Dynamic Status Signal Reflects Outcome of Social Interactions, but Not Energetic Stress

Abstract

Social defeat induces stress-responses in a wide array of vertebrates and can generate winner-loser effects. Dynamic condition-dependent signaling systems that reflect preparation for subsequent agonistic interactions, and thereby mediate winner-loser effects, should be more sensitive to competitive history than to non-social sources of stress. Bill color of female American goldfinches (Spinus tristus) is a dynamic condition-dependent ornament that functions as a signal of competitive status and mediates intrasexual agonistic social interactions. We tested the "social experience signaling hypothesis" in female goldfinches by (1) manipulating a non-social energetic stressor by experimentally elevating flight costs via wing-clipping in free-ranging birds, and (2) manipulating social experience by staging competitive interactions among captive birds. Bill color change did not differ between wing clipped and non-clipped females, even though stress-response, as measured by the heterophil to lymphocyte (H:L) ratio, increased significantly in clipped females relative to unclipped females. In contrast, winners and losers in the social experience experiment differed significantly in the degree and direction of bill color change following social contests, with bill color increasing in winners and decreasing in losers. These results suggest that dynamic bill color of female American goldfinches signals recent social history, but is less sensitive to some stressors stemming from non-social sources, and thereby suggest that signals can evolve sensitivity to specific types of processes relevant to the context in which they are used.

Evolution of female coloration: What have we learned from birds in general and blue tits in particular

“…Research in American goldfinches (Spinus tristis) found evidence for the badge-of-status hypothesis: in females, bill coloration was not affected when flying capacity was experimentally impaired. However, it was impacted when social costs were experimentally increased (i.e., artificially creating winners and losers during social interactions leads to respectively increase bill coloration in winners and decrease coloration in loser: Tarvin et al, 2016a). A comparative study found a similar result: carotenoid-based bill coloration seemed to be more correlated with indices of sociality (sociality over the winter, coloniality) than with indices of sexual selection .…”

The role of bare parts in avian signaling

“…By contrast, bill color mediates dominance interactions among female, but not male, American Goldfinches (Murphy et al 2009(Murphy et al , 2014. Bill color not only shapes the outcome of these interactions but responds to it, with color increasing in winners and decreasing in losers (Tarvin et al 2016). Additionally, it appears that social interactions could possibly have such a strong influence on bare-part color that it obscures relationships with condition.…”

“…Some degree of bare-part color is often found in both sexes. Despite clear evidence that females display condition dependence in bare parts (Gladbach et al 2010, Kelly et al 2012, Rosenthal et al 2012, Doutrelant et al 2013 and use them for signaling (Nolan et al 2010, Dey et al 2014, Tarvin et al 2016, there has been little study of female bare parts in relation to those of males. Females experience intrasexual competition largely for high-quality mates (Rosvall 2011), and their bare parts can play an important role in competitive interactions (Murphy et al 2009) and male mate choice (Torres and Velando 2005, Cornwallis and Birkhead 2007a.…”

Male Red-backed Fairywrens appear to enhance a plumage-based signal via adventitious molt

“…Despite clear evidence that females display condition dependence in bare parts (Gladbach et al 2010, Kelly et al 2012, Rosenthal et al 2012, Doutrelant et al 2013 and use them for signaling (Nolan et al 2010, Dey et al 2014, Tarvin et al 2016, there has been little study of female bare parts in relation to those of males. Females experience intrasexual competition largely for high-quality mates (Rosvall 2011), and their bare parts can play an important role in competitive interactions (Murphy et al 2009) and male mate choice (Torres and Velando 2005, Cornwallis and Birkhead 2007a.…”