arXiv subjects

Ryo Nakayama

Publications and source records attributed to Ryo Nakayama.

3 recordsLinked to original sources

arXiv2026

Predator-associated cues promote host riding, and coupling to mobile hosts improves survival in an epizoic limpet

Epizoic limpets may reduce predation risk by riding mobile gastropod hosts, but the behavioral steps leading to host attachment and the benefits of attachment remain poorly understood. We examined these issues in the epizoic limpet $\textit{Lottia tenuisculpta}$ using a host-riding assay, paired-trajectory analyses of pre-riding movement, a survival assay, and mucus-conditioning assays. In the host-riding experiment, involving 156 limpets in 39 chambers, crab-associated cues increased attachment within the observation window from 19 of 80 individuals in the cue-absent treatment to 42 of 76 individuals in the cue-present treatment. In the same assay, the high-frequency tail of the locomotor amplitude spectrum became shallower under cue-present conditions, with the posterior median slope shifting from -0.353 to -0.287. Direct analysis of visible paired host-limpet trajectories further showed stronger distance closure under crab-associated cues. Distance closure was quantified over the final visible five minutes before riding or before the final visible paired frame. In the survival assay, based on 31 valid trials, the fitted model indicated lower survival after attachment on fixed hosts than on mobile hosts: the posterior median hazard ratio for fixed versus mobile hosts was 2.111, and posterior median survival at the end of the observation window was 0.437 on mobile hosts but 0.175 on fixed hosts. In a separate single-limpet locomotion assay, gastropod mucus-conditioned surfaces yielded narrower final cumulative-distance ranges than the no-mucus control. Together, these results indicate that predator-associated cues promote host riding, visible paired trajectories reveal a pre-riding approach component, coupling to mobile hosts improves survival, and host-associated surface cues may narrow solitary-limpet movement.

q-bio.QM↗

arXiv2024

Multiple power laws and scaling relation in exploratory locomotion of the snail Tegula nigerrima

One of goals in soft robotics is to achive spontaneous behavior like real organisms. To gain a clue to achieve this, we examined the long (16-hour) spontaneous exploratory locomotion of snails. The active forager snail, Tegula nigerrima, from an intertidal rocky shore was selected to test the general hypothesis that nervous systems are inherently near a critical state, which is self-organized to drive spontaneous animal behavior. This hypothesis, known as the critical brain hypothesis, was originally proposed for vertebrate species, but it might be applicable to other invertebrate species as well. We first investigated the power spectra of the speed of locomotion of the snails ($N=39$). The spectra showed $1/{f^α}$ fluctuation, which is one of the signatures of self-organized criticality. The $α$ was estimated to be about 0.9. We further examined whether the spatial and temporal quantities show multiple power-laws and scaling relations, which are rigorous criteria of criticality. Although the satisfaction of these criteria is limited to a truncated region and provides limited evidence to demonstrate the aspect of self-organization, the multiple power-laws and the scaling relations were overall satisfied. Therefore, these results additionally support the generality of the critical brain hypothesis.

q-bio.OT↗

arXiv2012

Broadly Tunable Sub-terahertz Emission from Internal Branches of the Current-voltage Characteristics of Superconducting Bi2Sr2CaCu2O8+d Single Crystals

Continuous, coherent sub-terahertz radiation arises when a dc voltage is applied across a stack of the many intrinsic Josephson junctions in a Bi2Sr2CaCu2O8+d single crystal. The active junctions produce an equal number of I-V characteristic branches. Each branch radiates at a slightly tunable frequency obeying the ac Josephson relation. The overall output is broadly tunable and nearly independent of heating effects and internal cavity frequencies. Amplification by a surrounding external cavity to allow for the development of a useful high-power source is proposed.

cond-mat.supr-con↗