Effects of sterilization and vacuum exposure on potential heat shield materials for unmanned Mars mission

Sterilization and vacuum exposure effects on potential heat shield materials for unmanned Mars mission

The permeabilities of three porous graphites Final report

Permeability measurements of porous graphites measured from room temperature to 1000 deg F in gaseous nitrogen and heliu

An investigation of the mechanisms of heat transfer in low-density phenolic-nylon chars

Conductive heat transfer mechanisms in low density phenolic-nylon char

Molecular evolution of HoxA13 and the multiple origins of limbless morphologies in amphibians and reptiles

Developmental processes and their results, morphological characters, are inherited through transmission of genes regulating development. While there is ample evidence that cis-regulatory elements tend to be modular, with sequence segments dedicated to different roles, the situation for proteins is less clear, being particularly complex for transcription factors with multiple functions. Some motifs mediating protein-protein interactions may be exclusive to particular developmental roles, but it is also possible that motifs are mostly shared among different processes. Here we focus on HoxA13, a protein essential for limb development. We asked whether the HoxA13 amino acid sequence evolved similarly in three limbless clades: Gymnophiona, Amphisbaenia and Serpentes. We explored variation in ω (dN/dS) using a maximum-likelihood framework and HoxA13sequences from 47 species. Comparisons of evolutionary models provided low ω global values and no evidence that HoxA13 experienced relaxed selection in limbless clades. Branch-site models failed to detect evidence for positive selection acting on any site along branches of Amphisbaena and Gymnophiona, while three sites were identified in Serpentes. Examination of alignments did not reveal consistent sequence differences between limbed and limbless species. We conclude that HoxA13 has no modules exclusive to limb development, which may be explained by its involvement in multiple developmental processes

Cryptic, sympatric diversity in Tegu lizards of the Tupinambis teguixin Group (Squamata, Sauria, Teiidae) and the description of three new species

Tegus of the genera Tupinambis and Salvator are the largest Neotropical lizards and the most exploited clade of Neotropical reptiles. For three decades more than 34 million tegu skins were in trade, about 1.02 million per year. The genus Tupinambis is distributed in South America east of the Andes, and currently contains four recognized species, three of which are found only in Brazil. However, the type species of the genus, T. teguixin, is known from Bolivia, Brazil, Colombia, Ecuador, French Guyana, Guyana, Peru, Suriname, Trinidad and Tobago, and Venezuela (including the Isla de Margarita). Here we present molecular and morphological evidence that this species is genetically divergent across its range and identify four distinct clades some of which are sympatric. The occurrence of cryptic sympatric species undoubtedly exacerbated the nomenclatural problems of the past. We discuss the species supported by molecular and morphological evidence and increase the number of species in the genus Tupinambis to seven. The four members of the T. teguixin group continue to be confused with Salvator merianae, despite having a distinctly different morphology and reproductive mode. All members of the genus Tupinambis are CITES Appendix II. Yet, they continue to be heavily exploited, under studied, and confused in the minds of the public, conservationists, and scientists

Identifying Local Scale Food Web Variation Using Stable δ¹³C and δ¹⁵N Isotopes in a Central Indiana Reservoir and Downstream River

We used stable isotopes of δ¹³C and δ¹⁵N were measured from fish and macroinvertebrate consumers, terrestrial and aquatic primary producers, and detritus to describe food webs for a reservoir and downstream riverine habitat. Measurements of δ¹³C indicated that reservoir energy sources were primarily autochthonous while the riverine habitat was primarily a result of allochthonous carbon sources. Measurements of d 15N indicated that terrestrial primary producers were basal to organic matter, aquatic primary producers, macroinvertebrates, and fishes, respectively. We found significant differences between riverine and reservoir δ¹³C and δ¹⁵N levels among seven fish taxa representing Cyprinidae, Centrarchidae, Percidae, Ictaluridae, and Clupeidae families. Riverine and reservoir overall δ¹³C and δ¹⁵N levels differed by an average of 7.9% and 7.7% by taxa, respectively. Reservoir fish exhibited lower intra specific variation in δ¹³C and δ¹⁵N values compared to river fish indicating less variation in diet. Reservoir fish were also found to feed at more extreme trophic positions (high and low) compared to riverine fish. This evidence suggests the presence of habitat-induced variability in local scale food webs and has implications for understanding aquatic ecosystem diversity and organization

Next-generation mitogenomics: A comparison of approaches applied to caecilian amphibian phylogeny

Mitochondrial genome (mitogenome) sequences are being generated with increasing speed due to the advances of next-generation sequencing (NGS) technology and associated analytical tools. However, detailed comparisons to explore the utility of alternative NGS approaches applied to the same taxa have not been undertaken. We compared a 'traditional' Sanger sequencing method with two NGS approaches (shotgun sequencing and non-indexed, multiplex amplicon sequencing) on four different sequencing platforms (Illumina's HiSeq and MiSeq, Roche's 454 GS FLX, and Life Technologies' Ion Torrent) to produce seven (near-) complete mitogenomes from six species that form a small radiation of caecilian amphibians from the Seychelles. The fastest, most accurate method of obtaining mitogenome sequences that we tested was direct sequencing of genomic DNA (shotgun sequencing) using the MiSeq platform. Bayesian inference and maximum likelihood analyses using seven different partitioning strategies were unable to resolve compellingly all phylogenetic relationships among the Seychelles caecilian species, indicating the need for additional data in this case

Thermophysical properties of a low-density phenolic-nylon ablation material

Thermophysical properties of nondegradated and thermally degradated low density phenolic-nylon ablating materia

Cranial biomechanics in basal urodeles: the Siberian salamander (Salamandrella keyserlingii) and its evolutionary and developmental implications

Developmental changes in salamander skulls, before and after metamorphosis, afect the feeding capabilities of these animals. How changes in cranial morphology and tissue properties afect the function of the skull are key to decipher the early evolutionary history of the crown-group of salamanders. Here, 3D cranial biomechanics of the adult Salamandrella keyserlingii were analyzed under diferent tissue properties and ossifcation sequences of the cranial skeleton. This helped unravel that: (a) Mechanical properties of tissues (as bone, cartilage or connective tissue) imply a consensus between the stifness required to perform a function versus the fxation (and displacement) required with the surrounding skeletal elements. (b) Changes on the ossifcation pattern, producing fontanelles as a result of bone loss or failure to ossify, represent a trend toward simplifcation potentially helping to distribute stress through the skull, but may also imply a major destabilization of the skull. (c) Bone loss may be originated due to biomechanical optimization and potential reduction of developmental costs. (d) Hynobiids are excellent models for biomechanical reconstruction of extinct early urodeles

High Levels of Diversity Uncovered in a Widespread Nominal Taxon: Continental Phylogeography of the Neotropical Tree Frog

Species distributed across vast continental areas and across major biomes provide unique model systems for studies of biotic diversification, yet also constitute daunting financial, logistic and political challenges for data collection across such regions. The tree frog Dendropsophus minutus (Anura: Hylidae) is a nominal species, continentally distributed in South America, that may represent a complex of multiple species, each with a more limited distribution. To understand the spatial pattern of molecular diversity throughout the range of this species complex, we obtained DNA sequence data from two mitochondrial genes, cytochrome oxidase I (COI) and the 16S rhibosomal gene (16S) for 407 samples of D. minutus and closely related species distributed across eleven countries, effectively comprising the entire range of the group. We performed phylogenetic and spatially explicit phylogeographic analyses to assess the genetic structure of lineages and infer ancestral areas. We found 43 statistically supported, deep mitochondrial lineages, several of which may represent currently unrecognized distinct species. One major clade, containing 25 divergent lineages, includes samples from the type locality of D. minutus. We defined that clade as the D. minutus complex. The remaining lineages together with the D. minutus complex constitute the D. minutus species group. Historical analyses support an Amazonian origin for the D. minutus species group with a subsequent dispersal to eastern Brazil where the D. minutus complex originated. According to our dataset, a total of eight mtDNA lineages have ranges >100,000 km2. One of them occupies an area of almost one million km2 encompassing multiple biomes. Our results, at a spatial scale and resolution unprecedented for a Neotropical vertebrate, confirm that widespread amphibian species occur in lowland South America, yet at the same time a large proportion of cryptic diversity still remains to be discovered