Towards a trait-based framework for protist ecology and evolution

Protists comprise the vast majority of eukaryotic genetic and functional diversity. While they have traditionally been difficult to study due to their small size and varied phenotypes, environmental sequencing studies have revealed the stunning diversity and abundance of protists in all ecosystems. Protists are key primary and secondary producers across many biomes, with ecological specializations that range from mutualism to parasitism, complex predation behaviors, mixotrophy, detritivory, and saprotrophy. Current genomic and transcriptomic approaches provide valuable insights into protist diversity at the genetic level, but they fall short in capturing the morphological and behavioral traits critical for understanding the functional roles of protists in ecosystems. This knowledge gap hinders our ability to answer important questions about protist functional diversity, including how protist functional groups will respond to environmental change. In this opinion article, we advocate adopting a traits-based approach for studying protist diversity and developing a trait database for protists to support this goal. By integrating examples of recent work characterizing protist functional diversity using a range of approaches, we emphasize the opportunities that trait databases offer and propose strategies for moving towards a trait-based framework to guide future research in protist ecology and evolution.