Meeting Abstract
Jointed appendages are the hallmark of arthropods, and diversification of these segmentally repeated structures has helped generate the diversity of arthropod body plans. The resolved phylogenetic context for arthropods, combined with a well characterized model of appendage development in Drosophila, provides a baseline for comparative studies of ventral appendage diversification. The evolution of distinct appendage identities along the anteroposterior axis (i.e., diversification of serial homologues) occurred early in arthropod history with highly divergent morphologies homologized via differential retention and loss of components of an ancestrally biramous appendage. Although still piecemeal, comparative data on gene expression and/or function are available for all four major clades of arthropods, as well as from a lobopodous outgroup, the Onychophora. These data provide insight into the developmental basis for appendage diversification at three distinct levels: across lineages, serial homologues and life stages. Examples from each are used to highlight more general patterns and open questions in the evolution of development. For example, preexisting patterning information, including that provided by core network components, has been repeatedly coopted to regulate later development of novel species-specific features. Most structural divergence across serial homologues has occurred via tinkering with their ancestrally shared developmental network, but phylogenetic homeosis has also occurred repeatedly. Furthermore, as might be predicted based on the combination of early evolutionary divergence but a shared genome, serial homologues show a complex mixture of independent and dependent developmental evolution within lineages.
