Population genetic structure of the deep‐sea mussel Bathymodiolus platifrons (Bivalvia: Mytilidae) in the Northwest Pacific

Abstract

Studying population genetics of deep‐sea animals helps us understand their history of habitat colonization and population divergence. Here, we report a population genetic study of the deep‐sea mussel Bathymodiolus platifrons (Bivalvia: Mytilidae) widely distributed in chemosynthesis‐based ecosystems in the Northwest Pacific. Three mitochondrial genes (i.e., atp6, cox1, and nad4) and 6,398 genomewide single nucleotide polymorphisms (SNPs) were obtained from 110 individuals from four hydrothermal vents and two methane seeps. When using the three mitochondrial genes, nearly no genetic differentiation was detected for B. platifrons in the Northwest Pacific. Nevertheless, when using SNP datasets, all individuals in the South China Sea (SCS) and three individuals in Sagami Bay (SB) together formed one genetic cluster that was distinct from the remaining individuals. Such genetic divergence indicated a genetic barrier to gene flow between the SCS and the open Northwest Pacific, resulting in the co‐occurrence of two cryptic semi‐isolated lineages. When using 125 outlier SNPs identified focusing on individuals in the Okinawa Trough (OT) and SB, a minor genetic subdivision was detected between individuals in the southern OT (S‐OT) and those in the middle OT (M‐OT) and SB. This result indicated that, although under the influence of the Kuroshio Current and the North Pacific Intermediate Water, subtle geographic barriers may exist between the S‐OT and the M‐OT. Introgression analyses based on these outlier SNPs revealed that Hatoma Knoll in the S‐OT represents a possible contact zone for individuals in the OT‐SB region. Furthermore, migration dynamic analyses uncovered stronger gene flow from Dai‐yon Yonaguni Knoll in the S‐OT to the other local populations, compared to the reverse directions. Taken together, the present study offered novel perspectives on the genetic connectivity of B. platifrons mussels, revealing the potential interaction of ocean currents and geographic barriers with adaption and reproductive isolation in shaping their migration patterns and genetic differentiation in the Northwest Pacific.

Population Genetic Structure and Gene Expression Plasticity of the Deep-Sea Vent and Seep Squat Lobster Shinkaia crosnieri

“…The eastward spread is stronger in both winter and spring (You et al, 2005). Previously, by using genomewide SNP markers, Xu et al (2018) revealed a limited gene flow of the deep-sea mussel Gigantidas platifrons (previously known as Bathymodiolus platifrons) between the SCS and the OT. However, G. platifrons and S. crosnieri have different lifehistory traits.…”

“…Bathymodioline mussels produce planktotrophic larvae that take almost a year to develop, and their dispersal ability is largely influenced by the upper or surface currents (Arellano and Young, 2009). Consequently, the limited larval exchange of G. platifrons between the two sides of the Luzon Strait is suggested to be achieved by the looping path of the Kuroshio Current, which flows into the SCS via the middle part and exits via the northern part of the Luzon Strait (Nan et al, 2011), as well as by the North Pacific Intermediate Water (NPIW; Xu et al, 2018). In contrast, S. crosnieri produces large (2 mm) oil-rich eggs and equally oil-rich lecithotrophic larvae (Miyake et al, 2010;Nakajima et al, 2018), and its dispersal is expected to mainly occur within the middle and deep layers.…”

“…Kiel (2016) reported the Western Pacific as having the highest number of active, sedimentary back-arc vents in the world, which might provide a vital biogeographic link between vent and seep animals. Previous population genetic studies of deep-sea macrobenthos in the Western Pacific have mainly focused on macrobenthos with a planktotrophic larval stage, such as bathymodioline mussels (Kyuno et al, 2009;Miyazaki et al, 2010;Xu et al, 2017Xu et al, , 2018 and the deep-sea limpet Shinkailepas myojinensis (Yahagi et al, 2017). In this study, we aim to understand the population connectivity and local environmental adaptation of the squat lobster Shinkaia crosnieri (Decapoda: Munidopsidae), whose larvae are lecithotrophic and likely have a limited dispersal ability (Nakajima et al, 2018).…”

microRNAs facilitate comprehensive responses of Bathymodiolinae mussel against symbiotic and nonsymbiotic bacteria stimulation

“…Since it was rst discovered in 1987 in Sagami Bay, Gigantidas platifrons (formerly named as Bathymodiolus platifrons) has been found to be dominant in cold seeps and hydrothermal vents of Okinawa Trough and Formosa Ridge of the South China Sea [29][30][31]. It was found that G. platifrons only harbored MOBs in their bacteriocytes, making them an ideal model for investigating the immune response against symbionts.…”

microRNAs Facilitate Comprehensive Responses of Bathymodiolinae Mussel Against Symbiotic and Nonsymbiotic Bacteria Stimulation

“…Since it was rst discovered in 1987 in Sagami Bay, Gigantidas platifrons (formerly named as Bathymodiolus platifrons) has been found to be dominant in cold seeps and hydrothermal vents of Okinawa Trough and Formosa Ridge of the South China Sea [29][30][31]. It was found that G. platifrons only harbored MOBs in their bacteriocytes, making them an ideal model for investigating the immune response against symbionts.…”