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.     

Systematics of the Soft-plumaged Petrel Pterodroma mollis (Procellariidae): new insight from the study of vocalizations

The taxonomic status of the populations of the polytypic Soft-plumaged Petrel Pterodroma mollis is controversial. Previous taxonomic studies used morphological characters (measurements and colouration) and univariate statistics. In this study, I add the use of multivariate statistics on morphological (biometry and colouration) and behavioural characters (vocalizations) of the petrels. Vocalizations are especially relevant in nocturnal burrowing petrels (such as the Soft-plumaged Petrel) and act as behavioural isolating mechanisms. The analysis, based on 535 calls from seven of the 11 known breeding localities of the species, showed that physical parameters of the call did not overlap at all between breeding localities in the northern and southern hemispheres but did so within each hemisphere. Conversely, the morphological analysis, based on morphometries from ten localities, displayed wide and significant intra-hemisphere variation, whereas there was no consistent difference between northern and southern parts of the breeding range. Thus analysis of the two sets of characters gave contradictory results. Calls, owing to their role in species-specific recognition in these birds, should be given priority over other characters for species separation. I suggest that only two species should be recognized, Pterodroma mollis and Pterodroma feae, with three subspecies each. I also examined behavioural affinities between P. mollislfeae groups and other gadfly petrels and found that P. mollis/feae were closest to Pterodroma cahow, whilst Pterodroma hasitata on the one hand and Pterodroma phaeopygia and Pterodroma externa (which may comprise two species instead of one) on the other belong to other groups of gadfly petrels.     

The Expression of Tyrosinase,Tyrosinase-Related Proteins 1 and 2 (TRP1 and TRP2), the Silver Protein,and a Melanogenic Inhibitor in Human Melanoma Cells of Differing Melanogenic Activities

The expression of various melanogenic proteins, including tyrosinase, the tyrosinase-related proteins 1 (TRP1) and 2 (TRP2/DOPAchrome tautomerase), and the silver protein in human melanocytes was studied in six different human melanoma cell lines and compared to a mouse derived melanoma cell line. Analysis of the expression of tyrosinase, TRP1, TRP2, and the silver protein using flow cytometry revealed that in general there was a positive correlation between melanin formation and the expression of those melanogenic enzymes. Although several of the melanoma cell lines possessed significant activities of TRP2, the levels of DOPAchrome tautomerase in extracts of human cells were relatively low compared to those in murine melanocytes. Melanins derived from melanotic murine JB/MS cells, from melanotic human Ihara cells and HM-IY cells, from sepia melanin, and from C57BL/6 mouse hair were chemically analyzed. JB/MS cells, as well as Ihara cells and HM-TY cells, possessed significant amounts of 5,6-dihydroxyindole-2-carboxylic acid (DHICA) derived melanins, this being dependent on the activity of TRP2. Kinetic HPLC assays showed that 5,6-dihydroxyindole (DHI) produced during melanogenesis was metabolized quickly to melanin in pigmented KHm-1/4 cells, whereas DHI was stable in amelanotic human SK-MEL-24 cells. A melanogenic inhibitor that has been purified from SK-MEL-24 cells that suppressed oxidation of DHI in the presence or absence of tyrosinase, but had no effect on DHICA oxidation. The sum of these results suggest that the expression of melanogenic enzymes as well as the activity of a melanogenic inhibitor are critical to the production of melanin synthesis in humans.     

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 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.     

A longirostrine Temnodontosaurus (Ichthyosauria) with comments on Early Jurassic ichthyosaur niche partitioning and disparity

Abstract: We describe an almost complete ichthyosaur skeleton from the middle Toarcian (Lower Jurassic) of the Beaujolais foothills near Lyon, France, and assign it to Temnodontosaurus azerguensis sp. nov. This new species exhibits cranial peculiarities such as a thin, elongated and possibly edentulous rostrum, as well as a reduced quadrate. These characters indicate dietary preferences that markedly differ from other species referred to Temnodontosaurus, a genus previously considered as the top predator of the Early Jurassic seas. Despite a conservative postcranial skeleton, we propose that Temnodontosaurus is one of the most ecologically disparate genera of ichthyosaurs, including apex predators and now a soft prey longirostrine hunter. Ammonites collected from the same stratigraphic level as the described specimen indicate that the new species is somewhat younger (bifrons ammonite zone) than the most known Toarcian ichthyosaurs and therefore slightly postdates the interval of severe environmental changes and marine invertebrate extinctions known as the Toarcian Oceanic Anoxic Event. The present study therefore raises the question of whether postcrisis recovery of vertebrate faunas, including the radiation of Temnodontosaurus into a new ecological niche, may have been a consequence of marine ecosystem reorganization across this event.