Northern elephant seals were hunted to the point that their population size was reduced to as few as 20 in the late 1800s. Since
then, their populations have rebounded to over 30,000. However, the genetic diversity is significantly reduced in the rebounded population of elephant seals. What explains this lack of genetic diversity in a population of 30,000?
Population bottlenecks. but their genes still carry the marks of this bottleneck: they have much less genetic variation than a population of southern elephant seals that was not so intensely hunted.
Population bottleneck refers to drastic decrease in a population size due to environmental effects or human interference. When very low individuals survive and multiply, they might still recover the population size but the genetic diversity is reduced a lot. This is because allele frequency can decrease for a lot of alleles when the population size is decreasing, some alleles might even get eliminated completely from the population.
Here, even though Northern elephant seals regained their population to 30000 they had started from only the 20 remaining seals. Due to lack of diversity in remaining seals, even the progeny did not show genetic diversity.
