Meeting Abstract

S2-2.1  Thursday, Jan. 3  Is the amphibian skull segmented? Novel insights from neural crest labeling and functional studies HANKEN, J.; Harvard University hanken@oeb.harvard.edu

Many fundamental aspects of cranial anatomy in vertebrates were resolved initially well before the delineation and broad acceptance of Darwinian evolution, let alone recent technical and conceptual advances such as molecular genetics, cell lineage analysis and a broad recognition of the prominent role of the embryonic neural crest. Indeed, much of the anatomical terminology in use today�as well as its implications regarding cranial organization, homology and developmental process�can be traced to pre- and early post-Darwinian times. Contemporary studies have validated many classical observations, yet others mandate reassessment and reevaluation of fundamental assumptions and conventions. Segmentation of the vertebrate head is perhaps the most classical topic of all. Compelling accounts regarding the nature and extent of head segmentation abound, but the empirical database on which such accounts must be grounded is surprisingly thin, especially in regards to adult features and taxonomic sampling. We have utilized a novel transgenic line to map the pattern of neural crest derivation of the bony adult skull in clawed frogs (Xenopus laevis). This method circumvents technical limitations that have hindered previous studies of the embryonic origin of adult-specific features in frogs, which form first at metamorphosis. The bony adult skull of Xenopus is segmented, but in some important ways that differ from those predicted by conventional theories of cranial organization, and perhaps in ways that differ from those in some other vertebrates. Patterns of segmentation may be evolutionarily labile and susceptible to modification associated with the origin of specialized life history and developmental modes and other adaptive and cladogenic events. Supported by NSF (EF-0334846; AmphibiaTree).