Abstract:With ongoing global change, life is continuously forced to move to novel areas, imposing rapid changes in biotic communities and ecosystem functioning [1].As dispersal is central to range dynamics, factors promoting fast and distant dispersal are key to understanding and predicting range expansions. As the range expands, genetic variation is strongly depleted and genetic homogenisation increases [2][3][4]. Such conditions should reduce evolutionary potential, but also impose severe kin competition. Although kin competition in turn drives dispersal[5], we lack insights into its contribution to range expansions, relative to other causal processes. To separate evolutionary dynamics from kin competition, we combined simulation modelling and experimental range expansion using the spider mite Tetranychus urticae. Both modelling and experimental evolution demonstrated that plastic responses to kin structure increased range expansion speed by about 20%, while the effects of evolution and spatial sorting were marginal. This insight resolves an important paradox between the loss of genetic variation and earlier observed evolutionary dynamics facilitating range expansions. Kin competition may thus provide a social rescue mechanism in populations that are forced to keep up with fast climate change.

Predator–prey interactions heavily influence the dynamics of many ecosystems. An increasing body of evidence suggests that rapid evolution and coevolution can alter these interactions, with important ecological implications, by acting on traits determining fitness, including reproduction, anti-predatory defence and foraging efficiency. However, most studies to date have focused only on evolution in the prey species, and the predator traits in (co)evolving systems remain poorly understood. Here, we investigated changes in predator traits after approximately 600 generations in a predator–prey (ciliate–bacteria) evolutionary experiment. Predators independently evolved on seven different prey species, allowing generalization of the predator's evolutionary response. We used highly resolved automated image analysis to quantify changes in predator life history, morphology and behaviour. Consistent with previous studies, we found that prey evolution impaired growth of the predator, although the effect depended on the prey species. By contrast, predator evolution did not cause a clear increase in predator growth when feeding on ancestral prey. However, predator evolution affected morphology and behaviour, increasing size, speed and directionality of movement, which have all been linked to higher prey search efficiency. These results show that in (co)evolving systems, predator adaptation can occur in traits relevant to foraging efficiency without translating into an increased ability of the predator to grow on the ancestral prey type.