Population genetic structure and differential selection in mussel Mytilus chilensis

This study examines the genetic connectivity between natural banks of Chilean mussel, Mytilus chilensis, located in Reloncavi Fjord. This sector is the principal source of seed for commercial farming and has the second-largest aquaculture production volume in the country. The objects of this work are as follows: (1) to estimate the degree of connectivity between patches (microscale) located in the intertidal/subtidal zones, evaluating the presence of selection processes; and (2) to identify connectivity patterns by gene flow between subpopulations (mesoscale) in order to determine whether they all correspond to a common population (meta-population). We analysed individuals distributed in the intertidal and subtidal zones of five locations by sequencing the mitochondrial cytochrome oxidase I gene and eight nuclear DNA microsatellite loci. Comparison of the two tidal zones presented differences revealed by the COI gene. The locations presented low genetic differentiation; however, differences were found in both markers at the mouth of the fjord. The differences between the tidal zones may result from differentiated natural selection processes between the intertidal and subtidal environments, with those in the intertidal subjected to greater selective pressure. There is effective connectivity between the locations, facilitated by the capacity for dispersion of the larvae and certain oceanographic processes, which would also explain the differences observed in the location at the mouth of the fjord. Because these banks sustain mussel aquaculture activity throughout the country, it is important to take measures to ensure their proper maintenance, observing all the indicators including their genetic diversity and structure.