3.3.6 Heterozygosity and population history of NA blue whales
Genome-wide heterozygosity for the ten present-day samples
(> ~20X) and the historical sample from
Antarctica (~6X) was high. Genetic variation within the
NA population was also high ~0.0025 (other whale species
have ~0.001 (Árnason et al., 2018)). The Antarctic blue
whale had the highest heterozygosity within our samples (0.0053).
Our PSMC results suggest that blue whale population size was relatively
stable until approximately 400,000 years ago, when it began a decline
that continued during the subsequent glacial and interglacial. There is
also a suggestion of a precipitous decline during the latest glacial
maximum (approximately 14,000 to 115,000 years ago). The trajectory of
the fin whale population size through time is distinct from the blue
whales, in that there is an initial decline beginning with the onset of
the Pleistocene epoch approximately 2.5 million years ago, and a
population rebound coinciding roughly with the onset of the decline in
blue whales. The rebound ended and the fin whale population began to
decline again during the interglacial ~220,000 years
ago. The population then plateaued shortly after the onset of the last
glacial maximum.