70,000 years of isolation for the humpback whales of the Arabian Sea
Humpback whales (Megaptera novaeangliae) are generally migratory creatures, with the longest known migration of any mammal – 9000 km between their feeding grounds within the polar regions and their breeding areas in tropical waters. Genetic analyses are more frequently being used as a tool to identify new species’ and therefore alter the population numbers and appropriately designate an IUCN listing.
A population of these whales have caught the attention of researchers by going against the normal migratory behaviour of their species, and remaining within the Arabian Sea all year round. A recent investigation into the genetic structure of this particular group of humpback whales involved the collection of DNA samples from 67 individuals. When this was interpreted and compared to the migratory groups it was discovered that the Arabian Sea population has remained isolated for around 70, ooo years.
This lengthy separation has not led to the Arabian population becoming a distinct species in its own right but has led to speculation that this is the most isolated population of this species and the level of divergence has been described as ‘striking’ by Dr. Howard Rosenbaum. The isolation is thought to have been linked to glacial episodes in the late Pleistocene Epoch due to shifts in the Indian Monsoon and then the separation furthered by asynchronous breeding cycles. The closest population to the Arabian Sea are those that bread in the Western Indian Ocean, however the Arabian Population breeds at times that more closely match those who inhabit the Northern Hemisphere – leading to a lack of gene flow and the level of divergence which is now exhibited.
Humpback Whales are currently listed as ‘least concern’ on the IUCN , but the population in the Arabian Sea would be considered ‘endangered’ if listed separately, leading conservationists to suggest that there should be an increase in protection for this population and that the current species based protection measures are inadequate.
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