Genetic Diversity and Maternal Lineage of Indo-Pacific Bottlenose Dolphin (Tursiops aduncus) in the Andaman Sea of Thailand

Indo-Pacific bottlenose dolphins (Tursiops aduncus) are a coastal species found in Thai waters off the coasts of the Andaman Sea and the Gulf of Thailand. This species was recently re-listed as near-threatened by the IUCN Red List, though the population status in Thai seas is not known. Here, we investigated genetic diversity, population structure, maternal lineage, and demographics by analyzing skin tissue samples (n = 30) of T. aduncus stranded along the Andaman coastline of Thailand between 1990 and 2019. This study was based on 11 microsatellite loci and 265 bp mtDNA control regions compared to data available through the National Center for Biotechnology Information (NCBI). From microsatellites, the observed heterozygosity (Ho) ranged from 0.46 to 0.85. The mean fixation index (F) value for all loci was 0.10 ± 0.04, which suggests some degree of inbreeding. Two genetic clusters (the most likely K at K = 2) were observed in T. aduncus through the population structure analysis using multiple criteria. For the mtDNA control region, a total of 17 haplotypes were found for dolphins in Thai seas (14 haplotypes from our samples; three haplotypes from the NCBI database) with high levels of haplotype diversity (h) at 0.926 ± 0.027 and nucleotide diversity (π) at 0.045 ± 0.002. A decline in the effective population size from 0.05 million years ago also was observed in Thai T. aduncus through Bayesian Skyline Plots analysis. A unique set of haplotypes was identified in our samples, which may have originated from the Australian and Indian Oceans rather than the Western Pacific Ocean. These results improve our understanding of the maternal lineage of the Indo-Pacific bottlenose dolphin, which can be used for monitoring population status and establishing better conservation plans for this species in the Thai Andaman Sea.