Phenotypic Plasticity and Contemporary Evolution in Introduced Populations: Evidence from Translocated Populations of White Sands Pupfish (Cyrpinodon tularosa)

Contemporary evolution has been shown in a few studies to be an important component of colonization ability, but seldom have researchers considered whether phenotypic plasticity facilitates directional evolution from the invasion event. In the current study, we evaluated body shape divergence of the New Mexico State-threatened White Sands pupfish (Cyprinodon tularosa) that were introduced to brackish, lacustrine habitats at two different time in the recent past (approximately 30 years and 1 year previously) from the same source population (saline river environment). Pupfish body shape is correlated with environmental salinity: fish from saline habitats are characterized by slender body shapes, whereas fish from fresher, yet brackish springs are deep-bodied. In this study, lacustrine populations consisted of an approximately 30-year old population and several 1-year old populations, all introduced from the same source. The body shape divergence of the 30-year old population was significant and greater than any of the divergences of the 1-year old populations (which were for the most part not significant). Nonetheless, all body shape changes exhibited body deepening in less saline environments. We conclude that phenotypic plasticity potentially facilitates directional evolution of body deepening for introduced pupfish populations

The effect of gas-phase chemistry on aqueous-phase sulfur dioxide oxidation rates

The rates and mechanisms of both gas and liquid phase reactions for the oxidation of sulfur dioxide play an important role in the production of atmospheric acids and aerosol particles. Rhode et al. (198 1) concluded that sulfate production rates were highly non-linear functions of sulfur dioxide emission rates. Their modelling study used an HO(x) termination mechanism for the HO-SO2 reaction in the gas-phase. Stockwell and Calvert (1983) determined that one of the products of the overall reaction of HO with sulfur dioxide was an HO2 radical. The National Research Council (1983) using a version of the Rhode et al. (1981) model modified to include HO2 production from the HO-SO2 reaction concluded that sulfate production becomes much more linear with respect to reductions in sulfur dioxide emissions. However, the cause of this increased linearity was not explained by the National Research Council report. It is demonstrated that the increased linearity is due to the coupling of gas-phase a nd aqueous-phase chemistry. The gas-phase sulfur dioxide oxidation mechanism has a very significant effect on hydrogen perodide production rates

On the HO2 + HO2 reaction. Its misapplication in atmospheric chemistry models

The self-reaction of the HO2 radical is an important termination reaction for HO(x) and it is the major gas phase source of hydrogen peroxide in the atmosphere. It is well established that the rate of this reaction is sensitive to both pressure and water vapor concentrations. The NASA recommended rate parameter (DeMore et al., 1992) has been utilized in several detailed gas phase chemical mechanisms for modeling the troposphere, but several other recent studies have omitted one or both of the terms for the rate constant. If both the pressure and the water dependent terms are omitted the relative error can be as high as 75 per cent at the surface to near 30 per cent at 10 km for water vapor saturated conditions. Models which omit these terms will predict incorrect HO(x) budgets, underestimate gas phase hydrogen peroxide formation rates, and overestimate ozone and organic peroxide formation rates especially in clouds or under marine conditions

The influence of aqueous-phase chemical reactions on ozone formation in polluted and nonpolluted clouds

Aqueous-phase reactions among dissolved radicals and trace metals have been incorporated into a comprehensive gas-phase chemical reaction mechanism in order to quantify the influence of heterogeneous chemical processes on ozone (O3) formation under a wide range of NOx and hydrocarbon concentrations. In-cloud reactions of dissolved HO2 with itself, the reaction of dissolved O3 and HO2, and when trace metals are present, the reactions of dissolved HO2 and copper dramatically reduce total HO2 and other free-radical concentrations in clouds, thereby reducing the rate at which O3 is produced from anthropogenic NOx and hydrocarbon pollutants. Under typical urban or moderately polluted conditions, local ozone formation rates are reduced by 30-90 per cent when aqueous-phase radical reactions are occurring in the atmosphere. However, when NOx concentrations are less than about 200 ppt, O3 is slowly destroyed, and in-cloud reactions reducing HO2 concentrations decrease the rate at which ozone an d other reactive NOx and non-methane hydrocarbons (NMHC) are destroyed, resulting in longer atmospheric chemical lifetimes of O3, NOx, and NMHC. These results suggest that in-cloud reactions strongly influence local O3 production in polluted areas, but longer-term impacts of clouds on O3 formation would be much smaller due to compensating chemical processes in regions remote from NOx emissions. The effects of heterogeneous chemistry are highly dependent on the concentrations of NOx and hydrocarbons. In polluted clouds, aqueous reactions of dissolved copper and iron could be the dominant reactions influencing O3 formation, suggesting the need for further measurements of trace metals in the atmosphere