Genomic and gene regulatory signatures of cryptozoic adaptation: Loss of blue sensitive photoreceptors through expansion of long wavelength-opsin expression in the red flour beetle Tribolium castaneum

Magdalena Jackowska¹ , Riyue Bao¹ , Zhenyi Liu² , Elizabeth C McDonald³ , Tiffany A Cook³ and Markus Friedrich¹^,4

¹Department of Biological Sciences, Wayne State University, Detroit, MI 48202 USA

²Department of Molecular Biology and Pharmacology, Washington University in St Louis School of Medicine, 3600 Cancer Research Building, St. Louis, MO 63110 USA

³Division of Developmental Biology and Department of Pediatric Ophthalmology, Cincinnati Children's Hospital Medical Center, Cincinnati OH 45229 USA

⁴Department of Anatomy and Cell Biology, Wayne State University School of Medicine, Detroit, MI 48201 USA

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Frontiers in Zoology 2007, 4:24doi:10.1186/1742-9994-4-24


Published:	21 December 2007

Abstract

Background

Recent genome sequence analysis in the red flour beetle Tribolium castaneum indicated that this highly crepuscular animal encodes only two single opsin paralogs: a UV-opsin and a long wavelength (LW)-opsin; however, these animals do not encode a blue (B)-opsin as most other insects. Here, we studied the spatial regulation of the Tribolium single LW- and UV-opsin gene paralogs in comparison to that of the five opsin paralogs in the retina of Drosophila melanogaster.

Results

In situ hybridization analysis reveals that the Tribolium retina, in contrast with other insect retinas, constitutes a homogenous field of ommatidia that have seven LW-opsin expressing photoreceptors and one UV-/LW-opsin co-expressing photoreceptor per eye unit. This pattern is consistent with the loss of photoreceptors sensitive to blue wavelengths. It also identifies Tribolium as the first example of a species in insects that co-expresses two different opsins across the entire retina in violation of the widely observed "one receptor rule" of sensory cells.

Conclusion

Broader studies of opsin evolution in darkling beetles and other coleopteran groups have the potential to pinpoint the permissive and adaptive forces that played a role in the evolution of vision in Tribolium castaneum.