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

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 depe...

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Bibliographic Details
Published in:The American naturalist 2001-07, Vol.158 (1), p.75-86
Main Authors: Dale, James, Lank, David B., Reeve, Hudson Kern
Format: Article
Language:English
Subjects:
Breeding
Carpodacus mexicanus
Colors
Eggs
Finches
Frequency distribution
Male animals
Mating behavior
Phenotypic traits
Philomachus pugnax
Plumage
Quelea quelea
Ruffs
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Summary: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 sandpipersPhilomachus pugnaxand red‐billed queleasQuelea 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 finchesCarpodacus 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.
ISSN:0003-0147
1537-5323
DOI:10.1086/320861