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Chimpire turtles, the other Venezuelan border migrants

A species of turtles –immortalized in stories for being slow but wise– move between Colombia and Venezuela. It is the chimpire turtle of the Podocnemis genus, which has been impacted by illegal mining carried out by newcomers to this region.

This species can grow up to 32cms (1ft) long and has in its genetics the history already traced between 1799 and 1804 by famous German explorer Alexander von Humboldt in his travels through South America. The scientist followed the same route of this turtles, from the basin of the Orinoco River, through the Atabapo River and other black water rivers in the Province of Guanía in Colombia to the Negro and Casiquiare Rivers in Venezuela.

With genetic analysis techniques, Universidad Nacional de Colombia (UNal) researcher Mario Vargas Ramírez and University of Kiel (Germany) researcher Jan Michels followed the path of Von Humboldt to try to identify in detail the genetic structure and populational connection of Podocnemis erythrocephala on the border territory between Venezuela and Colombia.

Being “ancestral relics”, meaning organisms which were abundant in the past, these red, yellow, or orange head colored turtles come from the Cretaceous or Paleogene era. Since then they evolved and adapted to diverse bodies of water in tropical South American areas.

Genetics helped to demonstrate the separation and connection of chimpire turtles by identifying the demographic differences of the species. They also determined the genetic flow between populations and outlined mechanisms for the preservation of the species, as it is common for inhabitants to eat their meat and eggs.

According to Dr. Vargas, “The fact that the Colombian chimpire populations have been isolated from the rest of Amazonian populations for such a long time indicates they must be protected for being part of the species evolutionary potential. It also evidences that Colombian back water bodies are a safe haven with a unique biota which must be protected.”  

Of the other members of the Podocnemididae family of eight species, one is in Madagascar and the other seven in Colombia in the north of South America.

The theory of the molecular watch

Genes hide a history: “By using molecular methods we are beginning to read the history of life on Earth and in this particular case to the bodies of water where the Amazon communicates with the Orinoco. Within the neutral genome of the turtles, there are mutations which provide traces to try to understand this history. For chimpire turtles, the Orinoco and Amazon populations have 10 different mutations, meaning that far away in time there were processes that separated them. Our hypothesis is that this occurred during the Pliocene, approximately 3 million years ago,” said Vargas.

“The theory of the molecular watch shows a relationship between the mutation rate and time: using an algorithm which takes into consideration the mutation rate of the gene fragment in question, one can calculate approximately how much time ago they were a single population. In other words, time can be measured in mutations,” he added.

Heads of different colors

Back in 2003, Professor Olga Castaño Mora and her group carried out a research project which confirmed the presence of this species in Colombia. They discovered that the Orinoquia turtles had yellow and orange colored heads, as opposed to the Amazon turtles which had red heads. “This made us think about temporary differences; it could be a long time since the Orinoco turtles have been isolated from the Amazon turtles,” she said.

“What is interesting is that the species that share black waters of the Amazon and Orinoco can tell us the story through their genes. Reading them we can obtain information of the place where these tow basins connect,” said Vargas.

Several species of chimpire turtles are adapted to white waters such as Podocnemis unifilis, expansa and sextuberculata, but others are adapted to black waters, such as Podocnemis erythrocephala, where they thrived and continue to exist, despite the poorness of nutrients.

“In another research project we discovered that Podocnemis erythrocephala separated from her sister P. lewyana of Magdalena approximately 3 million years ago when the eastern Colombian Cordillera emerged,” explained Vargas.

White waters, a natural barrier

In the basins of the Amazon and Orinoco rivers, there are three types of water sources: white, black and clear. Podocnemis erythrocephala is exclusively adapted to clear and back waters, which are poor in conductivity and sediments. This means that white waters such as those found in the Guaviare and Amazon rivers are natural physiological barriers for these turtles.

White water sources are different for their physical-chemical features: they are rich in sediments and have high conductivity; therefore they allow great biological diversity and wealth. For instance, the Magdalena River is a white water river and has many ray-finned fish (bocachico, locally). There fishermen can fish due to the sediment that comes from the cordilleras that contribute with mineral and waster nutrients.

Black water sources, on the other hand, are black colored due to the tannins, as decomposed forest leaves are dark brown. These waters do not have any influence from the Andes Mountains but come from the Guiana Shield. They are in a part of the Orinoquia of the Guiana Shield, the Guainía region, Chiribiquete and part of the Amazon. They have low conductivity, acid and low in sediments, providing a very special biota and adapted to these conditions, such as the case of the chimpire turtle.

Lastly, white water sources, present in the Amazon and Orinoquia, are similar to black waters for their low conductivity and lack of sediments but do not have tannins, therefore they are clear. They are different ecoregions connected by the Casiquiare canal, a biogeographic corridor, where some species may travel, although for the chimpire turtle it is a physiological barrier.

Consejo Editorial