VENIT, E.P.; Duke University: All for one and one for all? A new method for quantifying individuation in colonial metazoans.

Biologists have long been fascinated by the problems of aggregation, hierarchy and biological complexity. How do more complex forms of life arise from an aggregation of simpler parts? At what point in its evolutionary history does a group of cells form an organism, or a group of organisms form an interdependent colony? The concept of �individuation�, or the degree to which a group of living parts acts as a single individual, is a key to better understanding these questions. However, previous attempts to quantify colony individuation have lacked much precision. Here colony individuation has been quantified using spatial point statistics and the example of cheilostome bryozoans to help understand the evolution of complexity in colonial metazoans. In polymorphic colonial organisms like cheilostome bryozoans, non-random organization of polymorphs is an indicator of colony-level individuation. Ecologists use spatial point statistics to measure the degree of non-randomness of tree distributions in a forest. This technique has been adapted here to measure the non-randomness of polymorph locations in two-dimensional encrusting colonial organisms. The more aggregated, or “clumpy”, the polymorphs are in a colony, the more individuated that colony is. The confidence interval of the spatial statistic is used as a quantification of the non-randomness, and thus individuation, of the colony. The confidence intervals from different species can then be combined with comparative techniques to study the evolution of complexity over geologic time. This can tell us whether or not individuation increases over time, and if this increase is driven or passive. This study demonstrates the above method on several species of fossil Cheilostomes collected from the Castle Hayne Formation (Eocene) in North Carolina.