1) What is Evo-Devo? (by Rey J. Rosa Morales)

           The great morphological complexity and diversity that we see in multicellular organisms is produced by developmental processes that have evolved in response to natural selection. But how do these developmental processes evolve? Direct development  occurs when embryos develop directly into adult-like forms instead of progressing through a larval stage (Indirect development). This striking divergence in developmental mode has evolved independently in many animal lineages, including sea urchins, ascidians, frogs, and salamanders. The evolutionary forces and genetic mechanisms promoting such radical, and sometimes rapid, changes in development and life history have mystified biologists for over a century. Comparisons of embryogenesis and larval morphogenesis, especially among marine invertebrates, are central topics in both classical developmental biology and modern evolutionary developmental biology.

            These examples suggest several questions: What are the selective pressures that favor such a novel evolutionary trajectory? How could such a profound alteration of early development evolve so many times? And, perhaps most challenging, what genetic and developmental processes are involved in these evolutionary alterations? It is likely that selection for rapid development promotes the evolution of direct development. But even though some of the genes that underlie these alternative developmental trajectories are beginning to be uncovered, the developmental mechanisms involved and more importantly, the reasons why these mechanisms are apparently more flexible in some groups of organisms than others are still mysteries.

            The field of evolutionary developmental biology, or EDB (often called "evo-devo"), seeks to understand the mechanisms by which development has evolved, both in terms of developmental processes (for example, what novel cell or tissue interactions are responsible for novel morphologies in certain taxa) and in terms of evolutionary processes (for example, what selection pressures promoted the evolution of these novel morphologies). Two of the main questions or themes that concern evolutionary developmental biologists are, first, what role has developmental evolution played in the history of life On Earth? and second, do the developmental trajectories that produce phenotypes bias the production of variation or constraint trajectories of evolutionary change? Natural selection acts on phenotypes produced by development, but ultimately we want to understand how the modes by which development produces those phenotypes affect evolutionary potentials and trajectories. 

Direct versus indirect development. (A) A pluteus larva of the indirect-developing sea urchin Heliocidaris tuberculata. (B) A nonfeeding larva of the direct developing congeneric species H. erythrogramma. In H. erythrogramma, the ancestral larval mode has been lost and embryos initiate the program for adult morphogenesis without an intervening pluteus stage. None of the complex morphological features of the pluteus are present in H. erythrogramma larvae, yet these two species are so closely related that they can be interbred in the laboratory. (Photos courtesy of R. Raff.)

Introductio to Evo-Devo (YouTube video: 8min 52seg)

References:

1. Futuyma, D.J. (2005). Evolution. Sinauer Associates, Inc. Publishers Sunderland, Massachusetts U.S.A.
2. Hall, Brian K. (2000). "Evo-devo or devo-evo-does it matter". Evolution & Development 2 (4): 177–178.
3. Palmer, RA (2004). "Symmetry breaking and the evolution of development". Science 306 (5697): 828–833.
4. Prum, R.O., Brush, A.H. (March 2003). "Which Came First, the Feather or the Bird?". Scientific American 288 (3): 84–93.