ELEPHANT SEAL GENETIC-VARIATION AND THE USE OF SIMULATION-MODELS TO INVESTIGATE HISTORICAL POPULATION BOTTLENECKS

Because the northern elephant seal (Mirounga angustirostrus) was heavi ly exploited during the 19th century, it experienced an extreme popula tion bottleneck. Since then, under legislative protection in the Unite d States and Mexico, northern elephant seals have recovered dramatical ly in number, although their genomic diversity was greatly reduced, ap parently as a consequence of the bottleneck. In this study we investig ated DNA sequence diversity in two mtDNA regions (the control region a nd 16S RNA) and found low genetic variation in the northern elephant s eal: there were only two control region haplotypes (sequence differenc e = 1%), which was consistent with an extreme founder event in the rec ent history of the northern species. We also reaffirmed the lack of al lozyme diversity in this species. In contrast, the Southern elephant s eal (M. leonina), which though similarly exploited never fell below 1, 000 animals, had 23 control region mtDNA haplotypes (average sequence difference = 2.3%). To investigate the extent of the founder event in the northern elephant seal we devised a simulation model based on exte nsive demographic data. This allowed a statistical analysis of the lik ely outcome of bottlenecks of different size and duration. Given these historical data, our results indicate (within 95% confidence) a bottl eneck of less than 30 seals and 20-year duration, or, if hunting was t he primary pressure on the population, a single-year bottleneck of les s than 20 seals.