Differential reproduction in multiple-queen colonies of the fire ant Solenopsis invicta (Hymenoptera: Formicidae)

Summary The contribution to maternity of workers and female sexuals over time by queens in six multiple-queen laboratory colonies of Solenopsis invicta was directly assessed by use of enzyme genetic markers. Queens contributed more equally to the worker pool than to the pool of sexuals in virtually all samples (Fig. 1), and individuals producing a substantial proportion of the workers often had low or no representation of their daughters in the pool of sexuals. Signficant disparity among queens in their relative production of sexual daughters was often evident, with dominance in production of sexuals by a given queen commonly occurring in association with a pronounced loss of weight followed shortly by her death. The results suggest that significant variability in short-as well as long-term reproductive success may occur among the distantly related queens associating in natural polygyne S. invicta nests. Variance in apportionment of maternity of sexuals did not appear to be simply related to varying levels of fecundity, suggesting that the common presumption that reproductive success can be equated with fecundity in polygyne social Hymenoptera may not be well founded. The observed variance also did not appear to result from a simple mechanism of kin recognition and discrimination by workers in the process of brood rearing. Rather, this variance may have largely resulted from either, 1) recognition of certain queens and their progeny coupled with preferential sexualization of these immatures by nurse workers, or, 2) queen biasing of eggs toward development as sexuals. The frequent association of weight loss and death of mother queens with high levels of sexual daughter production may be best explained by the latter mechanism.     

Organochlorine contaminants in seven species of Arctic seabirds from northern Baffin Bay

Organochlorine contaminants (OCs) were determined in liver and fat of seven species of seabirds (Alle alle, Uria lomvia, Cepphus grylle, Rissa tridactyla, Pagophila eburnea, Larus hyperboreus, and Fulmaris glacialis) collected in May/June 1998 from the Northwater Polynya in northern Baffin Bay. OC concentrations ranged over an order of magnitude between seabird species and OC groups, with PCBs having the highest concentrations followed by DDT, chlordane, HCH and ClBz. Positive relationships between delta15N (estimator of trophic level) and OC concentrations (lipid basis) were found for all OC groups, showing that trophic position and biomagnification significantly influence OC concentrations in Arctic seabirds. Concentrations of a number of OCs in particular species (e.g., HCH in P. eburnean) were lower than expected based on delta15N and was attributed to biotransformation. P. eburnea and F. glacialis, which scavenge, and R. tridactyla, which migrate from the south, were consistently above the delta15N-OC regression providing evidence that these variables can elevate OC concentrations. Stable isotope measurements in muscle may not be suitable for identifying past scavenging events by seabirds. OC relative proportions were related to trophic position and phylogeny, showing that OC biotransformation varies between seabird groups. Trophic level, migration, scavenging and biotransformation all play important roles in the OCs found in Arctic seabirds.     

Crude oil contaminated soil washing in air sparging assisted stirred tank reactor using biosurfactants

This study investigated the removal of crude oil from soil using air sparging assisted stirred tank reactors. Two surfactants (rhamnolipid and sodium dodecyl sulfate, SDS) were tested and the effects of different parameters (i.e. temperature, surfactant concentrations, washing time, volume/mass ratio) were investigated under varying washing modes namely, stirring only, air sparging only and the combination of stirring and air sparging. The results showed that SDS removed more than 80% crude oil from non-weathered soil samples, whilst rhamnolipid showed similar oil removal at the third and fourth levels of the parameters tested. The oil removal ability of the seawater prepared solutions were better than those of the distilled water solutions at the first and second levels of temperature and concentration of surfactant solutions. This approach of soil washing was noted to be effective in reducing the amount of oil in soil. Therefore we suggested that a field scale test be conducted to assess the efficiency of these surfactants.     

Distribution and diet of juvenile Patagonian toothfish on the South Georgia and Shag Rocks shelves (Southern Ocean)

The distribution and diet of juvenile (<750 mm) Patagonian toothfish are described from four annual trawl surveys (2003–2006) around the island of South Georgia in the Atlantic sector of the Southern Ocean. Recruitment of toothfish varies inter-annually, and a single large cohort dominated during the four years surveyed. Most juveniles were caught on the Shag Rocks shelf to the NW of South Georgia, with fish subsequently dispersing to deeper water around both the South Georgia and Shag Rocks shelves. Mean size of juvenile toothfish increased with depth of capture. Stomach contents analysis was conducted on 795 fish that contained food remains and revealed that juvenile toothfish are essentially piscivorous, with the diet dominated by notothenid fish. The yellow-finned notothen, Patagonotothen guntheri, was the dominant prey at Shag Rocks whilst at South Georgia, where P. guntheri is absent, the dominant prey were Antarctic krill and notothenid fish. The diet changed with size, with an increase in myctophid fish and krill as toothfish grow and disperse. The size of prey also increased with fish size, with a greater range of prey sizes consumed by larger fish.     

Electron paramagnetic resonance spectrometry of diesel particulate matter

Electron paramagnetic resonance (EPR) spectrometry has been used to study diesel particulate matter. The EPR signals for a graphitized carbon black and particles collected from two different diesel engines have been compared. Variations in the line widths and signal intensities due to various chemical and physical pretreatments of the particles were observed. The EPR signals for the diesel particulates were shown to be sensitive to oxygen, nitric oxide, nitrogen dioxide, and ultraviolet and visible radiation. These results suggest that EPR may be a convenient means for characterizing particles from different sources or for demonstrating particle reactivities. The demonstrated photochemical reactivities of the airborne particles have significant environmental health implications.     

Spatial and Temporal Distribution of Norovirus and <Emphasis Type="Italic">E. coli</Emphasis> in Sydney Rock Oysters Following a Sewage Overflow into an Estuary

This paper reports a study of norovirus (NoV) GII distribution and persistence in Sydney rock oysters (SRO) (Saccostrea glomerata) located in an estuary after a pump station sewage overflow. SRO were strategically placed at six sites spanning the length of the estuary from the pump station to the sea. The spatial and temporal distribution of NoV, hepatitis A virus (HAV) and Escherichia coli (E. coli) in oysters was mapped after the contamination event. NoV GI and GII, HAV and E. coli were quantified for up to 48 days in oysters placed at six sites ranging from 0.05 to 8.20 km from the sewage overflow. NoV GII was detected up to 5.29 km downstream and persisted in oysters for 42 days at the site closest to the overflow. NoV GII concentrations decreased significantly over time; a reduction rate of 8.5% per day was observed in oysters (p < 0.001). NoV GII concentrations decreased significantly as a function of distance at a rate of 5.8% per km (p < 0.001) and the decline in E. coli concentration with distance was 20.1% per km (p < 0.001). HAV and NoV GI were not detected. A comparison of NoV GII reduction rates from oysters over time, as observed in this study and other published research, collectively suggest that GII reduction rates from oysters may be broadly similar, regardless of environmental conditions, oyster species and genotype.     

Simulation of wildfire effects on the nitrogen cycle of a Pinus banksiana ecosystem in New Brunswick, Canada

A non-linear, deterministic model of biomass accumulation and nitrogen cycling in an even-aged, pure jack pine (Pinus banksiana Lamb.) stand was developed and used to explore effects of fire intensity and frequency of burning on the long-term nitrogen cycle. Given the model structure and assumptions, simulated results showed that successive fires at both light and severe fire intensities caused gradual depletion of the amount of N accumulated in the vegetation layers. Fires also reduced the amount of N in the litter and soil pools, with the initially large soil organically-bound N pool showing a particularly sharp decline, and decreased the productivity of the simulated stand. A frequency of one fire per 20 years for five successive burns produced declines of N accumulated in the tree stratum of 50–75% (depending upon fire intensity) in comparison with the undisturbed system at a corresponding age, whereas a 100-year frequency produced decreases of 10–22%. Similarly, declines in litter layer N were 54–72% at a 40-year frequency, compared with 30–55% at a 100-year frequency. The simulated results also suggested that both the stand age when burning occurred and the fire frequency were important, because distinctive patterns of accumulation and decline of N in ecosystem pools existed with increasing stand age. A serious lack of information regarding processes inherent in the model was found to exist in certain cases. Important processes which are currently poorly quantified include: (1) the factors controlling rates of tree growth; (2) the relation of foliar and other tissue N to soil N concentrations and foliar translocation; (3) the relation of forest floor conditions to decomposition and stand structural characteristics; and (4) the controls of a variety of soil N transformations, transfers, leaching and decomposition rates. Because of this basic lack of information and the great dependence of the model's behavior on these processes, the present version of the model is not suitable for real-world prediction. The model does have use as a means of combining hypotheses about a system into an explicit structure and examining the collective consequences of this, as well as pointing out future research needs for the system.     

Seasonal decline in intracolony genetic relatedness in eastern tent caterpillars: implications for social evolution

Summary Genetic relatedness in social insect colonies may vary spatially or temporally as a result of changes in colony membership due to immigration or to variation in patterns of maternity and paternity. We estimated relatedness for eastern tent caterpillars (Malacosoma americanum) in laboratory colonies derived from egg masses using multilocus genotypic data derived from electrophoresis. This estimate is compared with estimates obtained from colony samples taken in the field at four intervals spanning the larval developmental season. We found that average intracolony relatedness is close to 0.5 initially but declines through the developmental season due to colony merging, showing that caterpillars do not discriminate between siblings and nonsiblings in order to preserve colony family structure. Using the intracolony values together with relatedness values for higher levels of population structure, we estimated the effective mean number of simple families represented in single colonies through the season. The overall effective number of families per tent increased from one at the time of eclosion to 1.3 by the end of the season. Average intracolony relatedness remained relatively high despite the occurrence of colony merging, apparently as a result of the low density of tents on most trees, combined with high relatedness within the original colonies. Thus, high intracolony relatedness is maintained in M. americanum populations through the effects of adult dispersal, mating, and oviposition patterns, rather than through behavioral discrimination mechanisms of the larvae. These findings underscore the importance of considering the causes of temporal variation in genetic relatedness as well as the consequences for the indirect component of inclusive fitness. Correspondence to: J.T. Costa