A new species of wild cat in central and north-eastern Brazil has been confirmed, according to a study published today in the journal Current Biology.
This recognition formally separates the two known tigrina species (Leopardus tigrinus and Leopardus guttulus) which, until now, were regarded as one.
According to the authors of the study, Eduardo Eizirik from the Pontifical Catholic University of Rio Grande do Sul and Tatiane Trigo from the University Federal of Rio Grande do Sul, the possibility that these two wild cat populations were two distinct species was considered in the 1960s, but the hypothesis was never tested.
For the first time, scientists are able to assess the two previously-recognised subspecies using molecular markers to analyse their genetic relationship.
The results showed that the housecat-sized tigrina populations are, in fact, completely separate species.
“Our analysis showed strong genetic differentiation between the tigrina populations, with no gene flow between them, indicating that these two populations are actually reproductively isolated and should be recognised as distinct species,” said Professor Eizirik and Dr Trigo.
Data on the two tigrina species also revealed a distinct geographical distribution of both populations.
L. tigrinus, found in central and north-eastern Brazil, live primarily in open and dry vegetation (shrublands and savannahs). The southern and south-eastern Brazilian areas, occupied by L. guttulus, are dominated by denser and wetter Atlantic forest-type habitats.
Such distinct habitat conditions provide clues to their different ecological requirements and the adaptive differences that may have been responsible for their evolutionary divergence.
Hybridisation
The findings from this study also revealed the complexity of the relationships between the tigrinas and two other species of neotropical cats (commonly known as Geoffroy’s cats).
The evidence suggests that L. tigrinus’ evolutionary history includes hybridisation and movement of genes between them and the pampas cat, while extreme levels of interbreeding between L. guttulus and Geoffroy’s cats still occur along their contact zone.
Although there is no evidence that this interbreeding is expanding beyond the contact zone, it is clear that hybridisation can and does occur between distinct animal species.
Christopher Johnson, a professor of wildlife conservation from the University of Tasmania, said: “This study hints that hybridisation in the past has accelerated speciation. The acquisition of new genes by hybridisation can be a potent force in the evolution of species, and this could be a neat example where hybridisation in some parts of the range but not others has contributed to splitting of one species into two.
"We used to think that hybridisation between related species was not supposed to happen - by definition, species did not interbreed - but it’s clearly more significant than was realised.”
Professor Eizirik and Dr Trigo explained that hybridisation may occur quite frequently in the initial stages of species divergence, and the species involved may hybridise for some time and maintain a hybrid zone at their region of geographic overlap.
However, this may not necessarily lead to their complete admixture or the loss of the genetic and phenotypic integrity of each parental species.
“Currently, there is a strong genetic differentiation between these two cat species in areas farther from the contact zone. Selective pressure must be keeping the two species morphologically, ecologically, and even genetically distinct outside of this contact zone.
"Therefore, at this point, it seems adequate to keep them as separate species and continue to investigate the extent and biological consequences of their hybridisation.”
Implications on conservation
Gerry Ryan, from the University of Melbourne, warned that the evidence for a recent or continuing hybrid zone between the southern tigrinas and Geoffroy’s cats will need closer investigation to determine if any conservation management actions are needed.
“The two tigrina species are listed as one on the IUCN’s Red List of Threatened Species. Now that they are considered to be separate species, they both need to be re-assessed. Each one will be at a higher risk of extinction, than when considered as one species, because smaller numbers automatically increase the risks.
"If the hybridisation is spurred by human-induced habitat alteration, then conservation management actions must be considered. But, given the already extensive gene flow, this may be too late.”
Hamish Campbell, from the University of Queensland, believes that the use of modern genetic techniques is crucial in determining when one species or sub-species should be declared distinct from another, particularly when it comes to managing rare and threatened species.
He explained: “This study is similar to that of the Scottish wildcat (Felis silvestris) which, using molecular techniques, was found to be breeding with feral domestic cats (Felis felis).
"Feral domestic cats are an environmental disaster, devastating native wildlife, while the Scottish wildcat is a rare and ancient species that needs to be conserved. But where do you draw the eradication line? What level of hybridisation is acceptable to declare the species a threat rather than a pest?
"Molecular techniques are helping us to map the evolutionary history of species, but how those findings are applied to the successful management of rare and threatened species is still in its infancy.”
Future studies
According to Gerry Ryan, this case study shows us how modern genetic techniques can help clarify cryptic patterns of species diversity.
“As genetics and genomics continue to advance and be cheaper and faster, we can better understand the complex and dynamic nature of species boundary. We will then need to develop parallel conservation strategies to protect the diversity of life beyond linear concepts, and allow for adaptation and evolution in the face of global climactic change.”
Professor Eizirik and Dr Trigo agreed, saying: “Our study has opened new avenues for research, focusing on more in-depth evolutionary, genomic, morphological and ecological questions.
"We intend to further investigate Brazilian northeastern tigrinas which are virtually unknown with respect to most aspects of their biology. Some initial studies on its ecology (diet, feeding habits and habitat requirements) have been done, but information on its population density, habitat use and population trends remain unknown.
"There is also very little information on the ecological segregation between the two species. Thus, we consider studying L. tigrinus a priority for research and conservation actions.”