Abstract
IntroductionMany studies in behavioural endocrinology attempt to link territorial aggression with testosterone, but the exact relationship between testosterone and territorial behaviour is still unclear and may depend on the ecology of a species. The degree to which testosterone facilitates territorial behaviour is particularly little understood in species that defend territories during breeding and outside the breeding season, when plasma levels of testosterone are low. Here we suggest that species that defend territories in contexts other than reproduction may have lost the direct regulation of territorial behaviour by androgens even during the breeding season. In such species, only those components of breeding territoriality that function simultaneously as sexually selected signals may be under control of sex steroids.ResultsWe investigated black redstarts (Phoenicurus ochruros), a species that shows periods of territoriality within and outside of the breeding season. We treated territorial males with an anti-androgen and an aromatase inhibitor during the breeding season to block both the direct and indirect effects of testosterone. Three and ten days after the treatment, implanted males were challenged with a simulated territorial intrusion. The treatment did not reduce the overall territorial response, but it changed the emphasis of territoriality: experimental males invested more in behaviours addressed directly towards the intruder, whereas placebo-treated males put most effort into their vocal response, a component of territoriality that may be primarily directed towards their mating partner rather than the male opponent.ConclusionsIn combination with previous findings, these data suggest that overall territoriality may be decoupled from testosterone in male black redstarts. However, high levels of testosterone during breeding may facilitate-context dependent changes in song.
Highlights
Many studies in behavioural endocrinology attempt to link territorial aggression with testosterone, but the exact relationship between testosterone and territorial behaviour is still unclear and may depend on the ecology of a species
In combination with previous findings, these data suggest that overall territoriality may be decoupled from testosterone in male black redstarts
In contrast to the expectation that day of simulated territorial intrusions (STI) may have had an effect in Flut/Let-implanted males, it had an effect in placebo-implanted males: placebo- and Flut/Let-implanted males reduced their vocal response to the STI from day 3 to day 10, but the effect was stronger in placebo- compared to Flut/Let-implanted males
Summary
Many studies in behavioural endocrinology attempt to link territorial aggression with testosterone, but the exact relationship between testosterone and territorial behaviour is still unclear and may depend on the ecology of a species. The degree to which testosterone facilitates territorial behaviour is little understood in species that defend territories during breeding and outside the breeding season, when plasma levels of testosterone are low. We suggest that species that defend territories in contexts other than reproduction may have lost the direct regulation of territorial behaviour by androgens even during the breeding season. In songbirds, testosterone and estradiol play an important role in the activation of song during the breeding season [reviewed in 3] Sex steroids, such as testosterone and estradiol, orchestrate physiological, morphological and behavioural changes important for reproduction [e.g. 1]. Few species have been studied in this regard: these studies suggest that testosterone plays a role in the regulation of breeding season territoriality in species that defend territories outside a breeding context (Table 1).
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