Climate change and flooding create biodiversity in the Amazon

The climate changes the Ice Age and the ancient floods, not the barriers, could have accelerated the evolution of new insects appearing in the Amazon jungle region of South America.

The Amazon basin is home to the most formidable in the world, but the reason why it has this feature so far is not well understood.

A group of US and Brazilian researchers, led by former graduate student Scott Solomon of the University of Texas at Austin, studied three leaf-cut ants in Central and South America to determine how geography as well as climate can affect the process of forming new species. To be able to evaluate the three most popular hypotheses regarding why Amazon forests are most diverse, Solomon collected genetic samples of 194 leaf-cutting ants in the river basin. Amazon.

Ulrich Mueller, co-author of the study and professor of integrated biology and adviser of Solomon, said: 'Scott was the first to fully explore the importance of geographic barriers to the source. root of the diversity of insect species in South America by using a model of leaf-cutting ants. Scott is following in the footsteps of Alfred Wallace - the pioneering naturalist - who, along with Darwin - has found that many species found in geographically close areas are often species with close proximity to each other '.

By combining genetic information analysis with existing knowledge of species and ancient distribution patterns of the regions of activity throughout the last ice age, Solomon, Mueller and colleagues found Evidence in support of 'Pleistocene refugia hypothesis' and 'sea invasion' hypothesis .

Caterpillars in the Amazon forest of Peru.A new study shows that climate changes in the Ice Age and ancient floods, not barriers, may have accelerated the evolution of new insect species appearing in forest areas. Bushy Amazon in South America.(Photo: iStockphoto / Martin Persson)

However, genetic and climatic results suggest that the 'river barrier hypothesis' cannot explain the biodiversity of insects.

The Pleistocene refugia hypothesis suggests that a significant reduction in precipitation during the last ice age (about 21,000 years ago) affected the place where Amazon species, such as leaf-cut ants, could exist . Originally a single species, it later evolved into many different species after being split into isolated regions called 'refugia' , each species must adapt to the selective pressures from other environments. separate from each other.

The 'invading sea' hypothesis suggests that about 10 to 15 million years ago, a combination of stratigraphic events and rising sea levels flooded much of the Amazon basin, causing it to sink in saline or brackish water. . This event may cause some higher areas, such as the Andes mountain range, to turn them into islands where species can evolve independently of other island species.

The 'river barrier' hypothesis suggests that tropical rivers act as barriers to transgenic flow to land-based organisms . The children who live very large and many in Amazonia have promoted the separation of limited populations on both sides of the river.

However, according to the new study, even the Amazon River - in some places it is nearly 2 miles wide, cannot prevent the winged leaf queen or male ants from crossing the river. Solomon said: 'Interestingly, the rivers in Amazone act as barriers to some birds, but the small ants that cut leaves can still overcome them.'

According to Mueller, research results cannot solve all the mysteries surrounding tropical biodiversity. For example, it could be both an ancient flooding event in the Amazong basin as well as more recent ice-climatic changes that contribute to species formation. Even if these two factors cannot explain why the diversity of tropical insects is far superior to the diversity of temperate insects.

Mueller said: 'The results do not solve the big riddle that why the diversity of tropical insects is superior to the diversity of temperate insects in some levels. But they are also very meaningful. They focus on a number of key processes that other researchers will test on organisms. '

The study was conducted at the University of Texas (Austin) and São Paulo University in Brazil. Solomon is an international research member of the National Science Foundation at the Smithsonian Institution.

Refer:
Solomon SE, Bacci M Jr., Martins J Jr., Vinha GG, Mueller UG.Insight into the Origins of Amazonian Diversity by the Insight into the Origins of Amazonian Diversity.PLoS One, 3 (7): e2738 DOI: 10.1371 / journal.pone.0002738