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要旨

Nine-spined sticklebacks (Pungitius pungitius) are a species of fish which are widely distributed throughout a range of different habitats. Their expression of different morphological traits and/or body shapes among populations makes them an excellent model to understand mechanisms of phenotypic variation. Currently, there are no recent studies about the morphology of northern German populations as well as how environmental conditions drive natural selection on phenotypic variation in these populations. In this study divergences in morphological traits and body shape between populations of northern German nine-spined sticklebacks were investigated. Populations inhabiting an environment with a low predation pressure of piscivorous fish showed a larger body size and a decreased spine-armory in comparison to fish inhabiting an environment with a high predation pressure of piscivorous fish. Moreover, fish from populations exposed to similar environmental conditions showed a higher similarity to each other concerning their morphology than fish, that are located near each other geographically. These results demonstrate that differences in predation pressure, likely caused by sympatric piscivorous fish species, strongly influence morphological and body shape variation between different populations. In addition, the environment seems to have a higher effect on phenotypic variation than geographical distances between populations. Nonetheless, more work is needed to get a better impression about the interaction of environmental conditions affecting phenotypic variation in nine-spined sticklebacks. A comparison of more populations, inhabiting similar environments with a balanced sex ratio of specimens could be helpful to analyze sexual divergence. Additionally, a precise analysis of differences in food availability and water chemistry could help elucidate the influences of these factors on phenotypic variation.