Department of Ecology and Evolution
Stony Brook University
How the Stickleback Lost its Pelvis: Fossils, Genes, and Natural Selection
Friday, October 17, 2009
Lecture Hall 8, 4:00 PM
The genetics of adaptation during speciation is poorly understood because it is difficult to combine the necessary genetic and ecological information with long-term observations. This information is available for threespine stickleback fish (Gasterosteus aculeatus). Evolution of reduced pelvic structures during 17,000 years, within which a new fossil threespine stickleback species evolved, can be explained using paleoecological inferences and information on the ecology and genetics of modern sticklebacks. Absence of predatory fishes from the fossil deposit in which the stickleback occurs is consistent with selection for armor loss. Directional asymmetry (i.e., bias for larger left pelvic vestiges) and trimodal pelvic phenotype frequency distributions within the fossil samples implicate Pitx1, a gene that causes about 60% of pelvic reduction in modern populations. The complex temporal pattern of pelvic evolution in this fossil lineage conforms to expectations for the response to directional selection on a phenotype that depends on a major gene with dominance plus minor modifier genes, as is found in extant stickleback populations.
Mike Bell grew up in Los Angeles and became an avid fossil fish collector and volunteer worker at the local natural history museum at age 13. His interest in stickleback evolution formed during the summer after his freshman year at the University of California, San Diego, when he happened to collect fossil sticklebacks with pelvic girdle variation in Nevada. These fossils became the basis for his masters thesis at UCLA in 1975, where he also earned his Ph.D. for research on stickleback evolution in 1976. Bell joined the faculty at Stony Brook University in 1978, where he is now a professor in the Department of Ecology and Evolution. He started research on stickleback populations in Cook Inlet, Alaska in 1990, and these populations have become important for research on stickleback behavior, ecology, evolution, and genomics. He co-edited The Evolutionary Biology of the Threespine Stickleback (1994), which has stimulated research on stickleback genomics that led to sequencing of its genome in 2006.