Adaptation and correlated fitness responses over two time scales in Drosophila suzukii populations evolving in different environments

The process of local adaptation involves differential changes in fitness
over time across different environments. While experimental evolution
studies have extensively tested for patterns of local adaptation at a
single time point, there is relatively little research that examines
fitness more than once during the time course of adaptation. We allowed
replicate populations of the fruit pest Drosophila suzukii to
evolve in one of eight different fruit media. After five generations,
populations with the highest initial levels of maladaptation had mostly
gone extinct, whereas experimental populations evolving on cherry,
strawberry and cranberry media had survived. We measured the fitness of
each surviving population in each of the three fruit media after five and
after 26 generations of evolution. After five generations, adaptation to
each medium was associated with increased fitness in the two other media.
This was also true after 26 generations, except when populations that
evolved on cranberry medium developed on cherry medium. These results
suggest that, in the theoretical framework of a fitness landscape, the
fitness optima of cherry and cranberry media are the furthest apart. Our
results show that studying how fitness changes across several environments
and across multiple generations provides insights into the dynamics of
local adaptation that would not be evident if fitness were analyzed at a
single point in time. By allowing a qualitative mapping of an experimental
fitness landscape, our approach will improve our understanding of the
ecological factors that drive the evolution of local adaptation in D.
suzukii.