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A 3-D Tail Explant Culture to Study Vertebrate Segmentation in Zebrafish

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Published on: June 30, 2021

The segmented urbilateria: a testable scenario.

Guillaume Balavoine¹, André Adoutte

¹Centre de Génétique Moléculaire du CNRS, Avenue de la Terrasse, 91198 Gif-sur-Yvette, France.

Integrative and Comparative Biology

|June 18, 2011

Summary

The last common ancestor of bilaterian animals was likely segmented, with diverse body plans emerging through evolutionary mechanisms acting on this ancestral metameric (segmented) body. This hypothesis is supported by conserved mesodermal segmentation patterns.

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Area of Science:

Evolutionary biology
Developmental biology
Comparative genomics

Background:

Recent hypotheses suggest the Urbilateria (last common ancestor of bilaterians) was segmented.
Evidence stems from comparative molecular embryology, morphology, and development.
Molecular phylogenies of metazoans provide a framework for evolutionary analysis.

Purpose of the Study:

To discuss morphological and developmental evidence for a segmented Urbilateria.
To explore the challenges in defining and applying cladistic methods to ancestral segmentation.
To present a scenario for bilaterian diversification from a metameric ancestor.

Main Methods:

Review of morphological and developmental evidence for segmentation.
Analysis of mesodermal segmentation patterns across the bilaterian tree.
Application of cladistic character optimization (with noted complexities).

Main Results:

Striking similarities in posterior mesodermal segment/somite addition suggest ancestral segmentation.
A general definition of coelom and segmentation reveals conserved patterns.
Evolutionary mechanisms like specialization, tagmosis, and progenesis acting on a segmented plan explain Cambrian body plan emergence.

Conclusions:

The hypothesis of a segmented Urbilateria is supported by conserved mesodermal segmentation patterns.
A metameric ancestor provides a plausible model for bilaterian body plan diversification.
Future research should compare genes involved in mesodermal segmentation to test this hypothesis.