The transition from unicellular to multicellular life was one of a few major events in the history of life that created new opportunities for more complex biological systems to evolve. Predation is hypothesized as one selective pressure that may have driven the evolution of multicellularity. Here we show that de novo origins of simple multicellularity can evolve in response to predation. We subjected outcrossed populations of the unicellular green alga Chlamydomonas reinhardtii to selection by the filter-feeding predator Paramecium tetraurelia. Two of five experimental populations evolved multicellular structures not observed in unselected control populations within ~750 asexual generations. Considerable variation exists in the evolved multicellular life cycles, with both cell number and propagule size varying among isolates. Survival assays show that evolved multicellular traits provide effective protection against predation. These results support the hypothesis that selection imposed by predators may have played a role in some origins of multicellularity.
Figure 3
The script "Figure3.R" compiles Figure 3. It runs in R version 3.5.1 and requires the following R libraries: dplyr, reshape2, tools, ggplot2.
The data for Figure 3 are contained in the folder "Figure3Data". Files in this folder are plain-text, comma-separated. The naming convention is "strain replicate", so "B2.01 01b" contains data for strain B2-01, replicate 01b. Columns in these files are as follows:
ROI: Region of Interest
ROI Number: The individual ROI, selected from the image based on thresholding. This typically is a single cellular cluster.
Mean: Mean 8-bit brightness value for pixels within the ROI
Min: Minimum 8-bit brightness value for pixels within the ROI
Max: Maximum 8-bit brightness value for pixels within the ROI
IntDen: The product of the area of the ROI and its mean 8-bit brightness value
RawIntDen: The sum of the brightness values for all pixels in the ROI
Figure3.R
Figure 3 Data
Compressed archive of data files for Figure 3.
Figure3Data.zip
Figure 4
The script "Figure4.R" compiles Figure 4. It runs in R version 3.5.1 and requires the following R libraries: dplyr, reshape2, ggplot2.
The data for Figure 4 are contained in the plain-text, comma-separated file "Figure4Data.csv".
Figure4.R
Figure 4 Data
Data for Figure 4. Columns in this file are as follows:
Strain: Strain identifier
TechRep: Technical replicate
ClusterID: Unique, arbitrary identifier per cluster
Num.Cells.Progeny: The number of cells observed in a propagule after splitting from parent cluster
Num.Cell.Parent: The number of cells observed in the parent cluster after releasing a propagule (determined at same time-step as Num.Cells.Progeny)
RepTime.sec: The time at which reproduction (propagule splitting from parent cluster) occurred in the time-lapse. Initially this was reported in time-step, which was then converted to seconds.
EntersField.sec: Time at which the cluster entered the field of view
Figure4Data.csv
Figure 5 Data
Data for Figure 5 are contained in the file "Figure5Data.csv". The file format is plain-text, comma-separated. Columns in this file are as follows:
Strain: Strain idenitifier
nopred1: Absorbance reading for technical replicate 1, predator absent
nopred2: Absorbance reading for technical replicate 2, predator absent
nopred3: Absorbance reading for technical replicate 3, predator absent
nopred4: Absorbance reading for technical replicate 4, predator absent
pred1: Absorbance reading for technical replicate 1, predator present
pred2: Absorbance reading for technical replicate 2, predator present
pred3: Absorbance reading for technical replicate 3, predator present
pred4: Absorbance reading for technical replicate 4, predator present
Time(h): Number of hours post-inoculation at which the absorbance readings were made
MeanDiff: Mean difference between predator absent replicates and predator present replicates
Figure5Data.csv
