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The peculiar visual brain of the split-eyed whirligig beetle Dineutus sublineatus

Chan Lin1, 2* and Nicholas J. Strausfeld2, 3
  • 1 University of Arizona, Graduate Interdisciplinary Program in Entomology & Insect Science, United States
  • 2 University of Arizona, Center for Insect Science, United States
  • 3 University of Arizona, Department of Neuroscience, United States

Whirligig beetles (Coleoptera: Gyrinidae) are aquatic insects living on the water surface. They are equipped with two separate pairs of compound eyes, an upper pair viewing above the water and a lower pair viewing downwards beneath the water line. Little is known about how their optic lobes serve the split eyes. Using reduced silver-staining, immunolabeling and fluorescent tracer injections, we found that their elaborate optic lobes are split into two halves: separated upper and lower laminas; upper and lower medullas; and a bilobed partially split lobula. Visual relay neurons from the upper medulla send axons to the central brain where they provide the exclusive afferent supply to both ipsilateral and contralateral calyces of the paired mushroom bodies. The whirligig beetle is the only insect species so far found to be so equipped [1].
Lobula plate neuropil, which in other insects plays a major role in mediating stabilized flight, is found only in conjunction with the lower lobe of the lobula. Investigations of the larval visual system reveal a precious lobula plate that is supplied by three larval laminas serving the three dorsally located stemmata (single-lens larval eyes), which are adjacent to the developing upper compound eye [2]. Because the whirligig larvae are subaquatic ambush predators, it is theorized that the precocious development of a lobula plate may be employed for detecting movement by potential prey items, as has been reported previously from observations of larval tiger beetles (Cicindela) that are also ambush predators [3, 4]. In D. sublineatus, the precocious lobula plate appears to degenerate during pupal metamorphosis and, as a result, the adult whirligig beetle lacks the upper lobula plate. Other adult optic neuropils, including the lamina, medulla and lobula, begin developing alongside the larval optic neuropils as early as the 3rd instar larval stage. How this early development of adult neuropils contributes to the split optic lobes and how a new lower lobula plate is developed during pupal metamorphosis are presently under investigation. The unique organization and development scheme of the whirligig beetle’s optic lobes suggest distinct functional differences between the upper and the lower compound eyes.

Acknowledgements

The study was supported by the University of Arizona Regents’ Fund, the Air Force Office of Scientific Research (AFOSR FA95501010299) (to NJS), and stipends from the Taiwan Government Scholarship for Study Abroad and the University of Arizona’s Center for Insect Science (to CL).

References

1. Lin, C. and Strausfeld, N. J. 2012. Visual inputs to the mushroom body calyces of the whirligig beetle Dineutus sublineatus: Modality switching in an insect. J. Comp. Neurol. 520:2562-2574.
2. Lin, C. and Strausfeld, N. J. 2013. A precocious adult visual center in the larva defines the unique optic lobe of the split-eyed whirligig beetle Dineutus sublineatus. Front. Zool. 10:7.
3. Okamura, J. and Toh, Y. 2004. Morphological and physiological identification of medulla interneurons in the visual system of the tiger beetle larva. J. Comp. Physiol. A. 190:449-468.
4. Okamura, J. and Toh, Y. 2001 Responses of medulla neurons to illumination and movement stimuli in the tiger beetle larvae. J. Comp. Physiol. A. 187:713-725.

Keywords: Gyrinidae, Neuroanatomy, Vision, optic lobe, stemmata, motion detection

Conference: International Conference on Invertebrate Vision, Fjälkinge, Sweden, 1 Aug - 8 Aug, 2013.

Presentation Type: Poster presentation preferred

Topic: Development and evolution

Citation: Lin C and Strausfeld NJ (2019). The peculiar visual brain of the split-eyed whirligig beetle Dineutus sublineatus. Front. Physiol. Conference Abstract: International Conference on Invertebrate Vision. doi: 10.3389/conf.fphys.2013.25.00012

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Received: 23 Feb 2013; Published Online: 09 Dec 2019.

* Correspondence: Mr. Chan Lin, University of Arizona, Graduate Interdisciplinary Program in Entomology & Insect Science, Tucson, Arizona, 85721, United States, linch@si.edu