Hikaku seiri seikagaku(Comparative Physiology and Biochemistry)

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The evolution of cooperation remains a central paradox in biology. Inter-specific cooperation, called mutualism, is ubiquitous in nature. However, there are conflicts of interest among interacting partners, and theoretically, the emergence of selfish, non-rewarding cheaters will lead the collapse of interactions. To avoid the spreads of cheaters, the interacting individuals are needed to optimize its cooperative behavior by flexible decision-making processes based on the previous cooperative experiences, environmental factors, available resources, and social information. Recent studies in mutualism between plants-pollinators, lycaenid butterflies-ants, and cleaner-client fishes began to elucidate the proximate mechanisms underlying the flexible cooperative behaviors. These researches emphasize the importance of learning based cooperation and common neuroendocrine regulation of the cooperative behavior. Under the ecologically relevant conditions, further physiological approaches on cooperative behavior and the rules of decision-making will provide new insights into the theoretical framework of evolution and stability of mutualistic interactions.

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Free D-amino acids are widely distributed in living organisms, from bacteria to mammals, and play a key role in specific physiological functions. The origin of D-amino acids is not fully understood, but a specific racemase, which generates the D-form from its L-form, is responsible for this in at least some cases. In invertebrates, D-Ser, D-Asp, D-Ala and D-Arg have been found in various phyla species, and play important physiological roles. In contrast to the wide distribution of D-amino acids, amino acid racemase genes have been identified in few invertebrate species. We searched the nucleotide, EST, and SRA databases, and found 11 serine racemase homologous genes from eight invertebrate phyla species. The cloned genes were identified based on their maximum activity as serine racemase (SerR) and aspartate racemase (AspR). Our results revealed that SerR and AspR are more widely distributed among invertebrates than previously thought.

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