Identification of putative circadian and phototransduction orthologs in the western predatory mite (Metaseiulus occidentalis)

The recent sequencing of the Metaseiulus occidentalis genome and transcriptome allow the use of bioinformatic insights to direct research into interesting aspects of the biology of this beneficial predator. This mite has no known visual structure but has a strong response to light and exhibits phototaxis. In this study, we identify putative members of both the circadian and phototransduction pathways by comparison to orthologs in other species. After bioinformatic identification of circadian orthologs including clock, cycle, period, timeless, vrille, and clockwork orange, relative expression of these putative genes was examined by quantitative PCR. Periodic oviposition behaviors that adjusted under varied light:dark regimens also indicate circadian cycling. Putative orthologs were then identified for the major phototransduction cascade genes. Two opsin-like transcripts but no cryptochromes were identified. Phylogenetic analysis of these putative opsins clustered them with those most frequently found in non-visual structures in deep brain tissue. This indicates that M. occidentalis senses light directly through the cuticle rather than through a traditional visual structure.