Discovering diversity in humpback whales
New genetic studies have revealed oceanic divergence in humpback whales (Megaptera novaeangliae), with populations in the oceans of the North Pacific, North Atlantic and the Southern Hemisphere now recognised as separate subspecies.
Skin biopsies, collected and analysed by scientists from the British Antarctic Survey (BAS) and Oregon State University, showed that humpbacks in these three geographical regions are evolving semi-independently from each other. Breeding and calving in the winter in sub-tropical waters, humpbacks migrate around 16,000km to polar and sub-polar regions in the summer to feed. Despite these incredible migrations it is believed that the populations are separated by warm equatorial waters that they rarely cross, resulting in their genetic divergence.
The study looked at both mitochondrial DNA (inherited from the mother), and nuclear DNA (inherited from the father). Dr Jennifer Jackson of the BAS says, “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.”
The findings have revealed that although female whales have moved from one hemisphere to another at certain times in the last several thousand years, they have, in general, remained in the ocean of their birth, resulting in their evolution into distinct subspecies. For years, differences in body colour and in the underside of the tail (flukes) have been observed between whales from the northern and southern hemispheres. However, until this study these colour differences have not been linked to the long-term isolation between populations.
Dr Jackson believes that the results of this study have implications for how we think we about the conservation and recovery of humpbacks on a regional scale.
The paper has been published in Proceedings of the Royal Society B.
Photo credit D.W.H. Walton.
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