Date Published: December 31, 2018
Publisher: Public Library of Science
Author(s): Yasmeen R. Erritouni, Beth A. Reinke, Ryan Calsbeek, Michael Sears.
In animals, color signals that convey information about quality are often associated with costs linked to the expression of coloration and may therefore be honest signals of sender quality. Honest indicators are often seen in sexual signals that are used by males to advertise quality to females. Carotenoid and pterin pigments are responsible for yellow, orange, and red coloration in a variety of taxa, but can also serve important roles as antioxidants by reducing free radicals in the body. In this study, we test the effects of a novel full-bodied orange color phenotype of the brown anole, Anolis sagrei, on mate choice, physiology, and survival. We found no evidence that lizards expressing the orange phenotype were preferred by females. Additionally, they did not differ in immune function, running endurance, or maximum sprint speed from lizards that did not express the novel phenotype. Pigment extractions revealed that orange body coloration resulted from pterin pigments and not carotenoids. Visual models suggest that the orange phenotype is less conspicuous to bird predators than the brown phenotype and may provide an adaptive explanation for the persistence of this trait. Given its small, yet positive effect on fitness, we expect the orange color phenotype to increase in frequency in subsequent decades.
Bright, conspicuous color signals that communicate species identity, social status, and individual quality are ubiquitous in animals. For a signal to advertise sender quality, the signal must have some cost tied to its production and maintenance . Costs of signal production come in a variety of forms, such as increased physiological stress or predation risk [2, 3] and maintain “honesty” in the population, preventing the spread of cheaters. This concept is used to explain the evolution of signals that decrease the overall fitness of the sender .
Based on the two measures of female preference for males (ΔFH and ΔTime), females did not show a preference for orange or brown males (Table 1). Females spent a significantly greater amount of time with males who performed more head-bobs than their counterparts (Table 1) but this pattern was not driven by difference in male body coloration. The same pattern did not hold for dewlap flashes statistically accounting for variation in body mass. Females performed more head-bobs at males who performed more dewlap displays and more head-bob displays relative to their male counterparts (Table 1).
Based on the results of this study, orange A. sagrei do not experience a sexually selected advantage attributable to their body coloration. Females did not respond differentially to orange coloration despite the fact that they are predisposed to respond to orange coloration in the dewlap. This may be because the “orange” expressed in the body and the “orange” expressed in the dewlap exhibit very different spectral characteristics (Fig 2). Our data suggest that these colors may be dissimilar when perceived by A. sagrei. Additionally, while there may be costs associated with orange color in A. sagrei, they are unlikely to be related to physiological or immunological function. Taken together, our results provide no evidence that orange coloration outside of the dewlap is an honest signal of sender quality.