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.