Abstract
One of the surprising insights gained from research in evolutionary developmental biology (evo-devo) is that increasing diversity in body plans and morphology in organisms across animal phyla are not reflected in similarly dramatic changes at the level of gene composition of their genomes. For instance, simplicity at the tissue level of organization often contrasts with a high degree of genetic complexity. Also intriguing is the observation that the coding regions of several genes of invertebrates show high sequence similarity to those in humans. This lack of change (conservation) indicates that evolutionary novelties may arise more frequently through combinatorial processes, such as changes in gene regulation and the recruitment of novel genes into existing regulatory gene networks (co-option), and less often through adaptive evolutionary processes in the coding portions of a gene. As a consequence, it is of great interest to examine whether the widespread conservation of the genetic machinery implies the same developmental function in a last common ancestor, or whether homologous genes acquired new developmental roles in structures of independent phylogenetic origin. To distinguish between these two possibilities one must refer to current concepts of phylogeny reconstruction and carefully investigate homology relationships. Particularly problematic in terms of homology decisions is the use of gene expression patterns of a given structure. In the future, research on more organisms other than the typical model systems will be required since these can provide insights that are not easily obtained from comparisons among only a few distantly related model species.
Highlights
Evolutionary developmental biology seeks to unravel the bases of developmental changes in body plan evolution of complex organisms such as animals and plants
We provide a brief introduction to evolutionary developmental biology for newcomers to the field who may be overwhelmed by the abundant literature
Molecular evolutionary analyses will have to focus more on the interaction context of gene networks and the concept of modularity rather than on individual genes [49,107]. It emphasizes the need for correctly assessing the degree of homology vs. homoplasy in defining common components of developmental pathways
Summary
Evolutionary developmental biology (evo-devo) seeks to unravel the bases of developmental changes in body plan evolution of complex organisms such as animals and plants. Comparisons of gene expression patterns to assess homology hypotheses should be restricted to orthologous gene copies, since new expression domains evolving among paralogues are likely to be convergent (Fig. 5) These gene relationships may be complex and need to be tested based on a phylogenetic tree including the whole gene family by identification of the timing of speciation events relative to gene duplications [23] (Fig. 5). The bilaterian ancestor probably had no legs but perhaps some inconspicuous body wall outgrowths triggered by dll expression Cooption of this pre-existing mechanism into more specific building blocks (e.g., for structures that grow out distally but are historically non-homologous), could have subsequently occurred during the evolution of different animal phyla. This highlights the importance of reaching confidence on ancestral nodes as the crucial point in interpreting character evolution
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