Identification of three chitin synthase genes in the dimorphic fungal pathogenSporothrix schenckii

Degenerate PCR primers were used to amplify a 600-bp conserved gene region for chitin synthases from genomic DNA ofSporothrix schenckii, a dimorphic fungal pathogen of humans and animals. Three chitin synthase gene homologs were amplified as shown by DNA sequence analysis and by Southern blotting experiments. Based on differences among the predicted amino acid sequences of these homologs, each was placed within one of three different chitin synthase classes. Phylogenies constructed with the sequences and the PAUP 3.1.1. program showed thatS. schenckii consistently clustered most closely withNeurospora crassa in each of the three chitin synthase classes. These findings are significant because the phylogenies support by a new method the grouping of the imperfect fungusS. schenckii with the Pyrenomycetes of the Ascomycota.     

Patterns of sequence variation in the mitochondrial D-loop region of shrews

Direct sequencing of the mitochondrial displacement loop (D-loop) of shrews (genus Sorex) for the region between the tRNA(Pro) and the conserved sequence block-F revealed variable numbers of 79-bp tandem repeats. These repeats were found in all 19 individuals sequenced, representing three subspecies and one closely related species of the masked shrew group (Sorex cinereus cinereus, S. c. miscix, S. c. acadicus, and S. haydeni) and an outgroup, the pygmy shrew (S. hoyi). Each specimen also possessed an adjacent 76-bp imperfect copy of the tandem repeats. One individual was heteroplasmic for length variants consisting of five and seven copies of the 79-bp tandem repeat. The sequence of the repeats is conducive to the formation of secondary structure. A termination-associated sequence is present in each of the repeats and in a unique sequence region 5' to the tandem array as well. Mean genetic distance between the masked shrew taxa and the pygmy shrew was calculated separately for the unique sequence region, one of the tandem repeats, the imperfect repeat, and these three regions combined. The unique sequence region evolved more rapidly than the tandem repeats or the imperfect repeat. The small genetic distance between pairs of tandem repeats within an individual is consistent with a model of concerted evolution. Repeats are apparently duplicated and lost at a high rate, which tends to homogenize the tandem array. The rate of D- loop sequence divergence between the masked and pygmy shrews is estimated to be 15%-20%/Myr, the highest rate observed in D-loops of mammals. Rapid sequence evolution in shrews may be due either to their high metabolic rate and short generation time or to the presence of variable numbers of tandem repeats.      

大鼠胼胝体内神经肽Y免疫反应阳性纤维的发育

本实验用免疫组织化学ＡＢＣ法研究了大鼠胼胝体内神经肽Ｙ免疫反应阳性（ＮＰＹ－ＩＲ）纤维的生后发育。结果发现,许多ＮＰＹ－ＩＲ纤维在大鼠出生时便存在于胼胝体内。ＮＰＹ－ＩＲ胼胝体纤维的密度在生后１周内继续逐渐增高,在第２周内达到最高峰。之后,ＮＰＹ－ＩＲ胼胝体纤维的密度逐渐下降,至第３周末时接近成年时的水平,即仅有少量ＮＰＹ－ＩＲ纤维存在于胼胝体内。这些结果提示在大鼠早期生后发育过程中许多ＮＰＹ－ＩＲ胼胝体纤维是暂时性的,其作用可能与大脑皮质的机能发育有关。     

Water utilization of tropical hardwood hammocks of the Lower Florida Keys

Summary Predawn water potential of representative plant species, together with stable isotope composition of stem water and potential water sources were investigated in four low-elevation tropical hardwood hammocks in the Lower Florida Keys, during a one year period. Hammock species had the lowest water potentials when soil water content was low and/or soil salinity was high, but differences in groundwater salinity had no effect on the water potential. Comparison of D/H ratio of plant stem water with soil and ground water corroborates the conclusion that they are primarily utilizing soil water and not groundwater. Thus, tropical hardwood hammocks are buffered from saline groundwater, and are able to thrive in areas where groundwater salinity is as high as 25. The effect of sea level rise on these forests may depend more on changes in the frequency of tidal inundation of the soil surface than on changes in groundwater salinity.     

Climatic and geometric constraints as driving factors of butterfly species richness along a Neotropical elevational gradient

We tested the effects of temperature, humidity and geographical constraints upon butterfly species richness along an elevational gradient covering an altitude ranging from 117 to 3,104 m above sea level (m. a.s.l.), in Southern Mexico. Ten transect sites were sampled 219 times from May 2010 to May 2011, along the elevational gradient to estimate range and population abundance of butterfly species. The effects of temperature, humidity and geometric constraints (mid-domain effects) on species richness along the study gradient were assessed using ordinary least squares regression. A total of 7,005 specimens representing 193 species were recorded. Species richness was relatively higher at elevations between 117 and 1,000 m. a.s.l. with an observed decline in richness values as elevation increased. Butterfly species richness along the study environmental gradient was predominantly determined by climatic constraints, rather than geometric constraints—a mid-domain model fit well only for large-ranged Pieridae species. Temperature and humidity explained the variation species richness for the entire butterfly community and for the three families evaluated; however the effect of predictor variables varied according to the measure of species richness and taxonomic family. This discrepancy in the response of butterfly richness to temperature, humidity and geometric constraints emphasizes the need to evaluate the response of different taxa to elevational gradients, to establish general patterns that help us to prioritize conservation measures that reduce population declines and local extinctions predicted by climate change in highly diverse tropical mountain ecosystems.     

Seed dynamics of an endemic palm in a Northwestern Mexican tropical dry forest: implications for population spatial structure

Seed dynamics are an important part of the life history of plants and may have strong implications on abundance and spatial distribution of populations. In this study, we explored how seed dynamics (removal, predation, germination) interact with micro-environmental conditions to affect the spatial structure of populations of Brahea aculeata (Arecaceae) in a tropical dry forest. B. aculeata is distributed throughout arroyo basins and attains its highest densities near to arroyos/rivers. We hypothesized that: (i) seed removal, predation and germination vary across topographic positions resulting in greater palm abundances adjacent to arroyos and (ii) seed removers/predators respond to both a seed density-dependent effect and a microclimate effect. To test this, in six arroyos basins, seeds were sown across three topographic positions (stream, mid and top of basins) with two seed abundances (1 and 10), protected and non-protected from potential predators. Predation, removal and germination were then followed. After 107 days, 100 % of the exposed seeds were removed/predated and none germinated. For seed removal, we found differences among topographic positions and seed densities with higher removal (up to 80 %) and lower predation rates for grouped seeds. Germination was only observed for protected seeds with higher germination rates in single (17 % ± 9) than in grouped seeds (4 % ± 1). The highest germination and establishment rates were adjacent to the streams; areas which had the lowest light intensity (mean ± SE = 883 ± 160 lm/ft²) and temperatures (mean ± SE = 20.1 ± 0.6 °C), and highest humidity (mean ± SE = 50.8 ± 1.8 %), especially during the rainy season. Differential seedling establishment rates across the landscape due to spatial patterns of seed predation/removal as well as micro-environmental variables appear to have implications for shaping the spatial structure of B. aculeata population at Sierra de Álamos, Mexico.     

Assessment of the Resistance to Uranium (VI) Exposure by Arthrobacter sp. Isolated from Hanford Site Soil

Production of nuclear fuel has resulted in hazardous waste streams that have contaminated the soil and groundwater. Arthrobacter strains, G975, G968, and G954 were used in the prescreening tests to evaluate their tolerance to UO₂ ²⁺ and investigate bacteria-U(VI) interactions under oxidizing pH-neutral conditions. Experiments have shown G975 is the fastest growing and the most uranium tolerant strain that removed about 90% of uranium from growth media. Atomic Force Microscopy images exhibited an irregular surface structure, which perhaps provided a larger surface area for uranium precipitation. The data indicate that aerobic heterotrophic bacteria may offer a solution to sequestering uranium in oxic conditions, which prevail in the vadose zone.