Abstract
Climate change related effects threaten species worldwide; within species populations may react differently to climate-induced stress due to local adaptation and partial isolation, particularly in areas with steep environmental gradients. Populations of the marine foundation seaweed Fucus vesiculosus are established over a steep salinity gradient at the entrance of the brackish water the Baltic Sea (NE Atlantic). First, we analyzed genetic differentiation among populations using thousands of genetic markers. Second, we measured physiological tolerance to reduced salinity, a predicted effect of climate change in the study area, by measuring growth, phlorotannin (defense compounds) content, and maximum photochemical yield in tissue of the same individuals exposed to both current and projected future salinities. Our results show that despite short geographic distances (max 100 km) most populations were genetically well-separated. Furthermore, populations responded very differently to a salinity decrease of 4 practical salinity units corresponding to projected future salinity. At the high salinity end of the gradient, some populations maintained growth at the cost of reduced phlorotannin production. However, at the low salinity end, mortality increased and growth was strongly reduced in one population, while a second population from similar salinity instead maintained growth and phlorotannin production. Among genetic markers that appeared as outliers (showing more genetic differentiation than the majority of loci) we found that four were associated with genes that were potential candidates for being under selection. One of these, a calcium-binding protein gene, also showed a significant genotype-phenotype relationship in the population where this genetic marker was variable. We concluded that local selection pressure, genetic affinity, and possibly also population history could explain the very different responses to reduced salinity among these populations, despite being from the same geographic area. Our results highlight the importance of local perspective in management of species.
Highlights
Coastal ecosystems are variable environments and so naturally stressful, which places adaptive demands on the species that live there
Phenotypic performance differed in half of the comparisons between populations grown in the same salinities during the experiment (Supplementary Table S5). In three of these cases, the populations originating from a higher salinity than the treatment salinity had a lower phlorotannin content than the populations originating from the same salinity [D1 – D2; S2 – S3; D2 – D3]
The photochemical yield was higher in the treatment populations than in the populations maintained in their native salinity [S1 – S2; S2 – S3]
Summary
Coastal ecosystems are variable environments and so naturally stressful, which places adaptive demands on the species that live there. Salinity can change dramatically over short spatial and/or temporal scales (Gagnaire et al, 2006), due to, e.g. rainfall, tidal currents, upwelling, and freshwater input from rivers (Kirwan and Megonigal, 2013). In some areas, these changes are short-lived, while in others they can be permanent indicators of a new regime. In this entrance area around the Danish straits with strong horizontal and vertical gradients, relatively small changes in wind forcing and currents can rapidly change surface salinity at local scales (Bendtsen et al, 2009; Maar et al, 2011)
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