Abstract
Although humpback whales are among the best-studied of the large whales, population boundaries in the Southern Hemisphere (SH) have remained largely untested. We assess population structure of SH humpback whales using 1,527 samples collected from whales at fourteen sampling sites within the Southwestern and Southeastern Atlantic, the Southwestern Indian Ocean, and Northern Indian Ocean (Breeding Stocks A, B, C and X, respectively). Evaluation of mtDNA population structure and migration rates was carried out under different statistical frameworks. Using all genetic evidence, the results suggest significant degrees of population structure between all ocean basins, with the Southwestern and Northern Indian Ocean most differentiated from each other. Effective migration rates were highest between the Southeastern Atlantic and the Southwestern Indian Ocean, followed by rates within the Southeastern Atlantic, and the lowest between the Southwestern and Northern Indian Ocean. At finer scales, very low gene flow was detected between the two neighbouring sub-regions in the Southeastern Atlantic, compared to high gene flow for whales within the Southwestern Indian Ocean. 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 population structure patterns found in this study are likely to have been influenced by a combination of long-term maternally directed fidelity of migratory destinations, along with other ecological and oceanographic features in the region.
Highlights
The issue of population structure has remained a central one in the areas of molecular ecology and conservation biology
Genetic assessments to evaluate population structure are the backbone of Management Unit (MU) designations, which have proven key elements of prioritization in conservation and management strategies [1]
The combined genetic evidence suggests that there is a significant degree of population structure for humpback whale Breeding Stocks within the Indian and South Atlantic Oceans
Summary
The issue of population structure has remained a central one in the areas of molecular ecology and conservation biology. A recurrent topic in the marine environment centers on the varying degrees and plausible mechanisms of population structure for different species. Periods of inter-glacial warming have allowed episodic contact between populations in the Southern and Northern Hemispheres over evolutionary time scales [6]. Barriers to dispersal have not fluctuated to the same extent throughout large parts of the Southern Hemisphere (SH) [7], and populations of large migratory marine species in the SH may potentially show a higher degree of connectivity across ocean basins over evolutionary and demographic timeframes [8,9]
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