Synchronized file of allele frequencies for: Using seasonal genomic changes to understand historical adaptation to new environments: parallel selection on stickleback in highly-variable estuaries

Parallel evolution is considered strong evidence for natural selection.
However, few studies have investigated the process of parallel selection
as it plays out in real time. The common approach is to study historical
signatures of selection in populations already well adapted to different
environments. Here, to document selection under natural conditions, we
study six populations of threespine stickleback (Gasterosteus aculeatus)
inhabiting bar-built estuaries that undergo seasonal cycles of
environmental changes. Estuaries are periodically isolated from the ocean
due to sandbar formation during dry summer months, with concurrent
environmental shifts that resemble the long-term changes associated with
postglacial colonization of freshwater habitats by marine populations. We
used pooled whole-genome sequencing (Pool-WGS) to track seasonal allele
frequency changes in six of these populations and search for signatures of
natural selection. We found consistent changes in allele frequency across
estuaries, suggesting a potential role for parallel selection. Functional
enrichment among candidate genes included transmembrane ion transport and
calcium binding, which are important for osmoregulation and ion balance.
The genomic changes that occur in threespine stickleback from bar-built
estuaries could provide a glimpse into the early stages of adaptation that
have occurred in many historical marine to freshwater transitions.