Morphological and optical properties of the corneal lens and retinal structure in the posterior large stemma of the tiger beetle larva

Journal of Experimental Biology

2011

SUMMARYThe principal eyes of sunburst diving beetle, Thermonectus marmoratus, larvae are among the most unusual eyes in the animal kingdom. They are composed of long tubes connecting bifocal lenses with two retinas: a distal retina situated a few hundred micrometers behind the lens, and a proximal retina that is situated directly beneath. A recent molecular study on first instar larvae suggests that the distal retina expresses a long-wavelength-sensitive opsin (TmLW), whereas the proximal retina predominantly expresses an ultraviolet-sensitive opsin (TmUV II). Using cloning and in situ hybridization we here confirm that this opsin distribution is, for the most part, maintained in third instar larvae (with the exception of the TmUV I that is weakly expressed only in proximal retinas of first instar larvae). We furthermore use intracellular electrophysiological recordings and neurobiotin injections to determine the spectral sensitivity of individual photoreceptor cells. We find that photoreceptors of the proximal retina have a sensitivity curve that peaks at 374-375nm. The shape of the curve is consistent with the predicted absorbance of a singleopsin template. The spectral response of photoreceptors from the distal retina confirms their maximum sensitivity to green light with the dominant -peak between 520 and 540nm, and the secondary -peak between 340 and 360nm. These physiological measurements support molecular predictions and represent important steps towards understanding the functional organization of the unusual stemmata of T. marmoratus larvae.

Section: Introductionmentioning

confidence: 99%

Spectral sensitivity of the principal eyes of sunburst diving beetle, Thermonectus marmoratus (Coleoptera: Dytiscidae), larvae

Maksimovic

Layne

Journal of Experimental Biology

2011

“…This sheet of retinula cells forms a cupshaped, extended retina comprising 4,000 to 5,000 cells in the two largest stemmata (Toh and Mizutani 1994a). Optical and physiological measurements show that these eyes are indeed image-forming (Mizutani and Toh 1995;Toh and Okamura 2007). This renders the overall functional organization of each stemma more similar to our eyes than to the adult insect compound eye.…”

Section: Remodeling Of Larval Eyesmentioning

confidence: 90%

Evolution of Insect Eyes: Tales of Ancient Heritage, Deconstruction, Reconstruction, Remodeling, and Recycling

Friedrich

2008

Evo Edu Outreach

The visual organs of insects are known for their impressive evolutionary conservation. Compound eyes built from ommatidia with four cone cells are now accepted to date back to the last common ancestor of insects and crustaceans. In species as different as fruit flies and tadpole shrimps, the stepwise cellular patterning steps of the early compound eye exhibit detailed similarities implying 500 million years of developmental conservation. Strikingly, there is also a cryptic diversity of insect visual organs, which gives proof to evolution's versatility in molding even the most tenacious structures into something new. We explore this fascinating aspect in regard to the structure and function of a variety of different insect eyes. This includes work on the unique compound-single-chamber combination eye of twistedwinged insects and the bizarre evolutionary trajectories of specialized larval eyes in endopterygote insects.

“…4A) (MeyerRochow, 1974) and tiger beetles (Fig. 4B) (Toh and Okamura, 2007), which are examples of sophisticated image-forming stemmata. The low F-number organization (which in both these animals is around 1) means that most of the light is not caught by the light-guiding ability of the photoreceptors and thus would not be guided efficiently to subsequent tiers.…”

Section: Reduced Stemmata and General Considerations For The Evolutiomentioning

confidence: 99%

“…For example, the principal stemmata of Chaoborus, which are fused structures of three ancestral (Paulus, 1986), (C) Cicindela chinensis after Toh and Okamura (Toh and Okamura, 2007) and (D) Thermonectus marmoratus after Mandapaka et al (Mandapaka et al, 2006). ommatidia, have many rhabdomeres that are organized in a single tier (Melzer and Paulus, 1991).…”

Section: Advanced Image Resolution Through the Fusion Of Ommatidial Umentioning

confidence: 99%

“…4B) is characterized by a biconvex lens that is 400-500 μm in diameter, and focuses light on to a single layer of 4000-5000 photoreceptor cells (Toh and Mizutani, 1994). In contrast to the sawfly example, the retinal ultrastructure (Toh and Okamura, 2007) is not reminiscent of compound eyes with clustered photoreceptors. Based on this organization, and as the six stemmata typical for Coleoptera larvae are accounted for, it is likely that this eye evolved from a single ancestral unit rather than from the fusion of an equivalent compound eye area.…”

Section: Advanced Image Resolution Through the Expansion Of Individuamentioning

confidence: 99%

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Escaping compound eye ancestry: the evolution of single-chamber eyes in holometabolous larvae

Journal of Experimental Biology

2014

Stemmata, the eyes of holometabolous insect larvae, have gained little attention, even though they exhibit remarkably different optical solutions, ranging from compound eyes with upright images, to sophisticated single-chamber eyes with inverted images. Such optical differences raise the question of how major transitions may have occurred. Stemmata evolved from compound eye ancestry, and optical differences are apparent even in some of the simplest systems that share strong cellular homology with adult ommatidia. The transition to sophisticated single-chamber eyes occurred many times independently, and in at least two different ways: through the fusion of many ommatidia [as in the sawfly (Hymenoptera)], and through the expansion of single ommatidia [as in tiger beetles (Coleoptera), antlions (Neuroptera) and dobsonflies (Megaloptera)]. Although ommatidia-like units frequently have multiple photoreceptor layers (tiers), sophisticated image-forming stemmata tend to only have one photoreceptor tier, presumably a consequence of the lens only being able to efficiently focus light on to one photoreceptor layer. An interesting exception is found in some diving beetles [Dytiscidae (Coleoptera)], in which two retinas receive sharp images from a bifocal lens. Taken together, stemmata represent a great model system to study an impressive set of optical solutions that evolved from a relatively simple ancestral organization.