Using the functional response of a consumer to predict biotic resistance to invasive prey

Predators sometimes provide biotic resistance against invasions by nonnative prey. Understanding and predicting the strength of biotic resistance remains a key challenge in invasion biology. A predator's functional response to nonnative prey may predict whether a predator can provide biotic resistance against nonnative prey at different prey densities. Surprisingly, functional responses have not been used to make quantitative predictions about biotic resistance. We parameterized the functional response of signal crayfish (Pacifastacus leniusculus) to invasive New Zealand mud snails (Potamopyrgus antipodarum; NZMS) and used this functional response and a simple model of NZMS population growth to predict the probability of biotic resistance at different predator and prey densities. Signal crayfish were effective predators of NZMS, consuming more than 900 NZMS per predator in a 12-h period, and Bayesian model fitting indicated their consumption rate followed a type 3 functional response to NZMS density. Based on this functional response and associated parameter uncertainty, we predict that NZMS will be able to invade new systems at low crayfish densities (< 0.2 crayfish/m2) regardless of NZMS density. At intermediate to high crayfish densities (> 0.2 crayfish/m2), we predict that low densities of NZMS will be able to establish in new communities; however, once NZMS reach a threshold density of -2000 NZMS/m2, predation by crayfish will drive negative NZMS population growth. Further, at very high densities, NZMS overwhelm predation by crayfish and invade. Thus, interacting thresholds of propagule pressure and predator densities define the probability of biotic resistance. Quantifying the shape and uncertainty of predator functional responses to nonnative prey may help predict the outcomes of invasions.     

Carcinogenicity of diesel exhaust as tested in strain a mice

Groups of strain A mice were exposed to diesel exhaust by inhalation and diesel particulate by intraperitoneal injection. The animals were exposed from seven to eight weeks and then sacrificed 26–30 weeks postexposure. Other animals were exposed for up to seven months by the inhalation route. Some animals were promoted using urethane at a dose below which tumors would occur. There was no increase in incidence of pulmonary adenomas in the animals exposed to either diesel exhaust or diesel particulate over the control animals. In the animals which were promoted using urethane at a low dose, there was a significant increase in pulmonary adenomas. Diesel particulate was found in the lungs and bronchial lymph nodes of animals exposed to diesel exhaust 26–30 weeks after cessation of exposure.     

Mitigation of chlorpyrifos runoff using constructed wetlands

Constructed wetlands have been proposed as a potential best management practice (BMP) to mitigate effects of pesticide-associated agricultural runoff. Wetland mesocosms (14 m x 59-73 m) were amended with chlorpyrifos to simulate a storm runoff event at concentrations of 73, 147 and 733 microg/l. Water, sediment and plant samples collected weekly for 12 weeks indicated that chlorpyrifos rapidly sorbed to sediment and plant material, with approximately 47-65% of measured chlorpyrifos mass retained within the first 30-36 m of wetland mesocosms. Of the measured mass, approximately 55% and 25% were retained by sediments and plants, respectively. A field-scale evaluation of a constructed wetland's mitigation capability was performed in the Lourens River watershed of Cape Town, South Africa. Results indicate that the wetland was able to retain and considerably decrease the concentration (and hence toxicity) of chlorpyrifos and suspended sediment entering the receiving waterbody (Lourens River). This research provides fundamental answers concerning constructed wetland capabilities that are necessary for constructing field-scale systems within agricultural watersheds.     

Mechanical Properties, Water Vapor Permeability and Water Affinity of Feather Keratin Films Plasticized with Sorbitol

In poultry industry chicken feathers are normally hydrolyzed and used to prepare animal feed. In this work the use of this material to prepare films was investigated. Keratins were extracted from chicken feathers with 2-mercaptoethanol in concentrated urea solution using sodium dodecyl sulfate (SDS). The effect of varying the amount of sorbitol on properties of chicken feather keratin (CFK) was investigated. As the concentration of plasticizer increased, the moisture content (MC) of these films increase, the monolayer MC increased from 0.060 (without plasticizer) to 0.482 g water/g dry matter (0.30 g sorbitol/g keratin). The water vapor permeability (WVP) varied between 0.096 g/m s Pa and 8.098 g/m s Pa for films without sorbitol and with 0.30 g sorbitol/g keratin, respectively. Film strength decreased from 5.13 MPa to 0.45 MPa and the elongation at break achieved the maximum value of 52.75% for samples with 0.02 g sorbitol/g keratin. The dry matter density didn’t change significantly, varying between 0.86–0.89 g/cm³ for all samples. Films with potential applications in food packaging can be obtained from CFKs. However, further researches are necessary to decrease film solubility and increase mechanical resistance.     

Monitoring of the Degradation Activities and the Diversity of the Microbial Community Degrading Refinery Waste Sludge

The biodegradation of n-alkanes and branched alkanes from waste sludge were observed in landfarming soils of Motor Oil Hellas (a petroleum refinery) and changes in the bacterial communities in the soils were monitored during the remediation. Bacterial 16S rRNA gene (rDNA)-based community fingerprint patterns were obtained from soil samples by terminal restriction fragment length polymorphism (T-RFLP) analysis. Changes in T-RFLP fingerprints, as well as in the petroleum contaminant composition of the polluted soil, correlated with degradation activities in field tests.     

Population frequencies of alternative male phenotypes in tree lizards: geographic variation and common-garden rearing studies

Tree lizards (Urosaurus ornatus) vary in throat fan (dewlap) color. Earlier, we described five dewlap types (Orange, Orange-Blue, Yellow, Yellow-Blue, and Blue), and reported that only males had blue in the dewlap and that presence or absence of a discrete blue patch was correlated with male alternative reproductive phenotypes in a central Arizona population. Here, with a modified scheme characterizing two dewlap elements, background color (orange, yellow, blue) and blue patch occurrence, we assessed: (1) sexual, annual, and geographic variation in the frequencies of dewlap elements; (2) simple habitat correlates; and (3) the effects of laboratory rearing regime on dewlap type. Within a population, frequencies of males and females expressing orange or yellow backgrounds did not differ, suggesting that control of background is similar in the sexes. Within several populations, frequencies of the dewlap elements did not differ across years (and probably generations), indicating that phenotype frequencies are relatively stable. Among five populations frequencies of background colors varied, as did frequencies of male types (blue patch present or absent). Dewlap frequencies did not correlate with habitat (boulders or mesquite trees), although few populations were sampled. In male and female offspring reared from eggs to sexual maturity in a common-garden laboratory study, background color frequencies in both sexes and blue patch frequencies in males differed among offspring from different populations. Offspring frequencies matched respective parental population frequencies. Results suggest that among-population variation in frequencies of the two dewlap elements are mediated by differences in genetics, in maternal effects, or both. Thus, differences in male behavior functionally linked to the blue patch also may be controlled by genetic or maternal effects. Received: 17 January 1997 / Accepted after revision: 30 August 1997     

Metallothioneins and lysosomes in metal toxicity and accumulation in marine mussels: the effect of cadmium in the presence and absence of phenanthrene

It has been confirmed that metallothioneins play an important role in the accumulation of cadmium (Cd) in the digestive gland cells of mussels (Mytilus galloprovincialis Lam.). The content of Cd in the tissue of mussels exposed for 9 d to the metal (estimated dosage of 180 g Cd mussel^-1 d^-1) was 66.2 ppm. This value is about the same as the metal content found in the digestive gland of Cd-exposed mussels kept in clean water for a recovery period of 28 d. At the end of the recovery period, however, the Cd bound to thionein had increased by approximately 250%. Our data demonstrate that the stability of lysosomes, a biological parameter adopted as a cellular stress index, is extremely low in mussels exposed to Cd for 9 d, but returns to control values in the digestive gland cells of mussels allowed to recover for 28 d in uncontaminated sea water. At this point most of the Cd present in the cytosol is bound to thionein. These data demonstrate the importance of metallothionein induction in the reduction of the cytotoxic effects exerted by high levels of Cd accumulation. The results of tests designed to clarify the reasons for the long biological half-life of Cd demonstrated that, in the digestive gland of mussels, the lysosomes are not able to eliminate Cd either bound to insoluble thionein polymers or to lipid peroxidation products such as lysosomal lipofuscin, both of which are apparently involved in the elimination of copper. The absence of these two mechanisms of metal sequestration and elimination via excretion of residual bodies (tertiary lysosomes) is in agreement with the persistence of cadmium in the digestive gland of mussels. Finally, the results also demonstrate that simultaneous exposure of mussels to Cd and phenanthrene, an established lysosomal membrane destabilizer, did not significantly alter the accumulation of Cd or the kinetics of the metal in mussels.     

Ultrastructural changes in the lysosomal-vacuolar system in digestive cells of Mytilus edulis as a response to increased salinity

The effects of increasing salinity on the ultrastructural morphology of the lysosomal-vacuolar system in digestive cells of the common mussel Mytilus edulis were investigated in order to relate structural changes to previous biochemical and cytochemical observations. After 3 h of increased salinity, from 21 to 35%., the digestive cells showed an increase in numbers of heterolysosomes. There was some evidence of digestive cell breakdown, the contents forming membrane-bound bodies and being released into the tubule lumen. After 12 h of increased salinity, heterolysosomes were prevalent in the digestive cells. There was increased evidence for digestive-cell breakdown, many of the tubule lumina being packed with membrane-bound bodies. It is concluded that increasing salinity from 21 to 35%. stimulates the lysosomal-vacuolar system, as a result of autophagocytosis or apoptosis; this is consistent with the hypothesis that intracellular, lysosomally-mediated, catabolism of proteins is a source for free amino acids during the adaptation of mussels to increased salinity.