The paper studies the spatial heterogeneity and temporal dynamics of life-history traits, parasite invasion, and biochemical variables (e.g., tissue protein content and calpain activity) in adult and juvenile threespine stickleback Gasterosteus aculeatus. Samples were collected on three spawning grounds in Kandalaksha Bay, on the White Sea, located within a few kilometers of each other. These sites featured differences in temperature regime, water exchange, feed organism composition, predation load, aquatic vegetation, and spawner density. Whereas we found no parasite-related or size heterogeneity in adult fish on these grounds at the beginning of the spawning season, muscle protein reserves and protease (calpain) activity patterns in adults showed significant spatial heterogeneity, which increased as spawning progressed and was particularly pronounced in females. Sticklebacks expend much energy during spawning and are worn out by the end of the spawning period. To maintain individual viability, skeletal muscle proteins degrade, and the resulting amino acids are oxidized to produce energy. Protein-degrading calpains play a key role in these processes, and also mediate intense protein metabolism in juvenile stickleback, showing higher values in individuals growing under more favorable conditions. Thus, by studying the heterogeneous life-history traits and biochemical characteristics of adult and juvenile stickleback, we discovered the effects of environmental factors on their physiology, biochemical variables, and growth.
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