Why do some phenotypes evolve, such as butterfly wing patterns, while others do not, such as 9+2 axoneme architecture? Natural selection could maintain an optimal phenotype, but another possibility exists, that alternate developmental mechanisms do not exist to produce variations in a phenotype. A fundamental component of Drosophila spermtail axonemes, b 2 tubulin, has not evolved in 80 million years. Is the protein an ideal configuration maintained by selection, or is it the only configuration able to support the extreme length of the Drosophila spermtail axoneme?

My laboratory investigates the structure/function relationship between Drosophila melanogaster b 2 and the spermtail axoneme in an evolutionary context. An evolutionarily conserved feature of the b 2 protein, the axoneme motif, specifies an evolutionarily conserved feature of motile axonemes, the central pair microtubules, while evolutionarily variable features of b 2, the carboxy terminus and internal variable region (IVR), influence an evolutionarily variable feature of spermtails, their length. Moreover, even the variable regions of the protein are not wholly free to evolve, due to synergism in the function of the IVR amino acids. These data reveal that there are exciting details to be discovered in how protein function relates to protein and ultimately phenotypic evolution.