Dimensional limits for arthropod eyes with superposition optics

AbstractAn essential feature of the superposition type of compound eye is the presence of a wide zone, which is transparent and devoid of pigment and interposed between the distal array of dioptric elements and the proximally placed photoreceptive layer. Parallel rays, collected by many lenses, must (through reflection or refraction) cross this transparent clear-zone in such a way that they become focused on one receptor. Superposition depends mostly on diameter and curvature of the cornea, size and shape of the crystalline cone, lens cylinder properties of cornea and cone, dimensions of the receptor cells, and width of the clear-zone. We examined the role of the latter by geometrical, geometric-optical, and anatomical measurements and concluded that a minimal size exists, below which effective superposition can no longer occur. For an eye of a given size, it is not possible to increase the width of the clear-zone cz=dcz/R1 and decrease R2 (i.e., the radius of curvature of the distal retinal surface) and/or c=dc/R1 without reaching a limit. In the equations `cz' is the width of the clear-zone dcz relative to the radius R1 of the eye and c is the length of the cornea-cone unit relative to R1. Our results provide one explanation as to why apposition eyes exist in very small scarabaeid beetles, when generally the taxon Scarabaeoidea is characterized by the presence of superposition eyes. The results may also provide the answer for the puzzle why juveniles or the young of species, in which the adults possess superposition (=clear-zone) eyes, frequently bear eyes that do not contain a clear zone, but resemble apposition eyes. The eyes of the young and immature specimens may simply be too small to permit superposition to occur

Neka ekološka i etološka opažanja troglobita koji vidi, Hendea myersi cavernicola (Chelicerata: Arachnida: Opiliones)

Data on the visual behaviour of Hendea myersi cavernicola (Forster) are provided which demonstrate that this harvestman can see. Since no specimens could be trapped outside the cave and the integument of this species displays a reduction in pigmentation, we have to conclude that we are dealing with a troglobite which not only possesses eyes, but actually uses them.U radu se daju podaci o vizualnom ponašanju Hendea myersi cavernicola (Forster), a koji pokazuju da ovaj kosac vidi. Nije bilo moguće uloviti nijedan primjerak izvan špilje, a integument ove vrste pokazuje redukciju pigmentacije, pa moramo zaključiti da se radi o troglobitu koji ne samo da ima oči, nego ih i koristi

Bioluminescent Fishes and their Eyes

What shaped the evolution of vision in fish more than anything else is the need to see, be it to avoid obstacles or find shelters, and recognize conspecifics, predators and prey. However, for vision to be effective, sufficient light has to be available. While there is no shortage of light in shallow water depths, at least during the day, the situation for species occurring at greater depths is a different one: they live in an environment where sunlight does not reach, but which nevertheless, is not totally devoid of light. Numerous marine organisms, including fishes of at least 46 families, possess the ability to ‘bioluminesce’, i.e. they can produce biological light. This chapter focuses on the interaction between bioluminescence and specific photoreceptor adaptations in fishes to detect the biological light

A review of the nutritional potential of edible snails: A sustainable underutilized food resource

Despite the use of snails as food in many different communities in the world, the consumption of snail meat is still far from being appreciated. The authors compiled and reviewed the nutrient composition of edible snail meat based on the available scientific literature. The protein, fat, and ash content of snail meat were found to be 14.0, 1.4 and 2.1% on the basis of fresh matter respectively. Comparable protein content with conventional foods of animal origin along with the presence of all essential amino acids and less carbon footprint makes the snail meat a sustainable food source. Moreover, less fat content but higher proportion of polyunsaturated fatty acids, and considerable presence of minerals with nutritional importance especially calcium, zinc, and iron could exhibit human nutritional benefits. However, the establishment of heliciculture facilities is a necessity in order to support this sustainable food resource and also enhance the economic condition of certain local areas

Biomechanical properties of fishing lines of the glowworm Arachnocampa luminosa (Diptera; Keroplatidae)

Animals use adhesive secretions in highly diverse ways, such as for settlement, egg anchorage, mating, active or passive defence, etc. One of the most interesting functions is the use of bioadhesives to capture prey, as the bonding has to be performed within milliseconds and often under unfavourable conditions. While much is understood about the adhesive and biomechanical properties of the threads of other hunters such as spiders, barely anything is documented about those of the New Zealand glowworm Arachnocampa luminosa. We analysed tensile properties of the fishing lines of the New Zealand glowworm Arachnocampa luminosa under natural and dry conditions and measured their adhesion energy to different surfaces. The capture system of A. luminosa is highly adapted to the prevailing conditions (13–15 °C, relative humidity of 98%) whereby the wet fishing lines only show a bonding ability at high relative humidity (>80%) with a mean adhesive energy from 20–45 N/m and a stronger adhesion to polar surfaces. Wet threads show a slightly higher breaking strain value than dried threads, whereas the tensile strength of wet threads was much lower. The analyses show that breaking stress and strain values in Arachnocampa luminosa were very low in comparison to related Arachnocampa species and spider silk threads but exhibit much higher adhesion energy values. While the mechanical differences between the threads of various Arachnocampa species might be consequence of the different sampling and handling of the threads prior to the tests, differences to spiders could be explained by habitat differences and differences in the material ultrastructure. Orb web spiders produce viscid silk consisting of β-pleated sheets, whereas Arachnocampa has cross-β–sheet crystallites within its silk. As a functional explanation, the low tear strength for A. luminosa comprises a safety mechanism and ensures the entire nest is not pulled down by prey which is too heavy

Temporal variability of settlement in Carapidae larvae at Rangiroa atoll

Carapidae (or pearlfish) are eel-like fishes living inside different invertebrates, such as holothurians, sea stars or bivalves. In some Polynesian areas where they live in sympatry, several species (Carapus homei, Carapus mourlani, Carapus boraborensis and Encheliophis gracilis) are able to inhabit the same host species. The heterospecific infestation rate is very rare, suggesting that the four species can compete for their hosts. Some differences in settlement period, breeding period and in pelagic larval duration (PLD) could allow better characterisation of the life history of each species. More than 700 larvae were collected during an entire year on the Rangiroa atoll (French Polynesia). Each species was identified; their settlement pattern was examined and their PLD was deduced from otolith (sagittae) increments. In the four collected species, the settlement pattern differed: C. homei and C. mourlani settle on the reef during the entire year, and show an asynchronous and diffuse breeding cycle. C. boraborensis and E. gracilis have a shorter settlement period which could be compatible with breeding synchronisation. As most reef fishes, Carapidae larvae mainly settle during moonless nights. Moreover, each species presents some plasticity, allowing it to settle on the reef under suitable conditions

Can Molecularly Engineered Plant Galls Help to Ease the Problem of World Food Shortage (and Our Dependence on Pollinating Insects)?

The world faces numerous problems and two of them are global food shortages and the dwindling number of pollinating insects. Plant products that do not arise from pollination are plant galls, which as in the case of oak apples, can resemble fruits and be the size of a cherry. It is suggested that once research has understood how chemical signals from gall-inducing insects program a plant to produce a gall, it should be possible to mimic and to improve nature and “bioengineer” designer galls of different sizes, colorations and specific contents to serve as food or a source of medicinally useful compounds. To achieve this objective, the genes involved in the formation of the galls need to be identified by RNA-sequencing and confirmed by gene expression analyses and gene slicing. Ultimately the relevant genes need to be transferred to naïve plants, possibly with the aid of plasmids or viruses as practiced in crop productivity increases. There is then even the prospect of engineered plant galls to be produced by plant tissue culture via genetic manipulation without the involvement of insects altogether