When a parent virus replicates inside its host, it must first use its own genome as the template for replication. However, once progeny genomes are produced, the progeny can in turn act as templates. Depending on whether the progeny genomes become templates, the distribution of mutants produced by an infection varies greatly. While information on the distribution is important for many population genetic models, it is also useful for inferring the replication mode of a virus. We have analyzed the distribution of mutants emerging from single bursts in the RNA bacteriophage 6 and find that the distribution closely matches a Poisson distribution. The match suggests that replication in this bacteriophage is effectively by a stamping machine model in which the parental genome is the main template used for replication. However, because the distribution deviates slightly from a Poisson distribution, the stamping machine is not perfect and some progeny genomes must replicate. By fitting our data to a replication model in which the progeny genomes become replicative at a given rate or probability per round of replication, we estimated the rate to be very low and on the on the order of 10 ؊4 . We discuss whether different replication modes may confer an adaptive advantage to viruses.In recent years, viruses have been increasingly used in the laboratory to study the fitness effects of mutations (1,4,8,10,14,15,16,25). The increase is likely due to two reasons. First, these fitness effects, which are generally quantified as the distribution of the magnitude, the sign (deleterious versus beneficial), and the interaction (additive versus nonadditive) of the mutations, are key to many evolutionary models, and viruses have become a major focus of evolutionary studies. Much of our predictive theories in evolution have come from population genetic models that make assumptions about the fitness effects of mutations. For example, depending on whether the interaction between deleterious mutations is log-additive, the models predict distinctly different advantages for the evolution of recombination (5, 15). Second, many issues addressed by such models have now also been raised in the context of viruses, especially RNA viruses, which have a much higher mutation rate than DNA viruses (11,12). Evolutionary topics as wide ranging as the quasi-species concept, game theory, the origin of life, the constancy of the molecular clock, the divergence and convergence of isolated populations, and the evolution of recombination have all been recently considered in relation to viruses (1-3, 5-7, 15, 17, 18, 22, 24, 29, 31, 32).As the more qualitative aspects of the distribution of mutational effects and interactions have become known, it has become desirable to extract more quantitative information. However, more quantitative analyses require also more exact information on another type of distribution, that of mutations and mutants in a population. The distinction between mutations and mutants is important and is made herein. A mutation is the event...
– Two different Denil fishways on the Grand River, Ontario, were used as check‐points to evaluate the upstream movement of fishes past a low‐head weir and to examine the proportions and inferred swimming performance of non‐salmonid warmwater fishes that used each fishway type. Traps installed at fishway exits were used to collect fish during 24‐hour sampling periods, over 40–51 days each year, from 1995 to 1997. Passage rates, size selectivity, water temperature, water velocity and turbidity for the periods of maximum passage for each year were examined. General species composition from trap samples shifted from catostomids to cyprinids to ictalurids to percids and centrarchids, with some overlap, as water temperatures increased from 8 °C to 25 °C in the spring and early summer. Water depths, and therefore water velocities in each fishway, were independent of river discharge due to variable accumulations of debris on upstream trash‐racks. Relationships between the water velocity and the swimming and position‐holding abilities of several species emerged. Turbidity was directly related to river discharge and precipitation events, and many species demonstrated maximum fishway use during periods of increased turbidity. This study 1) provided evidence of strongly directional upstream movements among several species that were previously considered non‐migratory and 2) describes physical and hydraulic conditions during fishway use for 29 non‐salmonid fish species.
This study extends an original bioeconomic model of optimal duck harvest and wetland retention by bringing in amenity values related to the nonmarket (in situ) benefits of waterfowl plsi the ecosystem values of wetlands themselves. The model maximizes benefits to hunters as well as the amenity values of ducks and ecosystem benefits of wetlands, subject to the population dynamics. Results indicate that wetlands and duck harvests need to be increased relative to historical levels. Further, the socially optimal ratio of duck harvest to wetlands is larger than what has been observed historically. Including amenity values leads to a significant increase in the quantity of wetlands and duck harvests relative to models that focus only on hunting values.
A carbon tax is an economically efficient means to incentivize carbon-reducing investments in electrical generating systems. Along with growing demand for electricity and a desire to mitigate climate change, there has been renewed discussion about the role of nuclear power in meeting CO 2 emission reduction targets. However, recent concern about the failure of Japan's Fukushima Daiichi nuclear plant has reduced society's already low confidence in nuclear power. Thus, renewable sources of energy generation, such as wind, are seen as better alternatives to fossil fuels for reducing CO 2 emissions.Increasing reliance on wind generation poses challenges for electrical system operators because of the variable nature of wind, lack of storage, need for backup generation, transmission constraints and costs of building additional transmission capacity. The intermittent nature of wind requires that wind generation be supplemented by fast-ramping backup generation from open-cycle gas turbine (OCGT) and/or diesel power plants; CO 2 emissions from these plants are higher than usual due to operation at G. Cornelis van Kooten (kooten@uvic.ca) is a professor, and Craig Johnston (craig@uvic.ca) and Linda Wong (lindaw@uvic.ca) are
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