Dataset Information

Adaptations to fluctuating selection in Drosophila.

ABSTRACT: Time-dependent selection causes the adaptive evolution of new phenotypes, and this dynamics can be traced in genomic data. We have analyzed polymorphisms and substitutions in Drosophila, using a more sensitive inference method for adaptations than the standard population-genetic tests. We find evidence that selection itself is strongly time-dependent, with changes occurring at nearly the rate of neutral evolution. At the same time, higher than previously estimated levels of selection make adaptive responses by a factor 10-100 faster than the pace of selection changes, ensuring that adaptations are an efficient mode of evolution under time-dependent selection. The rate of selection changes is faster in noncoding DNA, i.e., the inference of functional elements can less be based on sequence conservation than for proteins. Our results suggest that selection acts not only as a constraint but as a major driving force of genomic change.

SUBMITTER: Mustonen V

PROVIDER: S-EPMC1892984 | biostudies-literature | 2007 Feb

REPOSITORIES: biostudies-literature

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Adaptations to fluctuating selection in Drosophila.

Mustonen Ville V Lässig Michael M

Proceedings of the National Academy of Sciences of the United States of America 20070207 7

Time-dependent selection causes the adaptive evolution of new phenotypes, and this dynamics can be traced in genomic data. We have analyzed polymorphisms and substitutions in Drosophila, using a more sensitive inference method for adaptations than the standard population-genetic tests. We find evidence that selection itself is strongly time-dependent, with changes occurring at nearly the rate of neutral evolution. At the same time, higher than previously estimated levels of selection make adapti ...[more]

PMID: 17287357

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Project description:While hybridization was viewed as a hindrance to adaptation and speciation by early evolutionary biologists, recent studies have demonstrated the importance of hybridization in facilitating evolutionary processes. However, it is still not well-known what role spatial and temporal variation in natural selection play in the maintenance of naturally occurring hybrid zones. To identify whether hybridization is adaptive between two closely related monkeyflower species, Mimulus guttatus and Mimulus laciniatus, we performed repeated reciprocal transplants between natural hybrid and pure species' populations. We planted parental genotypes along with multiple experimental hybrid generations in a dry (2021) and extremely wet (2023) year in the Sierra Nevada, CA. By taking fine scale environmental measurements, we found that the environment of the hybrid zone is more similar to M. laciniatus's seasonally dry rocky outcrop habitat than M. guttatus's moist meadows. In our transplants hybridization does not appear to be maintained by a consistent fitness advantage of hybrids over parental species in hybrid zones, but rather a lack of strong selection against hybrids. We also found higher fitness of the drought adapted species, M. laciniatus, than M. guttatus in both species' habitats, as well as phenotypic selection for M. laciniatus-like traits in the hybrid habitat in the dry year of our experiment. These findings suggest that in this system hybridization might function to introduce drought-adapted traits and genes from M. laciniatus into M. guttatus, specifically in years with limited soil moisture. However, we also find evidence of genetic incompatibilities in second generation hybrids in the wetter year, which may balance a selective advantage of M. laciniatus introgression. Therefore, we find that hybridization in this system is both potentially adaptive and costly, and that the interaction of positive and negative selection likely determines patterns of gene flow between these Mimulus species.

Project description:While hybridization was viewed as a hindrance to adaptation and speciation by early evolutionary biologists, recent studies have demonstrated the importance of hybridization in facilitating evolutionary processes. However, it is still not well-known what role spatial and temporal variation in natural selection play in the maintenance of naturally occurring hybrid zones. To identify whether hybridization is adaptive between two closely related monkeyflower species, Mimulus guttatus and Mimulus laciniatus, we performed repeated reciprocal transplants between natural hybrid and pure species' populations. We planted parental genotypes along with multiple experimental hybrid generations in a dry (2021) and extremely wet (2023) year in the Sierra Nevada, CA. By taking fine-scale environmental measurements, we found that the environment of the hybrid zone is more similar to M. laciniatus's seasonally dry rocky outcrop habitat than M. guttatus's moist meadows. In our transplants hybridization does not appear to be maintained by a consistent fitness advantage of hybrids over parental species in hybrid zones, but rather a lack of strong selection against hybrids. We also found higher fitness of the drought-adapted species, M. laciniatus, than M. guttatus in both species' habitats, as well as phenotypic selection for M. laciniatus-like traits in the hybrid habitat in the dry year of our experiment. These findings suggest that in this system, hybridization might function to introduce drought-adapted traits and genes from M. laciniatus into M. guttatus, specifically in years with limited soil moisture. However, we also find evidence of genetic incompatibilities in second generation hybrids in the wetter year, which may balance a selective advantage of M. laciniatus introgression. Therefore, we find that hybridization in this system is both potentially adaptive and costly, and that the interaction of positive and negative selection likely determines patterns of gene flow between these Mimulus species.

Dataset Information

Adaptations to fluctuating selection in Drosophila.

Publications

Adaptations to fluctuating selection in Drosophila.

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