Schmittmann, Lara (2017) Local adaptation of the common sea star Asterias rubens to different salinities. (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 93 pp.

Preview

Text LaraSchmittmann_thesis.pdf - Published Version Available under License Creative Commons: Attribution 4.0. Download (33MB) | Preview

Abstract

Hyposaline environments impose stressful conditions to marine organisms and limit their distribution. The common sea star Asterias rubens is one of the few echinoderm species that is able to survive and reproduce in hyposaline areas, like the brackish Baltic Sea. We expect populations inhabiting low salinity regions to be selected towards hyposalinity tolerance, visible in their physiology and population structure. As an osmoconformer, A. rubens relies on compatible organic osmolytes (OO) to adapt its cellular osmolality to that of the surrounding medium while intracellular ion concentrations are kept stable. The salinity at which OO are depleted was previously shown to correlate with fitness loss and is thus considered the critical salinity an organism can tolerate. For sea stars from the Baltic Sea, we experimentally determined the critical salinity to be 9.2 PSU which correlates with their distribution border in the field and our observations in the laboratory. Further, we conducted a reciprocal transplant experiment with animals from the North Sea (32 PSU) and the Baltic Sea (16 PSU) to investigate the effect of changing salinities on OO concentration and composition. Growth, feeding rate and righting time were determined and proton nuclear magnetic resonance spectroscopy was conducted on digestive tissue to quantify OO. Growth, feeding rate and righting time were negatively affected by low salinities whereas animals from the Baltic Sea showed higher growth and activity in 16 PSU than animals from the North Sea. Glycine was found to be the main osmolyte in A. rubens and contributed with up to 90 % to the total pool. We found no evidence for adaptation to hyposalinity on the level of OO and suggest the investigation of inorganic ions. To analyse the population structure of A. rubens in the North Atlantic, we sampled 14 populations from the Baltic Sea, the North Sea, Iceland and the Canadian East coast. Based on 7 newly developed microsatellites, we analysed the population structure with the aid of F-statistics, Bayesian clustering algorithms and NJ-trees. We applied Pearson’s correlation and Mantel tests to investigate IBD and IBE (salinity). The population structure of A. rubens in the North Atlantic is neither shaped by salinity nor by geographical distance. Nevertheless, a population structure is visible and probably shaped by water depth and stratification of water masses due to salinity. We show that sea stars from the same coordinates but from different water depth (5 m and 25 m) are genetically isolated. Additionally, Canadian A. rubens populations possess unique genotypes that hint towards a dispersal barrier to European populations. Despite the adaptation potential of A. rubens the critical salinity of 9.2 PSU and the projected desalination for the Baltic Sea due to climate change suggest a depression of the suitable habitat for A. rubens. This would lead to the loss of an important keystone species in some areas.

Actions (login required)

View Item