Abstract
The repeated transgression and regression of coastlines mediated by the late Quaternary glacial-interglacial cycles make the northwest Pacific to become a hotspot to study marine speciation and population diversity. The red alga Agarophyton vermiculophyllum is an ecologically important foundation species native to the northwest Pacific, capturing considerable research interest due to its range-wide invasiveness in Europe and North America. However, the knowledge of phylogeographic structure and intraspecific genetic diversity across the entire native range are still scarce. Here, we used 1214-bp of mitochondrial cytochrome c oxidase subunit 1 (cox1) to explore phylogeographic patterns, lineage structure and population genetic differentiation of 47 A. vermiculophyllum populations in the northwest Pacific. Our DNA data revealed overall high haplotype diversity and low nucleotide diversity, and five phylogeographically structured genetic lineages that diverged significantly from each other. S-DIVA analyses showed the ancestors of A. vermiculophyllum originating from multiple areas encompassing the Japan-Pacific coast, the Sea of Japan, East and South China Seas. These combined evidence indicate that A. vermiculophyllum might have survived in multiple scattered glacial refugia during the late Quaternary climate oscillations in the northwest Pacific. This knowledge may help to better understand how climate shifts interacted with contemporary environments to contribute to intraspecific genetic variation and adaptation capability of seaweed under current global climate warming.
Highlights
The northwest Pacific spans three major marginal seas, the Sea of Japan, the East China Sea, and the South China Sea (Figure 1)
The detected overall haplotype (Hd = 0.6632) and nucleotide diversity (π = 0.3766 × 10−2) are similar to previous results reported in A. vermiculophyllum in the northwest Pacific by Kim et al (2010) (Hd = 0.731, π = 0.329 × 10−2) and Liu et al (2016) (Hd = 0.589, π = 0.318 × 10−2), respectively
Such high haplotype diversity and low nucleotide diversity patterns suggest that A. vermiculophyllum in the native northwest Pacific may have experienced rapid population growth over a short period because sudden population expansion cannot support this species to have sufficient time to accumulate enough nucleotide mutations (Grant and Bowen, 1998)
Summary
The northwest Pacific spans three major marginal seas, the Sea of Japan, the East China Sea (including Yellow–Bohai Sea), and the South China Sea (Figure 1). In the northwest Pacific, the reduction of marginal seas during the late Quaternary is thought to have led to a large decrease of marine species, while some ancestral relict populations may have survived in isolated refugia The discontinuity of these refugia made an essential contribution to population-level isolation and differentiation (Ni et al, 2014). When sea levels rose after the Last Glacial Maximum (LGM), the surviving populations in marine refugia expanded to colonize new habitats, eliminating population differentiation caused by isolation in different refugia (Xue et al, 2014). Ocean currents form another important driving force of post-glacial population colonization. In the Yellow–Bohai Sea, for example, the Yellow Sea Warm Current originating from the Okinawa trough has been reported to drive genetic homogeneity in some marine organisms (Hu et al, 2015; Li et al, 2017; Liu et al, 2018)
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