The effects of operational sex ratio and food deprivation on copulation duration in the water strider (Gerris remigis Say)

Summary A North American water strider, Gerris remigis (Hemiptera) copulates for prolonged periods of time, apparently beyond the time necessary for insemination (Rubenstein 1984; Wilcox 1984; Clark 1987), I tested predictions from two different hypotheses of the adaptive significance of this behavior. Manipulations of the operational sex ratio in artificial streams revealed that water striders copulate significantly longer when the sex ratio is male-biased. This result is consistent with the hypothesis that prolonged copulation functions as a type of contact mate guarding, which reduces sperm competition by preventing the female from remating prior to oviposition. The finding is also consistent with the hypothesis that copulation is prolonged to enhance female foraging efficiency. In a second experiment, sex ratio and total population density were held constant, and the period of food deprivation of females was manipulated. Contrary to the predictions of the female foraging hypothesis, starved females did not copulate longer than fed females. Of the two hypotheses considered, only the copulatory guarding hypothesis explains both results. This does not mean, however, that there is no selective benefit from the enhanced foraging efficiency resulting from prolonged copulation. Nor does it exclude the possibility that this benefit has been necessary for the evolution of prolonged copulation in water striders.     

Modeling of breakpoint reaction in drinking water distribution pipes

A mathematical model accounting for concurrent mass transfer and a series of chemical reactions under the breakpoint chlorination is developed to predict disinfectant concentration profiles in the drinking water distribution pipe. The model is validated by comparing its numerical solutions to experimental data in the literature. The impact of important parameters on the model performance is examined by a sensitivity analysis. Practical applications of the model to minimize water quality deterioration in the distribution system are discussed in view of the results. This work can provide insight into the factors that influence all of the fundamental reactions and disinfectant transport of the breakpoint reaction. Operational criteria for the chlorination of distributed water are derived.     

Sexual dimorphism and the mating ecology of polar bears (Ursus maritimus) at Svalbard

We assessed the role of size, mass, and age in mating and non-mating polar bears (Ursus maritimus) at Svalbard, Norway, during the spring breeding season. The ratio of male to female mass, in male-female pairs, ranged from 1.00 to 3.02 ([`(x)] = 1.99 \overline x = 1.99 ) indicating that mating males were larger than mating females but with substantial variation. Paired males were older than unpaired males and male mass was related to age. However, males paired with females were not significantly different in body mass from those males caught alone. Wounds and scars resulting from fights between males began at about 6 years of age and peaked at about 17 and 20 years of age, respectively. The frequency of broken canines in males, presumably due to increased male-male conflicts, increased with age but showed little increase in females. The wide range of male size in male-female pairs and the age-related signs of injury suggest that male polar bears engage in both scramble competition and contest competition for access to breeding females. The mating system of polar bears is variable but is best described as female defense polygyny or serial monogamy.     

Interaction of phenanthrene and its primary metabolite (1-hydroxy-2-naphthoic acid) with estuarine sediments and humic fractions

Experiments were conducted to compare the sorption and desorption of phenanthrene and its primary degradation product, 1-hydroxy-2-naphthoic acid (HNA), in estuarine sediment, humic acid (HA) and humin. Ionic composition, ionic strength (0.4 M) and pH (7.6) were employed to mimic native estuarine pore water at the sediment-water interface. Sorption to whole sediment and organic matter (OM) fractions was significantly lower for HNA than for phenanthrene. Whereas HNA did not sorb to HA, uptake to sediment and humin was observed, suggesting that HNA does not bind directly to OM. Phenanthrene uptake was characterized by hysteretic behavior and exhibited slow desorption. In contrast, HNA initially was more readily desorbed from sediment and humic fractions, but a significant fraction was not recovered in repeated desorption runs. The lower sorption of HNA reflects its greater polarity and water solubility, but the consistent retention of a non-desorbing fraction suggests strong binding and/or chemical transformation reactions may be important. It was postulated that abiotic transformation of HNA may occur in estuarine sediments, in part due to the presence of redox active minerals (Fe(III) and Mn(IV) oxides). The presence of Fe and Mn solids in the estuarine sediment was verified by sequential extraction and studies were then conducted to investigate the transformation of HNA in the presence of synthetic goethite (alpha-FeOOH) and birnessite (delta-MnO2) as model solids. Reaction with birnessite led to transformation of all HNA in solution within 24 h and resulted in the formation of partial oxidation products (POPs). Following reaction with goethite, HNA was present in solution and POPs were observed in the weakly bound fraction. This study indicates that degradation products of polycyclic aromatic hydrocarbons (PAHs) may have distinctly different sorption affinities and reactivities toward environmental surfaces than their parent compounds.     

Remediation of MTBE from drinking water: air stripping followed by off-gas adsorption

The widespread use of methyl tertiary butyl ether (MTBE) as an oxygenate in gasoline has resulted in the contamination of a large number of ground and surface water sources. Even though air stripping has been proven to be an effective treatment technology for MTBE removal, off-gas treatment often is required in conjunction with it. This study evaluated the combined treatment technologies of air stripping followed by off-gas adsorption on a pilot scale for the treatment of MTBE-contaminated water. The effect of air/water ratios on the treatment efficiency was studied, and the mass transfer coefficient was determined. Air/water ratios of 105:1, 151:1, 177:1, 190:1, 202:1, and 206:1 were used, and a treatment efficiency of >99% was achieved for all the runs conducted. The depth of packing required to achieve maximum treatment efficiency decreased with increasing air/water ratio. Relative humidity (RH) impacts on the MTBE adsorption capacity of a granular activated carbon (GAC) and carbonaceous resin were determined from pilot plant studies. Breakthrough profiles obtained from the pilot plant studies conducted at 20, 30, and 50% RH indicated that GAC has a higher adsorptive capacity than resin. The adsorptive capacity of GAC decreased with increasing RH, whereas RH did not impact the resin adsorptive capacity.     

Photolysis of vinclozolin

Following photolysis of vinclozolin in methanol five products were detected and identified: 3,5-dichlorophenylisocyanate, 3,5-dichloroaniline, methyl 3,5-dichlorophenylcarbamate, 3-(3-chlorophenyl)-5-methyl-5-vinyl-oxazolidine-2,4-dione and methyl (3,5-dichlorophenyl) (2-hydroxy-2-methyl-1-oxo-buten-3-yl) carbamate. The major component identified from photolysis in benzene solution, 3-(3-chlorobiphenyl)-5-methyl-5-vinyl-oxazolidine-2,4-dione, was produced by replacement of one chlorine atom by a solvent molecule.     

Bioeconomic models of marine recreational fishing

The theory of recreational fishing is developed and conditions are derived for optimal management policy, with special attention given to functional relationships that must be empirically verified. Determinants of the optimal allocation between commercial and recreational fishing effort are derived. The theory is extended to include selected peculiar features of recreational fishing: Some anglers sell their catch; a small proportion of the fishing population accounts for a large proportion of the catch; and anglers throw back a fraction of what they catch. Optimal policies are derived under these more realistic conditions.