PT Unknown AU Schade, FM TI Coping with a changing world: adaptive mechanisms in marine three-spined stickleback Gasterosteus aculeatus PY 2014 PU Christian-Albrechts-Universität zu Kiel WP https://macau.uni-kiel.de/receive/diss_mods_00014392 LA en DE Climate change; fish; parasites; adaptation; phenotypic plasticity; transgenerational acclimation; Klimawandel; Fische; Parasiten; Phänotypische Plastizität; Transgenerationale Akklimatisierung AB Due to ongoing increases in carbon dioxide (CO2) concentrations in the atmosphere, the world’s climate is changing at an unprecedented rate, leading to rising global mean air and water temperatures. When atmospheric CO2 dissolves in seawater, ocean pH declines, causing an acidification of the ocean. These altered environmental conditions are highly probable to have severe impacts on marine organisms by affecting their performance and survival. When environmental stress is increasing, some species can migrate to habitats with more favourable conditions, others have to adapt to changing conditions. Whether species will be able to adapt fast enough to keep pace with changing environments will be one decisive factor for population persistence. In this thesis, a prime model organism, the three-spined stickleback Gasterosteus aculeatus, was used to study ecological and evolutionary effects of rising water temperatures and ocean acidification on marine fish populations. Rising temperatures are likely to stress marine species, dependent on their thermal tolerance. Thermal stress can alter immune functions of organisms, thereby increasing the susceptibility to infectious diseases. By combining the effects of elevated temperature and bacterial infection in a common garden experiment, the influence of thermal stress on evolutionary trajectories of disease resistance in three-spined stickleback populations could be investigated (chapter II). Environmental stress negatively impacted life-history traits and pathogen resistance of sticklebacks. Furthermore, thermal stress reduced genetic differentiation between populations by releasing cryptic within-population variation. While life-history traits showed positive genetic correlations between temperatures and genotype by environment interactions (GxE), thermal stress led to negative genetic correlations in disease resistance, showing that evolutionary responses in altered environments can be hard to predict from prevailing conditions. Rising temperatures, on the other hand, promote the development of many parasites and pathogenic bacteria, increasing the risk of infection and diseases during summer. To understand infection patterns in relation to water temperature, the parasite and bacterial communities of marine fish species were investigated over a period of two years (chapter I). Temporarily elevated water temperatures resulted in increased macroparasite and bacterial diversities in marine fish species. In addition, some parasite groups showed a forward shift and extension in infection peaks, following warmer spring seasons. This shows that even subtle changes in seasonal temperatures can have an effect on the epidemiology and phenology of parasites as well as opportunistic pathogens. Increased virulence of pathogens at higher temperatures in combination with immune-compromised hosts can have far fetching consequences for marine ecosystems. Next to rising ocean temperatures, marine organisms have to cope with ocean acidification. It has been shown, that elevated CO2 concentrations negatively impacted fish development and survival, particularly in early developmental stages. A powerful mechanism to mediate the effects of global change is transgenerational acclimation. By acclimating parents and offspring to different CO2 concentrations, within- and transgenerational effects of ocean acidification on life-history traits of marine sticklebacks were studied (chapter III). Exposure to elevated CO2 concentrations led to an increase in clutch size in adults as well as increased juvenile survival and growth rates. Transgenerational effects could be found for juvenile growth and for otolith characteristics, suggesting that parental acclimation can modify ocean acidification effects. To summarize, three-spined sticklebacks cope better with ocean acidification than with rising ocean temperatures. Transgenerational acclimation enables sticklebacks to respond quickly to environmental changes and provides time for genetic evolution, as long-term adaptive mechanism, to catch up. The high tolerance to fluctuations in water chemistry and temperature as well as the substantial amount of standing genetic variation suggest that stickleback populations can adapt fast enough to changing environmental conditions. PI Kiel ER