Sardines at a junction: seascape genomics reveals ecological and
oceanographic drivers of variation in the NW Mediterranean Sea
Abstract
By evaluating genetic variation across the entire genome, one can
address existing questions in a novel way while new can be asked. Such
questions include how different local environments influence both
adaptive and neutral genomic variation within and among populations,
providing insights not only into local adaptation of natural
populations, but also into their responses to global change and the
exploitation-induced evolution. Here, under a seascape genomic approach,
ddRAD genomic data were used along with environmental information to
uncover the underlying processes (migration, selection) shaping European
sardines (Sardina pilchardus) of the Western Mediterranean and adjacent
Atlantic waters. This information can be relevant to the (re)definition
of fishery stocks, and their short-term adaptive potential. We found
that studied sardine samples form two clusters, detected using both
neutral and adaptive (outlier) loci suggesting that natural selection
and local adaptation play a key role in driving genetic change among the
Atlantic and the Mediterranean sardines. Temperature and especially the
trend in the number of days with sea surface temperature (SST) above
19oC was crucial at all levels of population structuring with
implications on species’ key biological processes, especially
reproduction. Our findings provide evidence for a dynamic equilibrium
where population structure is maintained by physical and biological
factors under the opposing influences of migration and selection. Given
its dynamic nature, such a system postulates a continuous monitoring
under a seascape genomic approach that can benefit by incorporating a
temporal as well as a more detailed spatial dimension.