The Endangered Japanese Crayfish Exhibits Remarkable Historical Footprints
Current lands of Japan and the neighboring countries (greenish area with black contour).Presumed past land boundaries are indicated by brown-white area (white denotes 120–140 m) when sea levels decreased by 140 m during the last glacial maximum estimated from a bathymetric map (A). Top right and bottom right panels are magnified maps around the Tsugaru Strait (B) and Tsushima Strait (C), respectively, which are about the threshold levels for the existence of land bridges.
Mentions: The Japanese archipelago exhibits a high endemism in fauna and flora in which speciation has occurred in isolation after colonization from the eastern Eurasian mainland –. Because of the lack of freshwater fishes and considerable topological changes due to volcanic activities, past environments of Japanese archipelago and the colonization patterns of animals and plants are less well-known compared to Europe and North America. Land bridges are particularly important for understanding the mode and pace of species divergence in Japan; the Tsushima Strait (130–140 m in depth), Tsugaru Strait (130–140 m in depth) and Soya Strait (50–60 m) would have been land bridges during lower sea levels and the main colonization routes to the archipelago (Figure 1). Fauna and flora in Honshu, Kyushu and Shikoku islands have probably been colonized via the Korean Peninsula through the Tsushima Strait, whereas those in Hokkaido arrived from Sakhalin Island through the Soya Strait –. The Tsugaru Strait has acted as a significant barrier, creating the two Japanese bioregions (i.e. Hokkaido and the other main islands).
Koizumi I, Usio N, Kawai T, Azuma N, Masuda R
PLoS ONE (2012)
"Over the native range, most populations consisted of unique 16S mtDNA haplotypes, resulting in significant genetic divergence (overall F(ST) = 0.96).This study provides one of the best examples of how phylogeographic analysis can unravel a detailed evolutionary history of a species and how this history contributes to the understanding of the past environment in the region.Ongoing local extinctions of the crayfish lead not only to loss of biodiversity but also to the loss of a significant information regarding past geological and climatic events."
"Intra-specific genetic diversity is important not only because it influences population persistence and evolutionary potential, but also because it contains past geological, climatic and environmental information. In this paper, we show unusually clear genetic structure of the endangered Japanese crayfish that, as a sedentary species, provides many insights into lesser-known past environments in northern Japan. Over the native range, most populations consisted of unique 16S mtDNA haplotypes, resulting in significant genetic divergence (overall F(ST) = 0.96). Owing to the simple and clear structure, a new graphic approach unraveled a detailed evolutionary history; regional crayfish populations were comprised of two distinct lineages that had experienced contrasting demographic processes (i.e. rapid expansion vs. slow stepwise range expansion) following differential drainage topologies and past climate events. Nuclear DNA sequences also showed deep separation between the lineages. Current ocean barriers to dispersal did not significantly affect the genetic structure of the freshwater crayfish, indicating the formation of relatively recent land bridges. This study provides one of the best examples of how phylogeographic analysis can unravel a detailed evolutionary history of a species and how this history contributes to the understanding of the past environment in the region. Ongoing local extinctions of the crayfish lead not only to loss of biodiversity but also to the loss of a significant information regarding past geological and climatic events."