Allen's Turning Point

Allen G. Collins, Invertebrate Zoologist ,  National Systematics Laboratory of NOAA Fisheries Service and the National Museum of Natural History    It's fun to look back at the tangled pathway that led me to resolve, at least for now, the longstanding conundrum - was the first cnidarian an anemone-like polyp or a swimming jellyfish-like medusa? I could never have brought much new to the question if it had not been for two key innovations:

• DNA sequencing and explicit analysis of evolutionary relationships. The former provided numerous new characters that could reveal animal history and the latter provided a robust framework for assessing what they could actually tell us.
• Interestingly, our early efforts, with both morphological and molecular data, had not enough resolution to speak to this basic question of whether the polyp or the medusa came first. But two things happened.
• First, someone who had read our morphological work pointed out some errors and asked if we wanted help updating our analysis.
• Second, we kept adding new sequence data to our molecular data set.
• Both sets of evidence converged on the same answer: the swimming jellyfish evolved after the bottom-dwelling polyp because Stauromedusae arose earlier within Cnidaria than did the groups containing medusa stages.

This work has piqued interest (especially mine!) in these fascinating but little known beauties of the sea.