Social behaviour and collective motion in plant-animal worms.
Nigel R Franks, Alan Worley, Katherine A J Grant, Alice R Gorman, Victoria Vizard, Harriet Plackett, Carolina Doran, Margaret L Gamble, Martin C Stumpe, Ana B Sendova-Franks
Author Information
Nigel R Franks: School of Biological Sciences, University of Bristol, Bristol, UK nigel.franks@bristol.ac.uk. ORCID
Alan Worley: School of Biological Sciences, University of Bristol, Bristol, UK. ORCID
Katherine A J Grant: School of Biological Sciences, University of Bristol, Bristol, UK.
Alice R Gorman: School of Biological Sciences, University of Bristol, Bristol, UK.
Victoria Vizard: School of Biological Sciences, University of Bristol, Bristol, UK.
Harriet Plackett: School of Biological Sciences, University of Bristol, Bristol, UK.
Carolina Doran: School of Biological Sciences, University of Bristol, Bristol, UK Champalimaud Neuroscience Programme, Champalimaud Centre for the Unknown, Av. Brasília, Lisbon 1400-038, Portugal. ORCID
Margaret L Gamble: School of Biological Sciences, University of Bristol, Bristol, UK.
Martin C Stumpe: AnTracks Computer Vision Systems, Mountain View, CA, USA. ORCID
Ana B Sendova-Franks: Department of Engineering Design and Mathematics, UWE, Bristol, UK. ORCID
Social behaviour may enable organisms to occupy ecological niches that would otherwise be unavailable to them. Here, we test this major evolutionary principle by demonstrating self-organizing social behaviour in the plant-animal, Symsagittifera roscoffensis. These marine aceol flat worms rely for all of their nutrition on the algae within their bodies: hence their common name. We show that individual worms interact with one another to coordinate their movements so that even at low densities they begin to swim in small polarized groups and at increasing densities such flotillas turn into circular mills. We use computer simulations to: (i) determine if real worms interact socially by comparing them with virtual worms that do not interact and (ii) show that the social phase transitions of the real worms can occur based only on local interactions between and among them. We hypothesize that such social behaviour helps the worms to form the dense biofilms or mats observed on certain sun-exposed sandy beaches in the upper intertidal of the East Atlantic and to become in effect a super-organismic seaweed in a habitat where macro-algal seaweeds cannot anchor themselves. Symsagittifera roscoffensis, a model organism in many other areas in biology (including stem cell regeneration), also seems to be an ideal model for understanding how individual behaviours can lead, through collective movement, to social assemblages.
