How Does a History of Exposure to Varying Concentrations of Salt Influence the Evolution of Salt Tolerance in Ceriodaphnia When Subject to an Acute LC50 Test?

Introduction An increase of salinity in freshwater ecosystems can cause a loss of biodiversity and affect ecological function (Cañedo-Argüelles et al., 2016). Zooplankton are a key bioindicator when looking at the problem of salinization of freshwater environments. Evolutionary rescue is the “recovery and persistence of a population through natural selection acting on heritable variation” (Bell, 2017). This is relevant to my research because I am exploring evolutionary rescue within Ceriodaphnia populations; Specifically, I am researching salt tolerance within Ceriodaphnia. Thus, my research question is, “How does a history of exposure to varying concentrations of salt influence the evolution of salt tolerance in Ceriodaphnia when subject to an acute LC50 test?”. Methods The Ceriodaphnia used for this project were acquired from a previous study done at the Prairie Wetland Research facility. The Ceriodaphnia were cultured in mesocosms of varying salt concentrations ranging from 22mg/L of Cl to 2000mg/L of Cl including two control mesocosms. To begin, I first collected an individual Ceriodaphnia from a respective mesocosm concentration and added it to a test tube with COMBO media. I then repeated this so that I had 10 test tubes with a singular Ceriodaphnia from a single tank; This was done for each tank. To determine the evolved tolerance of Ceriodaphnia, I will be using acute 48 hours LC50 tests. The Ceriodaphnia will be tested at seven different salt concentration levels. To know if there is an evolved tolerance I will use the R package ‘drc’. Implications This research is important as it can inform policy and decision making practices surrounding environmental health within governmental bodies. Additionally, by understanding the evolved tolerance of freshwater organisms, we can use the information to begin remediation efforts. I expect that the outcomes of this research will exemplify that Ceriodaphnia are able to evolve a tolerance to salt with a history of exposure.