Age estimation by DNA methylation in the Antarctic minke whale

Determining the age of wild animals is very important in the study of their ecology and for stock assessment and management. In baleen whales, the most common approach for age estimation is by counting the growth layers appearing in earplugs. Although this method is actually considered the most reliable tool for age determination in whales, it cannot be performed on free-ranging individuals. A recent study reported that the CpG methylation frequency of specific genes (GRIA2 and CDKN2A) correlated significantly with age in humpback whales. The implication of this result is that DNA analysis based on biopsy samples is a potentially useful approach for age estimation in free-ranging whales. In this study, we investigated whether the age-related CpG sites in the GRIA2 and CDKN2A genes found in humpback whales are also found in Antarctic minke whales. Results showed that the CpG methylation frequency of the GRIA2 gene correlated positively with age in Antarctic minke whales, although the CpG sites were different from those in humpback whales. These findings suggest that age-related CpGs (AR-CpGs) can differ even between closely related species, and that it is necessary to find species-specific AR-CpGs for estimating animal age from DNA methylation patterns.