Data from: A century of intermittent eco-evolutionary feedbacks resulted in novel trait combinations in invasive great lakes Alewives (Alosa pseudoharengus)

Species introductions provide opportunities to quantify rates and patterns
of evolutionary change in response to novel environments. Alewives (Alosa
pseudoharengus) are native to the East Coast of North America where they
ascend coastal rivers to spawn in lakes, and then return to the ocean.
Some populations have become landlocked within the last 350 years and
diverged phenotypically from their ancestral marine population. More
recently alewives were introduced to the Laurentian Great Lakes (~150
years ago), but these populations have not been compared to East Coast
anadromous and landlocked populations. We quantified 95 years of
evolution in foraging traits and overall body shape of Great Lakes
alewives and compared patterns of phenotypic evolution of Great Lakes
alewives to East Coast anadromous and landlocked populations. Our results
suggest that gill raker spacing in Great Lakes alewives has evolved in a
dynamic pattern that is consistent with responses to strong but
intermittent eco-evolutionary feedbacks with zooplankton size. Following
their initial colonization of Lakes Ontario and Michigan, dense alewife
populations likely depleted large-bodied zooplankton, which drove a
decrease in alewife gill raker spacing. However, the introduction of
large, non-native zooplankton to the Great Lakes in later decades resulted
in an increase in gill raker spacing, and present-day Great Lakes alewives
have gill raker spacing patterns that are similar to the ancestral East
Coast anadromous population. Conversely, contemporary Great Lakes alewife
populations possess a gape width consistent with East Coast landlocked
populations. Body shape showed remarkable parallel evolution with East
Coast landlocked populations, likely due to a shared response to the loss
of long-distance movement or migrations. Our results suggest the
colonization of a new environment and cessation of migration can result in
rapid parallel evolution in some traits, but contingency also plays a
role, and a dynamic ecosystem can also yield novel trait combinations.