Evolution of clines in poorly-dispersing prey populations in response to spatial variation in selection by gape-limited predators

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My long-term rocky intertidal field sites in the Northeast Pacific, allows my research program to address novel questions about the evolution of antipredation traits in response to spatial and temporal changes in the risk of predation. Our study system includes four snail species in the genus Littorina that vary in shell thickness and dispersal potential, and an indigenous predator, the purple shore crab. In 1993, I constructed crab shelters on two wave-exposed shores to increase the local density of the purple shore crab. This has caused selection for size at maturity and shell thickness in adjacent snail populations. At the same time, climate change is causing poleward range extensions of a non-native predator crab that is impacting size-limited predation on indigenous prey species. In this context, I plan to address three short-term objectives over the next 5 years: 1. Determine genetic and plastic responses to increased risk of size-limited predation. We will determine how antipredator traits have evolved at our field site since we established a predation gradient by installing crab shelters 27 years ago, and how these changes differ between high and low dispersing snail species. Plasticity will be assessed by culturing field-collected snail eggs with and without crab effluent in a common environment. We will also examine how morphological changes may be related to behavioural adaptations (i.e., predator avoidance) in L. subrotundata. 2. Discover genetic architecture of genetic and plastic adaptations to predators. We will use whole genome sequencing to discover DNA markers which will be used to estimate snail dispersal. We will also genotype snails collected from different distances from crab shelters and then search for genome regions associated with antipredator traits. 3. Model changes in prey extinction risk caused by range extensions of predators into Canada. During two large El Nio events, my concrete shelters were invaded by the nonindigenous lined shore crab. To model the risk of extinction of native prey species, we will conduct laboratory experiments to determine consumption rates from this crab and other gape-limited predators on different size-classes of prey. We will forecast changes in the southern limits of prey species with differing dispersal abilities in response to northern range extensions of predators. What is novel about the proposed work is that it is based on a long-term field predator-addition experiment that has advanced our understanding of genetic adaptation at the whole organism level. Our expertise in modelling, parameter estimation, and genomics, will quantify how the dispersal and evolutionary potential of prey populations affects their persistence after poleward invasions of predators resulting from climate change. The proposed research will significantly advance my long-term goal of determining when high dispersal potential or rapid evolutionary adaptation can prevent populations from extinction.