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Genetics

High risk crossbreeding

The marine species of the manatee crossbreeds with the Amazonian one and generates sterile hybrids

Poque, an offspring of a manatee, landed at the end of 1993 in one of the tanks at the National Research, Conservation and Management of Aquatic Mammals Center (CMA) of the Brazilian Environment and Renewable Resources Institute (Ibama), on the island of Itamaracá, in the state of Pernambuco. At that time, it must have been a year and a half old. Found some months earlier in a lake close to the falls of the river Oiapoque – hence its name –, it had an injury on its back, on the right side, close to its fin, caused by a harpoon. Its recovery was swift, but it remained in captivity so that it could escape from other onslaughts of hunters. It is there until today, with another eight manatee.

This animal always caught the attention of the researchers – and not only because it would swim from one side to the other almost without a rest. With a course hide and nails on its fins, characteristics of the marine manatee specie (west Indian manatee) (Trichechus manatus), Poque also has white markings on its belly and a color that is less dark and more grayish, markings of the species that inhabit the rivers of the Amazon basin (Trichechus inunguis). Its weight (205 kilograms) and length (a little more than 2 meters) are less than that expected for the marine species. What seems to be even more puzzling is that, in spite of the various attempts at crossbreeding, it has never managed to make a female pregnant. “Poque was a major question mark”, tells Jociery Vergara-Parente, a veterinarian with the Aquatic Mammal Foundation (FMA), which is acting in partnership with the CMA in projects for the preservation of the manatee. “We’d believed that he could have been a mixture of the two species”, she completes.

This suspicion was confirmed with a study coordinated by Fabrício Rodrigues dos Santos, from the Federal University of Minas Gerais (UFMG), published in the magazine Molecular Ecology. Santos’s team analyzed the DNA of the mitochondria, the compartment within the cells that conserves energy and contains the maternal genetic hereditary information. After observing the DNA of the cell’s nucleus and identifying the alleles, as the genes that occupy the same position in the chromosome homologues are called, both in the marine specie and the Amazonian species. In the end, it was discovered that Poque has 50 chromosomes. Its parents that live in the rivers have 56; those in the sea have 48. If there were still any doubts they disappeared: Poque truly is the crossbreeding of the marine manatee with the Amazonian manatee – a so-called hybrid. One is dealing with the same situation verified when a horse crossbreeds with an ass, having as their offspring a mule or a donkey.

“He’s probably a second generation hybrid, the son of another female hybrid”, says Santos, who years before had verified endogamy – crossbreeding between close relations – in the marine species, which can lead to offspring that are unhealthy. “The consequences of this new reality are catastrophic, because probably all of the male hybrids  and most of the females with this hereditary are sterile.” According to him, the scenario is also serious because the two species run the risk of extinction – the situation of the marine manatee is even more critical. It has been calculated that on the Brazilian coast there are only 500 representatives of the species. On the coastline of the states of Bahia and Espirito Santo, where they appeared up until the 1960’s, this aquatic and herbivorous mammal, which feeds on an aquatic grass known as capim-agulha (Brachiaria humidicola) that grows close to the beaches, can no longer be found: they were extinct by hunting.

Curiously enough, the two species meet up in a natural manner, without any relation to hunting or the possible flight of the sea animals to the rivers, in search of protection against human persecution. Even though its natural habitat is the sea, the Trichechus manatus does not manage to drink sea water and quenches its thirst with river water. This species of manatee is capable of going up river a distance of 200 kilometers – when it can, therefore, it crossbreeds with the Amazonian species. “The solution is to preserve the species in captivity, mainly the marine species, and to stimulate breeding”, proposes Santos. His team analyzed samples of the genetic material of a further 49 animals, which live in Brazil and the Guianas. Hybridism was detected in seven of them (almost 15% of the total).

An offspring every four years – Another marked characteristic of the Amazonian manatee, in relation to the marine specie, is its elevated genetic diversity – when the gene sequence is different from one animal to the next, but without incorporating the information of another specie, according to a study from the Federal University of Amazonas (UFAM). In the opinion of Izeni Pires Farias, a professor at UFAM and one of the authors of another study with these conclusions also published in Molecular Ecology, this genetic diversity – in the order of 80% to 90% – can be seen as an advantage, since it is related to improved resistance to illnesses and to a better adaptation to environmental changes.

On the other hand, the marine manatee exhibits low diversity, approximately 50%, which could favor endogamy, debilitate resistance to illnesses and reduce its capacity to respond to environmental changes. “The marine manatee has lost its natural genetic diversity, since its population was brutally reduced over generations”, says Izeni. “As hybridism leads to sterility”, explains Fabrício Santos, “the chances of reproduction are becoming even smaller”. These animals reproduce every four years and generate only one offspring at a time.

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