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Genetics

Feathered history

Study associates the evolution of birds with transformations in the planet and quantifies the risk of extinction

EDUARDO CESAROpposite fates: a curassow (left) and a superciliated guan (right), reintroduced into the wild, and the saffron finch, almost disappeared EDUARDO CESAR

Typically Brazilian birds started to appear 76 million years ago. In those days, when the separation between the continental blocks that were to form South America, Africa, Australia and Antarctica was practically concluded, the species that previously used to share the same original territory became isolated. And then there was an intensification of the process of differentiation, which in South America led to today’s parrots, parakeets and macaws. Besides telling the history of Brazilian birds by means an analysis of the molecule of deoxyribonucleic acid, or DNA, a group of biologists under the coordination of Anita Wajntal, from the Institute of Biosciences of the University of São Paulo (IB-USP), analyzed the possibilities for survival of the current populations of birds, in particular those threatened by illegal trade and deforestation, and indicated those that really do run a risk of extinction.

To reach these results, the researchers assessed the populations of birds through the degree of variation in the genetic characteristics of each species, known as genetic variability – the higher it is, the greater the chance of a group maintaining itself, since its adaptation capacity to the changes in the environment is greater. Sometimes, a species with a wide distribution, but made up of populations with little genetic variability, may run the same risk of extinction as with a species with a more restricted distribution. This is the case of the blue and gold macaw (Ara ararauna), with a genetic similarity rate as high (0.31) as that of more threatened species, such as the hyacinth macaw (Anodorhynchus hyacinthinus).

This rate compares the degree of similarity between individuals from the same species and goes from zero (no similarity) to one (identical). Parrots, parakeets and macaws threatened with extinction have a similarity index equal to or higher than 0.25, while species out of risk are below this figure. “The greater the genetic variability”, explains Cristina Miyaki, from the IB-USP, and a close collaborator of Anita, “the probability increases that some representatives will survive and pass their characteristics to the following generations.”

One of the species that has proven to be most threatened, with a similarity rate of 0.27, is the red-tailed Amazon parrot (Amazona brasiliensis), of which about 3,000 individuals remain, in coastal stretches of the Atlantic Rain Forest. With the yellow-crowned Amazon parrot (Amazona ochrocephala xantholaema), the surprise was in the other direction: the expectation was to find a small population, with a high similarity index and isolated on the island. But it also lives on the continent, there is intercourse between the populations, and similarity is low (0.17).

“As it is not possible to preserve everything, priorities need to be set, and one has to know what each group of birds represents in the biodiversity of a region or of Brazil as a whole”, Anita comments. Her work has attracted researchers from all over the country, for the prospects for preserving Brazilian species and for the simplification of the examination of DNA, made feasible by the team from USP: instead of carrying equipment out to the field, one or two drops of blood are collected and sent for analysis in the laboratory. By this test, which results in a kind of bar code, unique for each individual, the sex of some birds may also be determined – just by the appearance, it is impossible to tell a male parakeet or macaw from a female one, for example. Previously, to find out the sex, the birds had to undergo minor surgery, in which a 1 centimeter cut was made in the abdomen, to observe the gonads.

Put together, the analysis of the sex and of genetic variability simplify the formation of couples for reproduction in captivity, and they allow the creation of a program for strengthening the populations through the mating of individuals that are more genetically distinct amongst themselves. This is what has happened with the Spix’s macaw (Cyanopsitta spixii), in one of the cases in which specialists from the Brazilian Institute for the Environment and Renewable Natural Resources (Ibama) asked for USP’s team to assist in saving the species, regarded as extinct in the wild – the last free specimen, located in December 2000, in Curaçá, Bahia, was male, according to the sexing done with the DNA taken from the feathers found in the region. This species’ situation is critical: an analysis of the specimens in captivity showed that they can be regarded as relatives, with a 70% degree of similarity. In the whole world, there are only some 60 Spix’s macaws.

Today, the team from USP works in partnership with researchers in seven states. The first of these partnerships was born ten years ago, with biologist Neiva Guedes, from the University for the Development of the State and the Pantanal Region (Uniderp), who is coordinating the project for the conservation of the hyacinth macaw (A. hyacinthinus), threatened with extinction, with a population estimated at 5,000 individuals. From the DNA analysis of the blood that Neiva sent, a piece of bad news: the hyacinth macaw shows a low genetic variability, at 0.34, which may make difficult the work to preserve this species. But among the offspring, the quantities of males and females are the same, which is important for to balance the population.

The work also made it possible to reconstitute the history and the relations between the species of the three groups of neotropical birds that live all the way from South America to Mexico: the psittacidae (parrots, parakeets and macaws), the ramphastidae (toucans and aracaris) and the cracidae (curassows, guans and chacalacas – the so-called Brazilian hens). In all, there are 122 species and 40 genera, which account for 85% of the genera of these groups of neotropical birds. On the basis of the DNA exams and the support of fossil records, the researchers calculated the number of mutations incorporated into the genome of each species, in the course of time, the so-called molecular clock, and they assembled a table for the evolution of the three groups and of the geological periods in which the differentiation amongst them occurred.

“76 million years ago, there was a separation in the psittacidae group, between the neotropicals and the Australians”, says Cristina. At that time, there was also the split of the Gondwana supercontinent, which broke up into Africa, South America and Antarctica. An analysis of the DNA indicates that it was not just the parrots, parakeets and macaws that became isolated and started their own history: Brazilian hens also separated from their Australian sisters at that same time. On this point, the team from USP has its own opinion, which diverges from that of the majority of ornithologists, who tend to think that their origin was not an event in Gondwana, but that the cracidae came from North America to South America. Anita and her collaborators sustain their point of view in an article that will be published in December, in the Systematic Biology magazine.

Far later, 35 million years ago, the separation between the short tailed psittacidae (parrots) and the long tailed ones (parakeets and macaws) took place. At the same time, the cracidae split: on the one side, the group of the curassows and the guans; on the other, the smaller gallinaceae known as chacalacas. It was the end of an era of paleographic changes in which the polar icecaps arose, the planet cooled down, the level of the oceans fell, and the rains diminished.

Cristina puts at between 22 and 18 million years ago the separation of genera between the long tailed psittacidae, at a time close to the separation of the genera of the cracidae, 19 million years ago. “These changes took place at the end of an age when the continental tectonic plates telescoped, lifting the Andes mountain range and changing the course of the great river basins, like the Amazon. This movement made the sea advance inside the continent and then to retreat”, she says. Finally, the definition of the current species also took place with a certain coincidence: between 12 million and 1 million years ago for the psittacidae, and between 9.8 million and 1.1 million years for the cracidae.

When she decided to work with Brazilian birds, Anita chose the endangered species, which are losing habitat and are hunted intensely for sport, to serve as food, or even to stock breeders and zoos abroad. The importance of studying the birds is due to their role they perform as a bioindicator: the disappearance of a species from a region indicates that its habitat has been destroyed. This is the case of the saffron finch (Sicalis flaveola), gradually disappearing as a result of one-crop farming, flooding by the hydroelectric dams, and hunting: its song is one of the most appreciated amongst bird fanciers. “Endangered can become symbols, to rally local communities in the effort to preserve the ecosystems”, suggests the researcher.

Anita is against letting animals loose in the wild, even though the act may bewell-meaning, without strict precautions to decide whether this may or may not jeopardize individuals from the same species. “Birds are often weakened from life in captivity, they can catch a virus and, when freed, spread the infection, with catastrophic results”, she warns. “The animals should only be set free after veterinary care, and even so in regions where they do not exist any more. Moreover, the releases should be monitored, for the impacts to be assessed later.”

As at every moment blood samples of birds arrive from all over the country, the laboratory at USP is always getting surprises. The blue and gold macaw (Ara ararauna), although being regarded as extinct in São Paulo, is common in the land where the mauritia palm grows and in the savannas of South America, from Paraguay to Panama. Even so, one population studied shows a similarity index close to that of the most threatened species, at 0.34. One of the reasons that may explain this exception is the fact that this population of the blue and gold macaw lives very isolated, so that mating only take place within the group – and this way the genetic variability tends to fall.

The team from USP has known for some time that all help is precious, when one really wants to preserve Brazilian species. The study of the carcidae, the group of curassows, guans and chacalacas, has made good headway with the participation of staff from the Paraibuna hydroelectric power station, in the Paraíba Valley. There, they created an aviary for these gallinaceae, caught before the lake was formed for the construction of the dam, which was concluded in 1978. After the reforestation of an area around the power station, the offspring of two species of guans (Penelope obscura and Penelope superciliares) were reintroduced into the wild. A later comparison of blood samples from the birds released and the captive ones show a high degree of kinship. “This indicates that the birds released stayed in the region and have adapted well”, says Anita gladly.

Around another hydroelectric power station, Porto Primavera, in the far west of São Paulo, some curassows (Crax fasciolatta) were given their freedom, after having been imprisoned on small islands. The biologists from USP did not expect to find in these birds, which are widely distributed, such a high genetic similarity (0,35). But looking at maps from before and after the flooding, they saw that the region had already been devastated and showed very little native vegetation, sparse undergrowth alongside the streams and abundant eucalyptus, an exotic species. Hardly a favorable situation for the curassows.

The Project
Study of the Populational Structure of and Phylogenetic Relations of Birds (nº 98/10018-2); Modality Thematic Project; Coordinator Anita Wajntal – Institute of Biosciences / USP;
Investment R$ 478,127.54

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