A grant has been awarded to Dr. Naomi E. Pierce and Mr. Nikolai Kandul at Harvard University to study the role of chromosomal evolution in species radiation. The karyotype, or number and structure of chromosomes in the nucleus of the cell, typically does not vary much from species to species. Humans, for example, have 23, while our closest relative, the chimpanzees, has 24. In contrast to this general pattern, three groups of butterflies, the genera Agrodiaetus, Lysandra and Plebicula, possess the greatest karyotype diversity in the animal kingdom, with chromosome numbers ranging from 7 to 225 among closely related species. Preliminary studies show that this chromosome diversity evolved independently within each of these groups. Dr. Pierce and Mr. Kandul will use this remarkable phenomenon to answer the following questions: Did karyotype diversification in these genera cause the production of new species, or is it merely the bi-product of other factors promoting speciation? What mechanisms have promoted karyotype diversification within these genera? In the course of the proposed research: (1) the evolutionary history of these genera will be reconstructed using characters from their DNA; (2) karyotypes will be examined and mapped on the evolutionary tree; (3) the amount of DNA in a single cell will be measured for species with different karyotypes; and (4) factors driving karyotype diversification will be assessed.
In terms of its broader impact, the results of this research will illuminate mechanisms underlying genome instability. This has practical applications in understanding medical conditions; many cancers are correlated with changes in karyotype. The proposed research will also enlarge our knowledge of mechanisms underlying speciation. We read every day about extinction, and the crisis confronting the natural world. But ecosystems are the product of two processes: speciation, which adds new species to the mix, and extinction, which eliminates them. If we are truly to grapple with today's conservation issues, we need to understand both sides of the equation. Finally, the research has already involved collaboration between U.S., Spanish, Australian, Turkish and Russian scientists, and will continue to foster international communication and understanding.
