Abstract
Social insects have a level of organization above the individual organism. Over the past century, scientists have explored individual and colony levels of organization, and how this links together. Division of labour is where workers specialize on different tasks performed by a colony. This can look different across species, and there are several different mechanisms that influence the organisation of these tasks. In honey bees, for example, individuals transition through tasks as they age (temporal polyethism); whereas in other species, tasks may be allocated based on physiology or spatial distribution inside the nest. In my first chapter, I discuss the current understanding of the division of labour through a literature review.
In my second chapter, I explore the differences in the literature on division of labour across different social insect taxa. I conducted a bibliometric study to determine how the quantity and quality (journal metrics, methods used) of published papers on division of labour was distributed across the different social insect taxa. Additionally, I compared the number of studies within each taxa that incorporated physiology, genetics and neurobiology. Honey bees and ants had the most papers and these were usually published in journals with better metrics. Honey bees have more papers published looking at mechanisms, while other taxonomic groups such as ants, other social bees, and wasps have less. The methods used to study social insects also differed across taxonomic groups. Overall, this study highlights that there are gaps in the literature when studying division of labour in social insects, both taxonomically and mechanistically.
Vespula wasps are social insects that have previously been found to show limited evidence of temporal polyethism. Many social insects that show temporal polyethism move from low-risk tasks to higher risk tasks as they age. Defenders perform the riskiest task in an individual’s life by protecting the nest when threatened. For the third chapter of my thesis, I look for evidence to determine whether individuals transition from foraging to nest defence, and the extent to which the same individuals consistently engage in foraging or defence over time. I compared the behavioural profiles of Vespula wasps with physiology (body weight and lipid content). I found evidence that Vespula transition from foraging to defensive behaviour. While foragers and defenders did not vary in terms of body size, defenders had significantly lower proportion of lipid content compared to foragers. As body fat gradually decreases with age, this further suggests that there is some level of temporal polyethism present. I discuss how the results from this will help in understanding temporal polyethism in Vespula wasps, and the physiological links that may influence it.