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Adaptation Satterwhite, Rebecca S. [1], Cooper, Tim F. [1]. Testing the limits of adaptation: Jacks-of-all-trades become masters of none after 6,000 generations. Can a population evolved in the presence of two resources reach the same fitness in each as populations evolved in the presence of only one? This question is essential to theories on ecological specialization, the maintenance of variation, and sympatric speciation, but has not yet been evaluated over a prolonged period of evolution, despite a wealth of literature aimed at elucidating the limits of adaptation. In this study, we compared the response of replicate Escherichia coli populations evolved for 6,000 generations in the presence of either glucose or lactose alone (specialists), or in varying combinations (generalists). To identify adaptive patterns, we measured the relative fitness of each population in the environment in which it evolved, and in at least one alternate environment. All populations saw significant increases in fitness in both glucose and lactose, but the specialists displayed distinct patterns of response that emerged only after 3,000 generations of evolution. The glucose population saw an equivalent fitness increase in both its selective and in an alternate environment; the lactose population, in contrast, improved significantly more in its selective environment than in an alternate environment. When comparing the response of the generalists, we found that for the first 4,000 generations, the geometric mean fitness of a majority of populations was not significantly different from a best-case fitness âidealâ calculated from the combined response of each specialist in the environment in which it evolved. However, by 6,000 generations, each of the generalists had fallen significantly behind the specialists, indicating the presence of a constraint on their ability to adapt to both environments simultaneously. Our results demonstrate a caution against extrapolating long-term trends from short-term results; constraints on adaptation can take some time to influence evolutionary trajectories, and may not be detected over relatively small numbers of generations.
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1 - University of Houston, Biology & Biochemistry, 369 Science & Research Building 2, Houston, TX, 77204, USA
Keywords:
Adaptation
Experimental Evolution
specialization
microbiology.
Presentation Type: Regular Oral Presentation
Session: 60
Location: Superior B/Cliff Lodge
Date: Sunday, June 23rd, 2013
Time: 9:15 AM
Number: 60004
Abstract ID:42
Candidate for Awards:W.D. Hamilton Award for Outstanding Student Presentation,Student Travel Awards from the ASN |
