Evolutionary stasis despite selection on a heritable trait in an invasive zooplankton

Area of Science:

• Ecology
• Evolutionary Biology
• Invasive Species Research

Background:

• Invasive species pose significant ecological threats, with evolution influencing their success.
• Understanding natural selection and evolutionary adaptation in invasive animals is crucial but understudied.

Purpose of the Study:

• To quantify natural selection on the defensive spine length of the invasive zooplankton Bythotrephes longimanus in Lake Michigan.
• To assess phenotypic changes in spine length since the species' invasion and identify evolutionary responses.

Main Methods:

• Analysis of distal spine length in wild-captured Bythotrephes longimanus over three growing seasons.
• Utilizing palaeoecological data from retrieved spines to reconstruct historical phenotypes.
• Quantifying natural selection by linking spine length to fitness proxies.

Main Results:

• Temporally variable selection was observed: selection for shorter spines early season and longer spines late season.
• This pattern aligns with seasonal shifts in fish predation (gape-limited vs. non-gape-limited).
• Despite strong selection and a genetic basis for spine length, a significant evolutionary response was not detected.

Conclusions:

• Natural selection on Bythotrephes longimanus spine length is dynamic and influenced by predator-prey interactions.
• Limited evolutionary response suggests constraints such as genetic correlations, fitness trade-offs, or phenotypic plasticity may be hindering adaptation.