Analysis of the opsin repertoire in the tardigrade Hypsibius dujardini provides insights into the evolution of opsin genes in panarthropoda.
Bottom Line: Our opsin phylogeny further suggests that two r-opsins, including an "arthropsin," were present in the last common ancestor of Panarthropoda.Although both r-opsin lineages were retained in Onychophora and Arthropoda, the arthropsin was lost in Tardigrada.The single (most likely visual) r-opsin found in H. dujardini supports the hypothesis of monochromatic vision in the panarthropod ancestor, whereas two duplications of the ancestral panarthropod c-opsin have led to three c-opsins in tardigrades.
Affiliation: Animal Evolution and Development, Institute of Biology, University of Leipzig, Germany email@example.com.Show MeSH
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Mentions: Tardigrades typically possess a pair of simple, ocellus-like eyes (Kristensen 1983; Dewel et al. 1993; Greven 2007)—a situation which is similar to that in onychophorans but different from that in arthropods, which show two types of visual organs: The median ocelli and the compound eyes (fig. 1A–C). Although the onychophoran eyes have been homologized with the median ocelli of arthropods (Mayer 2006), the homology of the tardigrade eyes remains obscure (Greven 2007). Experimental data revealed that tardigrades clearly respond to light (Marcus 1929; Baumann 1961; Ramazzotti and Maucci 1983; Beasley 2001), but beyond this nothing is known about the photoreceptive system in these animals.Fig. 1.—
Affiliation: Animal Evolution and Development, Institute of Biology, University of Leipzig, Germany firstname.lastname@example.org.