Dynamic interactions between ecological conditions and the phenotypic composition of populations likely play an important role in evolution, but the direction and strength of these feedbacks remain difficult to characterize. We investigated these dynamics across two generations of threespine sticklebacks from two evolutionary lineages undergoing secondary contact and hybridization. Independently manipulating the density and lineage of adults in experimental mesocosms led to contrasting ecosystem conditions with strong effects on total survival in a subsequent generation of juveniles. Ecosystem modifications by adults also varied the strength of selection on competing hybrid and non-hybrid juveniles. This variation in selection indicated (1) a negative eco-evolutionary feedback driven by lineage-specific resource depletion and dependence and (2) a large performance advantage of hybrid juveniles in depleted environments. This work illustrates the importance of interactions between phenotype, population density and the environment in shaping selection and evolutionary trajectories, especially in the context of range expansion with secondary contact and hybridization.
Ecosystem variables at the end of Phase I
Abundance and size of planktonic and benthic prey, and abundance of primary producers, surveyed in 50 mesocosms at the end of Phase I (occupation by adult stickleback from 2 lineages and at 2 densities).
Benthic invertebrate stable isotope values
SI values are for individual invertebrates sampled at the end of Phase I except for Zebra mussels and prosobranch snails, for which each sample is an assay of 3 pooled individuals.
Juvenile fish stable isotope values
Stable isotope values for individual juvenile fish sampled at the end of Phase II (muscle tissue).
Juvenile fish survival for each mesocosm
Total surviving juveniles of each type (Constance, Geneva, and F1 Hybrids).
Juvenile fish condition from mesocosms
Body condition for all mesocosm juveniles, calculated as residuals from a length-weight regression and standardized to weight of a fish of average length.
Juvenile fish condition from lab experiment
Body condition for all lab experiment juveniles, calculated as residuals from a length-weight regression and standardized to weight of a fish of average length.