Figure 4.

Detecting signatures of natural selection in the evolution of sensory receptors. (a) Selective sweep for the rapidly increased frequency of a black water–adapted blue-light-sensitive opsin (SWS2) variant in sticklebacks, which colonized dark water habitats after glaciation around 12,000 years ago. The black water–adapted sticklebacks were transplanted to a clear water habitat, and after 19 years, the alternate SWS2 clear water–adapted variant increased, consistent with a transient reversed selective sweep. (b) Archaic admixture into eastern gorillas includes adaptive introgression (adaptive transfer of variation between species through gene flow) of a taste receptor TAS2R14 variant. Since gorillas from eastern populations have more herbaceous diets than the frugivorous western gorillas, this introgression event likely shaped the adaptive perception of bitter taste in eastern gorillas. (c) TRPA1 channels underlie infrared perception in pit-bearing snakes. TRPA1 channels of pit-bearing snakes show accelerated rates of adaptive evolution compared to TRPA1 sequences of non-pit-bearing snakes. (d) Cephalopod CRs evolved from ancestral acetylcholine receptors. Key amino acid sites in the ligand-binding pocket of octopus CRs are under strong diversifying selection mediating the detection of hydrophobic molecules for contact-dependent aquatic chemosensation, in contrast to the ancestral detection of small polar neurotransmitters. Abbreviations: CRs, chemotactile receptors; LRT, likelihood ratio test. Panel a adapted from Marques et al. (2017) (CC BY 4.0). Panel b adapted from Pawar et al. (2023) (CC BY 4.0). Panel c adapted from Geng et al. (2011) (CC BY 4.0). Panel d adapted from Allard et al. (2023c). Illustrations of animals adapted from images created with BioRender.com.