Meeting Abstract

78.6  Wednesday, Jan. 6  Evolution of diverse asexual reproduction strategies and reversal of the primary body axis in Convolutriloba acoels SIKES, J.M.*; BELY, A.E.; Univ. of Illinois, Urbana-Champaign; Univ. of Maryland, College Park jsikes@illinois.edu

Acoels in the genus Convolutriloba are unusual among bilaterians in that morphologically similar species have evolved dramatically different modes of asexual reproduction that radically modify the primary body axis, including examples of transverse fission, longitudinal fission, and reversed polarity budding. We conducted parallel regeneration trials on Convolutriloba species to elucidate the regenerative capacities that may have allowed for the evolution of such different asexual reproduction strategies. Our data suggest that the Convolutriloba ancestor possessed a rich regeneration toolkit that may have allowed for extreme diversification of asexual reproduction in the group. We further investigated bud formation and axial properties of the parent-bud boundary in C. retrogemma, a species that reproduces by a remarkable process in which buds form with a body axis orientation exactly opposite that of the parent. Studies of axial patterning gene expression, cell proliferation, musculature organization, and regenerative potential indicate that manifestations of axial polarity of the bud develop only gradually after bud initiation and reveal a swath of tissue at the boundary between parent and bud that appears to remain completely unpolarized. Tissue excised entirely from within this boundary zone fails to regenerate or acquire any evidence of axial polarity, a phenotype identical to animals in which GSK-3 is pharmacologically inhibited, suggesting Wnt/β-catenin or Hedgehog signaling may mediate the establishment of this unpolarized boundary zone. The formation of unpolarized tissue may provide a buffer between opposing polarity cues and be a general mechanism by which budding animals establish and maintain linked body axes.