Relationship of stranded cetaceans in Thai territorial waters to global populations: Mitochondrial DNA diversity of Cuvier's beaked whale, Indo Pacific finless porpoise, pygmy sperm whale, and dwarf sperm whale

Abstract

Cetaceans inhabit oceans throughout the world. Four specific odontocetes, namely Cuvier's beaked whale ( Ziphius cavirostris), Indo Pacific finless porpoise ( Neophocaena phocaenoides), pygmy sperm whale ( Kogia breviceps), and dwarf sperm whale ( Kogia sima), have occasionally been found stranded along Thailand's coastal waters (the Andaman Sea and the Gulf of Thailand). Although shared haplotypes of each species for many locations have been found, and some species have revealed genetic structure through haplotype networks, cetaceans in Thai waters have never been investigated in terms of comparing haplotypes to those that have existed before. Herein, we have illustrated the matrilineally phylogeographic relationships among worldwide populations through Bayesian Phylogenetic tree computations using Markov Chain Monte Carlo (MCMC) and Median-Joining Networks (MJNs). Unique haplotypes of the control region mitochondrial DNA of Thai odontocetes were found for all species. Moreover, a high degree of worldwide haplotype diversity (hd) above 0.8 among the four species was detected, while the lowest degree of nucleotide diversity (π) was observed in the Indo Pacific finless porpoise (1.12% ± 0.184%). An expansion of the effective female population size worldwide of three odontocete species was detected using Bayesian Skyline Reconstruction, but this did not include the Indo Pacific finless porpoise. Because Thai seas are located within the Indo Polynesian province, where this biodiversity hotspot exists, we speculate that these odontocetes may also inhabit specific habitats within the Malay Peninsula and Thailand's territorial waters. Therefore, closer attention and monitoring of these cetacean populations will be necessary for future conservation efforts.