A project undertaken at the University of Melbourne and supervised by Luke Holman
Social insects, such as bees, ants, wasps and termites, have fascinated us since ancient times. Two puzzling questions stand out regarding social insects. The first is “How did workers evolve, given that they usually don’t produce offspring?” Generally speaking, social insects live with their close relatives – the queen lays all of the eggs, and is often the mother of all the workers, who take care of the nest and generally do not lay their own eggs. Thus, each worker passes on its genes indirectly, by helping their mother create additional brothers and sisters, which carry many of the same genes as the worker. Beyond relatedness, the factors that determine whether a species evolves workers are unclear. The second question is “How do social insects manage to produce two different body types – queens and workers – using a single set of genetic instructions (the “genome”)?”. In some ants and termite, the queen can live up to 30 years, be the size of a mouse, and lay a hundred million eggs over her lifetime, while workers are short-lived, completely sterile, and much smaller. It is remarkable that one set of genes can produce two individuals that are so different they could be mistaken for different species.
Figure 1. A female reed bee Exoneura robusta, and (below) a pair of females beginning to dig a new nest inside the stem of a tree fern. (Photos by Michael Whitehead).
In this project, we will tackle these two questions by conducting a detailed genetic study of a large population of Australian native bees living in the Dandenong Ranges, Victoria. The bees (Exoneura robusta, or “reed bees”) live in very small colonies (often 2 or 3 individuals, but occasionally more than 10) inside a hollowed-out stick from a tree fern. Unlike more ‘advanced’ species like the honeybee, they do not have distinct queens and workers – all females look the same. However, nests often contain a dominant female who does most of the breeding, and subordinate females who do most of the work. This lifestyle is very similar to the hypothesised ancestors of the advanced social insects, and so one can gain insight into the lives of the earliest social insects by studying this present-day species. The distinction between dominant and subordinate females is also akin to that between queens and workers, allowing us to study how the remarkable flexibility of social insect genomes came to be.
Specifically, this project will involve collecting a large number of nests, take detailed measurements of the bees and their offspring, and then analysing their genes. Among other things, the resulting data will allow us to investigate: the pros and cons of becoming a subordinate versus building a nest of your own, the role of “DNA methylation” in producing breeding and non-breeding body types (a chemical modification to DNA that potentially changes how a gene functions), and the genetic basis of fitness and natural selection in a wild insect population. We also hope to learn more about the fascinating social lives of this little-studied group of bees, which live only in Australia.