Biology subjects

Chikami, Y.

Publications and source records attributed to Chikami, Y..

7 recordsLinked to original sources

bioRxiv2026

Data-driven frame-by-frame analysis of surface swimming and terrestrial walking in the coastal beetle Phaleria atriceps

Background. Inter-leg coordination of insects changes depending on environmental conditions. Although locomotor changes between terrestrial and aquatic environments have been examined in various insects, relatively little is known about coastal insects living at the boundary between these environments. We therefore compared the inter-leg coordination during terrestrial walking with that during surface swimming in the coastal beetle Phaleria atriceps. Methods. Surface swimming was recorded in 17 individuals and terrestrial walking in 10 individuals using high-speed video at 1,000 frames/s. The six leg tips and anterior and posterior body landmarks were tracked frame-by-frame using DeepLabCut, and leg movements were quantified in a body-centered coordinate system. Leg movement periods were estimated from sinusoidal fits to longitudinal leg-tip trajectories. Inter-leg phase relationships were calculated for all 15 leg pairs and integrated to reconstruct a representative six-leg phase organization for each locomotor mode. Results. Leg movement periods were significantly longer during surface swimming than during terrestrial walking for all six legs. During walking, the six-leg phase relationship closely matched an alternating tripod pattern, with a left foreleg (L1), a right middle leg (R2), and a left hind leg (L3) forming one phase group and a right foreleg (R1), a left middle leg (L2), and a right hind leg (R3) forming the opposing group. The same broad grouping was observed in the six-leg phase relationship during surface swimming, although significant differences in relative phase were detected for L1-L2, L1-R2, and R1-R2. Conclusions. Phaleria atriceps exhibited six-leg phase relationships broadly consistent with an alternating tripod pattern during both terrestrial walking and surface swimming, whereas leg movement periods and certain inter-leg phase relationships differed between the two locomotor modes. These findings provide a quantitative description of the similarities and differences in inter-leg coordination between terrestrial walking and surface swimming in a coastal beetle. Further mechanical and comparative studies will be needed to clarify the functional and evolutionary significance of these findings.

animal behavior and cognition↗

bioRxiv2024

Soma-germ contact across the basement membrane in the ovary

Epithelial cells generally interact with other cells and environments at their apical side. At the basal surface, the basement membrane impedes such an interaction. One notable instance is communication between soma and germ cells within the ovary across numerous bilaterian taxa. This contact underlies proper oogenesis and subsequent embryogenesis through facilitating nutrient supply to gametes, exchange of molecules and ions, and participation in signal transduction for primary axis formation. Throughout layers of the history of morphology and cellular biology, there has been emphasis on this heterocellular interaction primarily occurring at the apical side of epithelial cells. Contrary to this long-standing understanding, we uncover that ovarian follicle cells in three myriapod species belonging to phylogenetically basal myriapod clades extend their cytoplasmic processes, penetrating the basement membrane to establish direct contact with oocytes. These discoveries demonstrate the ovarian soma-germ interaction transverse the basement membrane, suggesting that the basal matrix does not always a physical barrier to soma-germ communication. Furthermore, we find that the ovarian somatic cells in a myriapod directly connect with the oogonia or young oocyte before the formation of their basement membrane. This result suggests an overlooked construction manner of heterocellular communication at the basal domain of epithelial cells.

zoology↗

bioRxiv2023

Fruitless mating with the exes: the irreversible parthenogenesis in a stick insect

Parthenogenetic lineages, common in many animals, have sparked debate about their evolutionary persistence. While asexuality is expected to ensure reproductive assurance and provide a demographic advantage, parthenogens should suffer from the lack of gene shuffling with other individuals. On the other hand, occasional sexual reproduction has been theoretically predicted to be enough to mitigate the long-term costs of parthenogenesis. Recent studies have revealed instances of cryptic sex in some old parthenogenetic lineages, which is most likely mediated by rarely occurring males. Unlike female traits that rapidly become vestigial under asexuality, traits in males have been predicted to slowly decay due to the accumulation of neutral mutations over long evolutionary times. In fact, rare males often retain sexual functions, raising questions about the asexuality of these long-standing parthenogenetic lineages. Here, we intensively examined the possibility of sexual reproduction in the Japanese common stick insect, Ramulus mikado, which was also suggested to be an old parthenogen in our previous work. While asexual female reproduction appears to be quite predominant throughout Japan, we fortunately obtained the rare males from the field. These males exhibited typical stick insect male morphology and engaged in mating behaviors with conspecific females. However, no paternal-specific alleles were detected in the offspring; all embryos showed genotypes identical to their mothers. Our histological observations on a few males revealed that they had no sperm in their reproductive organs, although the degree of decay may be different among the lineages. We also found that females have sexual organs with signs of degeneration. All these results demonstrate the irreversible asexual reproduction of R. mikado and indicate their long history as a parthenogenetic species. Our present study provides unique insights into the maintenance of parthenogenesis and degenerative evolution of sexual traits in ancient asexual lineages.

evolutionary biology↗

bioRxiv2023

The structural and functional modularity of ovarian follicle epithelium in the pill-millipede Hyleoglomeris japonica (Myriapoda: Diplopoda: Pentazonia: Glomerida) and the morphological reconsideration of somatic tissues around oocytes in Myriapoda

Ovarian somatic tissues around oocytes are essential for oogenesis in many metazoans. The functional ovarian somatic tissues sometimes have structural properties specific to their roles. In contrast, there is no evidence of such structural modularity of the follicle epithelium in Myriapoda, suggesting that myriapod ovarian soma may not participate in oogenesis. The ultrastructural nature of follicle cells also supports solitary oogenesis in most myriapods investigated. In contrast, here, we report two structurally and developmentally distinct domains of the follicle epithelium in the Japanese pill millipede, Hyleoglomeris japonica. The follicle epithelium of H. japonica has a thick cell mass on the apex of the follicle. These thick cells contain the rich rough endoplasmic reticulum, mitochondria, and Goldi bodies and possess many microvilli, indicating synthetic/secretory activities, and become thicker along with the oogenetic progress. Another region of epithelium does not exhibit these features. These results show the structural and functional modularity specific to some functions of the follicle epithelium of H. japonica. Therefore, the follicle epithelium of Myriapoda is divided into 3 types: physiologically functional uniformly, nonfunctional only, and those with both. We suggest the need to reconsider the nature and roles of ovarian somatic tissues of Myriapoda and Arthropoda.

zoology↗

bioRxiv2021

Evolutionary history of sexual differentiation mechanism in insects

Gain of alternative splicing gives rise to functional diversity in proteins and underlies the complexity and diversity of biological aspects. However, it is still not fully understood how alternatively spliced genes develop the functional novelty. To this end, we infer the evolutionary history of the doublesex gene, the key transcriptional factor in the sexual differentiation of arthropods. doublesex is controlled by sex-specific splicing and promotes both male and female differentiation in some holometabolan insects. In contrast, doublesex promotes only male differentiation in some hemimetabolan insects. Here, we investigate ancestral states of doublesex using Thermobia domestica belonging to Zygentoma, the sister group of winged insects. We find that doublesex of T. domestica expresses sex-specific isoforms but is only necessary for male differentiation of sexual morphology. This result ensures the hypothesis that doublesex was initially only used to promote male differentiation during insect evolution. However, T. domestica doublesex has a short female-specific region and upregulates the expression of vitellogenin homologs in females, suggesting that doublesex may have already controlled some aspects of feminization in the common ancestor of winged insects. Reconstruction of the ancestral sequence and prediction of the protein structure show that the female-specific isoform of doublesex has a long C-terminal disordered region in holometabolan insects, but not in non-holometabolan species. We propose that doublesex acquired a female-specific isoform and then underwent a change in the protein motif structure, which became essential for female differentiation in sexual dimorphisms.

evolutionary biology↗

bioRxiv2021

Evolutionary origin of sex differentiation system in insects

The evolution of the functionality of genes and genetic systems is a major source of animal diversity. Its best example is insect sex differentiation systems: promoting male and female differentiation (dual-functionality) or only male differentiation (single-functionality). However, the evolutionary origin of such functional diversity is largely unknown. Here, we investigate the ancestral functions of doublesex, a key factor of insect sex differentiation system, using the apterygote insect, Thermobia domestica, and reveal that its doublesex is essential for only males at the phenotypic level, but contributes to promoting female-specific vitellogenin expression in females. This functional discordance between the phenotypic and transcription-regulatory levels in T. domestica shows a new type of functionality of animal sex differentiation systems. Then, we examine how the sex differentiation system transited from the single-functionality to the dual-functionality in phenotypes and uncover that a conserved female-specific motif of doublesex is detected in taxa with the dual-functional doublesex. It is estimated that the role of the sex differentiation system for female phenotypes may have evolved through accumulating mutations in the protein motif structures that led to the enhancement of its transcription-regulatory function.

evolutionary biology↗

bioRxiv2019

Acute feeding disorder after oral RNAi exposure results in efficient pest control

Selecting an appropriate target gene is critical to the success of feeding RNA interference (f-RNAi)-based pest control. Gene targets have been chosen based on their ability to induce lethality. However, lethality induction by f-RNAi is slow-acting and crop damage can progress during this time. Here, we show that f-RNAi of death-associated inhibitor of apoptosis protein 1 (diap1), but not two conventional targets vacuolar ATPase subunit A and E, induces acute feeding cessation in the solanaceous pest, Henosepilachna vigintioctopunctata during 24-48 hours. We also found that the feeding cessation by diap1 f-RNAi has species-specificity and occurs with only 1.6 ng dsRNA. Our results suggest that diap1 is an appropriate target in the context of rapid reduction of crop damage. We propose that acute feeding disorder should be assessed as a novel criterion for selecting appropriate target genes for RNAi-based pest control in addition to the conventional criterion based on lethality.

molecular biology↗