The Amazon rainforest is without a doubt one of our planet's most dramatic and species-rich ecosystems. But what do we know about the origins of its diversity? In a new study, an international team of scientists sheds light on its history, highlighting how a slow uplift of the Andes mountain range was responsible for the region's spectacular diversity. The findings, published in the journal Science, show that this diversity is more than 20 million years older than originally thought. 'With the results we present in this article, we've rewritten the entire history of Amazonia in terms of the development of its biodiversity,' explained Dr Alexandre Antonelli from the Department of Plant and Environmental Sciences at the University of Gothenburg in Sweden, one of the authors of the study. Theories about how the Andes impacted the diversity of the Amazonian rainforest abounded over the years, but researchers were unable to determine the causal links until now. Led by Dr Antonelli and Dr Carina Hoorn from the University of Amsterdam in the Netherlands, the researchers used 65 million-year-old geological, phylogenetic and molecular data to compare the pattern of the current biodiversity in Amazonia with uplift records from the Andes. 'We suspected from some scattered fossils and dated species trees that the Amazonian diversity arose after the separation from Africa,' Dr Antonelli pointed out. 'So we looked at the whole period. I worked mainly on coordinating a survey of DNA [deoxyribonucleic acid]-based studies of the relationships between different species of plants and animals. We've examined hundreds of scientific publications and have found that very few of the genera are as young as people thought.' According to their findings, Amazonian biodiversity is linked with the Andes, an area that was created after the tectonic plates along the Pacific coast were pressed together. 'Uplift in the central and northern Andes was a partially synchronous process caused by plate tectonic readjustments,' the authors write. 'Plate subduction along the Pacific margin caused uplift in the central Andes during the Paleogene. Posterior plate breakup in the Pacific and subsequent collision of the new plates with the South American and Caribbean plates resulted in intensified mountain building in the northern Andes.' This new mountain range also played a critical role in changing the environment, forcing flora and fauna to adapt to new living conditions. The team found that the changes made in the Earth's crust altered the large wetland areas of northern South America, which dried up as the Amazon River formed. The diverse plants and animals therefore had new, virgin land to call home. 'We were surprised that there was such a strong link between the formation of the Andes and the diversity in Amazonia,' Dr Antonelli said. 'The area was considered a kind of paradise where evolution could take place undisturbed, but this hasn't been the case at all - a lot has happened in the region.' The team pointed out that more research in this area is needed. 'Understanding the mechanisms that underlie the assembly and evolution of Amazonian biodiversity continues to be a major challenge that will require hitherto unrealised interdisciplinary scientific collaboration,' the authors write. 'Evolutionary studies linked to molecular phylogenies and fossil assemblages should focus on Neogene records and on species-rich but poorly sampled areas. Future research should be concentrated on the interface between the Cenozoic and cratonic areas, and on the transition zone between the Andes and Western (lowland) Amazonia. This area, together with the southern fringe of Amazonia, has become rapidly occupied by humans but nonetheless remains scientifically poorly known.' Researchers from Brazil, Chile, the Netherlands, Spain, Switzerland, the US and Venezuela contributed to this study.
Brazil, Switzerland, Chile, Spain, Netherlands, Sweden, United States, Venezuela