Seasonal Modulation of Testosterone during Breeding of the Rufous-Collared Sparrow (Zonotrichia capensis australis) in Southern Patagonia

Abstract

The roles of testosterone (T) during reproduction are often complex and vary among and within vertebrate taxa and locations, making general hypotheses relating T to breeding behavior and success difficult to integrate. In birds, T is thought to influence degrees of territoriality and associated aggression in males to maximize breeding success. Importantly, most work supporting these ideas has been conducted in the Northern Hemisphere. However, accumulating work on tropical species has shown divergent patterns of T in association with breeding behavior. The compilation of work from northern temperate and tropical species suggests that the function of T in relation to breeding behavior varies across latitude and environmental conditions. We investigate the patterns of T in relation to breeding behavior in a subspecies of the rufous-collared sparrow Zonotrichia capensis australis breeding at high latitude in the Southern Hemisphere (55°S). We then compare the T profiles and breeding behaviors of male Z. c. australis to conspecifics breeding in the tropics and congeners in North America to test the hypothesis that environments with breeding seasons of similar lengths will drive similar patterns of T in relation to breeding behavior. We found that Z. c. australis have high levels of T during the early-breeding periods when territories are being established and low levels of T during the parental phase of breeding, similar to temperate and Arctic birds in the Northern Hemisphere but unlike tropical Zonotrichia capensis costaricensis. In contrast, we found that Z. c. australis also exhibit similar aggressive behaviors in early breeding and midbreeding, unlike many birds in the Northern Hemisphere.

Highly context-specific activation of the HPG axis in the dark-eyed junco and implications for the challenge hypothesis

“…For example, several studies have suggested that playback alone is insufficient to bring about T elevation in circulation (Cramer, 2012; Dufty and Wingfield, 1990; Fokidis et al, 2011; Wingfield and Wada, 1989), and other studies have reported that the use of taxidermic mounts versus live decoys can influence the strength of hormonal responses to STI (Scriba and Goymann, 2008; Scriba and Goymann, 2010). The timecourse of STIs has also varied among studies: Most studies analyze hormonal responses within approximately 30 min of the beginning of the intrusion, but latencies from STI initiation to hormonal sampling have varied from roughly ten minutes to over two hours (Addis et al, 2013; Landys et al, 2007; McGlothlin et al, 2008; Moore et al, 2004a; Van Duyse et al, 2004; Wikelski et al, 1999; Wingfield and Wada, 1989), leaving null results open to the criticism that hormone levels may not have been assessed at the appropriate time.…”