LB 11-142 - Experimentally Testing Assisted Gene Flow as a Climate Adaptation Strategy

Background/Question/Methods:

Global temperatures are increasing at unprecedented rates and could cause extirpations and extinctions of many species in the coming decades. Consequently, practitioners are struggling to identify climate change adaptation strategies to help species persist. One of the most commonly recommended strategies is to move genotypes from warm to cooler locations to help populations in cooler locations adapt to warming temperatures (i.e., assisted gene flow). However, few rigorous experimental tests of this strategy exist because of perceived risks, a lack of information on species traits, and the logistical difficulties of tracking populations for many generations. To help bridge this knowledge gap, we provide a rapid experimental test of assisted gene flow using 23 genotypes of a model species (Daphnia magna) with known temperature tolerances. Specifically, we exposed 30 experimental populations of D. magna to warm and cool temperatures, including 5 replicates of the following population treatments: (1) a base population of 3 cold-adapted genotypes to simulate a vulnerable population, (2) the base population plus 3 hot-adapted genotypes to simulate assisted gene flow, and (3) the base population plus 3 additional cold-adapted genotypes as a control for increasing genetic diversity. We monitored population abundance weekly for 13 weeks (approximately 13 generations).

Results/Conclusions:

At week 10, after increasing the temperatures of the warm and cool environment on a weekly basis, the base population and the treatment with 3 additional cold-adapted genotypes decreased by 33% and 34% in the warm environment, respectively, whereas the populations including hot-adapted genotypes maintained high abundances in the warm environment as predicted under effective assisted gene flow. However, the following week, the populations including hot-adapted genotypes decreased by 45%. Most recently, in week 12, all populations in the warm environment recovered to match abundances in the cool environment. This indicates that the process of assisted gene flow is more complicated than originally hypothesized. Nevertheless, our results provide one of the first rigorous, multi-generational tests of assisted gene flow and support the idea that moving genotypes from warm to cooler locations could help ameliorate the negative impacts that climate change poses to vulnerable species. Moreover, this initial test provides the foundation for more nuanced tests of different approaches to assisted gene flow to help optimize and evaluate the risks of this commonly recommended climate change adaptation strategy worldwide.