Phylogeographic diversification and postglacial range dynamics shed light on the conservation of the kelp Saccharina japonica

Abstract

Studies of postglacial range shifts could enhance our understanding of seaweed species’ responses to climate change and hence facilitate the conservation of natural resources. However, the distribution dynamics and phylogeographic diversification of the commercially and ecologically important kelp Saccharina japonica in the Northwest Pacific (NWP) are still poorly surveyed. In this study, we analyzed the evolutionary history of S. japonica using two mitochondrial markers and 24 nuclear microsatellites. A STRUCTURE analysis revealed two partially isolated lineages: lineage H, which is scattered along the coast of Japan; and lineage P, which occurs along the west coast of the Japan Sea. Ecological niche modeling projections to the Last Glacial Maximum (LGM) revealed that the southern coasts of the Japan Sea and the Pacific side of the Oshima and Honshu Peninsulas provided the most suitable habitats for S. japonica , implying that these regions served as ancient refugia during the LGM. Ancient isolation in different refugia may explain the observed divergence between lineages P and H. An approximate Bayesian computation analysis indicated that the two lineages experienced post‐LGM range expansion and that postglacial secondary contact occurred in Sakhalin. Model projections into the year 2,100 predicted that S. japonica will shift northwards and lose its genetic diversity center on the Oshima Peninsula in Hokkaido and Shimokita Peninsula in Honshu. The range shifts and evolutionary history of S. japonica improve our understanding of how climate change impacted the distribution range and diversity of this species and provide useful information for the conservation of natural resources under ongoing environmental change in the NWP.

Climate-Driven Range Shifts of Brown Seaweed Sargassum horneri in the Northwest Pacific

“…Our study combined species distribution model and genetic analyses to give insight into impacts of climate change on the spatio-temporal distribution of S. horneri in the NW-Pacific. Based on our projections, the North-Pacific-Japan region may be a suitable habitat for S. horneri under ongoing global warming, which is also supported by projections done for S. japonica (Zhang et al, 2019). The cold Oyashio current in this region may mitigate the rate of ocean warming and facilitate the growth of cold-water adapted species kelps (Saccharina, Alaria, Costaria) (Sudo et al, 2020) and warmtemperate species, such as Undaria pinnatifida (Sato et al, 2016) and Sargassum thunbergii (Li et al, 2017a).…”

“…35-40 • N) may have served as a glacial refugium for S. horneri. Similarly, an ecological niche model also predicted that another seaweed, S. japonica, survived the LGM in this same area (Zhang et al, 2019). Lineage II also occurred along the coasts of Korea.…”

“…Within a species, lineage divergence reflects the occurrence of an allopatric distribution (Ni et al, 2014), and paleoclimatic oscillations are regarded as being one of the most crucial factors shaping the phylogeograhic structure of coastal species (Zhang et al, 2019). Highly structured phylogeographic patterns were detected in most marine species that occur along the NW-Pacific coasts, such as the seaweed Saccharina japonica (Zhang et al, 2019), Chondrus ocellatus (Hu et al, 2015), the yellowfin goby Acanthogobius flavimanus (Hirase et al, 2020), and the barnacle Chthamalus moro (Wu et al, 2015). Sargassum horneri populations in the NW-Pacific were also characterized by strong genetic variation among regions (Hu et al, 2011).…”

“…Due to anthropogenic emissions of greenhouse gases, the major consequence of climate change is an increase in both atmospheric and sea surface temperatures (SST) (Foo and Byrne, 2016), with SSTs expected to increase by 1.2-3.2 • C by the year 2100 (IPCC, 2013). The Northwest Pacific (hereon NW-Pacific) is among the most important and vulnerable marine regions for biodiversity, having lost most of the biomass because of global warming (Zhang et al, 2019;Sudo et al, 2020). Over the last three decades, from the Bering Strait to Southwestern Japan, the coastal SST has risen at a rate of 0.24 ± 0.11 • C per decade, while along the coasts of the Chinese marginal seas, the temperature has increased much faster (by 0.5 • C per decade) (Lima and Wethey, 2012), suggesting that global warming is far more complex than a simple monotonic increase of average temperatures.…”

Phylogeny and Evolution of the Brown Algae

“…Similar links between climatic shifts, range dynamics and intra-or inter-specific diversity are evident in other temperate assemblages as well Hu et al, 2017;Zhang et al, 2019). In the SE Pacific (Chile), many seaweeds show complex genetic subdivisions at 42 S (Guillemin et al, 2016), matching the limits of coastal ice during the last glacial maximum (LGM; McCulloch et al, 2000) and around 30 S, possibly matching the northward limit of the Western Drift during the same period (Guillemin et al, 2016).…”