New Tardigrade Opsins and Differential Expression Analyses Show Ontogenic Variation in Light Perception

James F Fleming, Davide Pisani, Kazuharu Arakawa

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Abstract

Opsins are light-sensitive proteins involved in many photoreceptive processes, including, but not limited to, vision and regulation of circadian rhythms. Arthropod (e.g. insects, spiders, centipedes and crabs) opsins have been extensively researched, but the relationships and function of opsins found in lineages that are evolutionarily closely-related to the arthropods remains unclear. Multiple, independent, opsin duplications are known in Tardigrada (the water bears), evidencing that protostome opsin duplications are not limited to the Arthropoda. However, the relationships, function and expression of these new opsins are still unknown. Here, we use two tardigrade transcriptomes with deep coverage to greatly expand our knowledge of the diversity of tardigrade opsins. We reconstruct the phylogenetic relationships of the tardigrade opsins and investigate their ontogenetic expression. We found that while tardigrades have multiple opsins that evolved from lineage-specific duplications of well-understood arthropod opsins, their expression levels change during ontogeny such that most of these opsins are not co-temporally expressed. Co-temporal expression of multiple opsins underpins colour vision in Arthropoda and Vertebrata. Our results clearly show duplications of both rhabdomeric and ciliary opsins within Tardigrada, forming clades specific to both the Heterotardigrada and Eutardigrada in addition to multiple independent duplications within genera. However, lack of co-temporal, ontogenetic, expression suggests that while tardigrades possess multiple opsins, they are unlikely to be able to distinguish colour.

Original languageEnglish
Article numberevab164
Number of pages10
JournalGenome Biology and Evolution
Volume13
Issue number8
Early online date13 Jul 2021
DOIs
Publication statusPublished - 3 Aug 2021

Bibliographical note

Publisher Copyright:
© The Author(s) 2021. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.

Keywords

  • Tardigrada
  • opsin
  • phylogeny
  • transcriptomics
  • Ecdysozoa

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