Transient nestmate recognition cues contribute to a multicolonial population structure in the ant,Leptothorax curvispinosus

Summary Individual nests of the facultatively polygynous and polydomous ant, Leptothorax curvispinosus, were mapped at two sites, collected, and maintained under uniform laboratory conditions. Tests of worker acceptability between nests were conducted 2–4 weeks and 13–17 weeks after collection. Nests collected near to one another (0.09–1.87 m) were sometimes nonaggressive, and were significantly less aggressive than those from different sites (7 km apart); and there was no significant difference in aggressiveness between tests for these distance categories. However, aggression between nests collected farther away from one another at the same site (1.52–4.65 m) decreased significantly between tests: initially, the level of aggressiveness was equivalent to that between nests from different sites but later it was reduced to that between near nests. These results indicate that polydomous colonies of this species occur within multicolonial populations; and that colony segregation within local populations is largely maintained by transient environmentally-based nestmate recognition cues. More stable cues of genetic or environmental origin (or both) are also present and contribute to discrimination even after extended periods of culture under uniform conditions. These results suggest that the maintenance of colony autonomy within genetically highly interrelated populations may be the prime function of environmentally-based nestmate recognition cues. Colony autonomy under such circumstances may be important to maintain a relatively small but optimal colony size, or because the mechanisms which regulate colony growth, development, etc., require a limited colony size.     

Economic Benefits of Improvements in Visibility: Acid Rain Provisions of the 1990 Clean Air Act Amendments

The Acid Rain Provisions (Title IV) of the Clean Air Act Amendments of 1990 call for about a 10 million ton reduction in annual SO₂ emissions in the United States. Although the provisions apply nationwide, most of the reduction will occur in the eastern half of the country, where use of high-sulfur coal for electricity generation is most common. One potentially large benefit of Title IV is the expected improvement in visibility conditions in the eastern United States due to the reductions in secondary sul-fate aerosols. This paper combines available economic estimates of willingness to pay for improvements in visibility with current estimates of the difference between expected visibility conditions in the eastern United States with and without Title I V, to estimate the expected visibility benefits of Title IV. The results suggest an annual value of $2.3 billion (in 1994 dollars) in the year 2010, as a result of visibility improvements due to Title IV in residential areas of the eastern United States. The results also suggest a possible additional annual value for eastern U.S. residents of as much as $1-2 billion for visibility improvements at national parks in the Southeast.     

Bioaccumulation of perfluoroalkyl acids in dairy cows in a naturally contaminated environment

Beef and dairy products may be important vectors of human exposure to perfluoroalkyl acids (PFAAs), but the understanding of how PFAAs are accumulated and transferred through agricultural food chains is very limited. Here, the bioaccumulation of PFAAs in dairy cows receiving naturally contaminated feed and drinking water was investigated by conducting a mass balance of PFAAs for a herd of dairy cows in a barn on a typical Swedish dairy farm. It was assumed that the cows were able to reach steady state with their dietary intake of PFAAs. Perfluorooctane sulfonic acid (PFOS) and perfluoroalkyl carboxylic acids (PFCAs) with 8 to 12 carbons were detected in cow tissue samples (liver, muscle, and blood) at concentrations up to 130 ng kg^?1. Mass balance calculations demonstrated an agreement between total intake and excretion within a factor of 1.5 and consumption of silage was identified as the dominant intake pathway for all PFAAs. Biomagnification factors (BMFs) were highly tissue and homologue specific. While BMFs of PFOS and PFCAs with 9 and 10 fluorinated carbons in liver ranged from 10 to 20, perfluorooctanoic acid (PFOA) was not biomagnified (BMF?<?1) in any of the investigated tissues. Biotransfer factors (BTFs; defined as the concentration in tissue divided by the total daily intake) were calculated for muscle and milk. Log BTFs ranged from ?1.95 to ?1.15 day kg^?1 with the highest BTF observed for PFOS in muscle. Overall, the results of this study suggest that long-chain PFAAs have a relatively high potential for transfer to milk and beef from the diet of dairy cows. However, a low input of PFAAs to terrestrial systems via atmospheric deposition and low bioavailability of PFAAs in soil limits the amount of PFAAs that enter terrestrial agricultural food chains in background contaminated environments and makes this pathway less important than aquatic exposure pathways. The BTFs estimated here provide a useful tool for predicting human exposure to PFAAs via milk and beef under different contamination scenarios.     

Pesticide and agro-ecological transition: assessing the environmental and human impacts of pesticides and limiting their use

Environmental Science and Pollution Research -     

Colony level and within colony level selection in honeybees

Summary Although honeybee workers are usually infertile, in queenless colonies some workers can develop ovaries and produce offspring. Therefore the classical Darwinian fitness of workers is not zero. Experimental studies in the Cape honey bee (Apis mellifera capensis) reveal a huge genetic variation for individual fitness of workers. The present study with a one locus, two allele model for reproductive dominance of workers shows that a balanced system between colony level and individual within colony selection plausibly explains the phenomenon of a high genetic variance of worker fitness. In particular, a frequent occurrence of queenless colonies in the population leads to stable polymorphic equilibria. Also the multiple mating system of the honey bee queen supports the propagation of alleles causing reproductive dominance of workers.     

Metal-contaminated potato crops and potential human health risk in Bolivian mining highlands

This study assessed metals in irrigation water, soil and potato crops impacted by mining discharges, as well as potential human health risk in the high desert near the historic mining center of Potosí, Bolivia. Metal concentrations were compared with international concentration limit guidelines. In addition, an ingested average daily dose and minimum risk level were used to determine the hazard quotient from potato consumption for adults and children. Irrigation water maximum concentrations of Cd, Pb and Zn in mining-impacted sites were elevated 20- to 1100-fold above international concentration limit guidelines. Agricultural soils contained total metal concentrations of As, Cd, Pb and Zn that exceeded concentration limits in agricultural soil guidelines by 22-, 9-, 3- and 12-fold, respectively. Potato tubers in mining-impacted sites had maximum concentrations of As, Cd, Pb and Zn that exceeded concentration limits in commercially sold vegetables by 9-, 10-, 16- and fourfold, respectively. Using conservative assumptions, hazard quotients (HQ) for potatoes alone were elevated for As, Cd and Pb among children (range 1.1–71.8), in nearly all of the mining-impacted areas; and for As and Cd among adults (range 1.2–34.2) in nearly all of the mining-impacted areas. Only one mining-impacted area had a Pb adult HQ for potatoes above 1 for adults. Toxic trace elements in a major regional dietary staple may be a greater concern than previously appreciated. Considering the multitude of other metal exposure routes in this region, it is likely that total HQ values for these metals may be substantially higher than our estimates.     

The People and Landscape Model (PALM): Towards full integration of human decision-making and biophysical simulation models

A model for simulating resource flows in a rural subsistence community is described. The People and Landscape Model (PALM) consists of a number of agents representing households, the landscape, and livestock. The landscape is made up of a number of homogeneous land units, or ‘fields’, each represented by an object containing data, methods and properties relevant to the field. Each field object consists of a number of soil layer objects, each of which contains routines to calculate its water balance and carbon and nitrogen dynamics. Organic matter decomposition is simulated by a version of the CENTURY model, while water and nitrogen dynamics are simulated by versions of the routines in the DSSAT crop models. The soil processes are simulated continuously, and vegetation types (crops, weeds, trees) can come and go in a field depending on its management. Crop growth and development are simulated by a generic model based on the DSSAT crop models, and which can be parameterised for different crops. Similarly, livestock growth and resource use is simulated by a generic model which can be parameterised for buffalo, cows, goats, sheep, chickens and pigs.