Conservation genetic units under future climate change scenarios: a case of the threatened freshwater pearl mussel (Margaritifera margaritifera)

Freshwater organisms are among the most vulnerable species being impaired by global climate change. Freshwater Pearl Mussel (Margaritifera margaritifera) is a keystone species that facilitates a number of important ecosystem functions in cold water oligotrophic streams, while is currently facing habitat alteration and degradation due to human activities. Global climate change is amplifying these negative impacts. Population decline is directly connected with transformation of population genetic structure and may result in significant loss of genetic diversity. In this study, we identified populations of M. margaritifera for conservation prioritization in the north-eastern part of the species’ range and investigated the potential impact of future climate scenarios on its conservation genetics. We used nine microsatellite loci to examine genetic diversity and differentiation in 17 populations of the species from rivers of the Barents, White, and Baltic Sea basins. To forecast the effects of climatic changes on the dynamics of genetic structure, we applied the Bayesian clustering algorithm. Genetic simulations were conditioned to mean summer temperatures estimated under future carbon emission projections, i.e., representative concentration pathway (RCP) scenarios 4.5 and 8.5. High genetic diversity and low genetic differentiation were found in the studied populations, with individuals being assigned to three genetic clusters. Future climate change will significantly rearrange cluster distribution resulting in lower population differentiation. The only exception were populations of the Baltic Sea basin that keep their genetic uniqueness under current and future climatic conditions. Obtained data allowed us to delineate three conservation units that play critical roles in securing the genetic diversity of the species currently and in the future: (1) populations of the Barents Sea basin with the highest contribution to the overall genetic diversity; (2) populations of northern Karelia which will lose significant part of their diversity under the climate change; and (3) populations of the Baltic Sea basin, with a unique gene pool which is threatened by climate change and other anthropogenic pressures.