Title: Jacks of All Trades or Masters of None: How diverse mixotroph strategies shape current and future oceans
Abstract: Microbial mixotrophs combine the capacity for photosynthesis and heterotrophy within a single cell, allowing them to simultaneously function as primary producers and consumers. How do these mixotrophs arise, what selection pressures shape their physiology, and what are their impacts on the global carbon cycle? In this seminar, I’ll describe our group’s work on the evolutionary origins of mixotrophy, combining mathematical models with empirical studies of the chloroplast-stealing Mesodinium genus (a model system for complex endosymbiosis). Our work identifies ecological conditions that may favor the heterotophy-to-mixotrophy transition. I will also evaluate the effects of mixotrophy on the marine carbon cycle, especially the possibility of a positive climate feedback loop if mixotrophs become more heterotrophic with warmer temperatures. New results using adaptive dynamics, ecosystem models, and evolution experiments on the nanoflagellate genus Ochromonas indicate that responses may ultimately be constrained by bottom-up resource limitation. Collectively, our findings show that mixotroph responses are as complex and variable as their energetic strategies, highlighting the challenges and opportunities of working with this diverse guild!