According to new genetic research reported in the Proceedings of the Royal Society B, populations of humpback whales (Megaptera novaeangliae) in North Pacific, North Atlantic and Southern Hemisphere should be recognized as three separate subspecies.
Humpback whale (Megaptera novaeangliae). Image credit: Marina C. Vinhal / CC BY 2.0.
Humpback whales are well known for their amazing acrobatics. They annually undertake the longest migration of any mammal between their winter breeding grounds and summer feeding grounds. Although they travel vast distances, it appears their populations do not cross paths.
Genetic researchers from New Zealand, Chile, the United States and UK analyzed the most comprehensive genetic dataset so far compiled for this species. The findings show that humpback whales of the North Pacific, North Atlantic and Southern Hemisphere are on independent evolutionary trajectories.
“Despite seasonal migrations of more than 16,000 km return, humpback whale populations are actually more isolated from one another than we thought. Their populations appear separated by warm equatorial waters that they rarely cross,” said study lead author Dr Jennifer Jackson of the British Antarctic Survey.
“The color of the bodies and undersides of the tail of humpback whales in the northern oceans tend to be much darker than those in the Southern Hemisphere.”
“Until this study we didn’t realize that these kinds of subtle differences are actually a sign of long-term isolation between humpback populations in the three global ocean basins.”
Using genetic samples, collected from free-swimming whales with a small biopsy dart, the scientists were able to look at two types of humpback DNA – the mitochondrial DNA which is inherited from the mother, and the nuclear DNA which is inherited from both parents.
Dr Jackson said: “we found that although female whales have crossed from one hemisphere to another at certain times in the last few thousand years, they generally stay in their ocean of birth.”
“This isolation means they have been evolving semi-independently for a long time, so the humpbacks in the three global ocean basins should be classified as separate subspecies. This has implications for how we think about their conservation and recovery on a regional scale.”
“Further genetic sequencing and analysis should also help us to understand more about the pattern of humpback migrations in the past. Big changes in the ocean can leave signatures in the genetic code of marine species.”
“For example, the last glacial maximum caused many to shift southwards until the ice retreated or to find ice-free areas in the north. Humpbacks are excellent oceanographers; they go where the food is and can travel long distances to get it, so their patterns of past migration can tell us a lot about the ocean thousands of years ago.”
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Jennifer A. Jackson et al. 2014. Global diversity and oceanic divergence of humpback whales (Megaptera novaeangliae). Proc. R. Soc. B, vol. 281, no. 1786; doi: 10.1098/rspb.2013.3222
