Conserved visual sensitivities across divergent lizard lineages that differ in an ultraviolet sexual signal

Abstract

The sensory drive hypothesis predicts the correlated evolution of signaling traits and sensory perception in differing environments. For visual signals, adaptive divergence in both color signals and visual sensitivities between populations may contribute to reproductive isolation and promote speciation, but this has rarely been tested or shown in terrestrial species. We tested whether opsin protein expression differs between divergent lineages of the tawny dragon (Ctenophorus decresii) that differ in the presence/absence of an ultraviolet sexual signal. We measured the expression of four retinal cone opsin genes (SWS1, SWS2, RH2, and LWS) using droplet digital PCR. We show that gene expression between lineages does not differ significantly, including the UV wavelength sensitive SWS1. We discuss these results in the context of mounting evidence that visual sensitivities are highly conserved in terrestrial systems. Multiple competing requirements may constrain divergence of visual sensitivities in response to sexual signals. Instead, signal contrast could be increased via alternative mechanisms, such as background selection. Our results contribute to a growing understanding of the roles of visual ecology, phylogeny, and behavior on visual system evolution in reptiles.

Variation and heritability of retinal cone ratios in a free‐ranging population of rhesus macaques

“…This method uses the total cone population to estimate the relative abundance of each individual cone (Dong et al. 2019). We then calculated the two cone ratios of interest.…”

“…Gene expression studies are informative about retinal cone populations in vertebrates, including primates (Deeb et al 2000;Neitz et al 2006;Iwanicki et al 2017;Dong et al 2019;Wright et al 2019). Specifically, Deeb et al (2000) have previously demonstrated that the relative expression of mRNA from OPN1LW and OPN1MW opsin genes correlates well with the relative abundance of the L and M cones in the retinas of macaques.…”

“…We calculated the relative abundance of each target by dividing the number of droplets positive for the target opsin gene by the sum of all positive droplets (i.e., L/(S+L+M)). This method uses the total cone population to estimate the relative abundance of each individual cone (Dong et al 2019). We then calculated the two cone ratios of interest.…”

Visible beyond Violet: How Butterflies Manage Ultraviolet

“…The theory of sensory drive claims that signalling systems should evolve so as to optimise the transmission between senders and intended receivers while, if at all possible, reducing visibility to eavesdroppers [ 40 , 76 , 152 ]. Highly directional and iridescent UV reflectance could be an example of such a trade-off.…”