The evolution of insect visual opsin genes with specific consideration of the influence of ocelli and life history traits

Background Visual opsins are expressed in the compound eyes and ocelli of insects and enable light detection. Three distinct phylogenetic groups of visual opsins are found in insects, named long (LW), short (SW) and ultraviolet (UV) wavelength sensitive opsins. Recently, the LW group was found to be duplicated into the LW2b and the LW2a opsins. The expression of LW2b opsins is ocelli specific in some insects (e.g., bees, cricket, scorpion flies), but the gene was not found in other orders possessing three or less ocelli (e.g., dragonflies, beetles, moths, bugs). In flies, two LW2b homologs have been characterised, with one expressed in the ocelli and the other in the compound eyes. To date, it remains unclear which evolutionary forces have driven gains and losses of LW opsins in insects. Here we take advantage of the recent rapid increase in available sequence data (i.e., from insect genomes, targeted PCR amplification, RNAseq) to characterize the phylogenetic relationships of 1000 opsin sequences in 18 orders of Insects. The resulting phylogeny discriminates between four main groups of opsins, and onto this phylogeny we mapped relevant morphological and life history traits. Results Our results demonstrate a conserved LW2b opsin only present in insects with three ocelli. Only two groups (Brachycera and Odonata) possess more than one LW2b opsin, likely linked to their life history. In flies, we hypothesize that the duplication of the LW2b opsin occurred after the transition from aquatic to terrestrial larvae. During this transition, higher flies (Brachycera) lost a copy of the LW2a opsin, still expressed and duplicated in the compound eyes of lower flies (Nematocera). In higher flies, the LW2b opsin has been duplicated and expressed in the compound eyes while the ocelli and the LW2b opsin were lost in lower flies. In dragonflies, specialisation of flight capabilities likely drove the diversification of the LW2b visual opsins. Conclusion The presence of the LW2b opsin in insects possessing three ocelli suggests a role in specific flight capabilities (e.g., stationary flight). This study provides the most complete view of the evolution of visual opsin genes in insects yet, and provides new insight into the influence of ocelli and life history traits on opsin evolution in insects.

Tiling mechanisms of the compound eye through geometrical tessellation

Tilling patterns are observed in many biological structures. Hexagonal tilling, commonly observed in the compound eyes of wild-type Drosophila, is dominant in nature; this dominance can probably be attributed to physical restrictions such as structural robustness, minimal boundary length, and space filling efficiency. Surprisingly, tetragonal tiling patterns are also observed in some Drosophila small eye mutants and aquatic crustaceans. Herein, geometrical tessellation is shown to determine the ommatidial tiling patterns. In small eye mutants, the hexagonal pattern is transformed into a tetragonal pattern as the relative positions of neighboring ommatidia are stretched along the dorsal-ventral axis. Hence, the regular distribution of ommatidia and their uniform growth collectively play an essential role in the establishment of tetragonal and hexagonal tiling patterns in compound eyes.

Substantial variability in morphological scaling among bumblebee colonies

Differences in organ scaling among individuals may play an important role in determining behavioural variation. In social insects, there are well-documented intraspecific differences in colony behaviour, but the extent that organ scaling differs within and between colonies remains unclear. Using 12 different colonies of the bumblebee Bombus terrestris , we aim to address this knowledge gap by measuring the scaling relationships between three different organs (compound eyes, wings and antennae) and body size in workers . Though colonies were exposed to different rearing temperatures, this environmental variability did not explain the differences of the scaling relationships. Two colonies had differences in wing versus antenna slopes, three colonies showed differences in wing versus eye slopes and a single colony has differences between eye versus antenna slopes. There are also differences in antennae scaling slopes between three different colonies, and we present evidence for putative trade-offs in morphological investment. We discuss the utility of having variable scaling among colonies and the implication for understanding variability in colony fitness and behaviour.

The first Nocticola Bolivar 1892 (Blattodea: Nocticolidae) from New Guinea

A new species of highly troglobitic cockroach, Nocticola baumi n. sp., is described from limestone caves of Papua Province, Indonesia. The new species is the first Nocticola reported in New Guinea island and differs from other known Nocticola spp. by the combination of the following characters: compound eyes and ocelli absent, tegmina fully developed extending beyond the abdomen, hind wings absent, legs extremely long. The discovery of the genus on New Guinea bridges the gap between Oriental and Australian distribution of the genus and stresses the unknown diversity of the genus.

Soft Array Surface-Changing Compound Eye

The field-of-view (FOV) of compound eyes is an important index for performance evaluation. Most artificial compound eyes are optical, fabricated by imitating insect compound eyes with a fixed FOV that is difficult to adjust over a wide range. The compound eye is of great significance in the field of tracking high-speed moving objects. However, the tracking ability of a compound eye is often limited by its own FOV size and the reaction speed of the rudder unit matched with the compound eye, so that the compound eye cannot better adapt to tracking high-speed moving objects. Inspired by the eyes of many organisms, we propose a soft-array, surface-changing compound eye (SASCE). Taking soft aerodynamic models (SAM) as the carrier and an infrared sensor as the load, the basic model of the variable structure infrared compound eye (VSICE) is established using an array of infrared sensors on the carrier. The VSICE model is driven by air pressure to change the array surface of the infrared sensor. Then, the spatial position of each sensor and its viewing area are changed and, finally, the FOV of the compound eye is changed. Simultaneously, to validate the theory, we measured the air pressure, spatial sensor position, and the FOV of the compound eye. When compared with the current compound eye, the proposed one has a wider adjustable FOV.

Spatial tuning of translational optic flow responses in hawkmoths of varying body size

To safely navigate their environment, flying insects rely on visual cues, such as optic flow. Which cues insects can extract from their environment depends closely on the spatial and temporal response properties of their visual system. These in turn can vary between individuals that differ in body size. How optic flow-based flight control depends on the spatial structure of visual cues, and how this relationship scales with body size, has previously been investigated in insects with apposition compound eyes. Here, we characterised the visual flight control response limits and their relationship to body size in an insect with superposition compound eyes: the hummingbird hawkmoth Macroglossum stellatarum. We used the hawkmoths’ centring response in a flight tunnel as a readout for their reception of translational optic flow stimuli of different spatial frequencies. We show that their responses cut off at different spatial frequencies when translational optic flow was presented on either one, or both tunnel walls. Combined with differences in flight speed, this suggests that their flight control was primarily limited by their temporal rather than spatial resolution. We also observed strong individual differences in flight performance, but no correlation between the spatial response cutoffs and body or eye size.

New species of bristletails of the family Machilidae (Archaeognatha) from Kazakhstan

The fauna of bristletails of the family Machilidae in Kazakhstan currently includes one species of the genus Silvestrichiloides Mendes, 1990 and 13 species of the genus Allopsontus Silvestri, 1911. The present study describes one new species of the genus Silvestrichiloides (S. berkarensis Kaplin, sp. nov. from South Kazakhstan) and two new species of the genus Allopsontus (A. (Kaplinilis) nigrostriatus Kaplin, sp. nov. and A. (Machilanus) perfectus Kaplin, sp. nov. from Southeastern Kazakhstan). Silvestrichiloides berkarensis sp. nov. differs from the other species of this genus in the structure of antennal flagellum, apical palpomere of labial palp and ovipositor. Among species of the subgenus Kaplinilis Mendes, 1990, A. nigrostriatus sp. nov. belongs to a group of species characterized by numerous short chaetae on the ventral surface of the 5–7th palpomeres of the male maxillary palp and by the absence on the labial palp. This group includes two species: A. volgensis Kaplin, 1999 from Samara Region and A. smelyanskii Kaplin, 1999 from Orenbourg Region (both Russia). The new species differs from A. volgensis and A. smelyanskii in the length of the body and antenna, color of scales on the upper surface of the body, shape of the compound eye and paired ocellus, structure of the flagellum and apical palpomere of the male labial palp. The subgenus Machilanus Silvestri, 1934 is represented only by A. bitschi Wygodzinsky, 1962 from Afghanistan and A. perfectus sp. nov., which are characterized by numerous short chaetae on the ventral surface of the 2nd–7th palpomeres of the male maxillary palp. Allopsontus perfectus sp. nov. differs from A. bitschi in the shape of compound eyes, paired ocellus, structure of male labial palp and genitalia.