BELY, A. E.; SIKES, J. M.; Univ. of Maryland, College Park; Univ. of Maryland, College Park: Evolution of annelid regeneration and asexual reproduction

The phylogenetic distribution of regeneration potential across animals suggests that the ancestral animal had extensive regeneration abilities and that loss of regeneration has been a major evolutionary trend in many animal lineages. Naidine annelids are an excellent, novel system in which to investigate the evolution of regeneration abilities. Naidines are small, aquatic worms which can reproduce asexually by fission. Gene expression and other data suggest that fission evolved from regeneration and that these two forms of development are very similar. However, we have identified two lineages (represented by at least four species) that have independently lost the capacity to regenerate anterior segments while retaining the ability to reproduce by fission. Interestingly, although they can not regenerate any segmental tissue, these �non-regenerating� species can regenerate the asegmental tissue at the extreme anterior end of the body (the prostomium and peristomium), suggesting that there may be different requirements for regeneration of segmental and asegmental tissues. To elucidate how regeneration abilities were lost, we are investigating which regeneration processes occur and which processes fail in non-regenerating species. Although non-regenerating naidines do seal the wound, at least one aspect of normal wound-healing (post-amputation autotomy at a stereotypical intrasegmental position) does not occur in non-regenerating species. Similarly, although some limited cell proliferation is initiated after amputation in non-regenerating species, it is not sustained and the worms never form a visible blastema. Our studies are pointing to particular processes, such as post-amputation autotomy and cell proliferation maintenance, that may be correlated with, or even reponsible for, the failure of anterior regeneration in these non-regenerating annelids.