Nurse Plant and Floral Biology of a Rare Night-Blooming Cereus, Peniocereus striatus (Brandegee) F. Buxbaum

The Sonoran night-blooming cereus ( Peniocereus striatus ) is a rare cactus found in the Sonoran Desert. Its survival is dependent on maintenance of its habitat and its ability to recruit. This study evaluates the role of nurse plants in P. striatus survival and the floral and pollination ecology controlling recruitment. A strong association was detected between P. striatus and its nurse plants, which include Olneya tesota and Larrea tridentata . Because of the harvesting of Olneya tesota and Prosopis velutina for charcoal over a 20,000 square km area of its range, this night-blooming cereus is vulnerable to rapid habitat degradation in both Sonora (Mexico) and adjacent Arizona (U.S.A.). The temporal and local scarcity of sphingid moths available for pollination caused by pesticides and small flower numbers, appear to produce low recruitment rates. These two important threats to the biotic associates of this cactus have increased its natural rarity. This can only be alleviated through international cooperation.     

System theory formulation of site-specific water quality standards and protocols

Habitat variability makes site-specific considerations a necessity in the specification of water quality standards. The U.S. Environmental Protection Agency (EPA) has recognized this in its development of procedures for site-specific modification of national standards. These procedures involves translation of laboratory toxicology data into field situations where such data are often poor predictors of biotoxicity. The whole problem is poorly specified.This paper formulates a system theory approach to better specification of the problems associated with setting water quality standards. A state space model of the general environmental protection problem is presented: Find a set of diagnostic variables whose maintenance within specifiable limits (standards) is both necessary and sufficient to protect all variables of a subject ecosystem. The program for this comprises a site-specific protocol.Stages in such a protocol include (1) choice of diagnostic variables, (2) establishment of necessity and sufficiency for these variables, and (3) determination of standards through (4) toxicity testing. Problems associated with the latter include (a) spatiotemporal variability, system (b) linearity-nonlinearity, and (c) stationarity-nonstationarity, and (d) monitoring for: baseline information, impact detection, determining compliance, establishing causality and making predictions. Each of these problems is structured in terms of the state space model. Then, current procedures of the EPA site-specific methodology are reviewed, and a set of recommendations proposed for their improvement using the system theory formulation to guide further developments.     

Fetal blood sampling demonstrating chimerism in monozygotic twins discordant for sex and tissue karyotype (46,XY and 45,X)

Fetal blood sampling has been used in the genetic work-up of twin gestations for rapid karotyping. We present a case of twins which on ultrasound evaluation revealed hydrops fetalis in one twin and a normal second twin. Fetal blood sampling revealed the presence of mosaicism for 46,XY/45,X in both twins. HLA antigen testing showed the twins to be identical. The patient elected pregnancy termination. Blood chromosomal analysis after delivery revealed both twins to have 46,XY/45,X mosaicism, but the twin with signs of hydrops fetalis had tissue chromosomes of 45,X and the normal twin had tissue chromosomes of 46,XY. Amniotic fluid chromosomal analysis revealed 46,XY in twin A and 45,X in twin B. This represents a case of identical (monozygotic) twins with sex discordance. In this case, there was the probable occurrence of post-zygotic chromosomal non-disjunction leading to the discordancy of the sex in this set of twins. With the presence of vascular communication in monozygotic twins, there is the possibility of exchange of blood in monozygotic twins and the result of blood chimerism in twins.     

Endangered light-footed clapper rail affects parasite community structure in coastal wetlands.

An extinction necessarily affects community members that have obligate relationships with the extinct species. Indirect or cascading effects can lead to even broader changes at the community or ecosystem level. However, it is not clear whether generalist parasites should be affected by the extinction of one of their hosts. We tested the prediction that loss of a host species could affect the structure of a generalist parasite community by investigating the role of endangered Light-footed Clapper Rails (Rallus longirostris levipes) in structuring trematode communities in four tidal wetlands in southern California, U.S.A. (Carpinteria Salt Marsh, Mugu Lagoon) and Mexico (Estero de Punta Banda, Bahia Falsa-San Quintin). We used larval trematode parasites in first intermediate host snails (Cerithidea californica) as windows into the adult trematodes that parasitize Clapper Rails. Within and among wetlands, we found positive associations between Clapper Rails and four trematode species, particularly in the vegetated marsh habitat where Clapper Rails typically occur. This suggests that further loss of Clapper Rails is likely to affect the abundance of several competitively dominant trematode species in wetlands with California horn snails, with possible indirect effects on the trematode community and changes in the impacts of these parasites on fishes and invertebrates.     

In vitro genotoxicity of exhaust emissions of diesel and gasoline engine vehicles operated on a unified driving cycle

Acetone extracts of engine exhaust particulate matter (PM) and of vapor-phase semi-volatile organic compounds (SVOCs) collected from a set of 1998-2000 model year normal emitter diesel engine automobile or light trucks and from a set of 1982-1996 normal emitter gasoline engine automobiles or light trucks operated on the California Unified Driving Cycle at 22 [degree]C were assayed for in vitro genotoxic activities. Gasoline and diesel PM were comparably positive mutagens for Salmonella typhimurium strains YG1024 and YG1029 on a mass of PM extract basis with diesel higher on a mileage basis; gasoline SVOC was more active than diesel on an extracted-mass basis, with diesel SVOC more active on a mileage basis. For chromosomal damage indicated by micronucleus induction in Chinese hamster lung fibroblasts (V79 cells), diesel PM expressed about one-tenth that of gasoline PM on a mass of extract basis, but was comparably active on a mileage basis; diesel SVOC was inactive. For DNA damage in V79 cells indicated by the single cell gel electrophoresis (SCGE) assay, gasoline PM was positive while diesel PM was active at the higher doses; gasoline SVOC was active with toxicity preventing measurement at high doses, while diesel SVOC was inactive at all but the highest dose.     

Riparian vegetation instream flow requirements: A case study from a diverted stream in the Eastern Sierra Nevada,California, USA

A methodology is described that allows determination of instream flow requirements for maintenance of riparian trees. Tree-ring data revealed strong relationships between tree growth and stream flow volume for riparian species at Rush Creek, an alluvial stream within an arid setting; these relationships allowed development of models that predict growth rates from hydrologic variables. The models can be used to assess instream flow requirements under the assumption that certain levels of growth are necessary to maintain the population. There is a critical need for development and use of instream flow methodologies for riparian vegetation, since present methodologies focus on needs of aquatic animals (e.g., fish) and may underestimate needs of the entire riparian ecosystem.     

The interaction of temperature and sucrose concentration on foraging preferences in bumblebees

Several authors have found that flowers that are warmer than their surrounding environment have an advantage in attracting pollinators. Bumblebees will forage preferentially on warmer flowers, even if equal nutritional reward is available in cooler flowers. This raises the question of whether warmth and sucrose concentration are processed independently by bees, or whether sweetness detectors respond to higher sugar concentration as well as higher temperature. We find that bumblebees can use lower temperature as a cue to higher sucrose reward, showing that bees appear to process the two parameters strictly independently. Moreover, we demonstrate that sucrose concentration takes precedence over warmth, so that when there is a difference in sucrose concentration, bees will typically choose the sweeter feeder, even if the less sweet feeder is several degrees warmer.     

Dynamic environ analysis of compartmental systems: A computational approach

Ecosystems are often modeled as stocks of matter or energy connected by flows. Network environ analysis (NEA) is a set of mathematical methods for using powers of matrices to trace energy and material flows through such models. NEA has revealed several interesting properties of flow–storage networks, including dominance of indirect effects and the tendency for networks to create mutually positive interactions between species. However, the applicability of NEA is greatly limited by the fact that it can only be applied to models at constant steady states. In this paper, we present a new, computationally oriented approach to environ analysis called dynamic environ approximation (DEA). As a test of DEA, we use it to compute compartment throughflow in two implementations of a model of energy flow through an oyster reef ecosystem. We use a newly derived equation to compute model throughflow and compare its output to that of DEA. We find that DEA approximates the exact results given by this equation quite closely – in this particular case, with a mean Euclidean error ranging between 0.0008 and 0.21 – which gives a sense of how closely it reproduces other NEA-related quantities that cannot be exactly computed and discuss how to reduce this error. An application to calculating indirect flows in ecosystems is also discussed and dominance of indirect effects in a nonlinear model is demonstrated.