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.
Highlights
When a species exists across habitats of varying physical and struc‐ tural properties, communication systems may adapt to the local environment to optimize the efficacy of signal transmission and in‐ terpretation (Endler, 1992, 1993a). This idea is central to the sensory drive hypothesis, which proposes a correlated divergence in signaling traits, sensory perception, and mate prefer‐ ences (Endler & Basolo, 1998)
We examined visual sensitivities of C. decresii and found no evidence that relative opsin gene expression levels corre‐ spond to divergence between lineages which differ in the presence/ absence of a UV sexual signal
We found differences in expression between the four opsin genes; this was similar to the relative ex‐ pression estimated from transcriptome sequencing in C. decresii wherein SWS1 and long‐wavelength sensitive (LWS) were the lowest and highest expressed genes but small sample sizes limited further statistical inferences
Summary
When a species exists across habitats of varying physical and struc‐ tural properties, communication systems may adapt to the local environment to optimize the efficacy of signal transmission and in‐ terpretation (Endler, 1992, 1993a) This idea is central to the sensory drive hypothesis, which proposes a correlated divergence in signaling traits (e.g., color), sensory perception (e.g., vision), and mate prefer‐ ences (Endler & Basolo, 1998). Evidence for an association between visual signals and color vision achieved by modifying the relative gene expression of cone opsins is currently limited in terrestrial spe‐ cies (Bloch, Morrow, Chang, & Price, 2015; Coyle, Hart, Carleton, & Borgia, 2012; Tseng et al, 2018; Yewers et al, 2015). We predicted that the southern lineage would exhibit higher expression of the UV sensitive SWS1 opsin gene due to the UV reflectance peak found on male throats
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