A non‐visual pigment melanopsin, which is localized in photosensitive retinal ganglion cells and is involved in the circadian photoentrainment and pupillary responses in mammals, is phylogenetically close to the visual pigments of invertebrates, such as insects and cephalopods. Recent studies suggested that melanopsin is a bistable pigment and drives a Gq‐mediated signal transduction cascade, like the invertebrate visual pigments. Because detailed electrophysiological properties are somewhat different between the visual cells and the photosensitive ganglion cells, we here expressed and purified the invertebrate visual pigment and melanopsin to comparatively investigate their Gq‐activation abilities. We successfully expressed and purified UV and blue light‐sensitive visual pigments of the honeybee as well as the amphioxus melanopsin. Although the purified UV‐sensitive pigment and the melanopsin lost their bistable nature during purification, reconstitution of the pigments in lipid vesicles resulted in return of the bistable nature. The light‐dependent Gq‐activation abilities among these reconstituted pigments are similar, suggesting that the electrophysiological differences do not depend on the Gq‐activation step but rather on the other signal transduction steps and/or on cell properties. Our findings are also important in that this is the first report describes a heterologous large‐scale expression of the Gq‐coupled invertebrate visual pigments in cultured cells.

We have found that giant hornets (Vespa mandarinia japonica) are killed in less than 10 min when they are trapped in a bee ball created by the Japanese honeybees Apis cerana japonica, but their death cannot be solely accounted for by the elevated temperature in the bee ball. In controlled experiments, hornets can survive for 10 min at the temperature up to 47 degrees C, whereas the temperature inside the bee balls does not rise higher than 45.9 degrees C. We have found here that the CO2 concentration inside the bee ball also reaches a maximum (3.6 +/- 0.2%) in the initial 0-5 min phase after bee ball formation. The lethal temperature of the hornet (45-46 degrees C) under conditions of CO2 concentration (3.7 +/- 0.44%) produced using human expiratory air is almost the same as that in the bee ball. The lethal temperature of the honeybee is 50-51 degrees C under the same air conditions. We concluded that CO2 produced inside the bee ball by honeybees is a major factor together with the temperature involved in defense against giant hornets.

The deep-sea bioluminescent squid, Watasenia scintillans, has three visual pigments: The major one (A1 pigment) is based on retinal and has 2max=484 nm, the second one (A2 pigment) is based on 3-dehydroretinal and has 2m~x = 500 rim, and the third one (A4 pigment) is based on 4-hydroxyretinal and has )[m.x = 470 nm. The distribution of these 3 visual pigments in the retina was studied by HPLC analysis of the retinals in retina slices obtained by microdissection. It was found that A1 pigment was not located in the specific region of the ventral retina receiving the down-welling light which contains very long photoreceptor cells, forming two strata. A2 and A4 pigment were found exclusively in the proximal pinkish stratum and in the distal yellowish stratum. The role of these pigments in the retina is hypothesized to involve spectral discrimination. The extraction and analysis of retinoids to determine the origin of 3-dehydroretinal and 4-hydroxyretinal in the mature squid showed only a trace amount of 4-hydroxyretinol in the eggs. Similar analysis of other cephalopods collected near Japan showed the absence of A2 or A4 pigment in their eyes.

Upon capture in a bee ball (i.e., a dense cluster of Japanese honeybees forms in response to a predatory attack), an Asian giant hornet causes a rapid increase in temperature, carbon dioxide (CO₂), and humidity. Within five min after capture, the temperature reaches 46°C, and the CO₂ concentration reaches 4%. Relative humidity gradually rises to 90% or above in 3 to 4 min. The hornet dies within 10 min of its capture in the bee ball. To investigate the effect of temperature, CO₂, and humidity on hornet mortality, we determined the lethal temperature of hornets exposed for 10 min to different humidity and CO₂/O₂ (oxygen) levels. In expiratory air (3.7% CO₂), the lethal temperature was ≥ 2° lower than that in normal air. The four hornet species used in this experiment died at 44-46°C under these conditions. Hornet death at low temperatures results from an increase in CO₂ level in bee balls. Japanese honeybees generate heat by intense respiration, as an overwintering strategy, which produces a high CO₂ and humidity environment and maintains a tighter bee ball. European honeybees are usually killed in the habitat of hornets. In contrast, Japanese honeybees kill hornets without sacrificing themselves by using heat and respiration by-products and forming tight bee balls.

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