Understanding testosterone variation in a tropical lek-breeding bird

Abstract

Male reproductive coalitions, in which males cooperate to attract females, are a rare strategy among vertebrates. While some studies have investigated ultimate aspects of these relationships, little is known about the mechanistic role that hormones play in modulating cooperative behaviours. Here, we examined male testosterone variation in a tropical lekking bird, the wire-tailed manakin (Pipra filicauda), which exhibits cooperative male -male display coalitions. We found that testosterone levels in territorial males were comparable to those of temperate breeding birds, a surprising result given their environmental, social and reproductive dynamics. In addition, social status rather than plumage was a strong predictor of testosterone variation. Territorial males had significantly higher testosterone levels than did two other plumage classes of floater males, who do not hold territories. We hypothesize that testosterone variation plays an important role in the establishment of male dominance hierarchies (competition), while concurrently facilitating stable display partnerships (cooperation).

Variation in song system anatomy and androgen levels does not correspond to song characteristics in a tropical songbird

“…Fourth, male social status in breeding groups is often associated with differences in androgen levels (e.g. DuVal & Goymann, 2011;Ryder, Horton, & Moore, 2011;Soares et al, 2010;Wingfield & Lewis, 1993).…”

Testosterone modulates status-specific patterns of cooperation in a social network

“…In territoryholding males, however, both observational and experimental evidence demonstrate that high 30 testosterone antagonizes cooperation. Moreover, circulating testosterone explains significant documented status-specific differences in circulating testosterone levels (Wingfield et al 1990; Schoech et al 1991;Peters et al 2001;Ryder et al 2011b), including the suppression of 64 androgens in subordinates (Brouwer et al 2009), no study has examined how androgens mediate the dynamics of cooperation and status within a social network. 66…”

“…Dakin and Ryder 2018). Previous work on this system has established that the status classes differ in their circulating testosterone levels, with territory-holders having higher levels than 104 floaters (Ryder et al 2011b), and that cooperation is socially contagious (Dakin and Ryder 2018). 106…”

“…After 166 centrifugation, plasma volume was measured to the nearest 0.25ul and stored in 0.75ml of 100% ethanol (Goymann et al 2007); plasma volumes averaged 38.6uL (SD ± 10.3uL). In the lab, 168 testosterone was double extracted from plasma with dichloromethane (Ryder et al 2011b). We used direct radioimmunoassay to determine the total plasma testosterone concentration (ng/mL), 170 adjusted by extraction efficiency and by the plasma volume of the sample (Eikenaar et al 2011).…”

The Unknown Life of Floaters: The Hidden Face of Sexual Selection

“…These juveniles may routinely end up breeding as they mature (Newton and Rothery, 2001;Sergio et al, 2011;Rivera et al, 2011;Loewenthal et al, 2015) and hence are only temporarily excluded from the breeding fraction of the population. Moreover, being juvenile floaters may be the general pattern for most individuals and not a characteristic of a particular fraction (Delgado et al, 2009;Ryder et al, 2011). Thus, excluding such floaters from analyses may not seriously affect an evaluation of the strength of sexual selection.…”