Are ants di- or trichromats? New insights from genome analysis and opsin mRNA expression studies
University of Wuerzburg, Behavioral Physiology and Sociobiology, Germany
Colour vision consisting of an ultraviolet (UV)-blue-green-trichromacy most likely belongs to the basic insect bauplan. Electrophysiological studies in the order Hymenoptera revealed that three photoreceptor types, which are most sensitive to UV, blue and green light respectively, are present in most families. However, one exception to this pattern constitutes the ants (Formicidae), where only UV and green-sensitive photoreceptors have so far been found. In this study we tested the hypothesis that the common ancestor of ants lost its functional blue opsin, i.e. the light-sensitive G-protein coupled receptor in photoreceptor cells, thus leading to dichromacy in ants.
We screened the genomes of three ant species (Acromyrmex echinatior, Camponotus floridanus and Harpegnathos saltator) for opsin genes. In all species we found five genes coding for intact opsins. Phylogenetic analyses revealed that the identified genes are homologous to the four invertebrate-like (UVop, BLop, LWop1, LWop2) and one vertebrate-like (pteropsin) opsins characterized in the honeybee (Fig.1A). Opsin cDNA sequences found in EST libraries from the heads of the three ant species showed that most of the genes are expressed. To test if the blue opsin (BLop) mRNA is actually expressed in the ant’s eye, along with the UV and LW1 opsins, we extracted mRNA from the compound eye of C. floridanus and measured mRNA levels using real-time qPCR. We found clear evidence for the expression of BLop mRNA, although its expression level was much lower compared to UVop and LW1op (Fig. 1B).
This means that ants have not entirely lost the ability to express the blue opsin. Future studies are required to determine if the BLop mRNA is expressed in particular photoreceptors and thus provide the basis for trichromatic colour vision in ants, or if the BLop is co-expressed with one of the other (UV, LW1) opsins in the compound eye.
Figure 1 - (A) Maximum likelihood tree based on amino acid sequences of the five identified opsins from three ant (A. echinatior, C. floridanus and H. saltator) and two bee (Apis mellifera, Bombus terrestris) species. (B) Expression levels of the four invertebrate-like opsins in the compound eye of C. floridanus.
International Conference on Invertebrate Vision, Fjälkinge, Sweden, 1 Aug - 8 Aug, 2013.
Oral presentation preferred
Colour and polarisation vision
(2013). Are ants di- or trichromats? New insights from genome analysis and opsin mRNA expression studies.
International Conference on Invertebrate Vision.
28 Feb 2013;
01 Aug 2013.
Dr. Johannes Spaethe, University of Wuerzburg, Behavioral Physiology and Sociobiology, Wuerzburg, 97074, Germany, email@example.com