Meeting Abstract
Conspecific aggressive encounters are highly dynamic, involve a spectrum of behavioral traits, and largely based on reciprocated interactions between or among individuals. The challenge hypothesis has long been the predictor of circulating androgen levels during male-male aggression. Females also display these behaviors, but the associated hormones are not widely studied. Bluebanded gobies, Lythrypnus dalli, are bidirectionally hermaphroditic fish, in which sex change occurs due to a change in social structure. In stable groups, L. dalli live in harems, such that one male dominates over many females and defends a nesting territory. Upon male removal (MR), the most dominant female exhibits rapid increases in rates of aggressive and territorial behavior. Little is known about the behavior exhibited by a resident male during territorial intrusion from another male. L. dalli is ideal for exploring the challenge hypothesis in both sexes, due to the plasticity of life history transitions. This study compares the behavioral and hormonal changes that occur amongst the group hierarchy, between MR groups and groups that have a male added (MA). We found that overall, the competition for dominance was similar across MA and MR groups, such that they all demonstrated spatial aggression, by competing for the nest. However, the aggressive intensity was different across the two contexts. In MA groups, the resident male and the intruding male showed high rates of aggression through physical contact inside the nest tube, whereas in MR groups, the most dominant female demonstrated high rates of approaches and displacements and prevented subordinates from entering the nest. Waterborne hormones were collected from fish in stable groups and from MA and MR groups 30 min after the aggressive change, to be analysed at a later date.
