Electrophysiological evidence for polarization sensitivity in the camera-type eyes of the aquatic predacious insect larva,Thermonectus marmoratus(Coleoptera: Dytiscidae)

Abstract

SUMMARYPolarization sensitivity has most often been studied in mature insects, yet it is likely that larvae also make use of this visual modality. The aquatic larvae of the predacious diving beetle Thermonectus marmoratus are highly successful visually guided predators, with a UV-sensitive proximal retina that, according to its ultrastructure, has three distinct cell types with anatomical attributes that are consistent with polarization sensitivity. In the present study we used electrophysiological methods and singlecell staining to confirm polarization sensitivity in the proximal retinas of both principal eyes of these larvae. As expected from their microvillar orientation, cells of type T1 are most sensitive to vertically polarized light, while cells of type T2 are most sensitive to horizontally polarized light. In addition, T3 cells probably constitute a second population of cells that are most sensitive to light with vertical e-vector orientation, characterized by shallower polarization modulations, and smaller polarization sensitivity (PS) values than are typical for T1 cells. The level of PS values found in this study suggests that polarization sensitivity probably plays an important role in the visual system of these larvae. Based on their natural history and behavior, possible functions are: (1)finding water after hatching, (2)finding the shore before pupation, and (3) making prey more visible, by filtering out horizontally polarized haze, and/or using polarization features for prey detection.

Extreme polarization sensitivity in the retina of the corn borer moth Ostrinia

“…Their PS exceeds the highest values ever measured in any arthropod species (e.g. PS>21 in the DRA of the bee Megalopta) (Greiner et al, 2007; review in Stowasser and Buschbeck, 2012), except for the case of the fly DRA cells R7marg and R8marg, which produce hyperpolarising responses to polarised stimuli in the non-preferred direction (Hardie, 1984;Weir et al, 2016). In the fly DRA, the high PS is, however, possible due to filtering in a tiered rhabdom and electrical interactions between the two photoreceptors in a polarisation-opponent pair (Weir et al, 2016).…”

An apposition‐like compound eye with a layered rhabdom in the small diving beetle Agabus japonicus (Coleoptera, Dytiscidae)

“…Many aquatic insects (including some diving beetles), capable of flight, detect water surfaces on account of their polarized light reflection (Schwind, 1991;Horv ath and Varj u, 2004;Stowasser and Buschbeck, 2012). Some aquatic insects also use polarization sensitivity to detect prey, as has been observed in the larvae of the sunburst diving beetle Thermonectus marmoratus (Stecher et al, 2010).…”

Stark trade-offs and elegant solutions in arthropod visual systems

“…The detection of linearly polarized light can also be used to find water bodies, as exemplified by the water bug Notonecta glauca (Schwind, 1984). Other aquatic insects, such as the larvae of the sunburst diving beetle Thermonectus marmoratus, can also detect polarized light (Stowasser and Buschbeck, 2012). Another example of polarized light aiding in object detection is the band-eyed brown horse fly Tabanus bromius, in which females have ventrally located specialized polarization-sensitive ommatidia that drive polarotaxis towards the fly's food source (Megličet al, 2019).…”