Hormones and honest signals: males with larger ornaments elevate testosterone more when challenged

Abstract

When male investment in mating varies with quality, reliable sexual signals may evolve. In many songbirds, testosterone mediates mating investment, suggesting that signals should be linked to testosterone production. However, because testosterone may change rapidly during behaviour such as territorial aggression and courtship, efforts to establish such a relationship have proved challenging. In a population of dark‐eyed juncos, we measured individual variation in the production of short‐term testosterone increases by injecting gonadotropin‐releasing hormone (GnRH). We found a positive correlation between the magnitude of these increases and the size of a plumage ornament (‘tail white’) previously shown to be important for female choice and male–male competition. We then measured naturally elevated testosterone levels produced during male–male competition and found that they covaried with those induced by GnRH. We suggest that the association between tail white and testosterone increases may allow conspecifics to assess potential mates and competitors reliably using tail white.

Up to the challenge? Hormonal and behavioral responses of free-ranging male Cassin's Sparrows, Peucaea cassinii, to conspecific song playback

“…Exposure to STI, indeed, increases plasma T in territorial males of some species (McGlothlin et al, 2008;Wingfield and Wada, 1989;Wingfield and Hahn, 1994), but not in others Goymann, 2009;Landys et al, 2007;Lynn et al, 2007Lynn et al, , 2008. Several factors may account for these differences.…”

Mates of Competitive Females: The Relationships between Female Aggression, Mate Quality, and Parental Care

“…Male ornamentation was estimated by quantifying individual differences in the amount tail-white each male displayed. Tail-white is important in courtship and aggressive interactions, and more tail-white is attractive to females [43,[46][47][48]. Further, previous research in this population has shown that male body size is positively correlated with tail-white and that large males with more tailwhite sired offspring with more females [43].…”

Neural sensitivity to sex steroids predicts individual differences in aggression: implications for behavioural evolution

“…(a) Behavioural quantification and tissue collection All subjects were captured during the breeding season (1 May-5 June 2010) in the area surrounding Mountain Lake Biological Station in Virginia, USA (37822 0 N, 80832 0 W), immediately after a short (6 min) simulated territorial intrusion (modified from [10,12]). All females were in the incubation stage.…”