Molecular Evolution of Ultraviolet Visual Opsins and Spectral Tuning of Photoreceptors in Anemonefishes (Amphiprioninae).

Many animals including birds, reptiles, insects, and teleost fishes can see ultraviolet (UV) light (shorter than 400 nm), which has functional importance for foraging and communication. For coral reef fishes, shallow reef environments transmit a broad spectrum of light, rich in UV, driving the evolution of diverse spectral sensitivities. However, the identities and sites of the specific visual genes that underly vision in reef fishes remain elusive and are useful in determining how evolution has tuned vision to suit life on the reef. We investigated the visual systems of 11 anemonefish (Amphiprioninae) species, specifically probing for the molecular pathways that facilitate UV-sensitivity. Searching the genomes of anemonefishes, we identified a total of eight functional opsin genes from all five vertebrate visual opsin subfamilies. We found rare instances of teleost UV-sensitive SWS1 opsin gene duplications that produced two functionally coding paralogs (SWS1α and SWS1ß) and a pseudogene. We also found separate green sensitive RH2A opsin gene duplicates not yet reported in the family Pomacentridae. Transcriptome analysis revealed false clown anemonefish (Amphiprion ocellaris) expressed one rod opsin (RH1) and six cone opsins (SWS1ß, SWS2B, RH2B, RH2A-1, RH2A-2, LWS) in the retina. Fluorescent in situ hybridization highlighted the (co-)expression of SWS1ß with SWS2B in single cones, and either RH2B, RH2A, or RH2A together with LWS in different members of double cone photoreceptors (two single cones fused together). Our study provides the first in-depth characterization of visual opsin genes found in anemonefishes and provides a useful basis for the further study of UV-vision in reef fishes.

Drosophila females receive male substrate-borne signals through specific leg neurons during courtship.

Substrate-borne vibratory signals are thought to be one of the most ancient and taxonomically widespread communication signals among animal species, including Drosophila flies.1-9 During courtship, the male Drosophila abdomen tremulates (as defined in Busnel et al.10) to generate vibrations in the courting substrate.8,9 These vibrations coincide with nearby females becoming immobile, a behavior that facilitates mounting and copulation.8,11-13 It was unknown how the Drosophila female detects these substrate-borne vibratory signals. Here, we confirm that the immobility response of the female to the tremulations is not dependent on any air-borne cue. We show that substrate-borne communication is used by wild Drosophila and that the vibrations propagate through those natural substrates (e.g., fruits) where flies feed and court. We examine transmission of the signals through a variety of substrates and describe how each of these substrates modifies the vibratory signal during propagation and affects the female response. Moreover, we identify the main sensory structures and neurons that receive the vibrations in the female legs, as well as the mechanically gated ion channels Nanchung and Piezo (but not Trpγ) that mediate sensitivity to the vibrations. Together, our results show that Drosophila flies, like many other arthropods, use substrate-borne communication as a natural means of communication, strengthening the idea that this mode of signal transfer is heavily used and reliable in the wild.3,4,7 Our findings also reveal the cellular and molecular mechanisms underlying the vibration-sensing modality necessary for this communication.