Data from: Crimson spotted rainbowfish (Melanotaenia duboulayi) change their spatial position according to nutritional requirement

Decision making in moving animal groups has been shown to be disproportionately influenced by individuals at the front of groups. Therefore, an explanation of state-dependent positioning of individuals within animal groups may provide a mechanism for group movement decisions. Nutritional state is dynamic and can differ between members of the same group. It is also known to drive animal movement decisions. Therefore, we assayed 6 groups of 8 rainbowfish foraging in a flow tank. Half of the fish had been starved for 24h and half had been fed 1h prior to experimental start. Groups were assayed again one week later but individuals were allocated to the opposite nutritional treatment. During the assay the positions of individually identified fish were recorded as were the number of food items they each ate and the position within the group they acquired them from. Food-deprived fish were more often found towards the front of the shoal; the mean weighted positional score of food-deprived fish was significantly larger than that of well-fed fish. Individuals were not consistent in their position within a shoal between treatments. There was a significant positive correlation between mean weighted positional score and number of food items acquired which displays an obvious benefit to front positions. These results suggest that positional preferences are based on nutritional state and provide a mechanism for state-dependent influence on group decision-making as well as increasing our understanding of what factors are important for group functioning.已有研究证实，移动动物群体的群体决策会受到群体前端个体的不成比例影响。因此，对动物群体内个体基于营养状态的位置分配（state-dependent positioning）规律进行阐释，可为群体移动决策的内在机制提供理论支撑。营养状态是动态变化的，同一群体内的不同个体间也可能存在营养状态差异，且已知营养状态会驱动动物的移动决策行为。为此，我们针对6组各8条在流水水槽中觅食的彩虹鱼开展了行为试验，其中一半个体被禁食24小时，另一半则在试验开始前1小时完成投喂。一周后我们对同一批群体重复开展试验，并将个体的营养处理组别进行互换。试验期间，我们记录了可被个体识别的每尾鱼的群体位置、其摄食的食物总量，以及其获取每一份食物时在群体中的位置。结果显示，禁食个体更多出现在鱼群（shoal）前端，其平均加权位置得分（weighted positional score）显著高于饱腹个体；不同营养处理组间，个体在鱼群内的位置并不固定。个体的平均加权位置得分与其获取的食物数量之间存在显著正相关，这表明占据群体前端位置具有明显的觅食优势。上述结果表明，个体的群体位置偏好基于其营养状态，既为基于状态的群体决策影响机制提供了实证依据，也加深了我们对影响群体功能关键因素的认知。