Data supporting: Invader at the edge - genomic origins and physiological differences of round gobies across a steep urban salinity gradient

Species invasions are a global problem of increasing concern, especially
in highly connected aquatic environments. Despite this, salinity
conditions can pose physiological barriers to their spread and
understanding them is important for management. In Scandinavia’s largest
cargo port, the invasive round goby (Neogobius melanostomus), is
established across a steep salinity gradient. We used 12 937 SNPs to
identify the genetic origin and diversity of three sites along the
salinity gradient and round goby from western, central and northern Baltic
Sea, as well as north European rivers. Fish from two sites from the
extreme ends of the gradient were also acclimated to freshwater and
seawater, and tested for respiratory and osmoregulatory physiology. Fish
from the high salinity environment in the outer port showed higher genetic
diversity, and closer relatedness to the other regions, compared to fish
from lower salinity upstream the river. Fish from the high salinity site
also had higher maximum metabolic rate, fewer blood cells and lower blood
Ca2+. Despite these genotypic and phenotypic differences, salinity
acclimation affected fish from both sites in the same way: seawater
increased the blood osmolality and Na+ levels, and freshwater increased
the levels of the stress hormone cortisol. Our results show genotypic and
phenotypic differences over short spatial scales across this steep
salinity gradient. These patterns of the physiologically robust round goby
are likely driven by multiple introductions into the high salinity site,
and a process of sorting, likely based on behaviour or selection, along
the gradient. Since this euryhaline fish risks spreading from this area,
seascape genomics and phenotypic characterisation can inform management
strategies even within an area as small as a coastal harbour inlet.