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J Comp Physiol A (2014) 200:911922 DOI 10.1007/s00359-014-0944-9
REVIEW
How aquatic waterbeetle larvae with small chambered eyes overcome challenges of hunting under water
Annette Stowasser Elke K. Buschbeck
Abstract A particularly unusual visual system exists in the visually guided aquatic predator, the Sunburst Diving Beetle, Thermonectus marmoratus (Coleoptera: Dytiscidae). The question arises: how does this peculiar visual system function? A series of experiments suggests that their principal eyes (E1 and E2) are highly specialized for hunting. These eyes are tubular and have relatively long focal lengths leading to high image magnication. Their retinae are linear, and are divided into distinct green-sensitive distal and UV and polarization-sensitive proximal portions. Each distal retina, moreover, has many tiers of photoreceptors with rhabdomeres the long axis of which are peculiarly oriented perpendicular to the light path. Based on detailed optical investigations, the lenses of these eyes are bifocal and project focused images onto specic retinal tiers. Behavioral experiments suggest that these larvae approach prey within their eyes near-elds, and that they can correctly gauge prey distances even when conventional distance-vision mechanisms are unavailable. In the near-eld of these eyes object distance determines which of the many retinal layers receive the best-focused images. This retinal organization could facilitate an unusual distance-vision mechanism. We here summarize past ndings and discuss how these eyes allow Thermonectus larvae to be such successful predators.
Keywords Invertebrate Stemmata Predator Range-nding Distance vision
Received: 15 August 2014 / Revised: 12 September 2014 / Accepted: 15 September 2014 / Published online: 27 September 2014 Springer-Verlag Berlin Heidelberg 2014
Abbreviations
PR Proximal retina DR Distal retina
Introduction
Aquatic predators such as Thermonectus marmoratus larvae (Coleoptera: Dytiscidae) need good vision and accurate distance perception to successfully hunt their prey.Visually guided hunting is a particular challenge for such small arthropods with chambered eyes. This is because small body size tends to force eyes to be small, and small eyes necessarily have short focal lengths, and hence low spatial resolution. To exacerbate the problem, visibility and contrast in water are often reduced due to the scattering of light (Cronin 2006). In addition, water movements render the environment unstable, confounding motion parallax, which arguably is the most prominent range-nding mechanism in insects (reviewed in Schwind 1989). This mechanism requires the performance of...