Submitted to: Animal Behaviour
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2009
Publication Date: 2/23/2009
Citation: Dolezal, A.G., Brent, C.S., Gadau, J., Hoelldobler, B., Amdam, G.V. 2009. Endocrine Physiology of the Division of Labour in Pogonomyrmex californicus Founding Queens. Animal Behaviour. 77 pg 1005-1010
Interpretive Summary: The role of hormones in regulating behavior was studied in the California harvester ant. When a new queen is starting her nest, she will go through different life stages during which she changes her activities. During the initial stage, she will focus on tasks inside their nest, such as digging and laying eggs. In a later stage she will spend more time foraging outside her nest. In some populations of these ants, two queens will start a new nest together and one will stay inside while the other spends more time outside. To determine if these different behaviors are regulated by the same mechanism controlling egg production, the concentrations of two key hormones were measured in queens showing the two different types of behavior. We found that the hormone principally associated with egg production was found in higher concentrations in queens that spent more time outside. This supports a theoretical model that proposes that the complex division of tasks among members of social insect colonies evolved from modifications to the control mechanisms that regulate reproduction.
Technical Abstract: The proximate controls of a behaviour in extant species can inform us about the evolutionary route toward that behavioural phenotype. In social insects, different behavioural phenotypes often correlate with divergent hormone levels, and, in honey bees (Apis mellifera), this insight has lead to the hypothesis that behavioural biases, or division of labour, emerged via co-option of endocrine regulatory systems that paced behavioural change during the reproductive cycle of solitary ancestors. Founding queens of the California harvester ant Pogonomyrmex californicus exhibit discrete behavioural changes during colony founding, with a dichotomy between nest-biased behaviour and field-biased behaviour. Additionally, a division of labour can develop if queens found nests together, with one queen being nest-biased and another being field-biased. To determine if behavioural diphenism can be associated with reproductive endocrine regulators in an ant, we measured ecdysteroid and juvenile hormone (JH) content in i) single-founding queens showing normal behavioural progression and ii) co-founding queens exhibiting a division of labour. We found that ecdysteroid levels did not correlate with behaviour. JH titres, on the other hand, were elevated during the foraging life-stage of single-founding queens as well as in the co-founding queens with a behavioural bias toward foraging. Our results suggest that JH affects the propensity for foraging task replication in P. californicus, and provide evidence for one common evolutionary route toward social behaviour in ants and bees.