COS 280-2 - When one size doesn't fit all: Inducible colony defense phenotypes exposed to diverse predator histories modify defense success in Chlamydomonas reinhardtii

Abstract: Plastic phenotypes, such as inducible anti-predator defenses, have well documented influences on the focal species central to the response. Broader community level consequences, however, can be difficult to characterize depending on study system, especially when considering impacts occurring over multiple generations. This presents a challenge in understanding complex dynamics resulting in natural systems, where similar defenses are employed but consequences at the population or community level vary dramatically. The green alga Chlamydomonas reinhardtii expresses an inducible anti-predator defense in response to a number of filter-feeding predators which serves as a robust model system for considering multigenerational experimental studies with diversely assembled communities. The overall goal of this work was to explore previously observed changes to the C. reinhardtii colony defense in response to different predators with the expectation that predator history would modify colony characteristics and assess subsequent changes in defense success. This design allowed me to test the hypothesis that predator history would reliably change colony characteristics and result in algal populations more or less susceptible to predation by novel predators as community composition was altered.

Here, I present the consequences of changes in predator history with an experimental system containing C. reinhardtii and three different predators with differing feeding strategies over dozens of generations in a factorial design. C. reinhardtii was cultured with each predator in isolation for multiple generations, and then colonies were compared before being exposed to alternate predators. The results of this work show that exposure to predators with differing feeding gape sizes results in populations of C. reinhardtii with significantly different colony sizes that correlate with predator size. Populations of all members of the alga-predator pairs were observed to be stable with similar abundances despite this difference in colony size. When populations of C. reinhardtii were exposed to new predators with different gape feeding sizes, however, dynamics become far less predictable and lead to crashes in populations of predator, prey, or both. Conversely, differing colony sizes can lead to coexistence of predators that normally do not culture together with C. reinhardtii due to intraspecific competition between those predators. In conclusion, this work suggests that predator history can have far reaching consequences for species expressing inducible anti-predator defenses as community composition changes over time. This result can help explain, in part, the complex dynamics observed when such defenses lead to seemingly contradictory results in different natural and experimental systems.