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The molecular processes behind adaptation

Adaptation is a key concept in evolutionary biology and underlies processes such as the ability of species to survive in changing environments and resistance to antibiotics and cancer chemotherapies. Recent advances in gene sequencing have made it easier than ever before to find evidence of adaptation at an unprecedented scale.
The molecular processes behind adaptation
Current methods for studying adaptation are often exclusively based on a priori candidate gene or on searching for signals of selection at the DNA level. However, this can result in a biased and incomplete picture of the processes behind adaptation.

This challenge was addressed by the ADAPT_EVOL (The molecular process and functional consequences of adaptation) project, which studied recent transposable element (TE)-induced adaptation in common fruit flies (Drosophila melanogaster). The TE is a DNA sequence that can change its position within a genome, while sometimes creating or reversing mutations.

Researchers identified adaptive TE insertions in natural populations from different geographical locations. Therefore, whole genome sequences were collected in the form of 27 strains from Sweden and 16 strains collected from southern Italy. The analyses of these 43 genome, together with the analyses of 141strains from North Carolina (USA) and 20 strains from a population in Rwanda enabled scientists to identify 39 putatively adaptive TEs.

It was found that these 39 TEs were either present in low frequencies or absent in the Rwanda population, while present in high frequencies in out-of-Africa populations. This suggested that these particular TEs are involved in adaptation to the out-of-Africa environment. It was also posited that 15 of the 39 putatively adaptive TEs had increased frequency as a result of positive selection.

Further studies of the molecular mechanisms and fitness of six putatively adaptive TEs revealed that five were involved in stress response and two in cold stress response. Furthermore, one TE was involved in oxidative stress response, one in heavy-metal stress response and one in xenobiotic stress response.

ADAPT_EVOL demonstrated that the ability to cope with a stressful environment is an important adaptive trait in natural D. melanogaster populations. It was found that 2 of the 6 adaptive TEs affect both the structure and expression of the nearby gene, with another three only affect the expression.

The project has shown that TEs are a useful tool for studying adaptation in natural populations. Since they are present in virtually all organisms studied so far, the role of TEs in adaptive evolution is unlikely to be restricted merely to fruit flies.

Related information


Adaptation, evolutionary biology, DNA, ADAPT_EVOL, transposable element, Drosophila melanogaster, population, adaptive evolution
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