DOI: 10.5061/dryad.x0k6djhr0
title: Linking temperature dependence in fitness effects of mutations to thermal niche adaptation

description: Fitness effects of mutations may generally depend on temperature that
 influences all rate-limiting biophysical and biochemical
 processes.  Earlier studies suggested that high temperatures may
 increase the availability of beneficial mutations (“more beneficial
 mutations”), or allow beneficial mutations to show stronger fitness
 effects (“stronger beneficial mutation effects”).  The “more
 beneficial mutations” scenario would inevitably be associated with
 increased proportion of conditionally beneficial mutations at higher
 temperatures.  This in turn predicts that populations in warm
 environments show faster evolutionary adaptation but suffer fitness loss
 when faced with cold conditions, and those evolving in cold environments
 become thermal-niche generalists (“hotter is narrower”).  Under
 the “stronger beneficial mutation effects” scenario, populations evolving
 in warm environments would show faster adaptation without fitness costs in
 cold environments, leading to a “hotter is (universally) better” pattern
 in thermal niche adaptation.  We tested predictions of the two
 competing hypotheses using an experimental evolution study in which
 populations of two model bacterial species, Escherichia coli and
 Pseudomonas fluorescens, evolved for 2,400 generations at three
 experimental temperatures.  Results of reciprocal transplant
 experiments with our P. fluorescens populations were largely consistent
 with the “hotter is narrower” prediction.  Results from the E.
 coli populations clearly suggested stronger beneficial mutation effects at
 higher assay temperatures, but failed to detect faster adaptation in
 populations evolving in warmer experimental environments (presumably
 because of limitation in the supply of genetic variation).  Our
 results suggest that the influence of temperature on mutational effects
 may provide insight into the patterns of thermal niche adaptation and
 population diversification across thermal conditions.
description: Data collected from an experimental evolution
 project.    Eighteen
 Escherichia coli evolution lines and 18 Pseudomonas fluorescens evolution
 lines evolved at three temperatures as isolated cultures.  Nine incubators
 were used in this study, randomly assigned into three blocks.  The three
 incubators in each block were set 19, 26 or 31°C.  There were two
 replicate microcosms for each species in every incubator.  Therefore, a
 total of 18 evolution lines were established for each species (3 blocks ×
 3 temperatures × 2 within-incubator replicates). 
   Population density was measured as
 colony formation units per ml.  
 Fitness of each evolved population against it ancestral strain
 at each of the three temperatures (19, 26 or 31°C) was measured by
 competition experiment.  Fitness of evolved E. coli populations and their
 ancestor, all of the strain REL606, relative to a reference strain,
 REL606Ara+, was measured by head-to-head competition assays.  Fitness of
 evolved and ancestral P. fluorescens populations, all of the strain
 SBW25EeZY6KX, was measured against a reference strain SBW25.  Relative
 fitness of each tested population against the reference strain was
 estimated from the Malthusian parameters.  Fitness of each evolved
 population relative to its ancestor (change in fitness during the
 evolution experiment) was calculated as difference between the two,
 analogous to the selection coefficient index. 
description: # Title of Dataset: Linking temperature dependence of fitness effects of
 mutations to thermal niche adaptation ## Description of the data and file
 structure There are three data files. The "Density data" file
 (cvs table) shows the mean population densities (log-transformed) over
 time of each evolution line during the selection experiment. Nine
 incubators were used in this study, randomly assigned into three blocks
 (A, B and C). The three incubators in each block were set 19, 26 or 31°C.
 There were two replicate microcosms for each species in every incubator.
 Variable "block" indicate which block an evolution line belong
 to; variable "evolution.temperature" indicates at which
 temperature the evolution lines are selected; variable
 "replicate" indicates the within-incubator replicate ID. Species
 "E" represents Escherichia coli and P, Pseudomonas fluorescens.
 Densities were measured as colony formation units per ml. The
 "Fitness data" file (cvs table) gives fitness assayed in home
 and alternative environments, in a format convenient for paired-t tests.
 Variable "assay.temnperature" indicates at which temperature
 fitness was measured. Variable "block" indicate which block an
 evolution line belong to; variable "evolution.temperature"
 indicates at which temperature the evolution lines are selected. Variable
 "replicate" indicates the within-incubator replicate ID. Species
 "E" represents Escherichia coli and P, Pseudomonas fluorescens.
 Variable "tag" indicates microcosm label which integrates
 information about block, evolution temperature and replicate ID. Variable
 "change.in.fitness" show the relative fitness of each evolved
 population against its ancetral strain (measured by head-to-head
 competition). The "R code" file (txt file) provide code used for
 data analysis presented in the article associated with the data. ##
 Sharing/Access information Links to other publicly accessible locations of
 the data: NA Data was derived from the following sources: NA