Built to change: dominance strategy changes with life stage in a primitively eusocial bee

Access to reproduction is determined by an individual’s dominance rank in
many species and is achieved through aggression and/or dominance
signalling. In eusocial insects one or several dominant females (queens)
monopolize reproduction but to what extent queens rely on aggression and
signalling remains obscure. Aggression is costly and its efficiency
depends on the group size, whereas signalling may reduce the risks and
costs of aggression. Both strategies are used to regulate reproduction in
social taxa, with aggression being more common in small social groups,
compared to signalling in larger societies. Here, we examine the use of
aggression and chemical signalling in a social species (Bombus impatiens)
where the dominant queen interacts with increasing numbers of workers as
she ages. We found that the queen’s strategy to monopolize reproduction
changes with life stage, shifting from overt aggression to chemical
signalling as the queen gets older. Particularly, old queens exhibited a
higher ratio of short to long cuticular hydrocarbons compared to young
queens, an endogenous shift that was attributed to age, as all egg-laying
queens were fecund and kept with the same number of workers. Our findings
contribute to the understanding of reproductive dominance in the context
of an individual’s life history.