Phylogeography and dispersal in the velvet gecko (Oedura lesueurii), and potential implications for conservation of an endangered snake (Hoplocephalus bungaroides).

ABSTRACT: BACKGROUND: To conserve critically endangered predators, we also need to conserve the prey species upon which they depend. Velvet geckos (Oedura lesueurii) are a primary prey for the endangered broad-headed snake (Hoplocephalus bungaroides), which is restricted to sandstone habitats in southeastern Australia. We sequenced the ND2 gene from 179 velvet geckos, to clarify the lizards' phylogeographic history and landscape genetics. We also analysed 260 records from a longterm (3-year) capture-mark-recapture program at three sites, to evaluate dispersal rates of geckos as a function of locality, sex and body size. RESULTS: The genetic analyses revealed three ancient lineages in the north, south and centre of the species' current range. Estimates of gene flow suggest low dispersal rates, constrained by the availability of contiguous rocky habitat. Mark-recapture records confirm that these lizards are highly sedentary, with most animals moving < 30 m from their original capture site even over multi-year periods. CONCLUSION: The low vagility of these lizards suggests that they will be slow to colonise vacant habitat patches; and hence, efforts to restore degraded habitats for broad-headed snakes may need to include translocation of lizards

Elasticity of Stiff Polymer Networks

We study the elasticity of a two-dimensional random network of rigid rods (``Mikado model''). The essential features incorporated into the model are the anisotropic elasticity of the rods and the random geometry of the network. We show that there are three distinct scaling regimes, characterized by two distinct length scales on the elastic backbone. In addition to a critical rigidiy percolation region and a homogeneously elastic regime we find a novel intermediate scaling regime, where elasticity is dominated by bending deformations.Comment: 4 pages, 4 figure

Scaling relation for determining the critical threshold for continuum percolation of overlapping discs of two sizes

We study continuum percolation of overlapping circular discs of two sizes. We propose a phenomenological scaling equation for the increase in the effective size of the larger discs due to the presence of the smaller discs. The critical percolation threshold as a function of the ratio of sizes of discs, for different values of the relative areal densities of two discs, can be described in terms of a scaling function of only one variable. The recent accurate Monte Carlo estimates of critical threshold by Quintanilla and Ziff [Phys. Rev. E, 76 051115 (2007)] are in very good agreement with the proposed scaling relation.Comment: 4 pages, 3 figure

The TD50: a proposed general convention for the numerical description of the carcinogenic potency of chemicals in chronic-exposure animal experiments.

A generally accepted format for the numerical description of the carcinogenic potency of a particular chemical in a particular strain of animals is desirable so that statements from different sources about potency and attempts by different authors to correlate potency with particular laboratory measurements will be comparable. The choice of an appropriate standard format is to a certain extent arbitrary. In this paper we recommend that the TD50 (tumorigenic dose rate 50) be used. TD50 can be calculated for a single target site or combination of sites. The TD50, in analogy with the LD50, is defined as that chronic dose rate (in mg/kg body weight/day) which would halve the actuarially adjusted percentage of tumor-free animals at the end of a standard experiment time--the "standard lifespan" for the species. This paper consists of a brief discussion of the TD50, sufficient to make the general reader familiar with the properties of such an index, an appendix discussing methods for its estimation and certain conventions we have adopted for use in analyzing "nonstandard" experiments. A major problem in calculating any index of carcinogenic potency is that much published material gives only the final crude percentage of tumor-bearing animals at each dose, instead of percentages adjusted for the effects of intercurrent mortality or data from which these adjusted percentages can be derived. If the dose level administered to the animals is toxic, then premature death from nonneoplastic causes may prevent some dosed animals that would have developed tumors from actually doing so. This will particularly affect the high-dose group.(ABSTRACT TRUNCATED AT 250 WORDS