Context matters: female aggression and testosterone in a year-round territorial neotropical songbird ( Thryothorus leucotis )

Abstract

Testosterone promotes aggressive behaviour in male vertebrates during the breeding season, but the importance of testosterone in female aggression remains unclear. Testosterone has both beneficial and detrimental effects on behaviour and physiology, prompting the hypothesis that selection favours an association between aggression and testosterone only in certain contexts in which intense or persistent aggression may be beneficial. We tested this hypothesis in a year-round territorial female buff-breasted wrens (Thryothorus leucotis), by exposing free-living females to experimental intrusions in different social (either single female or male, or paired decoys) and seasonal (pre-breeding or breeding) contexts. Females responded more aggressively to intrusions by females and pairs than to males. However, female intrusions elicited stronger responses during pre-breeding, whereas responses to pair intrusions were more intense during breeding. Territorial females had elevated testosterone levels after female intrusions and intermediate levels after pair intrusions during pre-breeding, but the levels of testosterone remained low after these intrusions during breeding. These results demonstrate seasonal differences in circulating testosterone following territorial aggression in female buff-breasted wrens and are suggestive of differences according to social context as well. Context-dependent elevation of testosterone implies that selection acts directly on female vertebrates to shape patterns of testosterone secretion.

Female aggression predicts mode of paternity acquisition in a social lizard

“…The importance of female aggression in shaping social and reproductive parameters linked to large-scale population processes has started to gain increased attention (Sandell & Smith 1997;Gill et al 2007;Sandell 2007;Smith & Blumstein 2008). However, to date, few studies have elucidated patterns of observed consistent individual differences in female aggression, and how this behavioural consistency may impact on an individual's social and reproductive strategies.…”

“…Female aggression, on the other hand, is assumed to be either subtle or inconspicuous and has received relatively little attention (Gill et al 2007). Recent work, however, suggests that female aggression may have important consequences in a number of functional contexts (Dunn & Hannon 1991;Slagsvold & Lifjeld 1994;Rosvall 2008), such as territory acquisition and eviction (e.g.…”

The agonistic adrenal: melatonin elicits female aggression via regulation of adrenal androgens

“…By contrast, in some species aggression is unchanged [3,6,13] or even increased [12,17,18] during the non-breeding season. For example, aggression persists during the non-breeding season in song sparrows, Melospiza melodia morphna [16], and is further elevated in Siberian hamsters, P. sungorus [17,18].…”

“…Numerous studies have demonstrated a positive relationship between gonadal steroids, particularly testosterone (T), and aggression in males and females of many vertebrates, including birds, lizards and mammals (e.g. [3][4][5][6]). Traditionally, these studies have focused on males in reproductive condition, often in laboratory animals such as rats and mice (reviewed in [7]).…”

Corticosterone, testosterone and life-history strategies of birds

“…Average intra-assay coefficient of variation was not determined, but ranges between 2 and 16 per cent in our laboratory for this kind of assay (e.g. Gill et al 2007). Average inter-assay coefficient of variation was 24.6 per cent.…”