Revisiting differential reproductive rates in Gulf of Maine humpback whales in relation to mitochondrial lineages

Variance in reproductive success among con-specific individuals can potentially result in changes in haplotype (i.e. alleles) frequencies. A prior study found differential reproductive rates in two clades of humpback whales (Megaptera novaeangliae) sampled in the Gulf of Maine, and predicted an 11% decline in one clade versus a 30% increase in the other over a 75-year period. Here, we re-examined evidence for this finding after increasing the sample size by an order of magnitude and extending the period of observation by 21 years. The mt control region (mtCR) was sequenced for 1507 individual humpback whales sampled in the Gulf of Maine, including 318 mature females. Twenty-three haplotypes were identified among the mature females and used to build a Bayesian genealogy which confirmed two well-differentiated clades (BCD and IJK). Calving rates were estimated annually by clade for the same period as the prior study (1979-1995) and also extended through 2016. Whereas significant differences were found in reproductive rates over time in the prior study, larger sample sizes revealed comparable trends for both clades, both within the prior period and in subsequent decades. No statistically significant differences in reproductive rates were found at different levels of the maternal co-ancestry. Our study indicates that mt haplotypes and mt clades are not correlated with a differential reproductive rate in female humpback whales in the Gulf of Maine, and suggests against significant short-term mtCR-based selection.