Abstract
A clear understanding of population structure is essential for assessing conservation status and implementing management strategies. A small, non-migratory population of humpback whales in the Arabian Sea is classified as “Endangered” on the IUCN Red List of Threatened Species, an assessment constrained by a lack of data, including limited understanding of its relationship to other populations. We analysed 11 microsatellite markers and mitochondrial DNA sequences extracted from 67 Arabian Sea humpback whale tissue samples and compared them to equivalent datasets from the Southern Hemisphere and North Pacific. Results show that the Arabian Sea population is highly distinct; estimates of gene flow and divergence times suggest a Southern Indian Ocean origin but indicate that it has been isolated for approximately 70,000 years, remarkable for a species that is typically highly migratory. Genetic diversity values are significantly lower than those obtained for Southern Hemisphere populations and signatures of ancient and recent genetic bottlenecks were identified. Our findings suggest this is the world's most isolated humpback whale population, which, when combined with low population abundance estimates and anthropogenic threats, raises concern for its survival. We recommend an amendment of the status of the population to “Critically Endangered” on the IUCN Red List.
Highlights
Understanding the patterns underlying the division of natural populations into smaller units is essential for the conservation and management of biodiversity
The Bayesian skyline plot obtained in BEAST with the mitochondrial DNA shows a decline of effective population size through time, which according to the molecular clock used, may have started at around 15,000 y.a until the present day (Figure 6)
Estimates of contemporary effective population size (Ne) for the Arabian Sea humpback whales (ASHW) resulted in values that range from 90.4 to 142.6 if we consider the method based on linkage disequilibrium (LD) and different allele frequencies (Table S1)
Summary
Understanding the patterns underlying the division of natural populations into smaller units is essential for the conservation and management of biodiversity This is relevant for species and populations that have been extensively exploited and require specific recovery measures. Humpback whales (Megaptera novaeangliae) were among those species heavily impacted by whaling, in the Southern Hemisphere [12] Distributed worldwide, they typically undertake long migrations between high latitude feeding grounds and low latitude breeding grounds, to which they show a high degree of site fidelity Patterns of differentiation have been extensively studied in Northern (e.g.[14, 17]) and some Southern Hemisphere populations (e.g.[16]), but understanding of population structure and gene flow in the Indian Ocean remains limited, for humpback whales in the Arabian Sea (Figure S1)
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