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

Area of Science:

• * Evolutionary biology
• * Molecular biology
• * Zoology

Background:

• * Opsins are crucial light-sensitive proteins for vision and circadian rhythms.
• * Arthropod opsin research is extensive, but opsins in closely related lineages like tardigrades are poorly understood.
• * Tardigrades exhibit multiple opsin duplications, indicating these events are not exclusive to arthropods.

Purpose of the Study:

• * To investigate the diversity, phylogenetic relationships, and ontogenetic expression of opsins in Tardigrada.
• * To determine if tardigrade opsins are co-expressed, a prerequisite for color vision.
• * To understand the evolutionary implications of opsin duplication in non-arthropod protostomes.

Main Methods:

• * Analysis of two tardigrade transcriptomes with deep sequencing coverage.
• * Phylogenetic reconstruction of tardigrade opsin relationships.
• * Investigation of opsin gene expression patterns throughout tardigrade development (ontogeny).

Main Results:

• * Identified multiple opsins in tardigrades, originating from lineage-specific duplications of arthropod opsins.
• * Observed duplications in both rhabdomeric and ciliary opsin types, with clades specific to Heterotardigrada and Eutardigrada.
• * Found that most tardigrade opsins are not co-temporally expressed during development, unlike in color-vision capable animals.

Conclusions:

• * Tardigrades have undergone significant opsin gene duplication events.
• * The lack of co-temporal opsin expression suggests tardigrades likely do not possess color vision.
• * This research provides insights into opsin evolution and function in a key invertebrate lineage.