In many bilaterian phyla, appendages are morphological traits that characterise the identity of the various body parts. In pterygote insects, wings are dorsal appendages on the thorax. The famous “bithorax” fly created by Ed Lewis is the emblematic example of the role of Hox genes.1 Now, Tomoyasu et al.,2 using classical genetics, transgenesis and RNAi, have examined the function of thoracic Hox genes in the beetle Tribolium castaneum. Beetles have rigid elytra in place of the first pair of wings. Instead (...) of the expected transformation of the elytron into a wing, loss of Hox genes' function leads to the homeotic transformation of the second pair of dorsal appendages, the wings, into elytra. This has important consequences for the way that we see the role of Hox genes in development and evolution. BioEssays 27:673–675, 2005. © 2005 Wiley Periodicals, Inc. (shrink)

The Crustacea present a variety of body plans not encountered in any other class or phylum of the Metazoa. Here we review our current knowledge on the complement and expression of the Hox genes in Crustacea, addressing questions related to the evolution of body architecture. Specifically, we discuss the molecular mechanisms underlying the homeotic transformation of legs into feeding appendages, which occurred in parallel in several branches of the crustacean evolutionary tree. A second issue that can be approached by the (...) comparative study of Hox genes and their expression in the Crustacea bears on the homology of the abdomen. We discuss whether the so‐called “abdominal” tagma of the crustaceans is homologous to the abdomen of insects. In addition, the homology of the abdomen between malacostracan and non‐malacostracan crustaceans has also been questioned. We also address the question of the molecular developmental basis of the apparent lack of an abdomen in barnacles. We discuss these issues in relation to the problem of constraint versus adaptation in evolution. BioEssays 25:878–887, 2003. © 2003 Wiley Periodicals, Inc. (shrink)

I review how both the parasegmental and segmental frames are used in constructing the body plan of the arthropods. The parasegment is the primary genetic unit, as shown by Hox gene expression, and the parasegmental design is maintained in the nerve cord. It is, however, not maintained in the epidermis, where the cuticle grooves are segmental, and in the musculature, which is segmental in organisation. This frame shift is reflected in the sensory and motor nerve connections between the ganglia and (...) the periphery. I suggest that the need for movement in an organism equipped with a hard exoskeleton was the functional constraint that shaped this apparently complex mode of development. BioEssays 26:1117–1125, 2004. © 2004 Wiley Periodicals, Inc. (shrink)