The making of an unusual eye: structure, function and development of the highly specialized eyes of diving beetle larvae.
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1
University of Cincinnati, Biological Sciences, United States
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2
Cincinnati Children’s Hospital Medical Center, Division of Pediatric Ophthalmology and Department of Ophthalmology, United States
The principal eyes of the Sunburst Diving Beetle larvae (Thermonectus marmoratus) are among the most bizarre and strangely organized eyes in the animal kingdom. Research in our laboratory has led to the discovery that they have multiple layered retinas, that one of the two main retinas expresses a green opsin whereas the other expresses a UV opsin, that the ultrastructure and physiology of the proximal retina supports polarization sensitivity, that larvae use scanning movements to track their prey, and, perhaps most excitingly, that their visual system operates with truly bifocal lenses. These eyes allow the animals to be extremely efficient visually guided predators, as one larva must capture several hundred mosquito larvae (or comparable prey) before entering metamorphosis. How can diving beetle larvae be such efficient visual predators?
Our previous findings raised two main questions in regards to the functional organization of these eyes: (1) Could the bifocal lenses in combination with the presence of multiple retinas comprise an organization of each eye functioning as “two eyes in one”, with each focal plane being focused on its own retina? (2) Are there any functional differences between the two dominating eyes on each side of the head? To address these questions, we expanded previous optical and anatomical measurements and now present a more complete model of how these eyes could perform several specific visual tasks that relate to visually guided prey capture. Specifically we find that retinal images have a relatively narrow depth of focus. In addition our data suggests that the proximal retina of one of the two principal eyes, Eye 1, is adapted to viewing objects at infinity, whereas the proximal retina of Eye 2 is adapted for objects at striking distance. The green-sensitive distal retinae in both eyes consist of many retinal tiers, and we find that in both eyes the image is focused near the top of these photoreceptor stacks when the object is at infinity. As the object moves closer, the best-focused image passes through the retinal tiers, so that the first few layers are passed when the object moves between infinity and ~7mm. As the object moves closer, the image moves through retinal layers progressively faster, so that it passes the entire stack at an object distance of 2-3mm. Taken together, our data suggests that specific retinal layers in these two eyes could be selectively activated over the relevant range of object distances, raising the possibility that this organization could assist range finding in these animals.
A second recent focus of our investigations has been the question of how specific known features of eye development may be altered in order to achieve the highly unusual eye organization of this animal. Recent evidence has accumulated that similar gene networks underlie the basic invertebrate and vertebrate eye types, and our preliminary data indicates that many common eye development genes are expressed in Thermonectus head tissue. Moreover, based on a morphological study on the embryonic development, as well as expression patterns of known genes, we propose that each of the unusual principal eyes of Thermonectus marmoratus larvae have evolved from an omatidial-like ancestor (Figure 1).
Figure1: Based on preliminary data on eye development, the functionally complex and highly specialized principal eyes of diving beetle larvae (right) may have evolved from an ommatidial like ancestor (left).
Acknowledgements
This work was supported by the National Science Foundation under grants IOS0545978 and IOS1050754 to EKB.
Keywords:
stemmata,
eye development,
Vision,
invertebreat,
insect
Conference:
International Conference on Invertebrate Vision, Fjälkinge, Sweden, 1 Aug - 8 Aug, 2013.
Presentation Type:
Oral presentation preferred
Topic:
Eye design, optics and spatial vision
Citation:
Buschbeck
EK,
Stowasser
A,
Stahl
A and
Cook
T
(2019). The making of an unusual eye: structure, function and development of the highly specialized eyes of diving beetle larvae..
Front. Physiol.
Conference Abstract:
International Conference on Invertebrate Vision.
doi: 10.3389/conf.fphys.2013.25.00018
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Received:
30 May 2013;
Published Online:
09 Dec 2019.
*
Correspondence:
Dr. Elke K Buschbeck, University of Cincinnati, Biological Sciences, Cincinnati, Ohio, 45221-0006, United States, elke.buschbeck@uc.edu