Loss of Genetic Diversity Means Loss of Geological Information: The Endangered Japanese Crayfish Exhibits Remarkable Historical Footprints

Itsuro Koizumi,Nisikawa Usio,Tadashi Kawai,Ryuichi Masuda,Noriko Azuma,Bengt Hansson

doi:10.1371/journal.pone.0033986

Abstract

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.

Highlights

Recent human activities have threatened considerable numbers of species and populations in nature that, in turn, have significantly affected ecosystem functioning and provision of ecosystem services [1,2]
But not fully stressed, aspect of genetic diversity is the historical footprints of past environments
We clearly show that a threatened freshwater crayfish contains significant paleo-geological and climatic information in the distribution of genetic variation and that such historical footprints are in danger of disappearing due to ongoing local extinctions

Summary

Introduction

Recent human activities have threatened considerable numbers of species and populations in nature that, in turn, have significantly affected ecosystem functioning and provision of ecosystem services [1,2]. Many animals and plants in Europe possess high genetic diversity and older genotypes in southern regions (e.g. the Balkan, Italian and Iberian peninsulas) and low diversity with more recent genotypes in northern regions (e.g. Scandinavia, UK) [6], indicating post-glacial colonization from the south, consistent with geological evidence that the northern regions had been covered by ice-sheet during the glacial periods [6]. Such genetic information is useful where geological processes are difficult to infer due to dynamic tectonic and volcanic activities

Methods

Results

Conclusion