The Evolution of Proteins: Unraveling Choanoflagellate Origins

Choanoflagellates are tiny, single-celled organisms that have been traditionally grouped based on their protective outer layer, or periplast. Craspedida species have a purely organic periplast, while Acanthoecida species have a silica-based one called a lorica. Previous studies have suggested that these two groups are closely related, but recent genetic analyses challenge this idea. One freshwater species, Codosiga hollandica, was thought to be a very early branch on the evolutionary tree of these organisms. However, these studies often yield inconsistent results.Researchers have now looked at proteins that evolve slowly over time for a new perspective. Their findings consistently show that Craspedida species are closely related and place Codosiga hollandica further along the evolutionary timeline. Adding more of these slow-evolving proteins to the mix makes the evolutionary tree more stable but can weaken the support for Craspedida's close relationship. The study highlights the need for more data—both more species and more genes—to clearly understand the earliest branches of the Craspedida family tree. It also identifies certain species that should be avoided in these studies because they can mix up the evolutionary relationships.