Manipulating the appearance of a badge of status causes changes in true badge expression

Abstract

Signals of dominance and fighting ability (i.e. status signals) are found in a wide range of taxa and are used to settle disputes between competitive rivals. Most previous research has considered status-signal phenotype as an attribute of the individual; however, it is more likely that signal expression is an emergent property that also incorporates aspects of the social environment. Furthermore, because an individual's signal phenotype is likely to influence its social interactions, the relationships between status signals, social environment and individual quality are probably much more complex than previously appreciated. Here, we explore the dynamic relationship between social interactions and signal expression in a previously undescribed status signal, the frontal shield of the pukeko (Porphyrio porphyrio melanotus: Aves). We demonstrate that frontal shield size is a strong predictor of dominance status within social groups, even after controlling for potentially confounding variables. Then, we evaluate the relationship between social interactions and signal expression by testing whether manipulating apparent shield size influences (i) dominance interactions and (ii) future signal expression. By showing that decreasing apparent shield size causes both an increase in the amount of aggression received and a decrease in an individual's true shield size, we provide the first evidence of dynamic feedback between signal expression and social interactions. Our study provides important insight into the role of receiver-dependent (i.e. social) costs in maintaining signal honesty and demonstrates a unique approach to studying status signalling applicable to future studies on dynamic morphological signals.

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.…”

Sex At Second Sight. Pitfalls of Sexing Water RailsRallus aquaticusand Spotted CrakesPorzana Porzanausing Morphology and Molecular Techniques

“…Mougeot et al, 2009). In the purple swamphen, shield size (determined by culmen length and shield width) is likely to be sexually determined and can be modified according to social status or season (Craig et al, 1980;Dey et al, 2014). The observed age differences in size suggest that the immatures can still grow slightly until they reach the adult size, as evidenced by some of the study characters in the sample of birds captured as immatures and recaptured as adults (see table S3).…”

“…however, this relationship was not met for culmen and shield width, which were bigger for adult females than immature males. These two characters are indicative of shield surface area, and the size of this ornament probably reflects reproductive and/or social status in P. p. melanotus (Craig et al, 1980;Dey et al, 2012Dey et al, , 2014. Shield size is testosterone-dependent in several species of the family Rallidae (Gullion, 1951;Eens et al, 2000) and may function as an indicator of individual quality, as found for many testosterone-dependent traits in birds (e.g.…”

Determinants of making success in female Tree Swallows (Tachycineta Bicolor)

“…Recently, several empirical studies and reviews have highlighted the importance of social feedback from potential mates and conspecifics about ornament quality on the physiology or behaviour of signallers (e.g., Safran et al, 2008;Rubenstein and Hauber, 2008;Vitousek et al, 2013;Dey et al, 2014;Vitousek et al, 2014b). hormonal data to support such a mechanism, female barn swallows with elevated levels of corticosterone prior to incubation were more likely to abandon their nesting attempt (Vitousek et al, 2014a) and experimentally elevating corticosterone of female tree swallows resulted in lower nestling survival (Ouyang et al, 2015).…”

“…Recently, it also has been suggested that social and physiological costs may act in concert to maintain signal honesty (Tibbetts, 2014;Vitousek et al, 2014b). For example, painting the shield of male pukekos (Porphyrio porphyrio) to reduce the quality of signal displayed resulted in increased aggression from conspecifics and a dynamic reduction in the natural size of the shield following manipulation compared to controls (Dey et al, 2014).…”