Although variation in intron divergence values across loci was greater than expected from binomial expectations in both seals and whales, there was no evidence that the variation could be explained by differences in nucleotide composition or in purifying selection. Further work is needed on methods to detect the causes of rate heterogeneity. Preliminary estimates of ancestral population size in elephant seals suggest that the contemporary southern species may provide a reasonable view of long-term population demography. As such, the southern elephant seal provides a suitable comparison with the northern elephant seal to judge the extent of genetic diversity loss experienced in the north from human harvests during the 19th century. It remains enigmatic to explain the lack of dramatic inbreeding depression in the northern elephant seals after suffering such a severe population bottleneck.
Insufficient data are available for a preliminary test of right whale ancestral population size.
A genetic estimate of ancestral population size in right whales. Presented at the Right Whale Consortium Annual Meeting, Boston, MA, October 2000. Theory suggests that when a population is severely reduced in size, one factor affecting the propensity for inbreeding depression is a population's history of inbreeding, or history of small population size. Measures of genetic diversity can be used to estimate effective population size under a neutral model of molecular evolution, but a recent population bottleneck will erase most information about historical population demography. Thus, to estimate pre-whaling genetic diversity in Eubalaena glacialis, most studies have used the contemporary diversity in Eubalaena australis as a proxy.