Appearances can be deceiving: scientists find genetic differences in birds considered of the same species

Not only do men evolve: nature changes as well. Eight years ago, the researcher of the National Scientific and Technical Research Council (CONICET) Gustavo Cabanne decided to study the evolution of two of the most important forests in South America: the Andean –with occupy the east face of the map of South America and from Colombia to La Rioja- and the forest of the Atlantic forest –of which ninety percent are in Brazil and reach the east of Paraguay and the south of Misiones-. But he did not focused on the evolution of the vegetation: Cabanne wanted to study the modifications the birds of those regions suffered –changes in the singing, coloration, morphology but specially in the genetic-. By analyzing those changes in the birds, Cabanne supposed he could explain the evolutionary history of those forests.

“Between these two regions, there is no type of rain forest that can serve as a bridge or communication channel. On the contrary, the weather that is in the middle of both is dry. Nevertheless, it is strange that the two regions have the organisms. There are the same species of mice and more than twenty species of the same bird. Or that was what experts thought: that they were the same species. I wanted to focus on the birds to learn about the evolutionary history of these two regions”, the scientist affirms. He works at the “Bernardino Rivadavia” Argentine Museum of Natural Sciences (MACN).

There, at the Ornithology Section, he shares the office with other four researchers. One of them is Pablo Tubaro, who is a CONICET scientist, director of the MACN, and one of the authors of the paper recently published in the journal Molecular Phylogenetics and Evolution with colleagues from Brazil, Bolivia, the United States and Canada. It was at that office that the researchers discovered that the birds found in both regions of the map, which historically had been considered to be the same species, did not belong to the same family. They analyzed blood samples and the muscles of certain birds. The scientists found that there is “cryptic diversity”, which means that there are unique lineages of each region, and that they are not all similar species, as people believed so far. “The fact that there is cryptic diversity means that what they initially identified as a unique family is actually two or more than two”, Cabanne says.

The last case the researchers confirmed is the bird Syndactyla rufosuperciliata. Previously, the experts had published that other birs –like Arremon flavirostris and Trichothraupis melanops- are not the same in the two sides of the map. “When we studied the genetic characters and population genetic structure, we started to see not only the history behind their distribution but also most in most of the cases we have “cryptic diversity.” In the common Syndactyla rufosuperciliata, which traditionally used to be considered the same species in Jujuy, Salta and Bolivia, in Misiones, for instance, we proved that although they look alike, they are not the same species.”

Lost connection

The reason why these two separate regions are both wet and tropical even though they have dry weather in the middle is still a mystery for science. How did it happen that two separate areas could be so similar? There are two hypothesis. The first one, provided by ornithologist from Córdoba called Manuel Nores, is that in ancient times the Atlantic forest and The Andes were connected through the gallery forests of the Chaco gallery. Nores suggested that in one previous cycle, when the weather was warmer, this area was more humid, which promoted its expansion and made the area work as a bridge between the species that inhabited in both regions. The second possible theory was formulated by a Brazilian scientist called José María Da Silva. He refuted Nores’ hypothesis: he stated that there is no evidence that forests have expanded in the past. Da Sliva affirmed that the contact between the two regions actually happened through the north, by the massif of Brasilia, a savannah today. What Da Silva means is that before the savannah was there, there were rain forests, which were dried after cyclic weather changes, but that worked as a bridge for the species.

“Current papers on that subject focused on the two options, the contact via Chaco as well as the contact via closed by Brazil. In our paper of Syndactyla rufosuperciliata, the most suitable hypothesis is contact via closed. This means that our study is more related to the theory designed by Da Silva”, Cabanne explains. But this does not mean that the mystery is solved, there is only more evidence to support this hypothesis considering the evolutionary history of the region.

Another variable that is being evaluated is to what extent these two large biomes, which are currently isolated, could function in the long term as a system of jungle shelters for species. “This means that in places where the species can take refuge from cold, in order to leave later on. It is necessary to bear in mind that the Atlantic rainforest is very degraded: nowadays, there is less than 10% of the territory that it originally occupied”, Cabanne says. “Our study also helps us to know better understand our species and apply conservation policies. If we do not know what species we have, it is harder. If we know that the organisms are not the same, we will conserve them better.”

Cabanne is hopeful about the genetic results of the bird populations. “We’ve found very high levels of cryptic diversity in these areas”, he says. Besides, the scientist highlights the fact that apparently the species have not passed through Chaco revalues that biome and makes the Chaco region even more unique. He adds: “We will continue analyzing how the birds evolved and their reaction to environmental, geological and distribution changes. And maybe in ten years science will say that in Argentina we have ten new species of animals.”