An empirical genetic assessment of the severity of the northern elephant seal population bottleneck

Abstract

A bottleneck in population size of a species is often correlated with a sharp reduction in genetic variation. The northern elephant seal (Mirounga angustirostris) has undergone at least one extreme bottleneck, having rebounded from 20-100 individuals a century ago to over 175,000 individuals today. The relative lack of molecular-genetic variation in contemporary populations has been documented, but the extent of variation before the late 19th century remains unknown. We have determined the nucleotide sequence of a 179 base-pair segment of the mitochondrial DNA (mtDNA) control region from seals that lived before, during and after a bottleneck low in 1892. A 'primerless' PCR was used to improve the recovery of information from older samples. Only two mtDNA genotypes were present in all 150+ seals from the 1892 bottleneck on, but we discovered four genotypes in five pre-bottleneck seals. This suggests a much greater amount of mtDNA genotypic variation before this bottleneck, and that the persistence of two genotypes today is a consequence of random lineage sampling. We cannot correlate the loss of mtDNA genotypes with a lowered mean fitness of individuals in the species today. However, we show that the species historically possessed additional genotypes to those present now, and that sampling of ancient DNA could elucidate the genetic consequences of severe reductions in population size.

Preliminary genetic status of the spotted seal Phoca largha in Liaodong Bay (China) based on microsatellite and mitochondrial DNA analyses

“…48 Furthermore, the nucleotide diversity of the LB population was even lower than that of the bottlenecked Northern elephant seal population (p=0.0065-0.0086). 49 However, BSPs investigating effective population size (N e ) over time did not detect any past bottleneck event (Supplementary Figure 1), a result similar to that obtained in the mismatch distribution analyses (data not shown). Hence, it seems that the recent reduction of the LB population size caused by human activities has not yet caused a severe bottleneck influencing the diversity indices, but rather that older and possibly recurrent events had a more profound effect on the population, as observed by mtDNA sequences.…”

Low genetic variation support bottlenecks in Scandinavian red deer

“…Loss of genetic variation from genetic drift during population bottlenecks has been demonstrated for many species (Weber et al 2000;Vila et al 2003;Goossens et al 2006), as a result of processes such as founder events and isolation after postglacial colonisation (Hewitt 2000; Communicated by P. Alves…”

Low Genetic Variation in the Heath Hen Prior to Extinction and Implications for the Conservation of Prairie-Chicken Populations

“…To date, relatively few studies of wild populations have examined the loss of genetic variation over the course of a population decline or recovery. In some populations there has been a significant loss of both genetic variation and fitness (Westemeier et al 1998), but in other cases the results are less clear, as the genetic changes have been relatively small (Miller and Waits 2003), the loss of genetic variation predated the population decline (Mundy et al 1997;Pertoldi et al 2001) or the loss of genetic variation was associated with relatively minor effects on fitness (Weber et al 2000;Groombridge et al 2000, Bellinger et al 2003. To date, only two studies of populations in the wild have demonstrated a positive association between genetic variation and the risk of population extinction (Newman and Pilson 1997;Saccheri et al 1998).…”