Genetic Research Reveals Three Unique Humpback Whale Subspecies
Gerard LeBlond for redorbit.com – Your Universe Online
The humpback whale is a large baleen whale that can weigh as much as 40 tons and can be up to 50 feet long. The female breeds and births its calf in sub-tropical waters during the winter and migrates to polar regions to feed in the summer. The humpback inhabits every ocean in the world except the Mediterranean sea. Its behavior includes leaping out of the water and slapping the water’s surface with its tail and long pectoral flippers. The male humpback will also sing long acoustic vocalizations.
In a new genetic study of this giant marine mammal in the oceans of the North Pacific, North Atlantic and Southern Hemisphere researchers found that they are much more distinct from each other than previously thought. The researchers also suggest the humpbacks of these three oceans should be recognized as separate subspecies. Understanding this and realizing how connected these populations are has important implications for the revival of the once hunted species.
The team of scientists from the British Antarctic Survey and Oregon State University, analyzed the largest and most comprehensive genetic dataset collected and assembled for this species. The findings were published in Proceedings of the Royal Society B this week and show that humpback whales of the North Pacific, North Atlantic and Southern Hemisphere are on independent evolutionary trajectories.
The DNA was collected from humpback skin samples during field studies over the course of several years and multiple locations around the South Pacific, North Pacific, North Atlantic and South Indian Oceans. The researchers used a small dart to collect the samples and occasionally the whale’s skin was found in the water near the whales.
“Despite seasonal migrations of more than 16,000 km return [sic], 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,” explained lead author, Dr Jennifer Jackson of the British Antarctic Survey.
“The colour of the bodies and undersides of the tail (the ‘flukes’) of humpback whales in the northern oceans tend to be much darker than those in the Southern Hemisphere. Until this study we didn’t realise that these kinds of subtle differences are actually a sign of long-term isolation between humpback populations in the three global ocean basins,” she continued.
“Using genetic samples, collected from free-swimming whales with a small biopsy dart, we’ve been 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. The mitochondrial DNA allows us to build up a picture of how female humpbacks have moved across the globe over the last million years. The nuclear DNA, which evolves more slowly, provides us with a general pattern of species movements as a whole,” said Jackson.
“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,” said Jackson in a statement.
“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.”