Distribution, Hybridization, and Taxonomic Status of Two-lined Salamanders (\u3ci\u3eEurycea bislineata\u3c/i\u3e complex) in Virginia and West Virginia

We used three diagnostic protein markers to examine salamanders of the Eurycea bislineata complex at 80 localities in Virginia and West Virginia. Two groups were strongly differentiated and met at a narrow contact zone. Rare hybridization was observed as well as limited introgression up to 5 km north and 10 km south of the contact zone. At the contact zone, 1% F1, 2% F2, 32% backcross, and 66% parental genotypes were observed. This pattern of parapatric distribution with limited hybridization and introgression argues for the recognition of Eurycea bislineata and E. cirrigera as separate species

Baffle aperture design study of hollow cathode equipped ion thrusters

A simple theoretical model which can be used as an aid in the design of the baffle aperture region of a hollow cathode equipped ion thruster was developed. An analysis of the ion and electron currents in both the main and cathode discharge chambers is presented. From this analysis a model of current flow through the aperture, which is required as an input to the design model, was developed. This model was verified experimentally. The dominant force driving electrons through the aperture was the force due to the electrical potential gradient. The diffusion process was modeled according to the Bolm diffusion theory. A number of simplifications were made to limit the amount of detailed plasma information required as input to the model to facilitate the use of the model in thruster design. This simplified model gave remarkably consistant results with experimental results obtained with a given thruster geometry over substantial changes in operating conditions. The model was uncertain to about a factor of two for different thruster cathode region geometries. The design usefulness was limited by this factor of two uncertainty and by the accuracy to which the plasma parameters required as inputs to the model were specified

Allometry and Sexual Dimorphism in the Snail-eating Turtle Malayemys macrocephala from the Chao Phraya River Basin of Central Thailand

Allometric growth and sexual dimorphism of the shell is evident in Malayemys macrocephala from the Chao Phraya River Basin of central Thailand. Differences in allometric growth between males and females produce sexually dimorphic adults. Adult females exhibit larger sizes and have relatively wider and higher shells and longer plastra than males

Geographic Distribution of the Southeast Asian Turtles in the Genus Malayemys (Testudines: Bataguridae)

Members of the genus Malayemys, Malayan snail-eating turtles, are small batagurid turtles reaching maximum sizes of 22 cm carapace length (Srinarumol, 1995). They have dark brown to mahogany carapaces with three discontinuous keels, yellow plastra with large dark blotches on each scute, and large black heads adorned with yellow or cream-colored stripes that extend onto their necks (Ernst et al., 2000). Malayemys inhabit lowland freshwater habitats throughout Southeast Asia including ponds, canals, streams, swamps, marshes and wet rice fields. These are diurnal bottom dwellers that feed primarily on mollusks (Smith, 1931; Taylor, 1970; Nutaphand, 1979; Srinarumol, 1995; Ernst et al., 2000; van Dijk and Thirakhupt, in press). Populations of Malayemys can be found in virtually all lowland areas of central Thailand, where they are the most commonly found wild turtle (van Dijk and Thirakupt, in press). Population status outside of central Thailand is poorly documented. Members of this genus are presumed to be abundant in southern Vietnam (Bourret, 1939; Geissler and Jungnickel, 1989; van Dijk and Thirakhupt, in press), less abundant in peninsular Thailand (van Dijk and Thirakhupt, in press), and rare on Java (van Dijk and Thirakhupt, in press; Peter C. H. Pritchard, pers. com.). Many Southeast Asian turtle species are in rapid decline because of serious pressure from commercial exploitation and habitat destruction (Behler, 1997; Thirakhupt and van Dijk, 1997; van Dijk et al., 2000). Improved legislation and enforcement, community education, population monitoring, and life history studies are all crucial to the long-term survival of most of these species. None of this can occur, however, without detailed records on the geographic distribution of these organisms. This paper presents a detailed table and map that clearly define the geographic distribution of turtles in the genus Malayemys. No other account is based on such a complete compilation of data

Geographic Variation and Systematics in the South-east Asian Turtles of the Genus Malayemys (Testudines: Bataguridae)

Geographic variation was studied in the south-east Asian turtles of the genus Malayemys (Testudines: Bataguridae). Discriminant function analysis of head-stripe and shell characters reveals a clear pattern of geographic variation that is consistent with the topography of south-east Asia and the poor dispersal abilities of these turtles. Two phenotypically and morphologically distinct groups of Malayemys occur allopatrically in lowland areas of mainland south-east Asia, and my data concludes that each should be recognized as a distinct species. Turtles from the Mekong River Basin retain the name Malayemys subtrijuga (Schlegel and Müller, 1844), whereas those from the Chao Phraya and Mae Klong river basins, coastal areas of south-eastern Thailand, and the Malay Peninsula are assigned the name Malayemys macrocephala (Gray, 1859). Malayemys macrocephala has four or fewer nasal stripes (99%) and an infraorbital stripe that is relatively wide at the loreal seam (98% of InfSW/HW=0.07-0.18) and does not extend or extends only slightly superior to the loreal seam (96%). Conversely, M. subtrijuga has six or more nasal stripes (89%) and an infraorbital stripe that is relatively narrow at the loreal seam (92% of InfSW/HW=0.02-0.06), extends completely superior to the loreal seam (96%), and usually joins the supraorbital stripe (64%). Female M. macrocephala also have relatively longer AnL and relatively shorter Vert5L and PecL than M. subtrijuga. Similarly, male M. macrocephala have relatively longer PPLL and AbdL, relatively shorter Pleu1L and PecL, and greater RLatK values than M. subtrijuga. Both species are potentially threatened by overcollection and habitat destruction, and should be protected as separate taxa of concern. In addition, discriminant function analysis of shell and head-stripe characters suggests that M. subtrijuga on Java are derived by human intervention primarily from the Mekong River Basin