PubMed · 7993484
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J A Shapiro. 1994-09-30. Adaptive mutation.. https://doi.org/10.1126/science.7993484
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Local adaptation represents a pivotal theme in evolutionary biology. The Opisthopappus genus, comprising Opisthopappus longilobus and O. taihangensis, thrives on the cliffs of the Taihang Mountains. During their evolutionary history, two species are hypothesized to have locally adapted to their cliff habitats. In the present study, we employed a combined approach of whole-genome sequencing of O. taihangensis and population genomic analysis from both species to gain deeper insights into their patterns of local adaptation. Our results revealed that the expansive genome of O. taihangensis (3010.18 Mb), a consequence of a whole-genome duplication (WGD) event, coupled with a high proportion of repetitive sequences (82.70%), was postulated as one of its adaptive strategies. A clear differentiation between O. taihangensis and O. longilobus was observed, with the two species diverging approximately 17.57 million years ago (Mya), with O. longilobus serving as the ancestor. Since their divergence, limited gene flow was observed between the two species. Post-divergence, the effective population sizes of both species expanded, yet underwent a dramatic reduction at approximately 0.07 Mya. Furthermore, a total of 798 adaptive genes were identified, of which 207 overlapped with expanded genes, and eight genes were found to be under positive selection. These genes primarily regulated the growth and development of both species via pathways such as oxidation-reduction and ubiquitin-proteasome, enabling them to withstand climate changes. These findings provide profound insights into the local adaptation of Opisthopappus species to the cliff environments and offer valuable clues for further exploring the local adaptation among various cliff-dwelling organisms.
In this report, we examine the hypothesis that the drivers of latitudinal selection observed in the eastern US Drosophila melanogaster populations are reiterated within seasons in a temperate orchard population in Pennsylvania, USA. Specifically, we ask whether alleles that are apparently favoured in northern populations are also favoured early in the spring, and decrease in frequency from the spring to autumn with the population expansion. We use SNP data collected for 46 metabolic genes and 128 SNPs representing the central metabolic pathway and examine for the aggregate SNP allele frequencies whether the association of allele change with latitude and that with increasing days of spring-autumn season are reversed. Testing by random permutation, we observe a highly significant negative correlation between these associations that is consistent with this expectation. This correlation is stronger when we confine our analysis to only those alleles that show significant latitudinal changes. This pattern is not caused by association with chromosomal inversions. When data are resampled using SNPs for amino acid change the relationship is not significant but is supported when SNPs associated with cis-expression are only considered. Our results suggest that climate factors driving latitudinal molecular variation in a metabolic pathway are related to those operating on a seasonal level within populations.
An analysis is presented of a continuous-culture technique named "Brown and Oliver Interactive-Continuous Selection" (BOICS; Brown and Oliver, 1982), that was devised for the selection of microbial mutants tolerant to extreme environmental stress. The case in which the stress is due to a growth inhibitor is considered. The possible steady outcomes of competition between mutants in BOICS are analyzed under the assumption that the specific growth rates of the competing mutants depend only on the inhibitor concentration. The analysis indicates that BOICS selects mutants that sustain a given specific growth rate (equal to the dilution rate in the selection experiment) at an increased concentration of the inhibitor. Simulation results support the steady-state analysis. Further simulation results show that BOICS may fail if the specific growth rate of a mutant has to be considered to depend on a factor beside the inhibitor concentration. The choice of experimental conditions that promote the success of BOICS is discussed. An interpretation of BOICS emerges from the analysis. Namely, that BOICS implements (at least approximately) a strategy for the selection of tolerant mutants in which (1) all factors in the growth environment, beside the stress of interest (inhibitor concentration) are maintained constant, and (2) the stress is adjusted as the culture evolves so that it is always maximized subject to a specified minimum value of the mean specific-growth rate being maintained. This interpretation suggests new (possibly improved) ways of implementing essentially the same selection technique. It is noted that a chemostat implements the same strategy in the case that the stress is due to the lack of a growth-rate-limiting nutrient. The outcome of selection for inhibitor tolerant mutants in chemostats, turbidostats, and in BOICS is compared. Only BOICS selects specifically for mutants tolerant to extreme concentrations of the inhibitor.