Ridley Et Al. @bullet Is Information from Both Quality Signaling and Social Recognition Really Redundant? a Comment on Sheehan and Bergman Understanding Antagonism: a Comment on Sheehan and Bergman

Indeed, they formalized this idea into their “prediction 2”: small stable societies should lack quality signals. Though they point out that robust phylogenetic comparative studies that directly address this prediction have not been conducted, they cite Bridge et al.’s (2008) study on Aphelocoma scrub-jays as a source of indirect support. In this study, sexand age-related color differences were not associated with cooperative breeding. A problem with this argument, however, is that using the presence of sexor age-dependent plumage coloration as a proxy for signaling is tenuous. Sexual dichromatism, for instance, could be reduced in cooperative breeders either because 1) quality signaling is less important in such systems (as argued by Sheehan and Bergman) or 2) quality signaling is still important in such systems and both males and females have evolved it (counter to Sheehan and Bergman). We can discriminate between these 2 possibilities. Sheehan and Bergman’s hypothesis predicts that reduced sexual dichromatism in cooperative breeders arises through males evolving less elaborate ornamentation. The alternative predicts that reduced sexual dichromatism in cooperative breeders evolves through females getting more elaborate. Rubenstein and Lovette (2009) have tested this in the African starlings and their results were clear: sexual dichromatism was reduced in cooperative breeders (as in the scrub-jays) and this was the outcome of females evolving increased ornamentation in such species. Rubenstein and Lovette (2009) interpret their results as evidence for “increased selection on females for traits that increase access to reproductive opportunities, other resources, or higher social status.” Under Sheehan and Bergman’s framework, such traits would not be necessary because social recognition in these small stable societies should suffice.