Dorsal skin color patterns among southern right whales (Eubalaena australis): genetic basis and evolutionary significance.

Distribution and inheritance of dorsal skin color markings among two populations of southern right whales (Eubalaena australis) suggest that two genes influence dorsal skin color. The grey-morph and partial-grey-morph phenotypes (previously known as partial albino and grey-blaze, respectively) appear to be controlled by an X-linked gene, whereas the white blaze appears controlled by an autosomal gene (recessive phenotype). Calving intervals, calf size, and length of sighting history data suggest that partial-grey-morph, white-blaze, and black cows experience similar levels of reproductive success. Grey-morph cows (XgXg) are rare or absent in the two populations, but this was not unexpected given observed population frequencies of grey-morph males (XgY) and partial-grey-morph females (XGXg). The proportion of partial-grey-morph calves produced by black cows (XGXG) suggests that the reproductive success of grey-morph males was equal to that of black males, however, larger sample sizes are required to determine whether grey-morph males tend to have shorter sighting histories. The reproductive success of white-blaze males appeared similar to that of black males among whales off Argentina. There were significantly fewer white-blaze calves than expected off South Africa, which could be due to white-blaze males experiencing reduced reproductive success or to sighting blases that result in white-marked calves being misidentified as black calves. The relative frequencies of both types of dorsal color markings varied between the South African and Argentinian right whale populations, suggesting limited nuclear gene flow between these populations; analyses using other nuclear markers are under way to confirm the extent of gene flow.