Regional variation in within- and transgenerational responses to an invasive predator

When confronted with environmental stress, individuals may enhance their fitness by altering their phenotype via within-generation plasticity (WGP) or their offspring's phenotype via transgenerational plasticity (TGP). Despite growing appreciation of TGP in adapting to environmental change, our understanding of how it may vary geographically among populations having different eco-evolutionary histories remains limited. In the Gulf of Maine, the carnivorous snail, Nucella lapillus, must solve the foraging-predation risk trade-off by reducing their vulnerability to invasive predatory green crabs while also acquiring the food necessary to survive. Nucella populations in the southern Gulf have been in contact with green crabs for ~125 years and are able to forage on an abundant supply of food. By contrast, populations in the northern Gulf have had limited contact with green crabs until ~25 years ago and must persist on a very limited food supply. In the southern Gulf, Nucella are known to exhibit TGP in response to green crab risk cues, but how these responses may vary along a spatiotemporal gradient in invasion history and food availability is unknown. We collected Nucella from six populations (three northern, three southern) and evaluated WGP and TGP in response to green crab predation risk in an 18-month laboratory experiment. We detected regional variation in Nucella life history traits, the expression of both forms of plasticity in response to predation risk, and Nucella foraging on key basal resources. Our results support the hypothesis that low food availability in the northern Gulf may reduce the sensitivity of northern Nucella to predation risk. Hence, geographic variation in TGP in response to predation risk may be shaped by regional differences in other factors such as food availability, thereby yielding outcomes not well predicted by current TGP theory.