title: Spectral sensitivity of cone photoreceptors and opsin expression in two colour-divergent lineages of the lizard Ctenophorus decresii.
abstract: Intraspecific differences in sensory perception are rarely reported but may occur when a species range extends across varying sensory environments, or there is coevolution between the sensory system and a varying signal. Examples in colour vision and colour signals are rare in terrestrial systems. The tawny dragon lizard Ctenophorus decresii is a promising candidate for such intraspecific variation, because the species comprises two geographically and genetically distinct lineages in which throat colour (a social signal used in intra- and inter-specific interactions) is locally adapted to the habitat and differs between lineages. Male lizards from the southern lineage have UV-blue throats, whereas males from the northern lineage are polymorphic with four discrete throat colours that all show minimal UV reflectance. Here, we determine the cone photoreceptor spectral sensitivities and opsin expression of the two lineages, to test whether they differ, particularly in the UV wavelengths. Using microspectrophotometry on retinal cone photoreceptors, we identified a long-wavelength-sensitive (LWS) visual pigment, a 'short' and 'long' medium-wavelength-sensitive (MWS) pigment and a short-wavelength-sensitive (SWS) pigment, all of which did not differ in λmax between lineages. Through transcriptome analysis of opsin genes we found that both lineages express four cone opsin genes, including the SWS1 opsin with peak sensitivity in the UV range, and that amino acid sequences did not differ between lineages with the exception of a single leucine to valine substitution in the RH2 opsin. Counts of yellow and transparent oil droplets associated with LWS+MWS and SWS+UVS cones, respectively, showed no difference in relative cone proportions between lineages. Therefore, contrary to predictions, we find no evidence of differences between lineages in single cone photoreceptor spectral sensitivity or opsin expression. However, we confirm the presence of four single cone classes, suggesting tetrachromacy in C. decresii, and we also provide the first evidence of UV sensitivity in agamid lizards.
authors.affiliation: The School of BioSciences, The University of Melbourne, Victoria 3010, Australia myewers@gmail.com.
authors.forename: Madeleine S
authors.initials: MS
authors.lastname: Yewers
authors.affiliation: The School of BioSciences, The University of Melbourne, Victoria 3010, Australia Sciences Department, Museum Victoria, Carlton Gardens 3053, Australia.
authors.forename: Claire A
authors.initials: CA
authors.lastname: McLean
authors.affiliation: Sciences Department, Museum Victoria, Carlton Gardens 3053, Australia.
authors.forename: Adnan
authors.initials: A
authors.lastname: Moussalli
authors.affiliation: The School of BioSciences, The University of Melbourne, Victoria 3010, Australia.
authors.forename: Devi
authors.initials: D
authors.lastname: Stuart-Fox
authors.affiliation: Centre for Integrative Ecology, School of Life and Environmental Sciences, Deakin University, Geelong, Victoria 3217, Australia.
authors.forename: Andrew T D
authors.initials: AT
authors.lastname: Bennett
authors.affiliation: Centre for Integrative Ecology, School of Life and Environmental Sciences, Deakin University, Geelong, Victoria 3217, Australia.
authors.forename: Ben
authors.initials: B
authors.lastname: Knott
mesh_terms: D000818:Animals; D003116:Color; D008116:Lizards / Q000502:physiology*; D008297:Male; D055355:Opsins / Q000235:genetics / Q000378:metabolism*; D010858:Pigmentation; D011110:Polymorphism, Genetic; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism*; D059467:Transcriptome; D014466:Ultraviolet Rays
chemical_list: D055355:Opsins
keywords: Agamidae; Ctenophorus decresii; Microspectrophotometry; Opsin; Visual pigment