Stealthy meetings

Inter-breeding between different types of wild cats is more common than was believed

Imagem: Eduardo CesarNo mixture: felines from the São Paulo Zoo are not the result of hybridizationImagem: Eduardo Cesar

Brazil has a wealth of wild cats. Just in the genus Leopardus there are Geoffroy’s wild cat, the small wild cat, the pampas cat, the margay and the ocelot. Rio Grande do Sul distinguishes itself by having more diversity than the Amazon in feline terms: Geoffroy’s wild cat and the pampas cat, originally from Patagonia, live there but not in the north of Brazil. Destruction of their natural habitats means that these five species, with the exception of the first, are considered vulnerable and figure in the Red book of Brazilian fauna species that are threatened with extinction, which was published by the Ministry of the Environment in 2008. For the specialists, however, the biggest risk these animals face is the lack of knowledge, which prevents effective strategies for their conservation being drawn up. This is what the biologist, Eduardo Eizirik`s group, from the Pontifical Catholic University of Rio Grande do Sul (PUC-RS), is looking to rectify – sometimes with surprising results, like the one Tatiane Trigo revealed in her PhD thesis: 60% of the wild cats in Rio Grande do Sul are hybrids; and encounters between different species for reproduction purposes are not restricted to that state.

Part of the results, published at the end of last year in Molecular Ecology, have to do with the gaucho region where Geoffroy’s wild cat (Leopardus geoffroyi) and the small wild cat (L. tigrinus) meet. These small spotted cats are very similar. The former is normally larger, weighing as much as 8 kg, with fur that tends to be grayish. The small wild cat, on the other hand, never weighs more than 3.5 kg and is more delicate and light brown in color. Their distribution, however, in Brazil is very different: the larger cat is only found in the south of Rio Grande do Sul, while the smaller one is to be found almost all over Brazil, with the exception of the extreme south of the country.

Tatiane says that the crucial area where these felines meet is Rio Grande do Sul’s central lowlands, the scene of remarkable ecological changes. To the north the countryside is dominated by a range of hills covered with Araucaria forests, the local version of the Atlantic forest, and to the south are the Pampas. It is in this transition region between two ecosystems, which because of the particular nature of the terrain is easily accessible to humans by road, that the researcher found more samples and, based on genetic studies, detected a preponderance of hybrids. In all she examined 57 samples of small wild cat and 41 Geoffroy wild cats that she collected in various Brazilian states: animals that had been killed on highways or by farmers or that live in zoos and whose origin was known. At least 14 proved to be hybrids, a record number so far in terms of hybridization in carnivores. Most of them came from the central region of Rio Grande do Sul. The work also included seven samples (only two of them from Brazil) of the pampas cat, Leopardus colocolo. She saw that this species also forms hybrids with the small wild cat. “The Brazilian populations of the small wild cat may have DNA from three different species”, says Eizirik.

Even so, the analyses left no doubt that the three species are genetically different. As far as can be detected, however, the hybrids are normally fertile, unlike mules, a cross between a female horse and a male donkey, which live normally but are infertile. In the case of the cats the possibility of detecting the hybrids only became a reality with the current techniques for untangling and comparing genetic material. In terms of appearance, in most cases the hybrids had the aspect of one of the two species from which they had descended. The surprise came when the DNA was examined; it retained some strands that are characteristic of the other species. Some of the animals, however, were obviously hybrids, being of an intermediate size and color. This is material to enliven any discussions about where each species begins and ends.

The group also observed reduced genetic diversity in the two wild cats, which indicates a recent expansion of the population. The results have already led the researchers to formulate a hypothesis about the history of Leopardus tigrinus and geoffroyi. Until further studies indicate otherwise Eizirik’s team believes that over almost 1 million years these wild cats evolved in different areas, without having the opportunity to meet. Only more recently, around 70,000 years ago, did the two species, or maybe just tigrinus, the small wild cat, expand their geographic distribution, meaning that the males and females of the two species could meet in the central lowlands of Rio Grande do Sul. One hypothesis is that the small wild cats followed the expansion of the forest, their favorite environment, during a period when the climate was more humid. “We need to develop more genetic markers to discover if the hybrids began to form at that time or if the phenomenon is more recent, since human intervention began to change the region’s ecology drastically”, says Tatiane.

The study published in Molecular Ecology forms part of the PhD thesis of the researcher, whose tutor is geneticist Thales de Freitas from the Federal University of Rio Grande do Sul (UFRGS) with Eizirik as a co-tutor. The thesis, which she defended in November 2008, is an update on the article – there are more samples, more genetic markers and more complete analyses in it. The results are already making the researchers more confident when it comes to interpretation, although the work is not yet finished. Even though Tatiane has concluded her PhD she is still trying to increase the number of samples and complete her analyses before sending more pieces of work for publication. At the same time other members of the group are helping fill in parts of this story. Such is the case with Alexsandra Schneider, who in her Master’s degree which she did this year, developed more genetic tools to help identify the hybrid cats and characterize this meeting between the species.

Separated by their stomachs
To unravel the ecological factors that might be involved in the isolation – and the meetings – of geoffroyi and tigrinus, Tatiane investigated the feeding habits of both species of cats. In principle, these two wild cats prefer different environments; the first lives in areas of open vegetation, like the gaucho Pampas, while the second seeks out damp forests, like the more enclosed areas of the Atlantic forest and the Cerrado [savannah]. The difference in the environments they frequent may be responsible for meetings between the two species being avoided, even within the same region. But apparently this is not what happens, because Geoffroy’s cat is sometimes seen in dense forests and the small cat is also seen among the thorny bushes of the Caatinga and the sparse vegetation that characterizes part of the Cerrado.

In seeking to characterize the ecology of these animals, which are rarely observed in nature, the researcher examined the contents of the stomachs of 13 Leopardus tigrinus and 17 geoffroyi that were found dead on the roads in Rio Grande do Sul. By identifying the animals that serve as food for the wild cats she saw that 50% of the diet of the two species coincides. The other half of the diet adds weight to the preferences of the cats for different habitats. The rodents that are found only in the stomachs of the small wild cats are generally typical of the forests. But the animals that are lunch for Geoffroy’s wild cat, like the cavy and the Mabuya dorsivittata lizard, are normally more associated with open areas. The results are promising, but Tatiane still considers them very preliminary. Besides the difficulty in obtaining a suitable sample, she also says that, generally speaking, the ecology of the rodents is even less well-known than that of the cats, which makes ecological associations difficult.

So far the results of the research show that Geoffroy’s cat and the small wild cat came from different places and when they met they discovered they had a reproductive affinity. The history of the pampas cat has still yet to be told, but the indications collected by Tatiane indicate a very different story altogether. Large doubts also surround the classification of this species, which at 4 kg seems to be a brownish domestic cat with striped legs and a short tail. It has long been known as Leopardus colocolo and today some researchers argue that in fact this cat is divided into three species, and the name colocolo is reserved for the Chilean species. According to this line of thinking, the pampas cats of Brazil should be called L. braccatus. The issue is not central to the gaucho group that is more interested in understanding the history and ecology of these cats.

Tatiane says she had difficulty in obtaining samples of the pampas cat, not only because its is the rarest of the three felines she examined in her work, but also because collaboration was necessary  in order to have access to animals that live in the northern part of the  distribution of the species, in Mato Grosso and Goiás. Now, an agreement signed with others researchers will allow her to obtain a much larger number of samples, and, who knows, have a more complete story to tell over the next few years. For the time being the data suggest that in the central region of Brazil there is an as yet undefined zone where the small wild cat and the pampas cat meet and produce hybrids. “We believe that this hybridization happened in the past, between colocolo females and tigrinus males”, says Eizirik, referring to differences between what her group observed between the Y chromosome, transmitted from father to son and the rest of the genetic material.

Geoffroy’s cat, on the other hand, does not mix with the pampas cat, although there is no lack of opportunity for them to get together. The two species originated in Patagonia and live in the same environment. The group of gaucho geneticists believes that the explanation for the absence of hybridization lies in their long shared history. Because they evolved together some as yet unknown mechanism certainly prevented these two species from producing hybrids, which also prevented them becoming established as different species.

Creatures with a discreet nature, felines do not give up their secrets easily. Eizirik also has a lot of work ahead of him, but considers that the results his group have already achieved are essential not only in order to know Brazilian cats better but also to protect these species.

Scientific article
TRIGO, T. C. et al. Inter-species hybridization among Neotropical cats of the genus Leopardus, and evidence for an introgressive hybrid zone between L. geoffroyi and L. tigrinus in southern Brazil. Molecular Ecology. v. 17, n. 19, p. 4.317-4.333. out. 2008.