Minami Kyushu University

The larvae of unionid mussels are obligate parasites. Their survival and metamorphosis into juvenile mussels depend on attaching to physically suitable hosts. Although unionid mussels are important ecosystem engineers, the effects of their shells on the host fish species remain poorly understood. The unionid species, Pronodularia japanensis, uses freshwater gobies (Rhinogobius) as hosts for its larvae. In this study, we conducted microcosm experiments under predation risk from a carnivorous fish, the Korean perch (Coreoperca herzi), to assess whether empty shells ofunionid musselscould provide anti-predator refuges for gobies. Additionally, we examined whether shells of the Asian clam (Corbicula) could serve as alternative refuges tothe unionidshells. The presence ofunionid shells substantially enhanced goby survival after a 48-h predation period, whereasAsian clamshells had no such effect. Video recordings revealed that gobies hid beneathunionidshells but not beneath Asian clamshells. Our findings indicate that the shells of deceased unionids can positively influence potential host fish, suggesting a mutualistic relationship between unionids and host fish mediated through shell-derived refuge effects. Furthermore, our results suggest that replacing unionids with non-native Asian clams in natural habitats may negatively affect host fish populations.

Bioactive peptides consist of multiple linked amino acids that are secreted from cells and act on specific receptors in order to transmit information from one cell to another. Through signal transduction, bioactive peptides regulate various physiological functions in the body, and the discovery of new bioactive peptides is therefore likely to lead to the development of various diagnostic and therapeutic agents. In this article, we have focused on the bioactive peptides that are known as feeding regulatory peptides. They are among the bioactive peptides discovered as ligands for G protein-coupled receptors (GPCRs), and we have reviewed their diverse functions. In addition, the status of structural analysis of GPCRs, which is necessary in the drug discovery process, and research on orphan GPCRs, for which new ligands are expected to be discovered in the future, is introduced to systematize modern peptide research and discuss future developments in bioactive peptide research.

The degradation of ground vegetation cover caused by large grazing herbivores frequently results in enhanced erosion rates in forest ecosystems. Splash erosion can be caused by drop impacts with high throughfall kinetic energy (TKE) from the canopy of the trees. Notably bigger canopy drips from structurally-mediated woody surface points appear to induce even higher TKE and generate concentrated impact locations causing severe focus points of soil erosion. However, TKE at these locations has rarely been reported. This study investigated the intensity of TKE at a concentrated impact location and compared it to general TKE locations under the canopy and freefall kinetic energy (FKE) outside the forest. We measured precipitation, TKE and FKE using splash cups at seven locations under Japanese beech trees and five locations outside the forest in the leafless and leafed seasons in a deciduous broadleaved forest of Japan, respectively. TKE at the concentrated impact location was 15.2 and 49.7 times higher than that at general locations under beech and FKE, respectively. This study confirmed that canopy drip from woody surfaces can be a hotspot of soil erosion in temperate forest ecosystems. Throughfall precipitation at the concentrated impact location was 11.4 and 8.1 times higher than that at general locations and freefall, respectively. TKE per 1 mm precipitation (unit TKE) at the concentrated impact location (39.2 ± 23.7 J m -2 mm -1 ) was much higher than that at general locations (22.0 ± 12.7 J m -2 mm -1 ) and unit FKE (4.5 ± 3.5 J m -2 mm -1 ). Unit TKE in the leafless season was significantly lower than in the leafed season because of fewer redistribution of canopy drips induced only by woody tissue. Nevertheless, unit TKE at the concentrated impact location in the leafless season (36.4 J m -2 mm -1 ) was still higher than at general locations in the leafed season. These results show that potentially high rates of sediment detachment can be induced by not only throughfall precipitation, but also larger throughfall drop size distributions at concentrated impact locations, even in the leafless season.

Bahia grass (Paspalum notatum Flugge) is an important tropical forage grass and sets seed by apospory. I) To clarify the mechanisms of aposporous embryo sac initial cell (AIC) appearance and apomictic embryo sac formation, and II) to make it clear the mechanism of multiple embryo seed set a development in polyembryonic ovules, several apomictic and sexual varieties of bahia grass were studied cytologically and quantitatively by Nomarski differential interference-contrast microscopy. The results were I) there was no difference between sexual and apomicts to megasporogenesis; and then, the megaspore degenerated in apomicts; at the same time, AIC originated from nucellar tissue appeared and its numbers increased as the ovary grew before anthesis; II) at anthesis, the sac derived from AIC located in the micropylar end (first sac) were 92.5 to 100%, and those in the chalazal ends (other sacs) were 40.4 to 86.0% among the apomicts; the first sac divided dominantly and were 56 to 87% comparable to 0 to 1% of the other sacs at 4 days after anthesis; however, 4 to 17% of the other sacs also showed embryo formations but endosperm. In final, the first sac occupied the whole space of the ovule, in which the embryos in the other sacs coexisted.

Petals of red chrysanthemum (Dendranthema grandiflorum) are habitually eaten in Japan. In the present study, plasma concentration profiles of two major acylated anthocyanins derived from the petals of red chrysanthemum were evaluated in rats after oral administration of an anthocyanin-rich fraction obtained from red chrysanthemum. The structures of the two major anthocyanins in the petals of red chrysanthemum were determined to be cyanidin 3-O-β-D-(3″, 6″-di-O-malonyl)-glucopyranoside and cyanidin 3-O-β-D-(6″-mono-O-malonyl)-glucopyranoside. Both malonyl anthocyanins were quickly absorbed from the gastrointestinal tract and were detected in rat blood plasma in their original acylated forms 15 min after the oral administration of the anthocyanin fraction obtained from the petals of red chrysanthemum. The absorption amounts of anthocyanins evaluated from the area under the plasma concentration curves during 8 h normalized to the orally administered dose were in the following order: cyanidin 3-O-β-D-(3″, 6″-di-O-malonyl)-glucopyranoside > cyanidin 3-O-β-D-(6″-mono-O-malonyl)-glucopyranoside > cyanidin 3-O-β-D-glucopyranoside. The present results demonstrated that the additional malonylation of the glucopyranosyl moiety of position 3″ and 6″ of cyanidin 3-O-β-D-glucopyranoside enhanced the intestinal absorption of anthocyanins.

Diapause induction in multivoltine insects is an ecophysiological event that is generally triggered by seasonal cues such as photoperiod and temperature. The rice leaf bug, Trigonotylus caelestialium (Kirkaldy), feeds on various Poaceae grasses and produces several generations a year. Previous studies have shown that adults produce diapause and nondiapause eggs under short-day and long-day conditions, respectively. However, there is a distinct mid-summer peak in diapause incidence before an autumnal increase in diapause incidence in the field, which cannot be explained by the laboratory results. The present study was performed to examine the environmental factors affecting the diapause incidence in mid-summer and the adaptive significance of this phenomenon. Seasonal trends in diapause incidence differed significantly among three sites located 150-400 m apart from each other and with different host plants. The suitability of host plants differs depending on species and seasonally. Therefore, the microhabitat difference in diapause trend is believed to be due to the difference in host plants. When field-collected female adults laying diapause eggs in late June were fed a seasonally deteriorating host (the orange foxtail, Alopecurus aequalis Sobol. [Poales: Poaceae]), they kept laying diapause eggs, whereas when fed a suitable host (the wheat, Triticum aestivum L. [Poales: Poaceae]) for 5 d, they changed oviposition mode to lay nondiapause eggs. These results indicate that host-plant suitability affects the oviposition mode of T. caelestialium. Diapause-egg oviposition in mid-summer in T. caelestialium has adaptive significance as a bet-hedging strategy against unpredictable dietary conditions.