Local adaptation in life history traits and population size estimation of aquatic organisms

Human society is dependent on healthy aquatic ecosystems for our basic needs and well-being. Therefore, knowledge about how organisms respond and interact with their environments is pivotal. The Baltic Sea is highly affected by human activity and future populations living in its catchment area will have to respond to multiple set of changing abiotic and biotic predictors. The first two papers of this thesis focus on local adaptation, adaptive capacity, and the response to changing temperature, salinity, and food conditions of different Eurytemora affinis populations, a ubiquitous zooplankton species in the Baltic Sea. Development time of zooplankton is an important trait and relates to how fast a population can increase in number. Common garden experiments showed that E. affinis populations from warmer southern areas had shorter development time from nauplii to adult at high temperature compared to populations from colder areas, which indicates an adaptation to temperature. The adaptation was explained by a correlation in development time between higher temperatures, 17 and 22.5 °C, while development between a colder temperature, 12 °C, and the two higher temperatures was uncorrelated. This implies that adaption to short development time at high temperature is unlikely for populations originating from cold temperatures. Hence, global warming will be disadvantageous for northern, compared to southern populations. However, development time is heritable and may change under selection, and may improve the competitive advantage of northern populations. The population with the shortest development time had comparably lower survival at high temperature and low food quality. This represents a cost of fast development, and emphasizes the importance of including multiple stressors when investigating potential effects of climate change. E. affinis inhabits a broad range of habitats from an epi-benthic life in freshwater lakes and river mouths, to pelagic life in estuaries. Paper III aims to link the morphology of different ...