Adaptation in a keystone grazer under novel predation pressure

Area of Science:

• Evolutionary Biology
• Ecology
• Genomics

Background:

• Understanding species adaptation to environmental change is crucial for biodiversity conservation.
• Rapid adaptation to novel pressures, such as invasive species predation, is observed, but its repeatability and predictability in wild populations are unclear.

Purpose of the Study:

• To investigate the evolutionary response of the keystone aquatic herbivore *Daphnia pulicaria* to predation by the invasive zooplanktivore *Bythotrephes longimanus*.
• To assess the repeatability and predictability of genetic adaptation in wild populations facing novel selection pressures.

Main Methods:

• Analysis of whole-genome sequencing data from *Daphnia pulicaria* resting embryos in 210Pb-dated sediment cores from 12 Ontario lakes.
• Comparison of *Daphnia* genetic structure and selection signatures between lakes with and without *Bythotrephes* invasion over a ~70-year period.
• Identification of loci under selection and analysis of phenotypic changes (body size).

Main Results:

• Significant genetic differentiation in *Daphnia* populations occurred after *Bythotrephes* invasion, with no changes in uninvaded lakes.
• An average of 64 times more loci were under selection in invaded lakes compared to uninvaded ones.
• Selected loci were linked to reproduction and stress responses, and mean body size increased by 14.1% in invaded populations.

Conclusions:

• *Daphnia pulicaria* populations repeatedly acquired heritable genetic adaptations to evade gape-limited predation by *Bythotrephes longimanus*.
• Environmental change can predictably shape genome evolution, highlighting the potential for adaptive responses in wild populations.