Shigeki Yamashita

Spectral sensitivities of jumping spider eyes

SummarySpectral sensitivities of the anterior lateral, posterior lateral and anterior median eyes of the jumping spider,Menemerus confusus Boes. et Str. have been studied by recording electroretinograms (ERGs) and receptor potentials. The anterior and posterior lateral eyes have a single type of visual cell with a maximum spectral sensitivity at about 535–540 nm. The anterior median eye has four types of visual cells with maximum sensitivities at about 360, 480–500, 520–540 and 580 nm, respectively. The ERGs recorded from the optic nerve side (posterior part of the retina) were affected greatly by long wave chromatic light and those on the corneal side (anterior part of the retina) by short wave chromatic light, suggesting that each receptor layer contains a different photopigment.

Molecular Evolution of Arthropod Color Vision Deduced from Multiple Opsin Genes of Jumping Spiders

Among terrestrial animals, only vertebrates and arthropods possess wavelength-discrimination ability, so-called “color vision”. For color vision to exist, multiple opsins which encode visual pigments sensitive to different wavelengths of light are required. While the molecular evolution of opsins in vertebrates has been well investigated, that in arthropods remains to be elucidated. This is mainly due to poor information about the opsin genes of non-insect arthropods. To obtain an overview of the evolution of color vision in Arthropoda, we isolated three kinds of opsins, Rh1, Rh2, and Rh3, from two jumping spider species, Hasarius adansoni and Plexippus paykulli. These spiders belong to Chelicerata, one of the most distant groups from Hexapoda (insects), and have color vision as do insects. Phylogenetic analyses of jumping spider opsins revealed a birth and death process of color vision evolution in the arthropod lineage. Phylogenetic positions of jumping spider opsins revealed that at least three opsins had already existed before the Chelicerata-Pancrustacea split. In addition, sequence comparison between jumping spider Rh3 and the shorter wavelength-sensitive opsins of insects predicted that an opsin of the ancestral arthropod had the lysine residue responsible for UV sensitivity. These results strongly suggest that the ancestral arthropod had at least trichromatic vision with a UV pigment and two visible pigments. Thereafter, in each pancrustacean and chelicerate lineage, the opsin repertoire was reconstructed by gene losses, gene duplications, and function-altering amino acid substitutions, leading to evolution of color vision.

Intracellular stainings of the large ocellar second order neurons in the cockroach

SummaryThe large ocellar second order neurons (L-neurons) in the cockroach,Periplaneta americana have been studied physiologically by intracellular recordings and morphologically by intracellular and whole nerve cobalt stainings. All the recorded L-neurons showed similar light responses, i.e., light on-hyperpolarization and a small number of off-spikes. All the stained L-neurons had an ocellar arborization covering the whole region of the ocellar neuropile and an central arborization in the region posterior to the protocerebral bridge.

Cerebral photosensitive neurons in the orb weaving spiders,Argiope bruennichii andA. amoena

Summary1.The frequency of efferent impulses in the optic nerves of the orb weaving spidersArgiope bruennichii andA. amoena increased by illumination of the brain. Addition of 2 mmol/l Co2+, a synaptic blocking agent, to the saline resulted in the generation of optic nerve impulses following cerebral illumination. Thus, efferent neurons within the brain appear to be sensitive to light. Maximum sensitivity of these neurons occurs at 420–440 nm.2.The frequency of efferent optic nerve impulses decreased during illumination of the eyes. The spectral sensitivity for this inhibition was measured, a large peak occurring at 480–540 nm and a smaller peak at 360 nm.3.The frequency of efferent optic nerve impulses increased transiently following a diminution in light intensity striking the eyes. Simultaneous diminution of light intensity striking both the eyes and the brain, however, increased the number of impulses from the optic nerve, suggesting that the cerebral photosensitive neurons play a role in increasing the response to dimming of light.