Data from: Social behaviour and collective motion in plant-animal worms

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 co-ordinate 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: (1) determine if real worms interact socially by comparing them with virtual worms that do not interact and (2) 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. S. 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.社会行为可帮助生物体占据原本无法进入的生态位（ecological niche）。本研究针对这一核心演化原则展开验证，通过证实植型共生生物（plant-animal）罗斯科夫合叶扁虫（Symsagittifera roscoffensis）存在自组织社会行为（self-organizing social behaviour），完成该原则的实验验证。这类海洋无肠扁形动物的全部营养均来源于体内共生的藻类，这也是其通用名称的由来。研究发现，单个扁虫会通过彼此互动协调运动：即便在种群密度较低的环境中，它们也会开始形成小型极化群体游动；随着种群密度逐步升高，这类游动集群会逐渐演变为环形涡旋群落。我们通过计算机模拟完成两项验证：其一，将真实扁虫与无社会互动行为的虚拟扁虫进行对比，以此判断真实扁虫是否存在社会性互动；其二，证实真实扁虫的社会相变现象仅需通过个体间的局部互动即可发生。我们提出假说：这类社会行为可帮助扁虫形成密集的生物膜或垫状群落——这类群落曾在东大西洋潮间带上部的部分日照充足的沙滩中被观测到；在大型藻类无法附着定植的生境中，这类扁虫群落可等效为一类超个体海藻。罗斯科夫合叶扁虫（S. roscoffensis）已作为模式生物被广泛应用于生物学诸多研究领域（包括干细胞再生），其同时也有望成为理解“个体行为如何通过集体运动形成社会集群”这一科学问题的理想模型。