it. These tactics render death adders vulnerable to toxic cane toads (Bufo marinus), because toads elicit caudal luring more effectively than do native frogs, and are more readily attracted to the lure. Moreover, the strategy of delaying ingestion of a toad after the strike does not prevent fatal poisoning, because toad toxins (unlike those of native frogs) do not degrade shortly after the prey dies. In our laboratory and field trials, half of the death adders died after ingesting a toad, showing that the specialized predatory behaviours death adders use to capture and process prey render them vulnerable to this novel prey type. The toads'' strong response to caudal luring also renders them less fit than native anurans (which largely ignored the lure): all toads bitten by adders died. Together, these results illustrate the dissonance in behavioural adaptations that can arise following the arrival of invasive species, and reveal the strong selection that occurs when mutually naive species first interact.     

Hinged teeth for hard-bodied prey: a case of convergent evolution between snakes and legless lizards

Savitzky (1981) described hinged teeth in several taxa of snakes, and interpreted this type of dentition as an adaptation to feeding on hard-bodied prey (scincid lizards). We tested this hypothesis by examining the dentition of insectivorous and saurophagous members of the Australian legless lizards, Pygopodidae. Insectivorous taxa ( Delma, Pygopus ) have peg-like pleurodont dentition, but the saurophagous Lialis has slender, recurved, sharply-pointed teeth, like those of many snakes. The teeth of Lialis are 'hinged' on their supporting bones: each tooth folds when pressure is applied to its anterior surface, but locks in an erect position when forced from behind, The tooth hinge is probably collagenous, and does not contain elastin. The presence of hinged teeth in Lids , which feeds predominately on scincid lizards, offers strong support for Savitzky's hypothesis.     

Functional plasticity of the venom delivery system in snakes with a focus on the poststrike prey release behavior

We explored variations in the morphology and function of the envenomation system in the four families of snakes comprising the Colubroidea (Viperidae, Elapidae, Atractaspididae, and Colubridae) using our own prey capture records and those from the literature. We first described the current knowledge of the morphology and function of venom delivery systems and then explored the functional plasticity found in those systems, focusing on how the propensity of snakes to release prey after the strike is influenced by various ecological parameters. Front-fanged families (Viperidae, Elapidae, and Atractaspididae) differ in the morphology and topographical relationships of the maxilla as well as in the lengths of their dorsal constrictor muscles (retractor vomeris; protractor, retractor, and levator pterygoidei; protractor quadrati), which move the bones comprising the upper jaw, giving some viperids relatively greater maxillary mobility compared to that of other colubroids. Rear-fanged colubrids vary in maxillary rotation capabilities, but most have a relatively unmodified palatal morphology compared to non-venomous colubrids. Viperids launch rapid strikes at prey, whereas elapids and colubrids use a variety of behaviors to grab prey. Viperids and elapids envenomate prey by opening their mouth and rotating both maxillae to erect their fangs. Both fangs are embedded in the prey by a bite that often results in some retraction of the maxilla. In contrast, Atractaspis (Atractaspididae) envenomates prey by extruding a fang unilaterally from its closed mouth and stabbing it into the prey by a downward-backwards jerk of its head. Rear-fanged colubrids envenomate prey by repeated unilateral or bilateral raking motions of one or both maxillae, some aspects of which are kinematically similar to the envenomation behavior in Atractaspis. The envenomation behavior, including the strike and prey release behaviors, varies within families as a function of prey size and habitat preference. Rear-fanged colubrids, arboreal viperids, and elapids tend to hold on to their prey after striking it, whereas atractaspidids and many terrestrial viperids release their prey after striking it. Larger prey are more frequently released than smaller prey by terrestrial front-fanged species. Venom delivery systems demonstrate a range of kinematic patterns that are correlated to sometimes only minor modifications of a common morphology of the jaw apparatus. The kinematics of the jaw apparatus are correlated with phylogeny, but also show functional plasticity relating to habitat and prey.     

Sequence tag scanning: a new explorative strategy for recognition of unexpected protein alterations by nanoelectrospray ionization-tandem mass spectrometry

Protein analysis by database search engines using tandem mass spectra is limited by the presence of unexpected protein modifications, sequence isoforms which may not be in the protein databases, and poor quality tandem mass spectrometry (MS/MS) of low abundance proteins. The analysis of expected protein modifications can be efficiently addressed by precursor ion scanning. However, it is limited to modifications that show such a characteristic loss in a peptide independent manner. We observed that proline and aspartic acid induced backbone fragmentation is accompanied by a low intensity signal for loss of H3PO4 for several pSer- or pThr-phosphopeptides. We describe here the use of peptide-specific fragments that can be used after a protein was identified to allow in-depth characterization of modifications and isoforms. We consider high abundance fragments formed by cleavage at the C-terminal side of aspartic acid, at the N-terminal side of proline and low mass ions such as a2, b2, b3, y1, y2, and y3. The MS/MS dataset is filtered for each sequence tag of interest by an in silico precursor ion scan. The resulting extracted ion traces are then combined by multiplication to increase specificity. Since the strategy is based on common peptide segments which are shared by different isoforms of peptides it can be applied to the analysis of any post-translational modification or sequence variants of a protein. This is demonstrated for the cases of serine and threonine phosphorylation, histone H1 acetylation and the spotting of multiple H1 isoforms.     

Neuroendocrine basis of social recognition

Studies conducted in the past two years have yielded several new insights about neuroendocrine regulation of social recognition. The social recognition deficits seen in oxytocin knockout mice have now been demonstrated in both males and females, as well as in female estrogen receptor knockout mice. The male vasopressin V1A receptor knockout mouse (but not V1B) has a profound social recognition deficit. Preliminary evidence suggests that female V1B receptor knockout mice could also have social memory deficits. Several lines of evidence have emerged that indicate that neuropeptide regulation is significantly modulated by gonadal and corticosteroid activation.     

p53: new roles in metabolism

Virtually all cancers show metabolic changes that result in upregulation of glycolysis and glucose consumption. Although discovered in the 1920s, how this glycolytic switch happens, and whether it is a cause or a consequence of the malignant process, has remained a matter of debate. The p53 tumor suppressor gene, discovered some 30 years ago, has a key role in preventing cancer development. Recent discoveries revealing new functions for p53 in the regulation of glucose metabolism and oxidative stress have brought together these two venerable fields of cancer biology. These activities of p53 appear to be key in tumor suppression, and shed some light on the pathways that underlie the metabolic changes in cancer cells.     

Canonical Wnt signaling: an unexpected new player

Canonical Wnt signaling, below the Fz/LRP receptor complex, induces the stabilization of beta-catenin via an unresolved mechanism. A recent study in Genes & Development introduces a new player and deepens our understanding of this signaling relay that plays pivotal roles during embryogenesis and tumorigenesis.