Avoiding dead ends: the experimental evolution of constraint as adaptation to environmental variation

A bet-hedging strategy is suboptimal over short timescales, but optimal over long time scales because it buffers temporal variance in fitness. However, it is unclear how such strategies can persist when selection is expected to purge suboptimal traits in the short term. It has been proposed that the persistence of bet hedging is possible only if adaptive evolution is constrained in the short-term (Simons, 2002). To test the constraint-as-adaptation hypothesis, we take an experimental evolution approach using Saccharomyces cerevisiae and predict that evolution under reduced-frequency detrimental events results in an increase in evolution-resistant bet-hedging. Specifically, we evolve bet-hedging by imposing fluctuating selection through repeated heat shocks separated by intervening benign environments in which the frequency of extreme environments is reduced across two sequential evolution regimes (Regimes A and B). Then, to measure evolved constraints lines from both regimes are furthe..., Data was collected from trait assays that were run simultaneously for all strains. Lines from the end of Regime A (EoR-A) and from the end of Regime B (EoR-B) were originally evolved from the T1 Ancestor which has an S288C background (MATα SUC2 gal2 mal2 mel flo1 flo8-1 hap1 ho bio1 bio6). The sequential experimental design implies that evolution proceeded along: T1 Ancestor --> Regime A (8 replicate lines) --> Regime B (8 replicate lines).  Heat Shock Tolerance was measured as % Survival on exposure to a transient  54°C heat shock for 75 mins. 
Relative fitness was calculated using a competitive fitness assay with a reference strain, YIR044CΔ with a BY4741 background (MATa his3Δ1 leu2Δ0 met15Δ0 ura3Δ0). This strain has the pseudogene YIR044C deleted and replaced with a gene conferring G418 resistance—used as a selectable marker for this assay. Proportions of focal strain/test population relative to the reference strain both before and ..., Experimental evolution and heat shock tolerance assays were performed in Synthetic Defined Media (SDM) containing 6.7 g of Yeast Nitrogen Base (without amino acids with ammonium sulfate) and 2% dextrose per liter.
Competition experiments were performed in SDM+ Histidine (10 mg/L), Leucine (30 mg/L), Methionine (10 mg/L), Uracil (10 mg/L) to account for auxotrophies in the reference strain., # Data from: Avoiding dead ends: the experimental evolution of constraint as adaptation to environmental variation

[https://doi.org/10.5061/dryad.zs7h44j9b](https://doi.org/10.5061/dryad.zs7h44j9b)

Heat shock tolerance & relative fitness data – EoR-A (Generation 0, 150), EoR-B (Generation 0, 150), T1 ancestor- Saccharomyces cerevisiae

## Description of the data and file structure: masterdata_updated

**Heat Shock Tolerance (hst):**

This was measured as % Survival when exposed to a transient 54 °C  heat shock for 75 minutes. Cell survival was measured by plating both heat-shocked and non-heat-shocked samples on YPD. Heat shock tolerance was measured for each replicate line, and at each time point. The T1 ancestor was measured 6 times.  HST was measured as duplicate technical replicates (hst_techrep1, hst_techrep2)

**Fitness under benign conditions (fitness):**

Fitness under benign conditions was measured using a reference strain, YIR044C*Δ* with a BY4741 background (*MATa his3Δ1 le...,