The Comparative - Phylogenetic Method of Reconstructing Evolutionary History
Friedman, William E. .
The generation gap: assessing homology and interpreting developmental evolution within the complex life cycle of land plants.
THE alternation of generations provides fertile ground to examine the origin of developmental innovations, and the potential transfer of these innovations between temporally, genetically, and morphologically distinct phases of the plant life cycle. Yet, we lack a precise means for discussing character innovation and homology assessment when the biological features in question can be found in both the gametophyte and sporophyte generations. Apical growth provides an example of the complexities of discussing character evolution within an alternation of generations. The underlying developmental mechanisms for apical growth (maintenance of a ‘‘stem cell’’ population at a growing tip) were initially present in the gametophytic common ancestors of land plants and it may be parsimonious (although not necessarily true) to posit that this developmental package was later co-opted for expression in the sporophyte generation. Understanding the evolutionary history of apical growth, in turn, bears significantly on the origin of “shoot systems” capable of producing leaves. How should the leafy shoot of a moss gametophyte be viewed when compared with the leafy shoot of a lycopsid or derived euphyllophyte? At the level of phylogenetically-structured character evolution, each of these leafy shoot systems is homoplasious. However, if the expression of apical growth in the common ancestor of all land plants is an essential and important precedent of leafy shoot systems, then the concept of an “underlying synapomorphy” and the role of “developmental constraint” become important elements in the analysis of the evolutionary history of leafy shoot systems. With the emergence of molecular developmental data, the improvement of phylogenetic hypotheses, and the centuries-old perspectives on morphological concepts of homology, we are moving into an age where a more precise and botanically-grounded language of character evolution will be essential to the integration of molecular, organismic and phylogenetic data that bear on the evolutionary history of plants.
Log in to add this item to your schedule
1 - University of Colorado, Department of Ecology and Evolutionary Biology, UCB 334, Boulder, Colorado, 80309, USA
Presentation Type: Symposium or Colloquium Presentation
Location: 314/Bell Memorial Union
Date: Wednesday, August 2nd, 2006
Time: 2:00 PM