Predictable genetic recruitment for luciferin sulfation in the convergent evolution of bioluminescence.

Determinism and contingency shape evolutionary trajectories and the extent to which evolution is predictable depends on the relative contribution of each. However, the causes of patterns of predictable evolution are poorly understood. Here we propose evolution may be more deterministic - and therefore predictable - if functional evolution is constrained to fewer genetic solutions. We examine the bioluminescence system of ostracods and synthesize our findings with those reported previously for fireflies and sea pansies to show one aspect of bioluminescence, substrate metabolism, evolved convergently by recruiting homologous enzymes. We use gene expression, recombinant protein expression, and in vitro functional analyses to identify genes capable of substrate metabolism in ostracods. Our results, taken together with knowledge of firefly and sea pansy bioluminescence systems, provide empirical evidence supporting that these convergent mechanisms for substrate metabolism repeatedly evolved by co-opting sulfotransferases, a ubiquitous family of enzymes with broad substrate specificity. From this synthesis, we propose the lack of diverse genetic solutions for sulfation constrains evolution, resulting in more evolutionary determinism and increasing our ability to predict evolution.