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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.
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