Biology Department

Dr. Mark Nielsen  

"Natural selection or bad luck: the evolution of giant sperm in fruit flies."

Thursday, September 29

12:00

Olin Auditorium

Dr. Nielsen is an Associate Professor in the Biology Department at the University of Dayton.  His research addresses why 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, b2 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?

Previous work showed that the structure/function relationship between Drosophila melanogaster b2 and the spermtail axoneme is highly constrained, and this constraint has a significant role in b2 evolution.  An evolutionarily conserved feature of the b2 protein, the axoneme motif, specifies an evolutionarily conserved feature of motile axonemes, the central pair microtubules, while evolutionary variable features of b2, 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 cooperativity 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.