Project: CAREER: How do mixotroph phenotypic plasticity and adaptive evolution constrain climate feedbacks?

NSF Award Abstract:
In the ocean, plankton that do photosynthesis remove carbon dioxide from the atmosphere, while plankton that respire carbon from captured prey return carbon dioxide to the atmosphere. One special type of plankton called mixotrophs combine both forms of metabolism, functioning as both plant and animal simultaneously. Because the extent to which mixotrophs rely on each process depends on environmental conditions, it can be difficult to predict their net impact on the carbon cycle. This is especially true in changing environments. For example, as Earth’s surface ocean temperatures increase, mixotrophs may respond both plastically (through reversible modifications of their physiological state) and through rapid evolution. This project combines mathematical models and laboratory experiments to test the hypothesis that more phenotypically plastic mixotrophs will not evolve as rapidly because their inherent metabolic flexibility will reduce the strength of natural selection. The project also supports training and outreach designed to broaden participation and expand math literacy. Project personnel will train K-12 teachers, provide educational programs for museum visitors, and conduct undergraduate teaching at the intersection of mathematics and biology. Undergraduate trainees will also lead independent research projects and develop science education modules that allow high school students to quantify the effects of temperature on biology. Postdoctoral and undergraduate researchers receive training and professional development as part of the project.

To link mixotroph phenotypic plasticity and evolution to climate feedbacks, researchers are integrating experiments with mathematical models. A number of mixotroph genotypes from the genus Ochromonas will be phenotyped, and a subset will be experimentally evolved to test their capacity for adaptive evolution. Researchers are measuring rates of photosynthesis and phagotrophy in evolved lineages to quantify impacts on the carbon cycle, and genome and transcriptome sequencing are being used to identify the molecular basis of adaptation. A series of mathematical models will be developed to understand the mechanistic bases of plasticity and evolution, and to connect these mechanisms to their climate impacts. First, researchers use a model of cellular investments to contrast empirical results with predictions of mixotrophs’ optimal plastic and evolved strategies. Validated model modules is being incorporated into upper ocean global ecosystem models to understand how these strategies change mixotroph abundance and contributions to the carbon cycle under future climate scenarios.

Funds for this award are provided by the Biological Oceanography and Ocean Education Programs.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.