Fission in a colonial marine invertebrate signifies unique life history strategies rather than being a demographic trait

Abstract

Each of the few known life-history strategies (e.g., r/K and parity [semelparity and iteroparity]), is a composite stratagem, signified by co-evolved sets of trade-offs with stochastically distributed variations that do not form novel structured strategies. Tracking the demographic traits of 81 Botryllus schlosseri (a marine urochordate) colonies, from birth to death, we revealed three co-existing novel life-history strategies in this long-standing laboratory-bred population, all are bracketed through colonial fission (termed NF, FA and FB for no fission, fission after and fission before reaching maximal colony size, respectively) and derived from organisms maintained in a benign, highly invariable environment. This environment allows us to capture the strategists’ blueprints and their net performance through 13 traits, each branded by high within-strategy variation. Yet, six traits differed significantly among the strategies and, in two, the FB was notably different. These results frame fissions in colonial organisms not as demographic traits, but as pivotal agents for life-history strategies.