The Amazon rainforest may be a hotspot for animal and plant diversity, but this week, scientists report that new species actually form there less often than previously thought. Places like deserts and mountaintops that do not have a lot of species provide more opportunity for rapid diversification. This paradox of diversity - that new species form at a faster pace in "cold spots" than hotspots - was reported this week in the journal Science.
A multinational team of scientists studied diversity in a major group of tropical birds and they found that although coldspots might be extreme with dry, unstable environments, they are also relatively empty, giving new species the elbow room to evolve. In contrast, biodiversity hotspots like the Amazon rainforest are the result of the gradual accumulation of species over time.
"Our results reveal a model in which species are forming faster in environmental extremes but have accumulated in moderate environments to form tropical biodiversity hotspots," said Robb Brumfield, the Louisiana State University (LSU) Department of Biological Sciences Roy Paul Daniels Professor, LSU Museum of Natural Science Curator of Genetic Resources and LSU College of Science Associate Dean of Research & Administration, who is a senior author on the paper published in Science.
This paradox was revealed because of samples in the vast collections maintained by natural history museums. The LSU Museum of Natural Science and its frozen tissues collection, which is the oldest and largest of its kind in the world, contributed tissues for 747 of the 1,287 bird species that are part of this study. The LSU sampling represented 24 countries.
"The remarkable sampling in this study comes from 40 years of fieldwork by curators, students, staff and others, who spent huge amounts of time and money, and risked their personal health, collecting specimens from around the world," said co-author Fred Sheldon, the LSU Department of Biological Sciences George H. Lowery, Jr. Professor and LSU Museum of Natural Science Curator of Genetic Resources.
Lead authors and LSU alumni Michael Harvey, who is an assistant professor at the University of Texas at El Paso, and Gustavo Bravo, who is a postdoctoral researcher at Harvard University, spent many months lugging around the essential, heavy cryogenic storage units filled with liquid nitrogen to preserve tissue samples up remote streams in Amazonia and into rugged mountain ranges in the Andes.
By analyzing the DNA from these museum tissue samples, the authors were able to map the genetic relationships of a predominant group of tropical birds called the suboscine passerines, which represent roughly one out of every three species of birds in the American tropics. Suboscines vary widely in characteristics and habitats -- from the Andean snow line to lowland Amazonia and from cloud forests to deserts.
"This shows that conservation efforts to save the rapidly changing tropical landscape need to focus not only on the species-rich Amazon, but also on regions that are less diverse but contribute disproportionally to the generation of new species, like the wind-swept, cold puna of the Andes Mountains," Brumfield said.
Notably, many of the ornithologists involved in this study are from groups historically underrepresented in the sciences including Latinx and women researchers.
"This paper marks not only a change in our understanding of evolution in the tropics but also an acknowledgement and valuation of the diversity of culture, expertise and perspective in the field of ornithology," said a senior author Liz Derryberry, formerly a postdoctoral researcher at the LSU Museum of Natural Science, who is an associate professor at the University of Tennessee at Knoxville.