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

Abstract

The fine structure of the compound eyes of the adult diving beetle Agabus japonicus is described with light, scanning, and transmission electron microscopy. The eye of A. japonicus is mango-shaped and consists of about 985 ommatidia. Each ommatidium is composed of a corneal facet lens, an eucone type of crystalline cone, a fused layered rhabdom with a basal rhabdomere, seven retinula cells (including six distal cells and one basal cell), two primary pigment cells and an undetermined number of secondary pigment cells that are restricted to the distalmost region of the eye. A clear-zone, separating dioptric apparatus from photoreceptive structures, is not developed and the eye thus resembles an apposition eye. The cross-sectional areas of the rhabdoms are relatively large indicative of enhanced light-sensitivity. The distal and central region of the rhabdom is layered with interdigitating microvilli suggesting polarization sensitivity. According to the features mentioned above, we suggest that 1) the eye, seemingly of the apposition type, occurs in a taxon for which the clear-zone (superposition) eye is characteristic; 2) the eye possesses adaptations to function in a dim-light environment; 3) the eye may be sensitive to underwater polarized light or linearly water-reflected polarized light.

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“…Facets are regular in the central area and irregular on the periphery of the eye. A similar arrangement has been observed in staphylinid beetles Creophilus erythrocephalus and Sartallus signatus [69], in the erotylid fungus beetle Neotriplax lewisi [70], and in the small diving beetle Agabus japonicus [71]. Generally, the presence of many irregularly shaped facets suggests decreased resolution, that most likely allows the beetle only to distinguish light intensity and/or to refer to the position of the sun, which is important for orientation [70].…”

Functional Anatomy of Split Compound Eyes of the Whirligig Beetles Dineutus mellyi (Coleoptera: Gyrinidae)

“…However, we also discovered a distinct feature in Adephaga. For instance, the compound eyes of Agabus japonicus, a dytiscid beetle species, exhibit an apposition type with highly directional and orthometric microvilli in the rhabdom [53]. In contrast, the microvilli in D. mellyi appear noticeably disoriented, indicating a lack of polarized sensitivity.…”

Black Phosphorus‐Based Absorbing Bionic Stacked Structured Linear Polarization Detector

“…Optical Mater. 2023, 11, 2201828 [14] Reproduced with permission. Copyright 2014, Wiley Periodicals, LLC.…”

“…[8] However, the methods can only perform post-calculation on the existing detection information, which is an approximate estimation of the real polarization information and cannot fundamentally solve the problem of spurious polarization.Insects, such as the family Dytiscidae, [9,10] Thysanura, [11] Coleoptera, [12] and Lepidoptera, [13] have evolved a very complex visual system. Take Agabus japonicus [14,15] as an example, as shown in Figure 1a,b are the actual photographs of the Polarization detection technology is developing toward miniaturization and high integration from the early time-division type, amplitude-division type, aperture-division type, etc., to a more integrated focal plane-integrated array type. Focal plane detectors that rely on metal nanogrids are not able to guarantee both temporal and spatial resolution for lossless polarized light detection with a guaranteed level of integration.…”

“…a) Photograph of Agabus japonicus (reproduced by courtesy of Dr. Ai Ping Liang). b) Compound eye image of A. japonicus [14]. Reproduced with permission.…”