Periodic Reporting for period 1 - THERMOPLAST (Adaptive plasticity meets unpredictability: how do organisms cope with changing environmental variability?)
Reporting period: 2016-01-01 to 2017-12-31
Thus, understanding responses to such changes in environmental variability requires detailed knowledge about how organisms can detect levels and predictability of variation, how they can respond to this through non-genetic, plastic mechanisms and if there is potential for such ‘plasticity’ to evolve given its specific costs and benefits. In this project, using the widespread clonally reproducing zooplankter Daphnia magna, I therefore investigated plastic, non-genetic changes in thermal tolerance, the ability to maintain basic body function at high temperature, in response to different patterns of temperature variability. The major aims of this project were:
1.) Investigate if temperature variability can cause a plastic response in thermal tolerance
2.) Are plastic shifts in thermal tolerance fixed or flexible and does this type of plasticity correspond to natural patterns of temperature variability?
3.) Is there genetic variation in thermal tolerance plasticity and does this carry a physiological cost?
To measure if plastic shifts in thermal tolerance are fixed (i.e. permanent) or flexible, we reared replicate populations of a single D. magna clone at either a constant low temperature, or a constant high temperature. Upon reaching sexual maturity, individuals from the low temperature were transferred to the high temperature and vice versa. Control animals were maintained at the initial developmental temperatures. Following the shift in rearing temperature, treatment and control animals were measured for thermal tolerance after 24 hrs and then at set intervals for 13 days. I observed that thermal tolerance was adjusted rapidly, within 24 hours, being increased in animals that experienced an increase in ambient temperature and decreased in animals that experienced a reduction in ambient temperature, demonstrating that thermal tolerance is not fixed but highly and rapidly adjustable.
Due to delays that occurred that were beyond my control, work towards Objective 3 is underway at the time of writing this report. However, additional scientific highlights during the fellowship included the development of a method for automating the measurement of thermal tolerance. The method utilizes video-based tracking software to record the movement of individuals when exposed to high, lethal temperature. I developed an algorithm in the R computing language that can objectively identify the loss of locomotory function from tracking data analyzed from videos. Using independent experimental data I validated this approach by demonstrating the expected response in thermal tolerance to different acclimation temperatures. This method was used to perform all measures of thermal tolerance conducted in this fellowship.