PATTERN DUPLICATIONS IN LARVAE OF THE POLYEMBRYONIC WASP COPIDOSOMA-FLORIDANUM

Copidosoma floridanum is a polyembryonic wasp that undergoes total cle avage of the egg followed by proliferation of blastomeres to produce u p to 2,000 embryos from a single egg. This unusual mode of development raises several questions about how axial polarity is established in i ndividual embryonic primordia. By examining embryonic development of l arvae with duplicated structures (conjoined larvae), we determined tha t conjoined larvae form by mislocalization of two embryonic primordia to a common chamber of the extraembryonic membrane that surrounds indi vidual embryos. Analysis of an anterior marker, Distalless, in misloca lized early embryos indicated that anterior structures form independen tly of one another. This suggests each embryonic primordium has some i ntrinsic polarity. However, during germband extension embryos usually fuse in register with each other, resulting in conjoined larvae with h eads facing each other. Analysis of the posterior segmental marker, En grailed, in conjoined embryos suggested that fusion in register initia tes during germband extension. Thus, even though embryonic primordia i nitially have a random axial orientation, conjoined larvae usually pos sess a common orientation due to reorientation during germband extensi on. These observations suggest that differential cellular affinities d uring segmentation play an important role in embryo fusion.