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Genetic Study Reveals Relationships Between Humpback Whale Populations

NEW YORK (GenomeWeb News) – Humpback whales in the Southern Hemisphere exhibit extensive population structure, according to a new genetic study.

An international research team sequenced mitochondrial DNA from about 1,500 humpback whales sampled at more than a dozen sites in the Atlantic and Indian Oceans. The research, appearing online recently in the journal PLoS ONE, suggests existing whale classification schemes encompass genetically differentiated whale groups in the region. The researchers also gained new insights into the relationships between these populations, which may prove useful for future whale conservation efforts.

"Molecular technology gives us a window into the lives of whales that can help us understand the ecological forces shaping their movements and distribution," lead author Howard Rosenbaum, a researcher affiliated with the Wildlife Conservation Society, the American Museum of Natural History, and Columbia University, said in a statement. "We can also use our findings to inform management decisions for a species that is only now beginning to recover from centuries of commercial whaling."

The International Whaling Commission cracked down on commercial humpback whale hunting in the mid-1960s following three centuries of intensive whaling, Rosenbaum and his co-authors noted. Even so, they explained, there is much debate over how well whale populations have recovered from this commercial whaling.

Past studies suggest population structure within humpback whale populations is influenced by everything from social structure and migratory behavior to environmental factors, the team explained, although populations in the Southern Hemisphere have not been as well characterized as those in other regions.

"Humpback whales are perhaps the most studied species of great whale in the Northern Hemisphere," Rosenbaum said, "but many of the interactions among Southern Hemisphere populations are still poorly understood."

In an effort to better characterize the humpback whale population structure in this part of the world, the researchers sampled 1,537 whales from 14 sites in the southwestern and southeastern Atlantic Ocean and the southwestern and northern Indian Ocean over several years.

The team selected the sampling locations from seven International Whaling Commission designated breeding grounds and migratory corridors — dubbed Breeding Stocks A through G — as well as an eighth proposed location called Breeding Stock X. They also consulted with historical whaling documents.

After collecting skin samples using biopsy darts or other approaches, the researchers amplified and sequenced about 520 bases of mtDNA. From there, the researchers narrowed in on a 486 base consensus sequence which they used for subsequent analyses looking at mtDNA structure and gene flow rates in whales from the various regions and sub-populations.

In so doing, the team identified 162 maternal haplotypes in the whale populations tested. They also detected differences between Breeding Stocks A, B, C, and X that are consistent with the International Whaling Commission's population designations.

"Our genetic results support the current management designations proposed by the International Whaling Commission of Breeding Stocks A, B, C, and X as four strongly structured populations," the researchers wrote.

Their results suggest that gene flow is highest between whales from populations found on either side of Africa but lower between whale populations from the coast of southern Africa and the Brazilian coast.

The team also detected very low gene flow rates and high mtDNA differentiation within sub-populations of Breeding Stock B — whales found on Africa's western coast. In contrast, gene flow was high within populations from the eastern coasts of Africa and Madagascar belonging to Breeding Stock C.

Meanwhile, humpback whale populations from Breeding Stock X, in the northern Indian Ocean near Oman, exhibited genetic patterns that were distinct from those detected in other regions. The team's analysis suggests that these whales don't migrate and are only distantly related to the nearest African whales.

The team argued that data from this and related studies will likely prove useful for gaining a better understanding of how well humpback whales have recovered from past whaling — and for coming up with effective conservation strategies.

"An integrative approach combining our genetic analyses with bi-parentally inherited molecular markers and contemporary movement data in various population-modeling scenarios may provide a more precise framework for evaluating whale recovery from previous exploitation, and hence its resilience to current and emerging threats, including the possibility of resumed hunting," the researchers concluded.

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