Hunting for “factor X”: the genetic basis of segmental mismatch

Abstract

Defending an evo-devo approach to the study of evolution in the pages of this journal may appear to be an unnecessary exercise. However, there are some case studies which, better than others, illustrate the necessity and the potential of considering developmental causes for explaining the evolution of organisms’ body architecture. An example involving the evolution of segmentation in arthropods is the recent study by Janssen et al. (2008). A zoology textbook would typically define a segmented animal as one whose body is composed of a series of modules (segments) that, more or less morphologically differentiated, are aligned along the main body axis. However, there are segmented animals in which such a modular composition is hardly recognizable, because different serial structures along the same axis of the same organism are repeated in discordant arrangement. This condition, termed ‘‘segmental mismatch,’’ characterizes the trunk of many arthropod taxa, in particular myriapods (millipedes, centipedes, and their allies), where the