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The segmented Urbilateria: a testable scenario (2003)
| Venue: | Int. Comp. Biol |
| Citations: | 12 - 0 self |
BibTeX
@ARTICLE{Balavoine03thesegmented,
author = {Guillaume Balavoine and Andre Adoutte},
title = {The segmented Urbilateria: a testable scenario},
journal = {Int. Comp. Biol},
year = {2003},
pages = {137--147}
}
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Abstract
SYNOPSIS. The idea that the last common ancestor of bilaterian animals (Urbilateria) was segmented has been raised recently on evidence coming from comparative molecular embryology. Leaving aside the com-plex debate on the value of genetic evidence, the morphological and developmental evidence in favor of a segmented Urbilateria are discussed in the light of the emerging molecular phylogeny of metazoans. Applying a cladistic character optimization procedure to the question of segmentation is vastly complicated by the problem of defining without ambiguity what segmentation is and to what taxa this definition applies. An ancestral segmentation might have undergone many complex derivations in each different phylum, thus rendering the cladistics approaches problematic. Taking the most general definitions of coelom and seg-mentation however, some remarkably similar patterns are found across the bilaterian tree in the way seg-ments are formed by the posterior addition of mesodermal segments or somites. Postulating that these striking similarities in mesodermal patterns are ancestral, a scenario for the diversification of bilaterians from a metameric ancestor is presented. Several types of evolutionary mechanisms (specialization, tagmosis, progenesis) operating on a segmented ancestral body plan would explain the rapid emergence of body plans during the Cambrian. We finally propose to test this hypothesis by comparing genes involved in mesodermal segmentation.
Keyphrases
segmented urbilateria testable scenario similar pattern com-plex debate cladistic character optimization procedure bilaterian tree bilaterian animal developmental evidence general definition ancestral segmentation body plan segmented ancestral body plan comparative molecular embryology last common ancestor evolutionary mechanism rapid emergence metameric ancestor way seg-ments molecular phylogeny genetic evidence posterior addition striking similarity several type mesodermal segmentation mesodermal segment different phylum undergone many complex derivation mesodermal pattern
