Meeting Abstract

99.3  Thursday, Jan. 7  A Developmental Model for the Evolution of Size Proportions in Fingers and Toes KAVANAGH, KD*; TABIN, CJ; University of Massachusetts Dartmouth and Harvard Medical School; Harvard Medical School kkavanagh@umassd.edu

Phalanges (finger and toe bones) originate from a single condensation that grows and segments sequentially along each digit, repeatedly deploying the same activator-inhibitor gene networks as each element is formed and each joint is initiated. We show that the size of the initially-segmented distal mesenchymal condensation predicts the final size of a given phalanx; as such, the location of the joint initiation along the developing digit is the central developmental “decision” determining the relative size of adjacent phalanges. The key developmental signals involved in this joint positioning are unknown. In this analysis, we use two approaches to understand how variation is produced in this system and assess how developmental variation may influence evolution. First, we experimentally dissect the activator-inhibitor logic of sequential joint formation along the digit, and secondly, we examine the patterns of evolutionary variation within taxa to explore the predictability within the system. We have found that simple developmental rules explain a huge range of variation in phalanges’ size proportions in nature.