Vision

Background:

With auditory organs lacking and antennae reduced, dragonflies possess noticeably large compound eyes. Their visual environments are subdivided into three categories:

Aquatic light condition for larval eyes
Short wavelength (SW) skewed aerial light condition for the dorsal region of adult eyes
Long wavelength (LW) skewed environmental light condition for the ventral region of adult eyes

Theoretical approaches have predicted that between four and seven photoreceptor types are all that is needed to accurately encode the colors of the visible spectrum (Thoen et. al, 2014); however, new knowledge about dragonfly vision has grouped dragonflies into alternative opsin category.

Recent Study:

A group of scientists reported an extreme diversity of opsin genes in dragonflies. The RNA sequencing of adult and larval eyes of 12 dragonfly species, representing 11 families, revealed as many as 15–33 opsin genes (Futahashi et. al, 2015). The expression patterns of the opsin genes showed noticeable differences between the adult and larval stage, and also between the dorsal and ventral region of adult compound eyes.

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Shown in Figure 1B, the dorsal region of an adult compound eye is structurally different from the ventral region. Specifically, the dorsal ommatidia have larger surfaces and orange screening pigment, whereas the ventral ommatidia have smaller surfaces and dark purple screening pigment (Fig. 2 C-D) (Futahashi et. al, 2015). These dissimilarities may explain functional differences; electroretinographic recording of spectral sensitivity showed that the dorsal eye region is sensitive to a SW range with a peak at 360 nm, whereas the ventral eye region is sensitive to a wider wavelength range with two peaks at 360 nm and 520 nm (Fig. 2) (Futahashi et. al, 2015).

Figure 1. Anatomy and spectral sensitivity of adult dragonfly compound eye. (B) Unstained dorso-ventral section of a compound eye. (C) Unstained dorsal region of a compound eye (D) Unstained ventral region of a compound eye (Roy et. al, 2015).

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RNA sequencing depicted in figure 3 further illustrates characteristics of dragonfly eyes:

In contrast to many SW and LW genes expressed in adults, only one SW gene and several LW genes are expressed in larvae, reflecting less visual dependence and also LW-skewed light conditions for their lifestyle under water.
Many SW genes and few LW genes are expressed in the dorsal region of adult compound eyes, presumably for processing SW-skewed light from the sky.
Few SW genes and many LW genes are expressed in the ventral regionof adult compound eyes, probably for perceiving terrestrial objects.
The dorsal and the ventral regions of dragonfly eyes are differentiated not only morphologically and physiologically, but also biochemically in terms of expression of the diverse visual opsin genes.

Figure 2. Spectral sensitivity of the dorsal and ventral regions of adult eyes measured by electroretinography (Futahashi et. al, 2015).

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In addition to the S. frequens and O. albistylum RNA sequencing data from Figure 3, the scientists found that the total number of opsin genes varied considerably among the other 10 dragonfly species. All of the species consistently possessed the four nonvisual opsin genes and the UV opsin gene as single-copies; however, the number of SW opsin genes ranged from 1 to 8 and the number of LW opsin genes from 8 to 21 (Futahashi, et. al, 2015).

These findings suggest that the stage- and region-specific expressions of the opsin genes underlie the behavior, ecology, and adaptation of dragonflies.

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Figure 3. Expression levels of 20 opsin genes in adult and larval visual organs of S. frequens and O. albistylum. (A–D) Nonvisual opsin genes. (E) Visual opsin gene of UV type. (F–J) Visual opsin genes of SW type. (K–T) Visual opsin genes of LW type. D, dorsal region of adult eyes; L, larval whole head; O, adult head region containing ocelli; V, ventral region of adult eyes. The numbers indicate FPKM values (Futahashi et. al, 2015).

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References:

Futahashi, R., Ryouka, K., Michiyo, K., Kazutoshi, Y., Shunsuke, Y., Kentaro, A., and Takema, F. (2015). Extraordinary Diversity of Visual Opsin Genes in Dragonflies.

Proceedings of the National Academy of Sciences Proc Natl Acad Sci USA, 112 (11).

Thoen, H. H., How, M. J., Chiou, T. H., Marshall, J. (2014). A Different Form of Color Vision in Mantis Shrimp. Science. 343:411-413. See also Nature News.

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