REU: Phylogenetic Relationships, Population Structure, and Hybrid Zone Dynamics Among Central Mexico Chromosome Races of the Sceloporus grammicus Complex (Iguanidae)

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This study, by Dr. Sites at Brigham Young University and Ira Greenbaum and Scott Davis at Texas A&M University, has three major objectives relating to the evolutionary history of the mesquite lizard, Sceloporus grammicus, in central Mexico. First, several molecular techniques (protein and recombinant DNA) will be used to test a chromosomally-based hypothesis of the evolutionary relationships of seven known chromosome races (populations of morphologically similar lizards with different chromosome numbers) from central Mexico. Reconstructing the patterns of chromosomal evolution in these races depends upon knowing their relationships from data sets independent of the chromosomes--hence the reason for the molecular markers. A closely related second objective will be to assess the amount of gene flow within two of these races, again using the molecular markers, to determine the likelihood with which a new chromosomal mutation may persist and eventually be spread throughout the range of the chromosome race. The third aspect of this work will be the detailed study of patterns of gene flow between two chromosome races that meet and hybridize in a limited part of their range. The second objective will also provide an internal "control" for this hybrid zone study. By comparing chromosome behavior in the sex cells of hybrid animals relative to that in pure "parental" chromosome races outside of the zone of hybridization, we can determine the role played by chromosomal differences in causing partial sterility in the hybrids and thereby contributing to a reduction of gene flow. If this occurs, the chromosomal changes may foster genetic divergence to the point that the chromosome races become distinct species.