Throat colour reliably signals status in male tree lizards, Urosaurus ornatus

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The use of small patches of colour, called badges, as signals of fighting ability (status signals) across age or sex classes has been well described. Examples of within age- or sex-class status signals are more poorly known. Most populations of adult male tree lizards, Urosaurus ornatus, are polymorphic in throat (dewlap) colour within the same age class; dewlap colour may be orange, yellow, or blue or bicolour combinations of an orange perimeter (background) surrounding a central blue spot that varies in size among individuals from 1 to 55% of the surface area of the unextended dewlap. To test the hypothesis that the size of the central blue spot signals status among males, laboratory contests were staged between pairs of size-matched males for a limiting resource. Contests were staged between males that had dewlaps with the (1) same background colour but different size central blue spots, and (2) same background colour and similar size central blue spots in which one male's dewlap was painted orange and the other male's was painted orange with a large blue centre. In both experiments, encounters were dominated by the male with the larger central blue spot. These results support the hypothesis that the size per se of the central blue spot reliably signals fighting ability among males both within and across age classes. Furthermore, this is the first documented case of an inexpensive (badge) status signal that develops prior to sexual maturity and remains phenotypically unchanged during adult life.