1993
Bennett A F; Lenski R E
Evolutionary Adaptation to Temperature II. Thermal Niches of Experimental Lines of Escherichia coli Journal Article
Evolution, 47 (1), pp. 1–12, 1993, ISSN: 0014-3820.
Abstract | Links | BibTeX | Altmetric | Tags: Descendant Experiments
@article{Bennett1993,
title = {Evolutionary Adaptation to Temperature II. Thermal Niches of Experimental Lines of \textit{Escherichia coli}},
author = {Albert F. Bennett and Richard E. Lenski},
url = {https://onlinelibrary.wiley.com/doi/10.1111/j.1558-5646.1993.tb01194.x},
doi = {10.1111/j.1558-5646.1993.tb01194.x},
issn = {0014-3820},
year = {1993},
date = {1993-02-01},
urldate = {1993-02-01},
journal = {Evolution},
volume = {47},
number = {1},
pages = {1--12},
abstract = {Groups of replicated lines of the bacterium \textit{Escherichia coli} were propagated for 2,000 generations at constant 32, 37, or 42°C, or in an environment that alternated between 32 and 42°C. Here, the authors examine the performance of each group across a temperature range of 12-44°C measuring the temperatures over which each line can maintain itself in serial dilution culture (the thermal niche). Thermal niche was not affected by selection history: average lower and upper limits remained about 19 and 42°C for all groups. No significant differences among groups were observed in rate of extinction at more extreme temperatures. Increases in mean fitness were temperature specific, with the largest increase for each group occurring near its selected temperature. Thus, the temperature at which mean fitness relative to the ancestor was greatest (the thermal optimum) diverged by 10°C for the groups selected at constant 32°C versus constant 42°C. Tradeoffs in relative fitness (decrements relative to the ancestor elsewhere within the thermal niche) did not necessarily accompany fitness improvements.},
keywords = {Descendant Experiments},
pubstate = {published},
tppubtype = {article}
}
Groups of replicated lines of the bacterium Escherichia coli were propagated for 2,000 generations at constant 32, 37, or 42°C, or in an environment that alternated between 32 and 42°C. Here, the authors examine the performance of each group across a temperature range of 12-44°C measuring the temperatures over which each line can maintain itself in serial dilution culture (the thermal niche). Thermal niche was not affected by selection history: average lower and upper limits remained about 19 and 42°C for all groups. No significant differences among groups were observed in rate of extinction at more extreme temperatures. Increases in mean fitness were temperature specific, with the largest increase for each group occurring near its selected temperature. Thus, the temperature at which mean fitness relative to the ancestor was greatest (the thermal optimum) diverged by 10°C for the groups selected at constant 32°C versus constant 42°C. Tradeoffs in relative fitness (decrements relative to the ancestor elsewhere within the thermal niche) did not necessarily accompany fitness improvements.
1992
Bennett A F; Lenski R E; Mittler J E
Evolutionary Adaptation to Temperature. I. Fitness Responses of Escherichia coli to Changes in its Thermal Environment Journal Article
Evolution, 46 (1), pp. 16-30, 1992, ISSN: 0014-3820.
Abstract | Links | BibTeX | Altmetric | Tags: Descendant Experiments
@article{nokey,
title = {Evolutionary Adaptation to Temperature. I. Fitness Responses of \textit{Escherichia coli} to Changes in its Thermal Environment},
author = {Albert F. Bennett and Richard E. Lenski and John E. Mittler},
url = {https://onlinelibrary.wiley.com/doi/10.1111/j.1558-5646.1992.tb01981.x},
doi = {10.1111/j.1558-5646.1992.tb01981.x},
issn = {0014-3820},
year = {1992},
date = {1992-02-01},
urldate = {1992-02-01},
journal = {Evolution},
volume = {46},
number = {1},
pages = {16-30},
abstract = {Replicate lines of \textit{Escherichia coli} were propagated for 2,000 generations in four different thermal regimes: constant 32, 37, or 42°C (thermal specialists), or a daily alternation between 32 and 42°C (32/42°C: thermal generalists). The ancestor had previously been propagated at 37°C for 2,000 generations. All experimental groups showed improved relative fitness in their own thermal environment (direct response of fitness), but rates of fitness improvement varied greatly among temperature groups. The 42°C group responded most rapidly and extensively, followed by the 32 and 32/42°C groups, whose fitness improvements were indistinguishable. The 37°C group, which experienced the ancestral temperature, had the slowest and least extensive fitness improvement.},
keywords = {Descendant Experiments},
pubstate = {published},
tppubtype = {article}
}
Replicate lines of Escherichia coli were propagated for 2,000 generations in four different thermal regimes: constant 32, 37, or 42°C (thermal specialists), or a daily alternation between 32 and 42°C (32/42°C: thermal generalists). The ancestor had previously been propagated at 37°C for 2,000 generations. All experimental groups showed improved relative fitness in their own thermal environment (direct response of fitness), but rates of fitness improvement varied greatly among temperature groups. The 42°C group responded most rapidly and extensively, followed by the 32 and 32/42°C groups, whose fitness improvements were indistinguishable. The 37°C group, which experienced the ancestral temperature, had the slowest and least extensive fitness improvement.
1991
Lenski R E; Rose M R; Simpson S C; Tadler S C
Long-term experimental evolution in Escherichia coli. I. Adaptation and divergence during 2,000 generations Journal Article
Am. Nat., 138 (6), pp. 1315–1341, 1991.
Abstract | Links | BibTeX | Altmetric | Tags: Fitness Trajectories, Parallelism and Divergence
@article{Lenski1991,
title = {Long-term experimental evolution in \textit{Escherichia coli}. I. Adaptation and divergence during 2,000 generations},
author = {Richard E. Lenski and M R. Rose and S C. Simpson and S C. Tadler},
url = {https://www.jstor.org/stable/2462549},
doi = {https://doi.org/10.1086/285289},
year = {1991},
date = {1991-01-01},
urldate = {1991-01-01},
journal = {Am. Nat.},
volume = {138},
number = {6},
pages = {1315--1341},
publisher = {JSTOR},
abstract = {We assess the degree to which adaptation to a uniform environment among independently evolving asexual populations is associated with increasing divergence of those populations. In addition, we are concerned with the pattern of adaptation itself, particularly whether the rate of increase in mean fitness tends to decline with the number of generations of selection in a constant environment. The correspondence between the rate of increase in mean fitness and the within-population genetic variance of fitness, as expected from Fisher's fundamental theorem, is also addressed. Twelve \textit{Escherichia coli} populations were founded from a single clonal ancestor and allowed to evolve for 2,000 generations. Mean fitness increased by about 37%. However, the rate of increase in mean fitness was slower in later generations. There was no statistically significant within-population genetic variance of fitness, but there was significant between-population variance. Although the estimated genetic variation in fitness within populations was not statistically significant, it was consistent in magnitude with theoretical expectations. Similarly, the variance of mean fitness between populations was consistent with a model that incorporated stochastic variation in the timing and order of substitutions at a finite number of nonepistatic loci, coupled with substitutional delays and interference between substitutions arising from clonality. These results, taken as a whole, are consistent with theoretical expectations that do not invoke divergence due to multiple fitness peaks in a Wrightian evolutionary landscape.},
keywords = {Fitness Trajectories, Parallelism and Divergence},
pubstate = {published},
tppubtype = {article}
}
We assess the degree to which adaptation to a uniform environment among independently evolving asexual populations is associated with increasing divergence of those populations. In addition, we are concerned with the pattern of adaptation itself, particularly whether the rate of increase in mean fitness tends to decline with the number of generations of selection in a constant environment. The correspondence between the rate of increase in mean fitness and the within-population genetic variance of fitness, as expected from Fisher's fundamental theorem, is also addressed. Twelve Escherichia coli populations were founded from a single clonal ancestor and allowed to evolve for 2,000 generations. Mean fitness increased by about 37%. However, the rate of increase in mean fitness was slower in later generations. There was no statistically significant within-population genetic variance of fitness, but there was significant between-population variance. Although the estimated genetic variation in fitness within populations was not statistically significant, it was consistent in magnitude with theoretical expectations. Similarly, the variance of mean fitness between populations was consistent with a model that incorporated stochastic variation in the timing and order of substitutions at a finite number of nonepistatic loci, coupled with substitutional delays and interference between substitutions arising from clonality. These results, taken as a whole, are consistent with theoretical expectations that do not invoke divergence due to multiple fitness peaks in a Wrightian evolutionary landscape.
