University of the Ryukyus · Faculty of Science · 教授

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• Evolutionary history influences the microbiomes of a female symbiotic reproductive organ in cephalopods2024 · ABSTRACT Many female squids and cuttlefishes have a symbiotic reproductive organ called the accessory nidamental gland (ANG) that hosts a bacterial consortium involved with egg defense against pathogens and fouling organisms. While the ANG is found in multiple cephalopod families, little is known about the global microbial diversity of these ANG bacterial symbionts. We used 16S rRNA gene community analysis to characterize the ANG microbiome from different cephalopod species and assess the relationship between host and symbiont phylogenies. The ANG microbiome of 11 species of cephalopods from four families (superorder: Decapodiformes) that span seven geographic locations was characterized. Bacteria of class Alphaproteobacteria, Gammaproteobacteria , and Flavobacteriia were found in all species, yet analysis of amplicon sequence variants by multiple distance metrics revealed a significant difference between ANG microbiomes of cephalopod families (weighted/unweighted UniFrac, Bray–Curtis, P = 0.001). Despite being collected from widely disparate geographic locations, members of the family Sepiolidae (bobtail squid) shared many bacterial taxa including (~50%) Opitutae (Verrucomicrobia) and Ruegeria (Alphaproteobacteria) species. Furthermore, we tested for phylosymbiosis and found a positive correlation between host phylogenetic distance and bacterial community dissimilarity (Mantel test r = 0.7). These data suggest that closely related sepiolids select for distinct symbionts from similar bacterial taxa. Overall, the ANGs of different cephalopod species harbor distinct microbiomes and thus offer a diverse symbiont community to explore antimicrobial activity and other functional roles in host fitness. IMPORTANCE Many aquatic organisms recruit microbial symbionts from the environment that provide a variety of functions, including defense from pathogens. Some female cephalopods (squids, bobtail squids, and cuttlefish) have a reproductive organ called the accessory nidamental gland (ANG) that contains a bacterial consortium that protects eggs from pathogens. Despite the wide distribution of these cephalopods, whether they share similar microbiomes is unknown. Here, we studied the microbial diversity of the ANG in 11 species of cephalopods distributed over a broad geographic range and representing 15–120 million years of host divergence. The ANG microbiomes shared some bacterial taxa, but each cephalopod species had unique symbiotic members. Additionally, analysis of host–symbiont phylogenies suggests that the evolutionary histories of the partners have been important in shaping the ANG microbiome. This study advances our knowledge of cephalopod–bacteria relationships and provides a foundation to explore defensive symbionts in other systems.
• Relationship between seasonal seagrass growth and egg case dynamics of the oval squid (Sepioteuthis lessoniana Ferussac in Lesson, 1832) in the coastal waters of the Ryukyu Archipelago2023 · Kimoto, S; Kawabata, R; Ikeda, Y
• Allometry for Eyes and Optic Lobes in Oval Squid (Sepioteuthis lessoniana) with Special Reference to Their Ontogenetic Asymmetry2022 · Eyes develop in relation to body size and brain area for visual processing in some vertebrates. Meanwhile, it is well known that many animals exhibit left–right asymmetry in both morphology and behavior, namely, lateralization. However, it remains unclear whether the eyes and visual processing brain areas synchronously develop for their asymmetry. Oval squid (Sepioteuthis lessoniana) exhibits lateralization of optic lobe volume and left or right eye usage toward specific targets during their ontogeny. We address the question of how left–right asymmetry of the eyes and optic lobes exhibit an allometric pattern. To examine this question, we estimated the left and right volumes of eyes and optic lobes using microcomputed tomography. We found that, for the optic lobe volume, the right enlargement that appeared at ages 45 and 80 days then shifted to the left at age 120 days. In contrast, the volume of eyes did not show any left–right asymmetries from hatching to age 120 days. We also found that the volume of the eyes and optic lobes showed a slower increase than that of the whole-body size. Within these two visually related organs, the eyes grew faster than the optic lobes until age 120 days. These results are discussed in the context of the survival strategy of oval squid that form schools, two months post-hatching.
• 広がりゆくタコ研究2022 · 池田 譲, 佐藤成祥

• 頭足類の視覚に関する研究2023 · ■■■
• 頭足類の「個のない社会」の形成維持機構に関する鳥類・哺乳類との比較研究2021 · 基盤研究(B)
• 琉球列島に固有なオクトポリスにおけるタコの社会性に関する検証1934 · 本研究は、琉球列島沿岸に形成されているタコ類の高密度分布域「オクトポリス」について、その実態とそこに暮らすタコ類の動態を社会性の観点から探ることを目的としている。今年度は、１）オクトポリスにおけるソデフリダコの個体間相互交渉の野外検証、および２）社会性に関わる脳領域の比較解剖学的検証を実施した。項目１）では、沖縄本島沿岸の岩礁帯を経時的に野外調査した。その結果、ソデフリダコは１回の調査あたり3個体から30個体観察された。また、個体識別標識付けした計14個体のうち、標識装着13日後に放流地から約10m離れた場所で1個体が確認された。さらに、3日間連続して同じ巣内にいた個体や２週間後も同じ巣にいた個体を確認した。また、隣接した巣や、巣外での接触・伸腕行動など相互交渉、他種タコ類への接近や接触など種間相互交渉も観察された。このように、本種の野外での個体間相互作用を明らかにできた。項目２）では、ソデフリダコの脳をmicro-CTで観察した。CT画像から、視覚学習、記憶に関係する領域である垂直葉（vtL）、上前葉（sfL）、腕から得られた情報の処理に関わる下前葉系(INFF）を特定した。本種ではvtL, sfLという視覚学習に深く関わる脳葉の容積が大きく、触覚に関わるINFFの容積が小さかった。また、形態的な特徴として、vtL後端の発達が確認された。さらに、これらの結果を他種のタコ類と比較したところ、ソデフリダコの脳は単独性と考えられるタコ類と独立した脳の形質を示した。これは、群れを作る社会性のツツイカ類に近い脳形態であった。これらの脳形態の特徴は、ソデフリダコに見られる社会性や生態に大きく関わっていると考えられた。
• 熱帯性イカ類の社会システムに関する比較行動学的研究

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