Does the wood pink provide the formula for surviving climate change?

The climate is warming increasingly quickly, especially in the Alps, which poses a challenge for organisms. If they do not spread to higher altitudes, they must very quickly adapt to higher temperatures in their current habitat, or else their populations will shrink and eventually die out.

The wood pink (Dianthus sylvestris) offers an example of climate adaptation. It is a perennial that is widespread in the Alps, occupying altitudes between 800 and 2,400 metres. Although there are similarities between high-altitude plants and those from low elevation areas, differences have evolved between the two over time.

A key characteristic is the flowering time: at high altitudes, wood pinks flower immediately after the snowmelt in June. At lower elevations, plants start to flower in May, but their growing season at lower elevations has already started much earlier. As an adaptation to the warmer lowland conditions, wood pinks growing in the valleys tend to be late bloomers.

Ten years ago, Simone Fior and other researchers working with Alex Widmer from the Institute of Integrative Biology at ETH Zurich began to investigate how the wood pink had genetically adapted to previous climate changes, and what this might mean for its reaction to current climate change. The study has just been published in the journal Science.

Flowering early to produce seeds

In their study, the researchers examined three wood pink populations from valley regions and three from mountain areas in the Swiss canton of Valais. They also analysed a specific gene from 1,000 individuals across the species¡¯ entire range, as well as carrying out transplantation experiments.

¡°Wood pinks in Alpine areas do not only flower as early as possible, but they also produce seeds as quickly as possible,¡± explains Widmer. ¡°This is an adaptation to the short season at high altitudes. In contrast, the plants in valley regions have more time.¡±

However, there was no fundamental change in flowering behaviour when the researchers transplanted wood pinks from the valleys to the mountains. Just like at lower elevations, they took more time, first building up plant mass and then producing many flowers. These plants also needed more time to produce seeds. When the snow came at the end of the short mountain summer, the seeds would not be ripe.

This ¡°behaviour¡± is controlled by a gene that the ETH researchers first discovered during this study, and which determines the wood pink's flowering time and growth. The gene is called DsCEN/2 and it has two variants, known as alleles, which differ between the two populations. Wood pinks growing in the valleys predominantly possess the ¡°warm¡± allele, while those in the mountains have the ¡°cold¡± allele.

The warm variant delays flowering and encourages general plant growth, which is beneficial in long, warmer summers. On the other hand, the cold variant controls the early flowering in alpine plants. ¡°Both alleles determine the wood pink¡¯s survival in different climate zones,¡± says Widmer.

A development that long pre-dates the wood pink

The ETH researchers used models to show that both alleles are incredibly old, ¡°older than the wood pink itself¡±, explains the plant geneticist.

To pinpoint when these alleles emerged within the evolution of the Dianthus species, the scientists also investigated genes from other species related to the wood pink. These analyses show that important differences between the warm and cold alleles are already present, even in very distantly related species.

The researchers concluded that the gene variants did not arise from mutations in the genome of the wood pink itself, but rather in other species of the Dianthus genus. One to two million years ago, these pinks experienced what is known as a radiation ¨C a rapid diversification of a single stem species into numerous new species.

During this time, the earth alternated between glacial and interglacial periods over thousands of years. As the different Dianthus species evolved, the two alleles also emerged as adaptations to the constantly changing climate.

Thanks to various mechanisms which distribute, reorganise and recombine genetic material, the two alleles eventually became part of the wood pink¡¯s genetic make-up ¨C and proved to benefit this species as well.

Existing variation is reorganised through recombination during sexual reproduction. This is how the warm and cold alleles emerged, which enabled the wood pink to genetically adapt more quickly to new environmental conditions than would be possible through new mutations alone. This process is likely particularly important where there is rapid radiation into many new species, like in the case of the Dianthus species. Evolutionarily new combinations of old gene variants such as this offer a broad foundation for adaptation to many different ecological conditions.

Although mutations do occur in wood pinks over time, the two alleles that determine the flowering time have been present for hundreds of thousands of years.

Future climate adaptation is possible

The two gene variants are likely to play a part in the wood pink's reaction to climate warming in the future: the ¡°warm¡± allele is already present in high-elevation populations, as the researchers showed. As temperatures continue to rise, this gene variant could continue to spread there and become dominant in the future.

¡°The wood pink possesses tools from the past to adapt to climate change in the present. We do not know if other alpine plants also have this ability. There are no other studies that address these questions in such depth,¡± emphasises Widmer.

However, he emphasizes that the current warm period is occurring at a pace unlike any other in history. Whether the wood pinks (and other alpine plants) are able to adapt quickly enough to this current situation is an open question, and one that needs to be researched going forward.

¡°The species can only utilise the existing genetic potential that enables adaptation to climate change, provided that there are sufficiently large, interrelated populations,¡± says Widmer. Small, isolated populations, on the other hand, risk dying out more quickly.