Signaling Individual Identity versus Quality: A Model and Case Studies with Ruffs, Queleas, and House Finches

Abstract

We develop an evolutionary model that predicts that characters selected to signal individual identity will have properties differing from those expected for indicator signals of quality. Traits signaling identity should be highly variable, often display polymodal distributions, not be condition dependent (i.e., be cheap to produce and/or maintain), not be associated with fitness differences, exhibit independent assortment of component characters, and often occur as fixed phenotypes with a high degree of genetic determination. We illustrate the existence of traits with precisely these attributes in the ornamental, conspicuously variable, and sexually dimorphic breeding plumages of ruff sandpipers Philomachus pugnax and red-billed queleas Quelea quelea. Although ruffs lek and queleas are monogamous, both species breed in high-density aggregations with high rates of social interactions (e.g., aggression and territory defense). Under these socioecological conditions, individual recognition based on visual cues may be unusually important. In contrast to these species, we also review plumage characteristics in house finches Carpodacus mexicanus, a nonterritorial, dispersed-breeding species in which plumage ornamentation is thought to signal quality. In keeping with expectations for quality signals, house finch plumage is relatively less variable, unimodally distributed, condition dependent, correlated with fitness measures, has positively correlated component characters, and is a plastic, environmentally determined trait. We briefly discuss signals of identity in other animals.

Assessing the potential information content of multicomponent visual signals: a machine learning approach

“…Comparative evidence from other primates, however, indicates that this confirmation and rejection, respectively, are likely to be correct. Interindividual discrimination on the basis of visual information is relatively widespread (reviewed in [8]), especially in species with complex social systems [47].…”

Adaptive evolution of facial colour patterns in Neotropical primates

“…For many social animals, including paper wasps, birds and primates, facial colour patterns provide rich sources of information that are essential for social interactions [3,[7][8][9][10]. In primates, facial cues are used to convey signals about identity, behaviour and condition [4,[11][12][13][14].…”

Cerebral and Behavioural Asymmetries in Animal Social Recognition

“…Quelea males (Quelea quelea), for example, have been shown to distinguish between neighbours and strangers, allowing the former to approach more closely to their nests and avoiding costly conflicts of territorial defence (Dale, 2000). Similarly, ruffs (Philomachus pugnax) are more aggressive with neighbours having experimentally altered plumage, a sign that they do not recognize them as familiar conspecifics (Dale, Lank and Reeve, 2001). In pigeons (Columba livia), social groups are based on monogamous pair bonds between adults, with a clear dominance hierarchy regulating competition for optimal breeding sites.…”