Abstract

Acquired photosynthesis transforms genotypically
heterotrophic lineages into autotrophs. Transient acquisitions of eu-
karyotic chloroplasts may provide key evolutionary insight into the
endosymbiosis process—the hypothesized mechanism by which eu-
karyotic cells obtained new functions via organelle retention. Here,
we use an eco-evolutionary model to study the environmental condi-
tions under which chloroplast retention is evolutionarily favorable.
We focus on kleptoplastidic lineages—which steal functional chloro-
plasts from their prey—as hypothetical evolutionary intermediates.
Our adaptive dynamics analysis reveals a spectrum of evolutionarily
stable strategies ranging from phagotrophy to phototrophy to obligate
kleptoplasty. Our model suggests that a low-light niche and weak (or
absent) trade-offs between chloroplast retention and overall digestive
ability favor the evolution of phototrophy. In contrast, when con-
sumers experience strong trade-offs, obligate kleptoplasty emerges
as an evolutionary end point. Therefore, the preevolved trade-offs that
underlie an evolving lineage’s physiology will likely constrain its evo-
lutionary trajectory.