Animals use light information not only for vision but for non-visual functions, such as circadian entrainment and pupillary light response. Opsins, underling molecules of these photoreceptions, are diversified. We aimed to reveal relationships between the diversity of opsins and that of photoreceptive systems by biochemical and spectroscopic analyses of varied opsins. We cloned seven opsins from amphioxus (Branchiostoma belcheri) and succeeded in functional expression of amphioxus homologues of the Go-coupled opsin and the perospin, whose molecular properties have been largely unknown, in HEK293 cells. Spectroscopic analyses revealed that the Go-coupled opsin and the peropsin bind 11-cis and all-trans retinals, respectively as a chromophore. The results strongly suggest that the physiological function of peropsin is a retinal photoisomerase, while 11-cis configuration is necessary for the Go-coupled opsin. We also demonstrated that the amphioxus homologue of melanopsin, which functions as the circadian photopigment in the photosensitive retinal ganglion cells in mammals, is considerably similar to invertebrate visual pigments in biochemical and photochemical properties for the first time. This finding suggested the evolutionary linkage between invertebrate rhabdomeric visual cells and vertebrate photosensitive retinal ganglion cells. We also showed that the parapinopsin is the UV pigment in the lamprey (Lethenteron japonica) pineal and is the bistable pigment having photointerconvertible two stable states, that is, the original and the G-protein-activating states. The bistable nature of the parapinopsin can account for the photorecovery of the pineal UV-sensitivity by background green light. Our approach could provide cues to understand the evolution of physiological functions.

View full abstract

Central place foragers such as ants and bees are prominent navigators displaying a variety of navigational systems. These navigational systems are roughly classified into three types, route-following system, such as trail pheromone; path integration system that is dependent on compass and odometer; and map-based system, based on memories of visual landmarks. Recent work on ants and bees has revealed a major role of long-term memories in the navigational systems. For example, the directional and odometric memories are acquired perfectly in no more than one trail in the path integration system. Navigators using the map-based system retain the visual landmark memories as “snap-shots” for a few days or a month, and recall the right memory in the appropriate context. Honeybees might assemble a cognitive map to integrate their landmark memories. In the present review, I emphasize how traits of the navigational memory such as acquisition, retention, recall and integration, are dependent on the navigation systems and behavioural backgrounds of the insect navigators.

View full abstract

Body size is one of the most important axes to understand a large biodiversity. An amazing diversity in body mass of lives ranges over about 21 orders of magnitude, from a tiny bacteria such as Mycoplasma weighing 10^-13g to a giant Sequoia tree weighing 10⁹g. As a consequence of this variation, nearly all the structures and functions of organisms are constrained with body size, from the molecular, cellular and whole-organism levels to the ecological and evolutionary dynamics. These relationships are well described by the allometric equation. In this note, we introduce backgrounds to focus on some important correlates and consequences of body size, in particular on energy metabolism at the level of individual organism. Metabolism of an individual organism reflects the energy and material transformations that are used for both the maintenance of existing structure and the production of new biomass. Although body size is a primary determinant for metabolic rates, metabolism-body size relationships, in particular within species, i.e., the ontogenetic changes of metabolism with growth have not been well established in many species. The metabolic scaling in biology still keeps an intriguing and enduring problems.

View full abstract