Division of labour and seasonality in the ant Leptothorax albipennis: worker corpulence and its influence on behaviour

We address the organization of workers in social insect societies. We disti nguish between changes in behavioural role over the nurse to forager role s equence, which may depend on changes in physiology, and potentially more ra pid changes of task within role. We investigated the association between ro le and nutrient status in the ant Leptothorax albipennis. Worker lipid stor es were quantified using a new body size-controlled method, and were relate d to worker behaviour. Worker lipid stores were evenly distributed amongst colony members at the end of winter, splitting rapidly into two distinct mo des (replete nurses and lean foragers) in spring. The proportion of lean fo ragers increased throughout spring and summer, until most colonies containe d only workers of this type. Callow workers then eclosed with intermediate lipid stores. We developed a computer vision system that tracks all nest an ts to extract detailed behaviour of individuals of known lipid stores. Lipi d storage was negatively correlated with a worker's foraging propensity, an d with measures of spatial occupation in the nest and of activity. Differen t colonies showed a similar quantitative correlation between lipid stores a nd behavioural role, suggesting that lipid stores were not only correlated with the relative organization of individuals within each nest, but may als o have influenced their absolute role. We reviewed the literature and found evidence that nutrient status influences role predisposition in social ins ect workers. We conclude that the distribution of worker roles may be linke d to the balance between foraging income and energetic consumption within t he colony directly via worker nutrient status. (C) 2000 The Association for the Study of Animal Behaviour.