Meeting Abstract
The ability to regenerate new body parts is broadly distributed across animals, yet this ability varies widely among them. To understand how regeneration evolves, we need to elucidate its gains and losses across the tree of life. Surveys across whole groups allow gains and losses of regenerative ability to be mapped onto phylogenies. We used this approach to study evolution of regeneration within the phylum Nemertea, the ribbon worms, a group of mostly marine animals known to have regenerative powers ranging from none to extraordinary. We collected 21 species across the phylum and assayed regenerative response to transverse amputations at 1/3 and 2/3 of body length. We mapped the regeneration experiments results onto a well-corroborated phylogeny. Our survey showed that while posterior regeneration ability is widespread, anterior regeneration, including regeneration of brain and eye structures, was relatively uncommon and found only for 5 out of 21 species. Four of the species represent first reports of successful anterior regeneration – two are first reports for a whole class, the Paleonemertea; and two are for species of the class Pilidiophora that were not known to regenerate heads. Our 6 examples of the third class, the Hoplonemertea, continues to confirm that members of this class are incapable of such feat. While ancestral character estimation analyses do not resolve if stem nemerteans could regenerate heads, they show that such ability has likely been gained multiple times within the Pilidiophora, including a recent gain in Ramphogordius sanguineus. Our work shows the potential of nemerteans as promising models for learning fundamental principles about regeneration mechanisms and their evolution.
