WISDOM OF THE CROWD AND CHEMOTAXIS IN FREE-LIVING PLACAZOA (TRICHOPLAX ADHAERENS)

Abstract

The wisdom of the crowds hypothesis describes the way in which larger groups of animals contribute to increased accuracy of decision-making and collective behavior. Recently, interesting parallels have been drawn between the highly coordinated patterns of behavior observed in animal collectives and cellular collectives, raising questions about the role of crowd wisdom in multicellular groups. In this project I studied Placozoa (Trichoplax adhaerens), the simplest known multicellular organisms, which are characterized by their high degree of intercellular organization despite the lack of a central nervous system. I investigated their patterns of movement in order to determine whether isotropic cellular groups can migrate collectively towards a target and how size may affect the accuracy and coordination of this behavior. Here, using an unprecedented in vivo experimental set-up, I show that starved Placozoa are able to chemotax, or respond to chemical cues, towards an algal food source in their local environment through the collective motion of all of their cells. Though the size of the animals did not seem to play a significant role in measures such as the directedness or speed of chemotaxis, it was positively correlated with accuracy (chemotactic index). Their initial proximity to the food source was also a strong factor in foraging success. These results suggest that detection of an appropriate chemoattractant can initiate coordinated and accurate multicellular movement towards the source. In addition to describing a previously unexplored area of Placozoan behavioral ecology, this study also addresses questions about the robustness of the wisdom of the crowd hypothesis in more complex environments. These findings have important applications that will advance current knowledge about the dynamics of coordination and migration in multicellular aggregations.