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Scientists from the Royal Botanical Garden of Madrid in collaboration with researchers from Ecuador and the United States have carried out the first evolutionary study with genetic data of the genusScalesia, a plant also known as Darwin's giant daisies in the Galapagos Islands.
Evolutionary radiation inoceanic islands have fascinated biologists ever sinceCharles Darwin carry out the exploration of theGalapagos archipelago. These radiations are groups of closely related species that have originated very quickly, explosively - in a few hundred thousand years - from a single ancestral species that arrived on the islands.
In addition to rapid speciation, radiation on islands, especially volcanic, often lead to accelerated evolution as a result of great ecological diversity, which is called “adaptive radiation”. The most famous of the examples is located in the animal kingdom and, specifically, in the so-called Galapagos finches or Darwin's finches.
Although there are some examples of studies in the plant kingdom in Hawaii or the Canary Islands, until recently limited resolution was obtained when investigating kinship relationships between species, which has hampered a detailed investigation of their patterns and processes of speciation and, in particular, its pace and mode of rapid diversification on the islands.
An international team of scientists including several researchers from the Higher Council for Scientific Research (CSIC) in theRoyal Botanical Garden (RJB) of Madrid, has just published a pioneering study on all species of the genusScalesia, also known as "Darwin's giant daisies”. This is the documentation of one of the most emblematic evolutionary radiations in geologically and environmentally very dynamic islands such as the Galapagos.
First genetic and evolutionary study of giant daisies
"It is a phylogenomic analysis using massive sequencing techniques (genotyping by sequencing) to investigate the relationships between species, their rate of diversification and their main evolutionary patterns," says the RJB-CSIC researcherMario Fernandez-Mazuecos, member of this team.
The results of this research, published in the journalCurrent Biology, point out that the lineage ofScalesia it separated from its closest relatives in South America about three million years ago. However, the current 15 species, all unique to the Galapagos Islands, would have diversified rapidly from a common ancestor in more recent times, probably in the last million years.
Another evolutionary pattern identified inScalesia it is the breach of the hypothesis known as the "rule of progression", according to which older species are expected to occupy older islands. In this case the rule is broken because the genus has diversified very recently, when most of the islands had already emerged from the seabed.
“Many times it is assumed that theisolation Inter-island is responsible for most of the diversity in the archipelagos. We found that the species have diversified for the most part within the largest islands of the archipelago, and not so much as a result of isolation between islands ”, indicates Fernández-Mazuecos.
During the study, it was also discovered that species of Darwin's daisies similar in their characters tend not to be closely related. This is the case of species that grow to the size of trees, or of those that have the same type of leaf. "This would be the result of convergent evolution, that is, these similar characters may have evolved several times as an adaptation to similar environments on different islands", adds the RJB-CSIC researcher.
Both finches andScalesia powerfully attracted Darwin's attention during his stay in the Galapagos, as reflected inThe Voyage of the Beagle. However, unlike the evolutionary history of finches, which has been extensively studied, the evolution ofScalesia it had hardly been investigated until now.
Mario Fernández-Mazuecos, Pablo Vargas, Ross A. McCauley, David Monjas, Ana Otero, Jaime A. Chaves, Juan Ernesto Guevara Andino and Gonzalo Rivas-Torres. "The Radiation of Darwin’s Giant Daisies in the Galapagos Islands"Current Biology, 2020. DOI: https://doi.org/10.1016/j.cub.2020.09.019.