Predictors of orbital convergence in primates: A test of the snake detection hypothesis of primate evolution

Traditional explanations for the evolution of high orbital convergence and stereoscopic vision in primates have focused on how stereopsis might have aided early primates in foraging or locomoting in an arboreal environment. It has recently been suggested that predation risk by constricting snakes was the selective force that favored the evolution of orbital convergence in early primates, and that later exposure to venomous snakes favored further degrees of convergence in anthropoid primates. Our study tests this snake detection hypothesis (SDH) by examining whether orbital convergence among extant primates is indeed associated with the shared evolutionary history with snakes or the risk that snakes pose for a given species. We predicted that orbital convergence would be higher in species that: 1) have a longer history of sympatry with venomous snakes, 2) are likely to encounter snakes more frequently, 3) are less able to detect or deter snakes due to group size effects, and 4) are more likely to be preyed upon by snakes. Results based on phylogenetically independent contrasts do not support the SDH. Orbital convergence shows no relationship to the shared history with venomous snakes, likelihood of encountering snakes, or group size. Moreover, those species less likely to be targeted as prey by snakes show significantly higher values of orbital convergence. Although an improved ability to detect camouflaged snakes, along with other cryptic stimuli, is likely a consequence of increased orbital convergence, this was unlikely to have been the primary selective force favoring the evolution of stereoscopic vision in primates

The oldest known snakes from the Middle Jurassic-Lower Cretaceous provide insights on snake evolution

The previous oldest known fossil snakes date from ∼100 million year old sediments (Upper Cretaceous) and are both morphologically and phylogenetically diverse, indicating that snakes underwent a much earlier origin and adaptive radiation. We report here on snake fossils that extend the record backwards in time by an additional ∼70 million years (Middle Jurassic-Lower Cretaceous). These ancient snakes share features with fossil and modern snakes (for example, recurved teeth with labial and lingual carinae, long toothed suborbital ramus of maxillae) and with lizards (for example, pronounced subdental shelf/gutter). The paleobiogeography of these early snakes is diverse and complex, suggesting that snakes had undergone habitat differentiation and geographic radiation by the mid-Jurassic. Phylogenetic analysis of squamates recovers these early snakes in a basal polytomy with other fossil and modern snakes, where Najash rionegrina is sister to this clade. Ingroup analysis finds them in a basal position to all other snakes including Najash.Fil: Caldwell, Michael Wayne. University of Alberta; CanadáFil: Nydam, Randall L.. Department Of Anatomy, Midwestern University, Glendale; Estados UnidosFil: Palci, Alessandro. South Australian Museum. Earth Sciences Section; AustraliaFil: Apesteguía, Sebastián. Fundación de Historia Natural Félix de Azara; Argentina. Universidad Maimónides. Área de Investigaciones Biomédicas y Biotecnológicas. Centro de Estudios Biomédicos, Biotecnológicos, Ambientales y de Diagnóstico; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Linking Snake Behavior to Nest Predation in a Midwestern Bird Community

Nest predators can adversely affect the viability of songbird populations, and their impact is exacerbated in fragmented habitats. Despite substantial research on this predator-prey interaction, however, almost all of the focus has been on the birds rather than their nest predators, thereby limiting our understanding of the factors that bring predators and nests into contact. We used radiotelemetry to document the activity of two snake species (rat snakes, Elaphe obsoleta; racers, Coluber constrictor) known to prey on nests in Midwestern bird communities and simultaneously monitored 300 songbird nests and tested the hypothesis that predation risk should increase for nests when snakes were more active and in edge habitat preferred by both snake species. Predation risk increased when rat snakes were more active, for all nests combined and for two of the six bird species for which we had sufficient nests to allow separate analyses. This result is consistent with rat snakes being more important nest predators than racers. We found no evidence, however, that nests closer to forest edges were at greater risk. These results are generally consistent with the one previous study that investigated rat snakes and nest predation simultaneously. The seemingly paradoxical failure to find higher predation risk in the snakes\u27 preferred habitat (i.e., edge) might be explained by the snakes using edges at least in part for non-foraging activities. We propose that higher nest predation in fragmented habitats (at least that attributable to snakes) results indirectly from edges promoting larger snake populations, rather than from edges directly increasing the risk of nest predation by snakes. If so, the notion of edges per se functioning as ecological traps merits further study

A STUDY OF THE DEFENSIVE BEHAVIORS OF FREE-RANGING DEKAY’S BROWNSNAKES, STORERIA DEKAYI (HOLBROOK, 1836)

The defensive behaviors of free-ranging Dekay’s Brownsnakes, Storeria dekayi, were studied at a site in Erie County, Pennsylvania, USA. Twenty-nine unique sequences of defensive behavior were documented. A total of 50 individual snakes (26 males and 24 females) provided 88 observations during the initial phase, of which 78% (n = 69) were of snakes that remained in place. Snakes were tapped with the investigator’s hand to elicit defensive behaviors during the contact phase. Snakes were more than twice as likely to attempt to flee during the contact phase (46%) than during the initial phase (22%). During the contact phase, mean surface body temperatures were significantly higher in snakes attempting to flee (22.3 ± 1.3 °C) than those that remained in place (16.1 ± 2.2 °C). The most frequently observed response during the contact phase was dorso-ventral flattening of the head and body (n = 42). During capture, most snakes (94%) smeared their cloacal contents on themselves and the investigator’s hand

Optimal Axes of Siberian Snakes for Polarized Proton Acceleration

Accelerating polarized proton beams and storing them for many turns can lead to a loss of polarization when accelerating through energies where a spin rotation frequency is in resonance with orbit oscillation frequencies. First-order resonance effects can be avoided by installing Siberian Snakes in the ring, devices which rotate the spin by 180 degrees around the snake axis while not changing the beam's orbit significantly. For large rings, several Siberian Snakes are required. Here a criterion will be derived that allows to find an optimal choice of the snake axes. Rings with super-period four are analyzed in detail, and the HERA proton ring is used as an example for approximate four-fold symmetry. The proposed arrangement of Siberian Snakes matches their effects so that all spin-orbit coupling integrals vanish at all energies and therefore there is no first-order spin-orbit coupling at all for this choice, which I call snakes matching. It will be shown that in general at least eight Siberian Snakes are needed and that there are exactly four possibilities to arrange their axes. When the betatron phase advance between snakes is chosen suitably, four Siberian Snakes can be sufficient. To show that favorable choice of snakes have been found, polarized protons are tracked for part of HERA-p's acceleration cycle which shows that polarization is preserved best for the here proposed arrangement of Siberian Snakes.Comment: 14 pages, 16 figure

Snake prices and crocodile appetites: Aquatic wildlife supply and demand on Tonle Sap Lake, Cambodia

Commercial trade is a major driver of over-exploitation of wild species, but the pattern of demand and how it responds to changes in supply is poorly understood. Here we explore the markets for snakes from Tonle Sap Lake in Cambodia to evaluate future exploitation scenarios, identify entry points for conservation and, more generally, to illustrate the value of multi-scale analysis of markets to traded wildlife conservation. In Cambodia, the largest driver of snake exploitation is the domestic trade in snakes as crocodile food. We estimate that farmed crocodiles consume between 2.7 and 12.2 million snakes per year. The market price for crocodiles has been in decline since 2003, which, combined with rising prices for their food, has led to a reduced frequency of feeding and closure of small farms. The large farms that generate a disproportionate amount of the demand for snakes continue to operate in anticipation of future market opportunities, and preferences for snakes could help maintain demand if market prices for crocodiles rise to pre 2003 levels. In the absence of a sustained demand from crocodile farms, it is also possible that alternative markets will develop, such as one for human snack food. The demand for snakes, however, also depends on the availability of substitute resources, principally fish. The substitutability and low price elasticity of demand offers a relatively sustainable form of consumerism. Given the nature of these market drivers, addressing consumer preferences and limiting the protection of snakes to their breeding season are likely to be the most effective tools for conservation. This study highlights the importance of understanding the structure of markets and the behaviour of consumer demand prior to implementing regulations on wildlife hunting and trade

Swift-Hohenberg equation with broken reflection symmetry

The bistable Swift-Hohenberg equation possesses a variety of time-independent spatially localized solutions organized in the so-called snakes-and-ladders structure. This structure is a consequence of a phenomenon known as homoclinic snaking, and is in turn a consequence of spatial reversibility of the equation. We examine here the consequences of breaking spatial reversibility on the snakes-and-ladders structure. We find that the localized states now drift, and show that the snakes-and-ladders structure breaks up into a stack of isolas. We explore the evolution of this new structure with increasing reversibility breaking and study the dynamics of the system outside of the snaking region using a combination of numerical and analytical techniques