CRANIAL NEURAL-CREST MIGRATION AND CHONDROGENIC FATE IN THE ORIENTAL FIRE-BELLIED TOAD BOMBINA-ORIENTALIS - DEFINING THE ANCESTRAL PATTERN OF HEAD DEVELOPMENT IN ANURAN AMPHIBIANS

We assess cranial neural-crest cell migration and contributions to the larval chondrocranium in the phylogenetically basal and morphological ly generalized anuran Bombina orientalis (Bombinatoridae). Methods use d include microdissection, scanning electron microscopy, and vital dye labeling, in conjunction with confocal and fluorescence microscopy. C ranial neural-crest cells begin migrating before neural-fold closure a nd soon form three primary streams. These streams contribute to all cr anial cartilages except two medial components of the hyobranchial skel eton (basihyal and basibranchial cartilages), the posterior portion of the trabecular plate, and the otic capsule, the embryonic origin of w hich is unknown. Chondrogenic fate is regionalized within the cranial neural folds, with the anterior regions contributing to anterior carti lages and the posterior regions to posterior cartilages. A neural-cres t contribution also was consistently observed in several cranial nerve s and the connective tissue component of many cranial muscles. Notwith standing minor differences among species in the initial configuration of migratory streams, cranial neural-crest migration and chondrogenic potential in metamorphosing anurans seem to be highly stereotyped and evolutionarily conservative. This includes a primary role for the neur al crest in the evolutionary origin of the paired suprarostral and inf rarostral cartilages, two prominent caenogenetic features of the rostr al skull unique to anuran larvae. Our results provide a model of the a ncestral pattern of embryonic head development in anuran amphibians. T his model can serve as a basis for examining the ontogenetic mechanism s that underlie the diversity of cranial morphology and development di splayed by living frogs, as well as the evolutionary consequences of t his diversity. (C) 1996 Wiley-Liss, Inc.