Abstract
The Irrawaddy dolphin (Orcaella brevirostris) is an endangered, small cetacean species which is widely distributed in rivers, estuaries, and coastal waters throughout the tropical and subtropical Indo-Pacific. Despite the extensive distribution of this species, little is known of individual movements or genetic exchange among regions in Thailand. Here, we evaluate the genetic diversity and genetic structure of O. brevirostris in the eastern, northern and western Gulf of Thailand, and Andaman Sea. Although phylogenetic relationships and network analysis based on 15 haplotypes obtained from 32 individuals reveal no obvious divergence, significant genetic differentiation in mitochondrial DNA (overall FST = 0.226, P < 0.001; ΦST = 0.252, P < 0.001) is apparent among regions. Of 18 tested microsatellite loci, 10 are polymorphic and successfully characterized in 28 individuals, revealing significant genetic differentiation (overall FST = 0.077, P < 0.05) among the four sampling sites. Structure analysis reveals two inferred genetic clusters. Additionally, Mantel analysis demonstrates individual-by-individual genetic distances and geographic distances follow an isolation-by-distance model. We speculate that the significant genetic structure of O. brevirostris in Thailand is associated with a combination of geographical distribution patterns, environmental and anthropogenic factors, and local adaptations.
Highlights
The Irrawaddy dolphin (Orcaella brevirostris) is a small cetacean species which is widely distributed in rivers, estuaries, and coastal waters throughout the tropical and subtropical Indo-Pacific (Stacey and Arnold, 1999; Minton et al, 2013)
We report 10 of 18 tested loci isolated from S. chinensis to be polymorphic among O. brevirostris individuals from the four geographic locations in Thailand
Based on analyses of both Mitochondrial DNA (mtDNA) and microsatellites, genetic diversity does not differ significantly among sampling locations in the Gulf of Thailand, but significant genetic differentiation is apparent between different region pairs
Summary
The Irrawaddy dolphin (Orcaella brevirostris) is a small cetacean species which is widely distributed in rivers, estuaries, and coastal waters throughout the tropical and subtropical Indo-Pacific (Stacey and Arnold, 1999; Minton et al, 2013). Estuarine and coastal populations of this species occur from the northwestern Bay of Bengal, east through the Gulf of Thailand to the Philippines, and south to the Indonesian Archipelago (Stacey and Arnold, 1999; Krützen et al, 2018). Other subpopulations occur in lagoons and marine appended lakes, such as Chilika in India, Songkhla in Thailand, and Malampaya Sound in the Philippines (Beasley et al, 2002; Dolar et al, 2002; Sutaria and Marsh, 2011).
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