Molecular phylogeography of common garter snakes (Thamnophis sirtalis) in western North America: implications for regional historical forces

Complete ND2 and partial ND4 and cytochrome b mitochondrial DNA (mtDNA) sequences were analysed to evaluate the phylogeographic patterns of common garter snakes (Thamnophis sirtalis) in western North America. This species is widely distributed throughout North America, and exhibits extensive phenotypic variation in the westernmost part of its range. The overall phylogeographic pattern based on mtDNA sequences is concordant with results from studies of other species in this region, implicating historical vicariant processes during the Pleistocene and indicating bottleneck effects of recent dispersal into postglacial habitat. Indeed, the topology is statistically consistent with the hypothesis of both southern (Great Basin and California) and northern (Haida Gwaii) refugia. Specifically, we identified genetic breaks among three major clades: Northwest Coastal populations, Intermountain populations, and all California populations. The California clade contained the only other well-supported branching patterns detected; relationships among populations within the two northern clades were indistinguishable. These molecular splits contrast sharply with all prior geographical analyses of phenotypic variation in T. sirtalis in this region. Our results suggest that the extensive phenotypic variation in western T. sirtalis has been shaped more by local evolutionary forces than by shared common ancestry. Consequently, we consider all morphologically based subspecies designations of T. sirtalis in this region invalid because they do not reflect reciprocal monophyly of the mtDNA sequences.     

Impact of pulmonary arterial endothelial cells on duroquinone redox status

The study objective was to use pulmonary arterial endothelial cells to examine kinetics and mechanisms contributing to the disposition of the quinone 2,3,5,6-tetramethyl-1,4-benzoquinone (duroquinone, DQ) observed during passage through the pulmonary circulation. The approach was to add DQ, durohydroquinone (DQH2), or DQ with the cell membrane-impermeant oxidizing agent, ferricyanide (Fe(CN)6(3)-), to the cell medium, and to measure the medium concentrations of substrates and products over time. Studies were carried out under control conditions and with dicumarol, to inhibit NAD(P)H:quinone oxidoreductase 1 (NQO1), or cyanide, to inhibit mitochondrial electron transport. In control cells, DQH2 appears in the extracellular medium of cells incubated with DQ, and DQ appears when the cells are incubated with DQH2. Dicumarol blocked the appearance of DQH2 when DQ was added to the cell medium, and cyanide blocked the appearance of DQ when DQH2 was added to the cell medium, suggesting that the two electron reductase NQO1 dominates DQ reduction and mitochondrial electron transport complex III is the predominant route of DQH2 oxidation. In the presence of cyanide, the addition of DQ also resulted in an increased rate of appearance of DQH2 and stimulation of cyanide-insensitive oxygen consumption. As DQH2 does not autoxidize-comproportionate over the study time course, these observations suggest a cyanide-stimulated one-electron DQ reduction and durosemiquinone (DQ*-) autoxidation. The latter processes are apparently confined to the cell interior, as the cell membrane impermeant oxidant, ferricyanide, did not inhibit the DQ-stimulated cyanide-insensitive oxygen consumption. Thus, regardless of whether DQ is reduced via a one- or two-electron reduction pathway, the net effect in the extracellular medium is the appearance of DQH2. These endothelial redox functions and their apposition to the vessel lumen are consistent with the pulmonary endothelium being an important site of DQ reduction to DQH2 observed in the lungs.     

Effect of altitude on thermal responses of Liolaemus pictus argentinus in Argentina

Reptiles that live in cooler environments hibernate longer and, when active, limit daily activity times, allocate more time and energy toward thermoregulation, and consequently experience life-history constraints such as reduced fecundity and supra-annual reproductive cycles. This pattern becomes more extreme with increasing latitude and altitude. We compared the thermal biology of two populations of Liolaemus pictus argentinus living at two altitudes (771 and ∼1700 m asl). Environmental, microenvironmental, and operative temperatures were studied in order to describe the capture sites, sources of heat, and availability of microenvironments appropriate for thermoregulation. The body temperatures of L. p. argentinus at capture (T_b) and the preferred temperatures in the laboratory (T_p) were recorded and integrated with operative temperatures to calculate the effectiveness of thermoregulation. The high-altitude population was found to have a lower mean T_b (29 °C compared to 33 °C), while the T_p values for both populations were similar (36.7 °C). The analysis of operative temperatures and T_b in relation to T_p showed that L. p. argentinus behaves as a moderate thermoregulator at high altitude and as a poor thermoregulator at the low-altitude site probably due in part to the avoidance of predation risk.     

A systems model for the pupil size effect

The human pupillary control system is a paradigm for linearized biological control systems. It also exhibits a series of interesting nonlinear behaviors, particularly asymmetry, “pupillary escape”, and “pupillary capture.” We present a nonlinear model in which a signal dependent upon pupil size is fed back internally to cause a change in system parameters related to gains and rates of light adaptation. The model was simulated on a digital computer, a variety of experimental data was well matched, and improvements over previous pupil models demonstrated. A candidate physiological mechanism for adaptive components of the model might have the form of an inverse “Henneman coded” neuronal pool.