| The goal of this project has been to determine the degree of genetic diversity at specific loci in species impacted by human behavior. Humans have impacted marine and terrestrial ecosystems for prolonged time periods, resulting in loss of numbers and genetic diversity in many species. The extreme nature of human impact was typified by sealing pressures on pinnipeds during the 1700–1800's, as exemplified by the near extinction of both Guadalupe fur seals (Arctocephalus townsendi) and northern elephant seals (Mirounga angustirostris). If a population contraction—a bottleneck—is severe only a few individuals may survive, leading to diminished genetic variability, loss in heterozygosity, and reduced fitness.; To determine the magnitude of bottlenecks, I assayed a section of the mitochondrial DNA (mtDNA) control region from pre- and post-bottleneck Guadalupe fur seals and northern elephant seals. Ancient Guadalupe fur seal samples gave 25 genotypes, but 24 of these have not been detected in post-bottleneck seals. Modern fur seals showed only seven genotypes in 32 individuals, indicating a significant loss of genetic diversity. Five pre-bottleneck northern elephant seals showed four genotypes, but only one was present in contemporary seals, suggesting greater mtDNA variation before the bottleneck. To address the consequences of repeated bottlenecks on contemporary genetic variation, I surveyed three major histocompatibility complex (MHC) loci in 110 northern elephant seal from two populations. I found: (i) a very small number of alleles at all three MHC loci; (ii) a significant association with geographic location for the DQA locus—inferring a possible fitness difference; and (iii) a nonrandom association of alleles, i.e. linkage disequilibrium, between DQB and DRB, a possible consequence of past population bottlenecks.; My investigation focused on the effects bottlenecks have on genetic diversity and in particular, on the pinnipeds described above. My data support the notion that the northern elephant seal is inbred but has overcome the apparent effects of inbreeding depression. The loss of mtDNA variation noted in this study may be mirrored in other nuclear genes, if so, this would give a “window” into loci that would be important when considering a species' ability to withstand extinction in the face of environmental perturbation. |
