Adaption to island life
Wild populations of the model plant Arabidopsis thaliana from the Cape Verde Islands reveal the mechanisms of adaptation after abrupt environmental change
Ever since Darwin, island populations have been central to our understanding of evolution. Now, an international team of collaborating scientists, led by Angela Hancock from the Max Planck Institute for Plant Breeding Research in Cologne, Germany, used wild populations of Arabidopsis from the Cape Verde Islands to identify the molecular changes that allow success in a drought-prone environment. The findings will have broader implications for plant breeding and sustainable agriculture.
Max Planck Researchers worked together with an international team, including researchers from the Cape Verde Islands and four other countries, to investigate how wild thale cress (Arabidopsis thaliana) colonized the Cape Verde Islands. The team collected hundreds of plants from sites across the range in Cape Verde and analyzed their genomes. On the basis of DNA changes they found, the scientists were able to reconstruct the colonization history and identify genetic changes responsible for adaptation. "We were surprised to find that Arabidopsis colonized Cape Verde naturally - well before humans. We found the colonists most likely originated from North Africa about 5000 years ago, whereas humans colonized the islands only about 500 years ago," said Andrea Fulgione, one of the first authors on the study.
By comparing the climate in Cape Verde to that from Arabidopsis sites in North Africa, the authors determined that the short length of the growing season in Cape Verde represented a novel challenge to the colonizers. To test whether this change really mattered, they conducted an experiment with live plants. "We grew plants from Cape Verde and North Africa together in a climate chamber set to track hourly temperature, humidity and precipitation data we collected from a Cape Verde field site. Then we measured their reproductive output based on the quantity of seeds," says Fulgione. "Consistent with the observed shorter growing season, we found that Cape Verde Arabidopsis plants outperformed their North African relatives and that this difference was strongly associated with reduced time to flower and set seed," said Célia Neto, a co-first author of the study.
Genetic changes enabled populations to escape drought
The researchers then asked which DNA changes were used in adaptation. They analyzed patterns of DNA variation to ask how the plants had adapted to the novel environment and found that mutations involved in adaptation arose after colonization of Cape Verde. "We often see cases where populations adapt rapidly to new environments using DNA variation that already existed," explained Hancock. "Surprisingly, here we find that plants adapted to this more extreme habitat using newly arisen DNA changes.
The authors discovered that two independent gene-disruptions - one in each island - were crucial for establishment of Arabidopsis plants in the archipelago. These mutations abolish the functions of core genes involved in reproductive timing, resulting in a faster progression to flowering and an earlier termination of the life cycle. “This allows them to flower more quickly, making it more likely that they will produce seeds before the onset of the dry season," said Neto.
Understanding how species adapt to challenging environments also has broader potential impacts. Information about the DNA changes that provide an advantage in Cape Verde could contribute to improvements in sustainable agriculture more generally as these could be used to produce crop plants that are better suited drought-prone environments. This research also relates to conservation. Small, isolated populations and species are at the greatest risk of extinction from global change. Findings from the isolated Cape Verde Arabidopsis population could be applied to overcome challenges in other species. "Ultimately, this research aims to enhance our ability to predict and ameliorate the impacts of environmental change in diverse species," concluded Hancock, "but there is still a lot of work to do."