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Dams and other anthropogenic barriers have caused global ecological and hydrological upheaval in the blink of the geological eye. In the present article, we synthesize 307 studies in a systematic review of contemporary evolution following reduced connectivity and habitat alteration on freshwater fishes. Genetic diversity loss was more commonly observed for small populations impounded in small habitat patches for many generations behind low-passability barriers. Studies show that impoundments can cause rapid adaptive evolution in migration timing, behavior, life history, temperature tolerance, and morphology, as well as reduce phenotypic variance, which can alter adaptive potential and ecological roles. Fish passage structures can restore migratory populations but also create artificial selection pressures on body size and migration. The accelerating pace of dam removals and the paucity of data for fishes other than salmonids, other vertebrates, invertebrates, and tropical and southern hemisphere organisms highlights the urgent need for more studies on the rapid evolutionary effects of dams.

Few studies have explored the relative strength of ecogeographic versus lineage-specific effects on a global scale, particularly for poikilotherms, those organisms whose internal temperature varies with their environment. Here, we compile a global dataset of life history traits in Daphnia, at the species-and population-level, and use those data to parse the relative influences of lineage-specific effects and climate. We also compare the thermal response (plasticity) of life history traits and their dependence on climate, temperature, precipitation, and latitude. We found that the mode of evolution for life history traits varies but that the thermal response of life history traits most often follows a random walk model of evolution. We conclude that life history trait evolution in Daphnia is not strongly species-specific but is ecogeographically distinct, suggesting that life history evolution should be understood at the population level for Daphnia and possibly for other poikilotherms.