When species shift their ranges to new regions, their success at establishment and population growth is determined by their phenotypic match to the local environment (Valladares et al., 2014). Fish of brackish origin spawned successfully in freshwater, pointing to an increased risk of introducing populations of brackish origin into freshwater. Limits to the species’ reproductive success, and therefore invasion processes, are likely dependent on environment-phenotype matches. Alternative hypotheses such as local adaption should be further investigated. Short-term acclimation to new salinities does not affect sperm performance in the round goby. Among fertilized eggs, zygote development was similar regardless of salinity treatment of either eggs or parents. Significantly lower fertilization success was measured for individuals that reproduced outside their salinity of origin despite recurring spawning events in all treatment groups. Sperm velocity was highest in the salinity similar to the males’ origin. ResultsĪfter a month, the fish showed no plasticity in sperm performance to their acclimation salinity, regardless of their origin. Responses were analysed using generalized mixed models. Clutches were split and allowed to develop in both 0 and 16 PSU salinity, and reproductive success (zygote development) was measured 20 ± 1 days later. After 4 weeks, we measured their sperm performance in both 0 and 16 PSU fertilization success of each egg clutch was measured through visual analysis of eggs. We cross-exposed round gobies of freshwater and brackish origin to 0 and 16 practical salinity units (PSU), and the fish were given nest boxes in which to spawn. Locationīrackish and freshwater systems of northern Europe and the Baltic Sea. We aim to understand if reproduction in different salinities is affected by an ability to acclimate. The invasive round goby ( Neogobius melanostomus) is spreading in Eurasia and the Americas, into both fresh and brackish water. The few fish species able to reproduce across wide osmotic ranges either plastically acclimate sperm performance to, or are locally adapted to, different salinities.
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