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Michael A. Bell

Stony Brook University
Department of Ecology and Evolution
Stony Brook University
Stony Brook, NY 11790


Taxa Studied: Vertebrate Animals, Threespine stickleback, Gasterosteus aculeatus Ninespine stickleback, Pungitius pungitius
Techniques Employed: Comparative morphology, embryology, paleontology
Research Description: My research concerns the evolution of phenotypic diversity in threespine stickleback fish (Gasterosteus aculeatus) and to a lesser extent ninespine stickleback (Pungitius pungitius). My interests range from stickleback evolution in the fossil record to nucleotide sequence evolution, but evo-devo is the nexus for my research on pelvic girdle reduction. Lake populations of threespine stickleback in Cook Inlet, Alaska are less than 22,000 years old. Yet, they exhibit extraordinary phenotypic diversity, including frequent pelvic girdle reduction. Pelvic reduction is associated with low ionic strength water and absence of predatory fishes, which is expected because the pelvis is a large bony armor structure. Having discovered several populations with extreme pelvic reduction, it became possible to investigate the history and genetics of pelvic reduction. My lab focuses on characterization of spatial variation and environmental correlates of pelvic reduction, and I have collaborated with other labs (particularly David Kingsleyƒ??s) to study pelvic evo-devo. Linkage analysis and complementation crosses indicated that one major locus and several minor loci cause pelvic reduction in three Cook Inlet populations. The major locus mapped to the region of Pitx1 in the linkage group 7, but complementation suggested involvement of different modifier loci in different populations. The spatial distribution of pelvic reduction in Cook Inlet stickleback suggested repeated independent evolution, allowing comparative studies. Reduced alleles of Pitx1 reduce pelvic size and cause the right vestige to be smaller. We used directional asymmetry to identify 20 Cook Inlet populations that apparently use Pitx1 for pelvic reduction and four that apparently use other major loci. Research, is under way to identify the major loci for pelvic reduction in these populations. Chan et al. (2010; Science 327:302-305) used several Cook Inlet populations from which I provided samples. Linkage mapping and association analysis localized the mutation in Pitx1 of a null allele for pelvic expression. Sequence alignment was used to show that several null alleles had different deletions in his region but all share 488 bp sequence. Transgenesis was used to rescue the pelvic phenotype in progeny from the Bear Paw Lake population (used to sequence the stickleback genome) that never expresses the complete pelvis, demonstrating existence of a pelvis-specific Pitx1 enhancer within this 488 bp sequence. My research also integrates stickleback pelvic evo-devo with patterns of change in fossil stickleback. We showed that directional selection caused reduction of three armor traits within a 21,500-year period but pelvic reduction was delayed for 2500 years. The distribution of pelvic phenotypes is bimodal, indicating control by a major locus. Asymmetry analysis showed that the right pelvic vestige tends to be smaller, implicating Pitx1. Since Pitx1 is recessive, the 2500-year delay in pelvic reduction is probably due to ineffectiveness of selection on a recessive allele. Thus, pelvic evo-devo was crucial to interpret the tempo of evolution in this fossil sequence. Evo-devo of the stickleback pelvis and other traits (e.g., lateral plates) can be used to understand how phenotypes map to genotypes through developmental processes, and how this mapping influences evolution.
Lab Web Page: http://life.bio.sunysb.edu/ee/belllab/
Willing to Host Undergraduates: YES
Actively Seeking Undergraduates: YES
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