Conflicts,social economics and life history strategies in ants

Summary This paper presents a life history model for a perennial social insect colony. The model's purpose is to explore the evolutionary consequences, in terms of fitness of different parties within the colony, of alternative life history strategies. The model has been specifically developed for colonies of the slave-making ant, Harpagoxenus sublaevis, which has reproductive workers organized in dominance orders. It incorporates empirically obtained parameters, and uses computer algorithms based on numerical optimization to determine the optimum policy for a colony queen in allocating resources between workers, queens, and males. Variants of the model also consider alternative situations in which either (1) orphaned workers do not slave-raid, or (2) workers are sterile. The results correspond closely to data on colony growth and reproductive allocation obtained from the field. They suggest that a colony queen would suffer reduced fitness in the two theoretical cases as compared to the real situation. Reproduction by orphaned workers posthumously enhances the colony queen's fitness because a queen with sterile workers cannot produce enough extra sexuals in her lifetime to balance her loss in grandson production. The results also suggest that the division of labour between slave-raiding and nonraiding workers observed in H. sublaevis colonies can be explained as an outcome of worker-worker reproductive conflict: reproductively-inhibited subordinate workers can increase their inclusive fitness by slaveraiding for dominant, nonraiding egg-layers. These findings emphasize the evolutionary importance of the orphanage period and of intracolony conflict in monogynous social insect colonies.     

Sex ratio determination and worker reproduction in the slave-making ant Harpagoxenus sublaevis

Summary In a population of the monogynous slave-making ant Harpagoxenus sublaevis in S.E. Sweden, the mean proportion of dry weight investment in queens was 0.54. This result differed significantly from 0.75 but not from 0.5, matching the prediction from the genetic relatedness hypothesis of sex ratio applied to slave-makers, given (as confirmed by this study) single mating of queens, population-wide mate competition, and relatively low levels of worker male production. Sex investment appeared unaffected by resource availability. In the same 47 colony population sample, fertile slave-maker workers were found in every queenless colony (ca. 30% of all colonies), and in 58% of queen-right colonies. Fertile workers occurred at a significantly higher frequency in the queenless colonies (19.2%) than in the queenright ones (9.8%), confirming that queenless conditions promote worker fertility. Fertile and sterile workers were similar in size. Electrophoretic allozyme analysis of ants from 49 colonies showed that: 1) queens mated singly; 2) female nestmates were full sisters (their regression coefficient of relatedness (±SE) was 0.735±0.044); 3) inbreeding did not occur; 4) queen and worker siblings were not genetically differentiated. Worker male production in queenright colonies was neither confirmed nor ruled out by the genetic data. However, production data indicated that queenless workers produced between 4.4 and 21.6% of all males. Overall colony productivity was largely determined by slave number, itself positively correlated with the number of slave-maker workers. There was an abrupt switch from all worker to all sexual production as colony size rose, as predicted by life history models. In queenright colonies, fertile slave-makers did not discernibly reduce colony productivity. Such workers occurred in queenright colonies with most slaves, suggesting they exploited energetic surpluses. Worker reproduction in H. sublaevis therefore appears to have greater influence at the level of individual behaviour than at colony or population level.     

Laboratory system enabling long-term exposure (⩾ 30 d) to hydrostatic pressure (⩽ 101 atm) of fishes or other animals breathing water

A high-pressure water-circulation system is described which enables fish (or other animals breathing water) to be maintained at pressures up to 101 atm for at least one month. A typical experiment, measuring the oxygen consumption of the eelAnguilla anguilla over a period of 31 d, revealed a metabolic acclimation to pressure in this fish. This system has numerous advantages; e.g. it is possible to reproduce in situ environmental conditions at depth, thus enabling the study of the problems of pressure adaptation, and also to simulate vertical migrations of animals, allowing the study of associated physiological phenomenon.     

Distribution of mercury in the atmosphere over Idrija, Slovenia

Idrija mine, the second largest mercury mine in the world, was in use since 1490. More than 107 000 tons of Hg were produced in its five centuries of history until 1990 when production was reduced to a few hundred kilos per year. The average recovery rate of mercury has been estimated to 73%; much of the remaining 27% was dissipated into the environment. In spite of present minimal levels of production, and only a few days of smelter operation per year, a real time survey with a mercury Zeeman analyser in a car showed relatively high mercury concentrations in the air. Amounts of 300--4000 ng Hg ^m-3 have been found around both the major sources of mercury vapour, the smelter and mine ventilation shaft -- while the amounts at the Old Place, at the City Museum, and near the Nikova-Idrijca confluence are of the order of 50 ng m^-3. Polluted air will be transported from those sources to a degree which depends on the weather conditions, mainly the direction and intensity of the wind. The high mercury contents in the air are not only due to anthropogenic sources (smelter and the ventilation shaft, dumps and smelter slag used in construction), but may also partly be natural as in the Pront area, where the outcropping bedrock contains native mercury.