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A general model of locomotion of brittle stars with a variable number of arms.

ABSTRACT: Typical brittle stars have five radially symmetrical arms that coordinate to move the body in a certain direction. However, some species have a variable number of arms, which is a unique trait since intact animals normally have a fixed number of limbs. How does a single species manage different numbers of appendages for adaptive locomotion? We herein describe locomotion in Ophiactis brachyaspis with four, five, six and seven arms to propose a common rule for the movement of brittle stars with different numbers of arms. For this, we mechanically stimulated one arm of individuals to analyse escape direction and arm movement. By gathering quantitative indices and employing Bayesian statistical modelling, we noted a pattern: regardless of the total number of arms, an anterior position emerges at one of the second neighbouring arms to a mechanically stimulated arm, while arms adjacent to the anterior one synchronously work as left and right rowers. We propose a model in which an afferent signal runs clockwise or anticlockwise along the nerve ring while linearly counting how many arms it passes through. With this model, the question on how 'left and right' emerges in a radially symmetrical body via a decentralized system is answered.

SUBMITTER: Wakita D

PROVIDER: S-EPMC7014800 | biostudies-literature | 2020 Jan

REPOSITORIES: biostudies-literature

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A general model of locomotion of brittle stars with a variable number of arms.

Wakita Daiki D Kagaya Katsushi K Aonuma Hitoshi H

Journal of the Royal Society, Interface 20200108 162

Typical brittle stars have five radially symmetrical arms that coordinate to move the body in a certain direction. However, some species have a variable number of arms, which is a unique trait since intact animals normally have a fixed number of limbs. How does a single species manage different numbers of appendages for adaptive locomotion? We herein describe locomotion in <i>Ophiactis brachyaspis</i> with four, five, six and seven arms to propose a common rule for the movement of brittle stars ...[more]

PMID: 31910773

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Project description:Next generation sequencing (NGS) technology allows to obtain a deeper and more complete view of transcriptomes. For non-model or emerging model marine organisms, NGS technologies offer a great opportunity for rapid access to genetic information. In this study, paired-end Illumina HiSeqTM technology has been employed to analyse transcriptomes from the arm tissues of two European brittle star species, Amphiura filiformis and Ophiopsila aranea. About 48 million Illumina reads were generated and 136,387 total unigenes were predicted from A. filiformis arm tissues. For O. aranea arm tissues, about 47 million reads were generated and 123,324 total unigenes were obtained. Twenty-four percent of the total unigenes from A. filiformis show significant matches with sequences present in reference online databases, whereas, for O. aranea, this percentage amounts to 23%. In both species, around 50% of the predicted annotated unigenes were significantly similar to transcripts from the purple sea urchin, the closest species to date that has undergone complete genome sequencing and annotation. GO, COG and KEGG analyses were performed on predicted brittle star unigenes. We focused our analyses on the phototransduction actors involved in light perception. Firstly, two new echinoderm opsins were identified in O. aranea: one rhabdomeric opsin (homologous to vertebrate melanopsin) and one RGR opsin. The RGR-opsin is supposed to be involved in retinal regeneration while the r-opsin is suspected to play a role in visual-like behaviour. Secondly, potential phototransduction actors were identified in both transcriptomes using the fly (rhabdomeric) and mammal (ciliary) classical phototransduction pathways as references. Finally, the sensitivity of O.aranea to monochromatic light was investigated to complement data available for A. filiformis. The presence of microlens-like structures at the surface of dorsal arm plate of O. aranea could potentially explain phototactic behaviour differences between the two species. The results confirm (i) the ability of these brittle stars to perceive light using opsin-based photoreception, (ii) suggest the co-occurrence of both rhabdomeric and ciliary photoreceptors, and (iii) emphasise the complexity of light perception in this echinoderm class.

Dataset Information

A general model of locomotion of brittle stars with a variable number of arms.

Publications

A general model of locomotion of brittle stars with a variable number of arms.

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