Meeting Abstract
29.3 Monday, Jan. 4 Evolution of developmental trajectories: regeneration and fission in naidid annelids ZATTARA, E.E.**; BELY, A.E.; University of Maryland,College Park ezattara@umd.edu
Fission has evolved in many phyla, and several lines of evidence suggest that this new developmental trajectory arises by modification of pre-existing regenerative capabilities. To investigate how fission evolves from regeneration, we studied naidid annelids, small freshwater worms. Most naidids can regenerate a head or tail, and many can also reproduce asexually by fission. We performed a detailed comparison of fission and regeneration in one focal species, Pristina leidyi, as well as comparative studies of the two processes across multiple naidids. We focused on cell proliferation, general morphogenesis, muscle development and neural development, paying close attention to relative timing of events during regeneration and fission. When these trajectories are compared side by side, extensive similarities are apparent. However, several elements demonstrate timing shifts, most notably in the innervation of developing tissues and during reconstruction of the central nervous system, and each trajectory shows a number of exclusive elements, including aspects of muscle development, gut modification, and final number of segments formed. While similarities between fission and regeneration reflect a common developmental origin, differences may reflect adaptations in each trajectory to distinct functions (survival vs. reproduction) or may result from developmental systems drift between these two trajectories. Preliminary studies in other naidid species indicate that while the regenerative process looks similar across species, fission shows some striking differences, providing evidence, initially suggested by recent molecular phylogenies, that there have been two independent gains of fission within this group. Future comparative work will be aimed at identifying which components of regeneration and fission are robust to change and which are most evolutionarily labile.
