Final Report Summary - NEUROANT (NEUROanatomy, neurochemistry and genotype: genetic diversity and division of labour in leaf-cutting ANTs) The discovery and characterizations of neuromechanisms that mediate the genotypic changes in behaviour is a premier paradigm in biology today. The difficulty in finding defined answers rests in the multiplication of confounding factors (environment, individual behavioural flexibility, genotypic variation, and polygenic traits) and the limited sample size for comparison. This project has used social insect colonies to overcome these issues to answer this question. The project has used the leaf-cutting ant, Acromyrmex echinatior, as the model species because this ant has recently been shown to exhibit genetic influences on caste specialization, has colonies headed by single queens mated to multiple mates, thus producing genetically diverse offspring, and has colony sizes that will produce numerous individuals from each paternal line. Therefore, ants from a single colony share a common environment, the same maternal genotype on average but can differ in their paternal genotype, and are behaviourally specialized. We have used microsatellite sequencing to characterize the genotypic variations among behaviourally specialised ants of different patrilines from single colonies. We then combined this with testing whether there were neuroanatomical and neurochemical differences between these ants to establish the neuromechanisms underpinning genetic variation in division of labour, and behaviour more generally. Ant brains were assayed utilizing immunocytochemistry and confocal microscopy, combined with direct measurement of biogenic amine levels with HPLC. The results show that while gross brain morphology differs little between behaviourally specialized worker ants or between patrilines, there are significant differences in the levels of biogenic amines, which are likely to play a key role in the behavioural variation seen. Foragers were found to have higher levels of both dopamine and octopamine, and a higher octopamine to serotonin ratio, than waste management workers. Patriline did not appear to have a strong direct effect on the levels of the biogenic amines, but did affect body size, which in turned had a significant effect on the levels of the amines. The results suggest that differences in biogenic amines may play an important role in regulating task specialization, but that genotypic effects on behavioural specialization may be mediated by other mechanisms.
