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| Example of Chaco vegetation, area of Porto Murtinho-MS (credit: Fábio Alves) |
The Chaco is the smallest and least known Brazilian biome. The little that remains is being cut for grazing. Brazilian researchers reveal that, If the destruction were to end today, the genetic diversity of the Brazilian Chaco would need up to 3,000 years to recover
Brazilian Science Communication Agency
The Gran Chaco, or simply Chaco, is a large dry forest biome with almost one million square kilometers (386,000 sq mi), twice the size of Spain, in the center of South America. It occupies a vast plain between northern Argentina, Paraguay, and Bolivia. Few people know, but the Chaco is also a Brazilian biome, as it invades portions of the states of Mato Grosso and Mato Grosso do Sul. But the Chaco in Brazil is disappearing. Fast.
This rich biome that took millions of years to establish and diversify is being rapidly destroyed by cattle ranchers for the opening of new pastures. In Mato Grosso do Sul there are only a handful of fragmented areas of Chaco within large farms in the region of Porto Murtinho, near the border with Paraguay. The vegetation of each of these fragments preserves an important part of the genetic diversity of that threatened biome.
"This genetic heritage must be preserved before it disappears forever. It is time to protect what is left of the Brazilian Chaco and not to cut any more trees!" says plant geneticist Anete Pereira de Souza, leader of the Laboratory of Molecular Genetic Analysis at the Center for Molecular Biology and Genetic Engineering, Institute of Biology, State University of Campinas (Unicamp).
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| Burnt Chaco at Porto Murtinho-MS (credit: Fábio Alves) |
"The data we have obtained shows that we are at the end of the line. Now is the last chance to do something and save the Brazilian Chaco, avoiding the definitive loss of an entire biome," warns Souza. "The data show that we will soon be entering the stage of genetic degradation of plant species, which will mean the end of the diversity needed to maintain the Chaco. If we lose plants, we will lose animals, birds, insects, microorganisms The climate of the region, which is already dry, could worsen with less rainfall and higher temperatures, and it is a huge cascade of problems that are about to happen, if the federal and state governments do not decide to act now! "
If the destruction of the Brazilian Chaco were to end today, and permanent conservation areas were created, how long would it take to recover the lost genetic diversity? Between 300 and 3,000 years, suggests a study done by the biologist from Brazil, Fábio Alves, a member of Souza's team. The work has been published in Ecology and Evolution.
"The area of Chaco that remains is very small, but it has an important genetic diversity that needs to be conserved," says Souza. "With this in mind, we decided to investigate the state of loss of diversity in that biome. Thanks to the work of Fábio Alves and collaborators, we diagnosed the loss of diversity of two species of plants characteristic of the Chaco, and formulated a proposal for conservation of both species and, consequently, the Chaco."
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| Chaco, Porto Murtinho-MS (credit: Fábio Alves) |
Shy exuberance
The devastation of the Brazilian Chaco is directly linked to the devastation of another neighboring biome, the Pantanal, the largest wetland in the world, due to the advance of the agricultural frontier in the last 40 years. "Even though extensive livestock farming has existed in the region since 1740, the Pantanal has remained relatively undisturbed for the last 200 years. However, since the 1970s, with the creation of government incentives for the occupation of the Central-West region of Brazil, in less than 40 years the devastation has spread throughout the Pantanal. The region of Porto Murtinho, on the border between the Pantanal and Chaco (on the border of Brazil and Paraguay), is one of the most degraded areas," says Alves.
With the growth of the Brazilian livestock industry - Brazil is the world's largest producer and exporter of cattle meat - mainly due to the increase in meat consumption in China, cattle farms are now advancing over the areas of the Brazilian Chaco.
In 1998, the area of the Brazilian Chaco was estimated at 12,400 km2 (4,800 sq miles). In 2008, however, technicians from the Ministry of Environment found that a third of all that native cover had disappeared. That was ten years ago. We do not have an estimate of the area of Chaco that has been lost in Brazil since then. But the devastation continues.
Such rapid destruction triggered the alert among biologists at the Federal University of Mato Grosso do Sul (UFMS) in Campo Grande, the state capital. Among them is the biologist Ângela Sartori. In the mid-2000s, Sartori's group began researching the biodiversity of the Brazilian Chaco.
One of them was Fábio Alves. The first time he went to the Chaco was in 2007. It would be only the first of 14 expeditions promoted in the following years, during which Alves has witnessed the continuous and unbridled destruction of the little that remains of Chaco in Brazil.
One reason for the Chaco biome to be so little known in Brazil, and therefore there is practically no awareness among the population of the need for its preservation, is that the Chaco vegetation is not exuberant, such as those of the Amazon and the Atlantic Forest, nor to have significant economic or tourist importance (as is the case of the neighboring Pantanal).
At first glance the vegetation of the Chaco does not look beautiful. After all, it is a dry forest. There grows a thorny, wild vegetation that practically does not arouse economic interest, but ornamental. "On the farms of Porto Murtinho you see a few species cultivated in gardens or pots, because of the beauty of its flowers," observes Alves. "In Mato Grosso do Sul, people think the Chaco is ugly, so they cut everything, but the plants have beautiful flowers," says Souza.
Alves studied the genetics of two plant species that are very representative of the Brazilian Chaco. They are part of the Fabaceae family. Both belong to the genus Prosopis. "Although there are more than 40 species of the genus Prosopis in the world, of which 31 in South America, there are only five species registered in Brazil, I chose to work with the two most abundant species in the Chaco areas of Brazil. The other species are quite difficult to find and, and when they are found, the number of individuals per area is very low, making population work unfeasible," says Alves.
Prosopis rubriflora is a large shrub that reaches 4 to 6 meters high, and produces beautiful red flowers all year round. It has a thinner cup, which makes its flowers more evident. After pollination by bees, the plant produces fruits that grow in the form of pods hanging from the branches. When they mature, they fall to the ground.
According to the International Union for Conservation of Nature (IUCN) Red List, since 1997 P. rubriflora has been classified as endangered in Paraguay, where half of Chaco's original coverage has already been lost. "Knowing that this species has records only in Brazil and Paraguay, I think that P. rubriflora should be classified as endangered also in Brazil, since here the species is limited to a single region, which has suffered a lot with the deforestation," says Alves.
Prosopis ruscifolia, the second plant studied, is a tree of 6 to 15 meters. It blooms once a year, between the months of November and December, when small white flowers sprout. The species has a dense crown. Its ripened fruits encapsulate inside pods between January and February.
"Between 2007 and 2012, I visited the Porto Murtinho region 14 times. In order to do the work with the two species of Prosopis, I collected seeds and leaves in 19 different areas, located in 17 farms or settlements. Although there are still a few well preserved areas, they are the exception rather than the rule," explains Alves.
The work of Alves involved the collection of leaves of 241 individuals of P. rubriflora and 308 individuals of P. ruscifolia. A single area was chosen for the collection of P. rubriflora seeds, to be germinated in the laboratory. Over two years, Alves collected 393 seeds at the site.
Alves' idea was to collect seeds and leaves of the two Prosopis species that grow in several Chaco fragments, in order to compare - through DNA extraction - the genetic variability of plants that survive in the various fragments of Chaco. In this way it would be possible to evaluate the genetic loss resulting from the destruction of the Chaco.
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| A tree of Prosopis rubriflora in the Brazilian Chaco (Fábio Alves) |
Why does this matter?
Why is it important to assess the stage of loss of genetic variation in the Chaco? The history of life on Earth is the history of evolution of species from the diversification of other species that lived before them. Diversification happens naturally, through the crossing of individuals to the production of embryos that will germinate forming a new generation. At each breeding new mutations appear in the DNA chain where the hereditary code of each individual is stored.
When mutations are beneficial, for example giving the plant greater resistance to aridity, greater heat tolerance, or better adaptation to more acidic or chemically poor soils (as at the Chaco), individuals with such characteristics are more likely to survive. Hence, such mutations are eventually incorporated into the genetic code, being fixed in the form of genes, which are in turn transmitted to subsequent generations.
After thousands of generations, the accumulation of specific genes in a particular group of individuals of the same species may lead to the emergence of a new species, adapted to germinate, grow and bloom in a specific biome, in this case the Chaco.
Imagine DNA as a toolbox in which genes are specific tools designed to deal with specific needs or constraints faced by a species and imposed on it by the environment. Thus, the variety of instruments in the "genetic toolbox" of the Chaco plants is their guarantee to face adverse situations.
The problem is that not all the different variations of a gene of a species are present in all individuals. Genetic variability within a species implies that some variants of specific genes, such as those conferring protection against a particular fungus or disease, will be present in the DNA of some individuals but not in the DNA of others.
When a biome is devastated and most individuals in a population disappear, the chances of missing sets of genes essential to species survival are high. Hence, it is important to diagnose the degree of loss of genetic diversity in Chaco plants to see if irreversible damage has already occurred, and to assess what can be done to recover lost genetic diversity - or at least prevent genetic variability keep getting lost.
"There was an area that had an abundance of P. rubriflora, so in 2010 I decided to go back and collect it, but when I stopped in front of the farm, the Chaco forest had disappeared completely. I even checked the GPS coordinates to make sure that was the correct location. It was... There was nothing left. There was nothing else to be done."
Genes that were restricted to plants living in that area were lost forever. "If there were any major gene or group of genes that were lost, and that would be crucial to the species' adaptation to some future event, such a loss will hardly be recovered, since the mutations that provide the genetic variability are random. The genes are lost forever. Our focus was to sample what still exists in terms of genetic diversity, to be able to point out priority areas for conservation, or at least that a management is done to maintain the current diversity," says Alves.
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| Prosopis ruscifolia leafs and flowers (Fábio Alves) |
Conservation for millennia
"The area of the Chaco we studied was greatly reduced by the establishment of pastures, with few clusters of trees left, distant from each other in the middle of the pastures," explains Souza. "Despite this, there is still hope of being able to save the biome, because the trees of the different populations of P. ruscifolia and P. rubriflora are still exchanging pollens, thanks to the work of pollination carried out by the various species of bees that inhabit the region."
Until now, P. ruscifolia and P. rubriflora do not show diversity loss because they are not only reproducing with the closest plants, their sisters, daughters of the same mother plant. The two species surveyed are still maintaining a certain level of diversity by acquiring pollen from trees of different populations, located in more distant clusters.
"However, our study identified that the species P. ruscifolia has a greater risk of loss of diversity than P. rubriflora, since signs of less genetic diversity appear when analyzed with molecular markers," Souza says. "P. ruscifolia species has already been on the list of threatened plants in Paraguay since 1997. The situation is really very serious!"
According to Anete Pereira de Souza, the work allowed to measure the imminent loss of Chaco genetic variability, through the study of two species typical of this biome. "As a practical result we indicate a conservation program to be implemented, if possible immediately to save what remains of the Chaco. The program was based on the two species studied, however, it can be replicated to other species. Professor Ângela Sartori, together with her collaborators, has been working for years on this Chaco conservation project (including plants and animals), and our results taken together will allow the conservation of the fragmented areas that still remain."
If and when the Ministry of the Environment creates permanent protection areas to save the little that remains of the Brazilian Chaco, which areas should be preserved? with which time scale should be worked?
According to Fábio Alves, "Our results suggest that 42 areas of the Chaco must be conserved to maintain the minimum of 500 individuals necessary to maintain genetic diversity between one hundred and one thousand generations."
Individuals of the genus Prosopis reach reproductive age at three years of age, this means that in order to recover lost genetic diversity, it would be necessary to maintain intact reserves between 300 and 3,000 years. "
Contacts for interviews:
Anete Pereira de Souza
Phone: (5519) 3521-1132
Mobile: (5519) 99111-6547
e-mail: anete@unicamp.br
Ângela Sartori
Phone: (5567) 3345-7755
Mobile: (5567) 98453-2493
e-mail: albsartori@gmail.com
Alves FM, Sartori ÂLB, Zucchi MI, et al. Genetic structure of two Prosopis species in Chaco areas: A lack of allelic diversity diagnosis and insights into the allelic conservation of the affected species. Ecol Evol. 2018;00:1-17. https://doi.org/10.1002/ece3.4137
Alves FM, Sartori ÂLB, Zucchi MI, et al. A high level of outcrossing in the vulnerable species Prosopis rubriflora in a Chaco remnant. Australian Journal of Botany 66(4) 360-368 https://doi.org/10.1071/BT17195
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0)
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