QUINN, V.S.; HEWS, D.K.*: Dermal melanin density explains variation in a phylogenetically labile color signal in Sceloporus lizards: correlational and experimental evidence

We examined the production of a signaling trait, blue abdominal patches, in three Sceloporus lizard species. Sexes and species can differ in the occurrence of the patches. We tested the hypothesis that blue patches require a high density of melanin in the dermis underlying the iridophore layer, and that the mechanism is conserved among Sceloporus expressing the patches. Measurements of relative melanin density using light microscopy images of abdominal skin from Sceloporus undulatus consobrinus, S. virgatus, and S. jarrovii support this hypothesis. Lizards with blue patches (male undulatus, and male and female jarrovii) have more melanin than white abdominal skin from lizards lacking patches (female undulatus, and male and female virgatus). Within the sexually dimorphic undulatus (males blue females white), melanin abundance in blue abdominal skin was higher than melanin in white skin of females removed from the male patch location. In jarrovii (both sexes have blue abdominal patches) and virgatus (neither sex has blue abdominal patches), the pattern of higher melanin density in blue skin was consistent regardless of species or sex. We are quantifying melanin density of blue skin from undulatus females (normally white) that were androgen-manipulated as hatchlings for an experimental test of the melanin hypothesis.