SREL Reprint #2633

Low mitochondrial DNA variation among American alligators and a novel non-coding region in crocodilians

Travis C. Glenn1,2, Joseph L. Staton3, Alex T. Vu1, Lisa M. Davis1,2, Jaime R. Alvarado Bremer1,
Walter E. Rhodes4, I. Lehr Brisbin, Jr.2, and Roger H. Sawyer1

1Department of Biological Sciences, University of South Carolina, Columbia, South Carolina 29208
2Savannah River Ecology Laboratory, University of Georgia, Aiken, South Carolina 29802
3Belle W. Baruch Institute for Marine and Coastal Research, University of South Carolina, Columbia,
South Carolina 29208
4South Carolina Department of Natural Resources, Dennis Wildlife Research Center, Bonneau,
South Carolina 29431

Abstract: We analyzed 1317-1823 base pairs (bp) of mitochondrial DNA sequence beginning in the 5' end of cytochrome b (cyt b) and ending in the central domain of the control region for 25 American alligators (Alligator mississippiensis) and compared these to a homologous sequence from a Chinese alligator (A. sinensis). Both species share a non-coding spacer between cyt b and tRNAThr.
Chinese alligator cyt b differs from that of the American alligator by 17.5% at the nucleotide level and 13.8% for inferred amino acids, which is consistent with their presumed ancient divergence. Only two cyt b haplotypes were detected among the 25 American alligators (693-1199 bp surveyed), with one haplotype shared among 24 individuals. One alligator from Mississippi differed from all other alligators by a single silent substitution. The control region contained only slightly more variation among the 25 American alligators, with two variable positions (624 bp surveyed), yielding three haplotypes with 22, two, and one individuals in each of these groups. Previous genetic studies examining allozymes and the proportion of variable microsatellite DNA loci also found low levels of genetic diversity in American alligators. However, in contrast with allozymes, microsatellites, and morphology, the mtDNA data shows no evidence of differentiation among populations from the extremes of the species range. These results suggest that American alligators underwent a severe population bottleneck in the late Pleistocene, resulting in nearly homogenous mtDNA among all American alligators today.

SREL Reprint #2633

Glenn, T. C., J. L. Staton, A. T. Vu, L. M. Davis, J. R. A. Bremer, W. E. Rhodes, I. L. Brisbin, Jr., and R. H. Sawyer. 2002. Low mitochondrial DNA variation among American alligators and a novel non-coding region in crocodilians. Journal of Experimental Zoology/Molecular Development & Evolution 294:312-324.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).