Intra-specific variation in metal tolerance modulate competition between two marine diatoms

This project contains data for the manuscript Intra-specific variation in metal tolerance modulate competition between two marine diatoms. The experiments tests how different  toxic concentrations of heavy metals modulates competition between an artificially assembled community of Baltic Sea diatoms (four clonal strains each of the two diatom species Skeletonema marinoi (SM) and Thalassiosira  baltica (TB). Briefly we use toxic Dose Response curves (DRC) to model how inter and intra specific selection between strains is expected to be modulated under Cadmium, Copper and Silver stress. The stress level was set at the average 50% inhibition concentration (EC50) between all eight strains. Strains were mixed at even biomass based on Relative Chl a Fluorescence Units (RFU) and cultivated semi-continuously to maintain exponential growth. The growth of individual species was measured through microscopy observations and the photosynthetic capacity was monitored using Pulse Amplitude Modulation (PAM) fluorometry. A experimental design flow figure is included as a supplement.

The complete functional set of scripts, statistical analysis, and graphical illustrations in R can be found on github: https://github.com/Bearstar85/Selection_Competition_2021 

Methods
The directories/sections break down the data into three components or experiments. Each directory contains data and a README file with more detailed metadata. 

1. DRC

Contains acute (72-h) toxic dose response data for all eight strains against seven heavy metals although competition is only modeled and experimentally tested under Ag, Cu and Cd stress. This is only mono-cultures observations. The concentrations of each metal is nominal in this dataset and experiments where carried out in 24-well plates, with 6 concentrations steps replicated 3 times, and 5 controls, with 1 mL culture per replicate. Culture density was measured using in vivo relative fluorescence units (RFU), and inhibition is computed based on specific growth rate estimates, scaled towards the control (so that 0 is no change in growth rate and 1 is no or negative growth). Dose response curves for S. marinoi strain RO5AC towards Cu in different media conditions is also included, mainly with or without EDTA.

2. Models

Results of deterministic selection model based on variability in intrinsic growth rate and predicted metal inhibition traits between strains. In the end (section 3), models are contrasted against experimental observations. This includes predicted strain specific inhibition values (using drc package in R) and specific growth rates, as well as predicted changes in biomass densities over time, and evolution of growth rates based on selection.

3. Competition

Experimental observational data of co-cultivation experiment, including changes in total community biomass (RFU) as well as species biomass based on microscopic observations. The latter was used to compute species-specific growth rates. Fv/Fm was also monitored using Pulse Amplitude Modulation (PAM) fluorometry.