The evolution of gastrulation morphologies.
During gastrulation, early embryos specify and reorganise the topology of their germ layers. Surprisingly, this fundamental and early process does not appear to be rigidly constrained by evolutionary pressures; instead, the morphology of gastrulation is highly variable throughout the animal kingdom. Recent experimental results demonstrate that it is possible to generate different alternative gastrulation modes in single organisms, such as in early cnidarian, arthropod and vertebrate embryos. Here, we review the mechanisms that underlie the plasticity of vertebrate gastrulation both when experimentally manipulated and during evolution. Using the insights obtained from these experiments we discuss the effects of the increase in yolk volume on the morphology of gastrulation and provide new insights into two crucial innovations during amniote gastrulation: the transition from a ring-shaped mesoderm domain in anamniotes to a crescent-shaped domain in amniotes, and the evolution of the reptilian blastoporal plate/canal into the avian primitive streak.
Peer reviewed: True
Acknowledgements: G.S.N. gives special thanks to Dillan Saunders for helping to crystallise many of the concepts included in this Hypothesis, and Ben Steventon for his clarifications and insights.
Funder: University of Cambridge; Id: http://dx.doi.org/10.13039/501100000735
Biotechnology and Biological Sciences Research Council (BB/T006781/1)
Engineering and Physical Sciences Research Council (EP/W023946/1)