Effects of microclimate on daily flight activity ofSimulium arcticum Malloch (Diptera: Simuliidae)

Microclimate was found to affect the daily flight activity ofSimulium arcticum in a pasture situation in central Alberta, Canada. Vapour pressure, air temperature, light intensity, and wind gust velocity had the greatest correlation to flight activity. These variables were correlated to support the concept that they influence the energy and water balances of a black fly. Flight activity is a response of the black fly to alterations of its energy and water balances.     

Relationships among recent models for insect population dynamics with variable rates of development

A classification scheme for those population models which allow variation in development rates is proposed, based on two ways of modifying standard age-structured models. The resulting classes of models are termed development index models and sojourn time models. General formulations for the two classes of models are developed from two basic balance equations, and numerous specific models from the literature are shown to fit into the scheme. Concepts from competing risks theory are shown to be important in understanding the interplay between mortality and maturation. Relationships among the classes are investigated both for the most general forms of the models and for the simpler forms often used. The scheme can provide guidance in developing appropriate insect population models for specific modelling situations.Contribution 3878871     

Effects of predation environment and food availability on somatic growth in the Livebearing Fish Brachyrhaphis rhabdophora (Pisces: Poeciliidae)

Variation in somatic growth rates is of great interest to biologists because of the relationship between growth and other fitness‐determining traits, and it results from both genetic and environmentally induced variation (i.e. plasticity). Theoretical predictions suggest that mean somatic growth rates and the shape of the reaction norm for growth can be influenced by variation in predator‐induced mortality rates. Few studies have focused on variation in reaction norms for growth in response to resource availability between high‐predation and low‐predation environments. We used juvenile Brachyrhaphis rhabdophora from high‐predation and low‐predation environments to test for variation in mean growth rates and for variation in reaction norms for growth at two levels of food availability in a common‐environment experiment. To test for variation in growth rates in the field, we compared somatic growth rates in juveniles in high‐predation and low‐predation environments. In the common‐environment experiment, mean growth rates did not differ between fish from differing predation environments, but the interaction between predation environment and food level took the form of a crossing reaction norm for both growth in length and mass. Fish from low‐predation environments exhibited no significant difference in growth rate between high and low food treatments. In contrast, fish from high‐predation environments exhibited variation in growth rates between high and low food treatments, with higher food availability resulting in higher growth rates. In the field, individuals in the high‐predation environment grow at a faster rate than those in low‐predation environments at the smallest sizes (comparable to sizes in the common‐environment experiment). These data provide no evidence for evolved differences in mean growth rates between predation environments. However, fish from high‐predation environments exhibited greater plasticity in growth rates in response to resource availability suggesting that predation environments may exhibit increased variation in food availability for prey fish and consequent selection for plasticity.     

Developmental toxicity of carbon black oil in mice

BACKGROUND: Carbon black oil (CBO) is a refinery side-stream product used to produce asphalt and other commercial products. CBO contains several classes of hydrocarbons, several of which are known to exhibit systemic and gestational toxicities, making this mixture a candidate for causing reproductive toxicity. METHODS: Swiss-Webster mice were administered CBO (300, 350, 400 mg/kg/day) via oral gavage in a dosage volume of 10 microl/g body weight on gestation days (GD) 6-15. Uterine contents were evaluated on GD 18. RESULTS: Treatment with CBO at all dosage levels resulted in a high frequency of maternal clinical symptoms and a decrease in maternal weight gain. Decreased fetal viability was observed, manifested as a decrease in viable implants and, in a high percentage of treated dams, as early resorption of the entire litter. A significant reduction in fetal weight was also observed. However, neither structural malformations nor developmental delays in ossification were observed in any of the living offspring. To minimize maternal toxicity, the dosage range was lowered (100, 200, 300 mg/kg/day), and the concentration was adjusted such that the volume administered to each dam was decreased by 20%. In this trial, the only maternal effect observed was an increase in maternal liver weight at 200 and 300 mg/kg. The fetal lethality effects observed previously were reduced substantially. Nevertheless, the frequency of resorption among all treatment groups was higher statistically than in controls. CONCLUSIONS: These data support the hypothesis that CBO is reproductively toxic in Swiss-Webster mice at oral doses of >/=100 mg/kg/day.     

Aerobic and resistance exercise sequence affects excess postexercise oxygen consumption

Excess postexercise oxygen consumption (EPOC) may describe the impact of previous exercise on energy metabolism. Ten males completed Resistance Only, Run Only, Resistance-Run, and Run-Resistance experimental conditions. Resistance exercise consisted of 7 lifts. Running consisted of 25 minutes of treadmill exercise. Vo(2) was determined during treadmill exercise and after each exercise treatment. Our findings indicated that treadmill exercise Vo(2) was significantly higher for Resistance-Run compared with Run-Resistance and Resistance Only at all time intervals. At 10 minutes postexercise, Vo(2) was greater for Resistance Only and Run-Resistance than for Resistance-Run. At 20 and 30 minutes, Vo(2) following Resistance Only was significantly greater than following Run Only. In conclusion, EPOC is greatest following Run-Resistance; however, treadmill exercise is more physiologically difficult following resistance exercise. Furthermore, the sequence of resistance and treadmill exercise influences EPOC, primarily because of the effects of resistance exercise rather than the exercise combination. We recommend performing aerobic exercise before resistance exercise when combining them into 1 exercise session.     

Culture variability associated with the U.S. Environmental Protection Agency Tuberculocidal Activity Test Method.

Tuberculosis continues to be a major world health threat. The etiologic agent is among the vegetative organisms most resistant to chemical disinfection. Tuberculocidal efficacy testing for regulatory approval of chemical germicides has evolved considerably over the past decade. A method currently in use is the Environmental Protection Agency Tuberculocidal Activity Test Method, a suspension test using a Mycobacterium bovis culture grown under specific conditions and stored frozen until used. Differing tuberculocidal label claims on products with similar formulations have raised questions concerning the equivalence of test suspensions prepared by different laboratories. Five M. bovis suspensions from laboratories currently performing this test were compared against a battery of three disinfectants at a single test site. A significant difference between test cultures was found, with two of the five exhibiting a significant difference from the other three and also from each other. There was a significant culture-by-disinfectant interaction, indicating that the five cultures did not respond in a consistent manner across the different disinfectants used. However, these differences were due to cultures that were not prepared in accordance with the standard procedure or otherwise did not meet the test suspension criteria. In addition, a 0.55% sodium hypochlorite solution was found to be a sensitive indicator of culture variability. These data reinforce the need to adhere to published procedures and guidelines when growing and preparing a tuberculocidal test suspension and shed light on the variables associated with this type of testing.     

Ground-truthing the impact of invasive species: spatio-temporal overlap between native least chub and introduced western mosquitofish

Western mosquitofish (Gambusia affinis) are one of the most destructive introduced species in the American West. The negative impact of introduced species on native taxa depends on their spatio-temporal overlap, which will determine the availability of refugia for native species. Experiments on the mechanisms underlying the interactions between introduced and native species rarely address habitat use, overlap, and refugia because individuals are confined to enclosures. In a previous study we used cages, microcosms, and aquaria to show that mosquitofish could prey on and out-compete native least chub (Iotichthys phlegethontis). In this study, we examined the spatio-temporal overlap between mosquitofish and least chub under natural conditions. We found periods of overlap and partitioning in the seasonal and diel habitat use of these species. Both species used shallow habitats during the day and night throughout the spring when least chub were spawning. Predation by adult mosquitofish on young least chub during the spring likely explains the reduction in least chub recruitment in the presence of mosquitofish. During the summer least chub avoided mosquitofish by exclusively using cooler habitats, or by occupying deeper, cooler habitats during the day when mosquitofish were active, and shallower, warmer habitats at night when mosquitofish were inactive. A shift to cooler habitats in the presence of mosquitofish may result in decreased growth and fecundity of least chub. However, we suggest that a reduction of warm shallow habitat may have a disproportionately greater negative impact on mosquitofish than species native to temperate regions, such as least chub. Habitat manipulations that reduce or eliminate warm habitats may ameliorate the harmful effects of mosquitofish and promote the long-term persistence of native taxa.     

The tetrad-pollen model fails to explain the bias in Mendel's pea (Pisum sativum) experiments

For >40 years, geneticists and science historians have appealed to the tetrad-pollen model as an explanation of the bias toward expectation in Mendel's data, albeit without experimental support. Our experiments demonstrate that pollen sampling during self-pollination in pea conforms to the binomial distribution with no evidence of a tetrad-pollen effect.