Are testosterone pulses a physiological mechanism for expanding activity beyond territories?

Abstract

We ask whether artificially induced testosterone pulses (T-pulses), administered to males in the wild at the territory boundary, adjust location preferences within the territory. Multiple transient T-pulses occurring after social interactions in males can alter behaviour and spatial preferences. We previously found that T-pulses administered at the nest induce male California mice, a biparental and territorial species, to spend more time at the nest likely through conditioned place preferences. We hypothesized that T's reinforcing effects would increase future time by the T-injected males at the boundary and promote territorial defence. Contrary to predictions, T-pulses induced a decrease in male time at the boundary, and instead appeared to promote male territorial/home range expansion, accompanied by shorter sustained vocalizations (SVs) and decreased proportion of three SV bouts. Shorter SVs are associated with aggression in the laboratory. Furthermore, in response to T-male behavioural changes, uninjected female partners decreased boundary time. Our results suggest new functions for socially induced T-pulses, such as extending territorial boundaries/home ranges. Location preferences induced through reinforcing/rewarding mechanisms may be more plastic and dependent on physical and social contexts than previously thought. Moreover, the results suggest that location preferences produced through rewarding/reinforcing mechanisms can be viewed from adaptive perspectives to influence future behaviour.