CARTWRIGHT, P.; University of Kansas: Patterns and processes of hydrozoan polyp and colony evolution

The notion that developmental processes hold clues into the order and classification of animal life can be traced back to the earliest recordings of biological investigations. Not until recently however, due to advances in phylogenetics and developmental biology, has it been possible to rigorously test hypotheses regarding developmental mechanisms underlying metazoan evolution. Cnidarians are an important group for studying the role of development in evolution because of their basal position within the Metazoa. Modern studies on cnidarian development have been largely confined to the model system Hydra. These studies have uncovered many developmental regulatory genes responsible for the patterning of important axial structures in Hydra, such as tentacles, hypostome and basal disk. Evolutionary changes in these and other axial structures have played a prominent role in the history of cnidarians in general, and hydrozoans in particular. Knowledge of regulatory mechanisms underlying Hydra axial patterning provides an opportunity to generate hypotheses regarding the role of developmental regulatory genes/pathways in the evolution of those morphological transitions important in cnidarian evolution. Testing these hypotheses require robust phylogenies in conjunction with comparative expression data of developmental regulatory genes. A review of higher level cnidarian phylogenetics, with emphasis on morphological transitions in hydrozoan polyp and colony form, will be presented. In light of current phylogenetic and developmental information, hypotheses regarding the developmental mechanisms underlying these transitions will be proposed.