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    Species range evolution of the rocky intertidal leaf oyster Isognomon nucleus (Lamarck, 1819) in the Indo-Pacific
    (2026-08-01)
    Mahyotsanun, Patteera
    ;
    Shahdadi, Adnan
    ;
    Ganmanee, Monthon
    ;
    Chan, Benny K.K.
    The small-sized leaf oyster, Isognomon nucleus, inhabits intertidal rock crevices across the tropical and subtropical Indo-Pacific (IP). This study examines the phylogeography of I. nucleus across the IP and the evolution of its distribution range using three mitochondrial markers, COX1, 12S, and 16S, and the nuclear ITS1 marker. Our phylogenetic analyses revealed a widely distributed Indo-Pacific lineage of I. nucleus from the Andaman Sea to Hawaii, and two further deeply diverged but morphologically cryptic lineages: Isognomon cf. nucleus 1, restricted to Taiwan, and Isognomon cf. nucleus 2, occurring in Taiwan and Hainan (China). Phylogeographic analyses revealed extensive gene flow within I. nucleus, spanning from the Andaman Sea in the Indian Ocean through the Philippines and Taiwan in the western Pacific to Hawaii in the Central Pacific. This high dispersal capacity is likely facilitated by west–east flowing equatorial currents and the species’ strong environmental tolerance. Higher pairwise Φst values between Hawaii and other localities indicate reduced gene flow between Hawaii and the Indo–West Pacific, consistent with Hawaii's geographic isolation. The Hawaiian endemic Isognomon californicus is closely related to I. cf. nucleus 1, suggesting that both evolved from a common ancestor and diverged as a result of limited dispersal between Taiwan and Hawaii. Demographic analyses detected clear signals of population expansion in I. nucleus coinciding with the sea level changes in the Last Glacial Maximum.
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    Molecular characterization of three digeneans parasitizing marine fish in the Gulf of Thailand
    (2025-01-01)
    Suwannarat, Nannaphat
    ;
    Gilardoni, Carmen
    ;
    Ribas, Alexis
    ;
    Miquel, Jordi
    ;
    Poonlaphdecha, Srisupaph
    The Gulf of Thailand is a highly diverse marine ecosystem, yet knowledge of its helminth fauna remains fragmentary. Marine fishes were obtained in 2024 from accidental catches of crab-trap fishers or captured by local fishermen using boats in Chumphon Province, Thailand. In this study, we molecularly characterize three digenean trematode genera parasitizing marine fishes from this area: Lecithocladium (Hemiuridae) from the short mackerel (Rastrelliger brachysoma), with a prevalence of 77% in 22 fishes and ten worms examined for morphology; Prodistomum (Lepocreadiidae) from R.brachysoma, with a prevalence of 18% in 22 fishes, and from Rastrelliger kanagurta, with a prevalence of 100% in one fish, with 10 worms examined for morphology; and Lepocreadioides (Lepocreadiidae) from the double-lined tonguesole (Paraplagusia bilineata), with a prevalence of 75% in four fishes, and eight worms examined for morphology. Sequences of nuclear ribosomal markers (18S, ITS2, and 28S) were generated, providing the first molecular data for Lepocreadioides orientalis. Our analyses confirm the presence of Lecithocladium angustiovum and Prodistomum sp. in the Gulf of Thailand, contribute new molecular data, and provide a morphological description of Prodistomum sp. Despite the Gulf of Thailand’s high ichthyofaunal diversity, its helminth communities remain insufficiently investigated, highlighting the need for future research.
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