Molecular and phenotypic diversity in Chionactis occipitalis (Western Shovel-nosed Snake), with emphasis on the status of C. o. klauberi (Tucson Shovel-nosed Snake).

Chionactis occipitalis (Western Shovel-nosed Snake) is a small colubrid snake inhabiting the arid regions of the Mojave, Sonoran, and Colorado deserts. Morphological assessments of taxonomy currently recognize four subspecies. However, these taxonomic proposals were largely based on weak morphological differentiation and inadequate geographic sampling. Our goal was to explore evolutionary relationships and boundaries among subspecies of C. occipitalis, with particular focus on individuals within the known range of C. o. klauberi (Tucson Shovel-nosed snake). Population sizes and range for C. o. klauberi have declined over the last 25 years due to habitat alteration and loss prompting a petition to list this subspecies as endangered. We examined the phylogeography, population structure, and subspecific taxonomy of C. occipitalis across its geographic range with genetic analysis of 1100 bases of mitochondrial DNA sequence and reanalysis of 14 morphological characters from 1543 museum specimens. We estimated the species gene phylogeny from 81 snakes using Bayesian inference and explored possible factors influencing genetic variation using landscape genetic analyses. Phylogenetic and population genetic analyses reveal genetic isolation and independent evolutionary trajectories for two primary clades. Our data indicate that diversification between these clades has developed as a result of both historical vicariance and environmental isolating mechanisms. Thus these two clades likely comprise ‘evolutionary significant units’ (ESUs). Neither molecular nor morphological data are concordant with the traditional C. occipitalis subspecies taxonomy. Mitochondrial sequences suggest specimens recognized as C. o. klauberi are embedded in a larger geographic clade whose range has expanded from western Arizona populations, and these data are concordant with clinal longitudinal variation in morphology.     

Ecological and ecophysiological patterns in a pre-altiplano shrubland of the Andean Cordillera in northern Chile

We report on community structural, ecophysiological, phenological, and morphological measurements made on woody plant species in the high elevation pre-altiplano zone on the western slopes of the Andean Cordillera of northern Chile. Notwithstanding extreme conditions of low rainfall, high atmospheric vapour demand and diurnal temperature fluctuation, a diversity of habitats (associated with drainage and slope aspect), appreciable local plant species richness (28 woody perennial plant species in a small area), and an array of adaptive morphological ecophysiological and phenological traits are present among woody species in these shrublands. Family diversity was low with four families accounted for 82% of the species. A range of gas exchange and watering use efficiency strategies was present ranging from highly efficient CAM species with a carbon isotope discrimination (Δ) of 3.7–7.5‰ through C₃ species with varying stomatal and gas exchange characteristics with a Δ of 14.4 to 19.8‰. Drought-deciduous small-leaved amphistomatic species from arid slopes generally had high stomatal conductance and high carbon assimilation rates during the rainy season. These drought deciduous species were largely leafless and, with one exception had low water potentials, during the dry season. Wash and less xeric site species commonly had broader evergreen to semi-evergreen leaves, higher dry season water potentials, and relatively consistent and moderate rates of gas exchange throughout the year. For all species, intrinsic water use efficiency (as estimated from the inverse of c _i :c _a ratio) correlated positively with mean leaf width (broader leaves had a lower higher intrinsic WUE) and dry season water potential. The charismatic high altitude tree, Polylepis rugulosa (Roaceae), had a population structure that suggests highly episodic establishment of seedlings, likely in sequences of wet years. Little of the area of these significant shrublands is currently protected. It would be desirable to add areas of pre-altiplano shrublands to adjacent national parks to ensure the persistence of these important communities. This revised version was published online in June 2006 with corrections to the Cover Date.     

Patterns of vegetation along a spatiotemporal gradient on shoreline strands of a desert basin lake

Shoreline strands of Mono Lake, California, show clear evidence ofregular temporal change in plant communities and the soils associated with themalong a primary successional sere, contradicting the traditional notion thatsuccession sensu stricto does not occur in aridenvironments. We documented spatial patterns, and inferred temporal patternsfrom aerial photographs taken each decade from 1930, in communities ofperennialshrubs and in characteristics of the physical environment in sand-duneand shoreline ecosystems on the north shore of Mono Lake, a receding terminalQuaternary lake in the Great Basin desert of the United States that is highlysaline and alkaline. Our study plot was aligned with an extreme physicochemicalgradient, representing a primary sere beginning with the historic, acceleratedregression of Mono Lake since 1940 and ending with upland surfaces exposed bylake regression between 500 and 1000 years ago. Four shrub species composedmost of the 7–11% percent coverof perennial vegetation: populations of Sarcobatusvermiculatus extended farthest toward the lake and colonized themostrecently exposed and toxic surfaces; populations of Chrysothamnusnauseosus, Tetradymia tetrameres, andC. viscidiflorus ended at increasing distances (inthis order) from the lake shore, reflecting each species'respectivelylower tolerance of soil salinity, alkalinity, and toxic soil elements ratherthan the ability to disperse. Values of soil variables that decrease plantgrowth and establishment (EC, pH, B, S) were lower in oldersubstrates, in the upper soil horizons, and at increasing distances from thelake, reflecting leaching and other pedogenic processes with time. Individualsof S. vermiculatus appeared to promote dune building bytolerating burial, enhancing their own growth and establishment, and catchingmore sand. We hypothesize that this process also facilitates the establishmentof less stress tolerant species. Plant nutrients (N, P) decreasedwithdepth, evidence of progressive soil enrichment by litter and leaf fall. Thusboth allogenic processes (weathering of parent material) andautogenicprocesses (facilitation in particular) resulting fromplant-environment interactions occurred and contributed to ecosystemchange in this extreme primary sere, adhering to the strictest definition ofsuccession.     

Unexpected relationships and valuable mistakes: non‐myrmecochorous Prosopis dispersed by messy leafcutting ants in harvesting their seeds

Abstract Ants generally disperse seeds while feeding on fruits or structures attached to the seed. Seed dispersal as a by‐product of seed predation (dyszoochory) was recognized in specialized harvester ants, but not in ants predating seeds opportunistically. Leafcutting ants are the main herbivores in much of the Neotropics, and they have been reported to remove fruits and seeds, but their role as seed predators and dispersers has not been acknowledged. Prosopis flexuosa D.C. (Fabaceae, Mimosoideae) is the most abundant tree species in the central Monte Desert, Argentina, and it is likely to depend on secondary animal dispersal. Mammalian frugivores are usually considered its main dispersers, but the opportunity for dispersal may be small since the removal of fruits and seeds by seed predators is very intense. The objective of this study was to identify which ant species interact with P. flexuosa fruits and to evaluate their relative importance as seed predators and dispersers. In a field experiment, whole and segmented pods were offered and several ant species exploiting the fruits were identified. Additionally, all pod segments remaining around nests of the three ant species able to remove them (the leafcutters Acromyrmex lobicornis Emery and Acromyrmex striatus Roger, and Pheidole bergi Mayr) were examined during and after the P. flexuosa primary dispersal season. Up to 753 pod segments and 90 sound seeds were found accumulated in a circle of 1 m radius over nests of A. lobicornis, and even more in an examined trail. Acromyrmex striatus left a smaller proportion of sound seeds and P. bergi left a smaller number of pod segments. All tendencies were similar during shorter known periods of accumulation. Leafcutting ants are acting as important seed predators, and ‘by mistake’ may be dispersing a key non‐myrmecochorous tree. This is an unexplored path in the seed dispersal cycle of P. flexuosa that challenges the tendency to predict interactions based on classifications made with other goals.     

Aboveground net primary production dynamics in a northern Chihuahuan Desert ecosystem

Aboveground net primary production (ANPP) dynamics are a key element in the understanding of ecosystem processes. For semiarid environments, the pulse-reserve framework links ANPP to variable and unpredictable precipitation events contingent on surficial hydrology, soil moisture dynamics, biodiversity structure, trophic dynamics, and landscape context. Consequently, ANPP may be decoupled periodically from processes such as decomposition and may be subjected to complex feedbacks and thresholds at broader scales. As currently formulated, the pulse-reserve framework may not encompass the breadth of ANPP response to seasonal patterns of precipitation and heat inputs. Accordingly, we examined a 6-year (1999–2004), seasonal record of ANPP with respect to precipitation, soil moisture dynamics, and functional groups in a black grama (Bouteloua eriopoda) grassland and a creosotebush (Larrea tridentata) shrubland in the northern Chihuahuan Desert. Annual ANPP was similar in the grassland (51.1 g/m²) and shrubland (59.2 g/m²) and positively correlated with annual precipitation. ANPP differed among communities with respect to life forms and functional groups and responses to abiotic drivers. In keeping with the pulse-reserve model, ANPP in black grama grassland was dominated by warm-season C₄ grasses and subshrubs that responded to large, transient summer storms and associated soil moisture in the upper 30 cm. In contrast, ANPP in creosotebush shrubland occasionally responded to summer moisture, but the predominant pattern was slower, non-pulsed growth of cool-season C₃ shrubs during spring, in response to winter soil moisture accumulation and the breaking of cold dormancy. Overall, production in this Chihuahuan Desert ecosystem reflected a mix of warm-temperate arid land pulse dynamics during the summer monsoon and non-pulsed dynamics in spring driven by winter soil moisture accumulation similar to that of cool-temperate regions. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Does hydraulic lift or nighttime transpiration facilitate nitrogen acquisition?

Water movement from roots to soil at night in the process of hydraulic lift (redistribution) rehydrates the rhizosphere and has been proposed to improve plant nutrient acquisition. Another process that has now been found in many plant species is nighttime transpiration and this could also affect nutrient relations by influencing supply of mobile nutrients to roots at night. The effects of these soil/root water relations interactions have not been adequately tested. We chose ten Sarcobatus vermiculatus (Hook.) Torrey shrubs with different magnitudes of hydraulic lift (i.e. diel range in soil water potential) to test the hypothesis that the magnitude of lift would be positively related to the amount of nitrogen (N) uptake over a period of days. A ¹⁵N tracer was injected in the 20–30 cm soil layer at locations with hydraulic lift to determine plant ¹⁵N acquisition by shallow roots conducting hydraulic lift. Half of the plants were also placed in large humidified tents (i.e. “bagged”), which suppressed nighttime transpiration, and thus were expected to have greater magnitudes of hydraulic lift, although they did not. All plants took up the ¹⁵N tracer, but contrary to our hypothesis the magnitude of hydraulic lift had no significant effect on the amount of ¹⁵N acquired over a 9-day period following labeling. However, plants that were bagged tended to have lower ¹⁵N acquisition (P = 0.07). These data indicate that decreased nighttime transpirational water loss or some other effect of bagging may decrease nutrient acquisition by these nutrient-limited phreatophytic shrubs and more generally suggests a possible nutritional benefit of nighttime transpiration by plants. This suggestion needs more thorough testing to elucidate an important potential link between plant water and nutrient relations.     

Growth Characteristics and Enzyme Activity in Batrachochytrium dendrobatidis Isolates

Eighty soil samples were collected from various sites of Bahrain and screened for presence of keratinophilic fungi using hair baiting techniques for isolation. Thirty-six isolates were recovered and identified. The cultures were identified using macro- and micromorphological features. Their identification was also confirmed by the BLAST search of sequences of ITS1-5.8S-ITS2 rDNA region against the NCBI/Gene bank data and compared with deposited sequences for confirmation. Eight species of five genera were isolated viz. Aphanoascus fulvuscence (8.75%), Aphanoascus punsolae (20.00%), Chrysosporium indicum (2.50%), Chrysosporium tropicum (2.50%), Chrysosporium zonatum (3.75%), Spiromastix warcupii (1.25%), Microsporum gypseum (3.75%), and Trichophyton mentagrophytes (2.50%). In conclusion, our study indicates that keratinophilic fungi do occur in the various soils of Bahrain. Moreover, the narrow diversity and low density of keratinophilic fungi in the investigated soils is expected and is emblematic to other hot arid environments.     

新疆古尔班通古特沙漠南部沙垄不同部位藻类的垂直分布特征

 通过2005和2006年夏季两次对新疆古尔班通古特沙漠南部荒漠土壤中藻类植物进行采样、培养、鉴定和生物量测定,分析了该区沙漠沙垄不同部位藻类物种组成、优势种和生物量的垂直变化。结果表明：1）在不同地貌部位的不同层次中,藻类的种类组成均有所差异。2）藻类优势物种主要集中在0～2 cm层次中,2 cm以下的土层中藻类细胞很少,绝大部分土层以具鞘微鞘藻(Microcoleus vaginatus)为第一优势种,有些部位的土层中第一优势种是伪双点颤藻(Oscillatoria pseudogeminata),如垄间低地和迎风坡的1～2 cm中。此外,大型集胞藻（Synechocystis crassa）、舟形藻 (Navicula sp.)、卵圆双眉藻(Amphora ovalis)数量也较多。3）除垄顶外,藻类生物量在其它3个部位不同层次的差异呈极显著水平（p<0.01）,生物量由表及里锐减;在同一土层,藻类生物量基本表现为垄间低地最高,迎风坡与背风坡居中, 垄顶最低,不同地貌部位对藻类生物量影响呈显著或极显著水平。     

中国新疆塔克拉玛干沙漠井下奥陶系的牙形刺

共测制了13条新疆塔时木塔克拉玛干沙漠中部和北部井下的奥陶系剖面,并在不同的相区发现了不同的牙形刺序列。在北部地区牙形刺带由上而下为：Aphelognathus pyramidalis,Yaoxianognathus yaoxianensis-Belodi-na confluens,Baltoniodus alobatus,Pygodus anserinus,P.serra,Paroistodus proteus,Glyptoconus quadraplicatus和Rossodus manitouensis-Cordylodus rotundatus等带;在中部区,牙形刺带由上而下为：Serratognathus diver-sus,Chosonodina和Rossodus manitouensis-Cordylodus rotundatus等带,另外,本文也讨论了牙形刺带的对比,生物相及本区的古地理轮廓变化,描述了新种Pygodus xinjiangensis。