Convergence in trophic morphology and feeding performance among piscivorous natricine snakes

Piscivory has independently evolved numerous times amongst snakes, and therefore these animals provide a powerful opportunity to test for convergent evolution in a vertebrate feeding system. In this study, we integrate performance trials with comparative methods to test the hypothesis that piscivory drives convergence in trophic morphology and feeding performance among natricine snakes. Within and across species, increasing the relative length of the quadrate bone in the skull is positively and strongly linked to a reduction in the time needed to swallow large fish prey. Thus, our feeding experiments suggest that a longer quadrate bone enables snakes to better conform their head shape to the shape of the prey during swallowing. Ancestral diet reconstructions and phylogenetically corrected multiple regression analyses further reveal that evolutionary increases in piscivory are coupled to the evolution of relatively longer quadrates, and hence improved feeding performance on fish prey in these animals. The exploitation of similar dietary niches drives the evolution of convergent trophic morphologies and feeding performances in natricine snakes.     

Ontogeny of intersexual head shape and prey selection in the pitviper Agkistrodon piscivorus

Different animal intraspecific classes commonly differ in their prey selection. Such differences in feeding ecology are thought to reduce resource competition between classes, but other factors (i.e. behavioural, morphological, and physiological differences) also contribute to this widespread phenomenon. Although several studies have correlated the size of the feeding apparatus with prey selection in many animals, few studies have examined how the shape of the feeding apparatus is related to prey selection. Furthermore, even though the dietary regimen of many animals changes during ontogeny, few studies have examined how shape changes in the feeding apparatus may be related to these ontogenetic dietary shifts. Here we address these issues by examining how head shape, head size and prey selection change over ontogeny in adult males, adult females and juveniles of the cottonmouth snake Agkistrodon piscivorus . Our scaling data for head characteristics showed that all head measurements in adult male and female A. piscivorus scaled with significant negative allometry, whereas juvenile head measurements typically scaled isometrically, except for head volume (positive) and head length (negative). Thus, juveniles have relatively broad and high, but short, heads. Large adult male and female A. piscivorus have relatively small head dimensions overall. Thus, juveniles appear to undergo a rapid change in head volume, which subsequently slows considerably as sexual maturity is achieved. However, our multivariate analysis of size-adjusted head dimensions showed that juveniles differed only slightly in their head shape compared with adult male and female A. piscivorus . In general, prey size increased with snake size across all age and sex groups, but an ontogenetic shift in prey type was not detected in either males or females.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 81 , 151–159.     

THE ACTION OF METALDEHYDE ON THE SLUG AGRIOLIMAX RETICULATUS (MÜLLER)

Metaldehyde both as powder and in solution can act on slugs either by contact or as a 'stomach poison'. The characteristic effects of metaldehyde poisoning were immobilization broken by outbursts of unco-ordinated muscular activity and sliming which usually resulted in severe water loss. 24 hr. after treatment with moderate doses slugs were still abnormal and rarely fed within 30 hr. of treatment. It was not possible to determine the M.L.D. with the methods used, but 0·06 nig. solid metaldehyde taken orally could be lethal to slugs of 400–800 mg. body weight. Lethal effects were produced by contact of 1 hr. with concentrations equivalent to 0·0063 mg./cm.². Toxicity increased with rise in temperature and recovery from moderate doses was dependent on slugs being in a saturated or almost saturated atmosphere. No obvious gut lesions were found in slugs which had been dosed with or had eaten metaldehyde. Its action was not by depolymerization in the gut or body cavity. In the light of laboratory and small scale field trials it is suggested that broadcasting and spraying are the best methods of applying the material.     

Using Viscoelastic Properties of the Woody Tissue from Tobacco Plants (Nicotiana tabacum) to Comment on the Molecular Structure of Cell Walls

Lignin in the cell walls of woody tissue has a much lower crosslinkdensity in tobacco wood than in tree wood. This causes tobaccowood to show very different viscoelastic behaviour. With theaid of genetically modified plants, it is shown that the ligninin tobacco plant cell walls behaves in much the same way asa polymer solution. It exhibits both rate stiffening and ratethinning behaviour due to the entangled nature of the ligninnetworks. The hydrophobic portions of lignin have a very lowpolymer chain crosslink density, hence entanglements make asignificant contribution.Copyright 1998 Annals of Botany Company Tobacco plants, lignin, polymer solution, shear thinning, stress relaxation.     

Determinants of feeding performance in free-ranging pit-vipers (Viperidae: Ovophis okinavensis): key roles for head size and body temperature

Feeding performance (handling time, capture success) in numerous animal species is well known to be influenced by a variety of ecological, functional, and physiological factors. Nonetheless, few studies have tested which factors are the strongest determinants of animal feeding performance in the wild. Using a field-based experiment, we examined the relationships among a number of functionally important variables and the predatory behaviour of free-ranging pit-vipers ( Ovophis okinavensis ) from Okinawa Island, Japan. Our main findings were: (1) strike latency was negatively related to snake body temperature and, hence, hotter snakes struck at frogs more readily than colder snakes; (2) initial bite position was correlated with ingestion direction (headfirst versus hindfirst) but ingestion direction was not correlated with ingestion duration; and (3) both snake head length and body temperature were negatively related with ingestion duration and, thus, snakes with longer heads and higher body temperatures had shorter ingestion durations. In O. okinavensis , head size and body temperature are therefore likely to have direct ecological consequences in terms of its feeding rate on explosively breeding frogs. More generally, however, this field-based study adds to the growing body of literature demonstrating that temperature has a pervasive influence on the feeding performance of ectotherms in general.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 53–62.     

The origins and diversification of C4 grasses and savanna-adapted ungulates

C₄ grasses constitute the main component of savannas and are pervasive in other dry tropical ecosystems where they serve as the main diet for grazing animals. Among potential factors driving C₄ evolution of grasses, the interaction between grasses and grazers has not been investigated. To evaluate if increased grazing pressure may have selected for higher leaf silica production as the grasses diverged, we reconstructed the phylogeny of all 800 genera of the grass family with both molecular (combined multiplastid DNA regions) and morphological characters. Using molecular clocks, we also calculated the age and number of origins of C₄ clades and found that shifts from C₃ to C₄ photosynthesis occurred at least 12 times starting 30.9 million years ago and found evidence that the most severe drop in atmospheric carbon dioxide in the late Oligocene (between 33 and 30 million years ago) matches the first origin of C₄ photosynthesis in Chloridoideae. By combining fossil and phylogenetic data for ungulates and implementing a randomization procedure, our results showed that the appearance of C₄ grass clades and ungulate adaptations to C₄-dominated habitats match significantly in time. An increase of leaf epidermal density of silica bodies was found to correspond to postulated shifts in diversification rates in the late Miocene [24 significant shifts in diversification ( P <0.05) were detected between 23 and 3.7 million years ago]. For aristidoid and chloridoid grasses, increased grazing pressure may have selected for a higher leaf epidermal silica production in the late Miocene.     

The Role of Membrane Carriers in the Regulation of the Free Glucose Pool in Metabolizing Cells

SYNOPSIS. Equations have been derived which relate the intracellular concentration of a metabolized sugar to its extracellular concentration and the kinetic constants for transport and phosphorylation. The equations show that the maximum intracellular, concentration of a metabolized sugar is a constant determined by the kinetic constants for transport and phosphorylation.     

Axenic Cultivation and Electron Microscopy of Two Species of Choanoflagellida1

SYNOPSIS. Semi-defined basal media have been formulated for 2 species of axenically reared choanoflagellates. High cell yield of Acanthoecopsis sp. is routinely obtained. Diaphanoeca grandis grows less well, but continuous serial transfers assure cells in good phyiologic condition. Loricas of both species have been examined by electron microscopy for gross structural details.