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A Brazilian daily newspaper (Folha de Sao Paulo) has an article today about the discovery of a small population of preas (a small mammal of the Cavia intermedia species) in an island in Santa Catarina, a Southern state of Brazil. In an area of less than one hectare, approximately 40 of these animals have been living in isolation for 8.000 years (according to researchers from the Pontifica Universidade Catolica of Rio Grande do Sul). The interesting thing is that there is practically no DNA diversity in this population. They have been practising "incest" left and right, but are none the worse for it!
Sandro Bonatto, a geneticist, states: "According to classic patterns, they should be dead. These animals could change our understanding of the biology of small populations"
If you can read Portuguese, here'sthe full article.
Here's a rough translations, courtesy of Google, linked to by Karl (see comment #1.3 below). I've corrected one or two details, but it's still a rough and unpolished translation. It will give you the gist of the article anyway, with no factual errors (I've checked the translation)
Brazilian researchers found a species that, after 8000 years alone maintaining a population of about 40 individuals, has almost no more genetic diversity.
The animals are so similar between them that a test of paternity through DNA, as used in humans, would not be feasible between them.
The island of Santa Catarina preas live very well, thanks, in an area equivalent to that of a football field - less than one hectare. By traditional genetic theories, it should be long extinct.
"It seems clearly to be the most extreme known case of a species living so long with a population so small," says geneticist Sandro Bonatto, the PUC (Pontificia Universidade Catolica) of Rio Grande do Sul
"By traditional standards, it could not be alive. These animals may change our understanding of the biology of small populations."
The researchers found the animals in the islands of the archipelago of Moleques do Sul, 8 km from the southern tip of the island of Florianopolis.
The species, Cavia intermedia, is the cousin of the preas that live on the coast of the continent, Cavia magna. One possibility is that, after the last ice age, about 8000 years, when sea level rose, they were separated.
The few isolated individuals have then created a new species, which over time has adapted to the conditions of the island: little space, low vegetation and no predator.
The limited space resulted in a small population. The island is about ten hectares, but much of the terrain is rocky. There remains for the preas a tenth of that area with grass. The low vegetation made them become smaller than their cousins, who have access to more food.
The preas are the only mammals on the island. The absence of predators, coupled with the stability of the local climate, apparently no natural disaster happened in recent times - has allowed them to have millennia of peace.
Scientists know that the population was never large because they are all genetically similar, as if all the species were one big family.
To verify the genetic proximity between preas, the group of Bonatto used the same type of DNA test used in paternity tests.
"It is one of the lowest genetic diversity observed in the animal kingdom," says Ricardo Kanitz, also of the PUCRS.
Incest is therefore common. In humans, children of relatives may born with some types of deformation.
It is not the case with these animals: as the population is very small, the crossings that could generate defective puppies already happened and the alleles (versions of the same gene) that could cause problems have been eliminated by natural selection.
It is normal, therefore, that a baby be the son of brothers.
These deformations are not frequent enough to extinguish a species, but the lack of them is a sign that the preas have adapted to survival in a small group.
Threats
As any small and isolated group, however, the animals are at risk. The island is within the State Park of Serra do Tabuleiro, which should limit access to it. But in practice, it doesn't.
"Some fishermen go there, and use it as a basis for work. The danger is releasing a cat, a dog or something unintentionally, and extinguishing the preas," says Bonatto.
Besides run away cats, possible natural disasters also offer danger to preas. "A hurricane, for example, could kill everyone," says Bonatto.
And one has already happened in 2004. Besides Bonatto and Kanitz, Carlos Salvador participated in the work, then at the Federal University of Santa Catarina.
Unlike preas, all species with few individuals known up to today were going in the direction of death, either natural, or by humans.
"Some studies say that a species, to survive in the long term, should be at least 500 individuals," Kanitz said. "Perhaps the preas will provide important lessons for conservation strategies," agrees Bonatto.
