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A treasure on the banks of São Francisco River

Recent discoveries confirm the dunes of the São Francisco River as a unique area for the study of the formation of new species in Brazil

Over there the scenery merges into one. We are high in the Assuruá range of   hills, 680 meters up, in the village of Santo Inácio, in the northern region of the state of Bahia. From a rocky countryside, rich in cactus and bromeliads, one can see the valley of the São Francisco, which begins to run east in the direction of the sea. We can see the first Itaparica Lake – a diversion of the river which has been sealed – together with others which are smaller. Further away, on the two river banks and forming mounts of up to 150 m high, lie the São Francisco dunes.

A surprising ecological reserve, this is one of the areas of Brazil with the greatest endemicity – the occurrence of species that are exclusive to that particular area which have adapted to the sandy soil and the lack of water. Take lizards as an example: there is a diversity that exceeds that of the North American and African deserts. Of the 44 species of lizard in the Caatinga (the semi-arid region of Brazil), 40 are found there and 20 are endemic to the dunes – an area of little more than 5 thousand square kilometers which is only 0.6% of the Caatinga and extends for 120 km along the river, between the cities of Barra and Sobradinho.

A surprise: in the dunes on each side of the river, measuring 200 to 300 meters wide, there are animals which are very similar with those on the other side, but of distinct species. They are sister species, with small differences in appearance or genetic constitution, resulting from a history of separate evolution. For this reason, these dunes are a unique area for the study of the formation of species – comparable with the Galapagos archipelago in the Pacific, on whose fauna, Charles Darwin (1809-1882) based his Theory of Evolution.

The wildlife of the dunes is so typical that it lives in isolation: the adaptations to life in the sand are so elaborate that it impedes any of the animal inhabitants from venturing into the surrounding Caatinga. And the typical species of the Caatinga, such as the cavy (Cavia aperea), has never been seen in the dunes.

“It was all new”
There, in the middle of the sparse vegetation and fine sand, where the temperature can reach 60 degrees Celsius, the discoveries never stopped. Miguel Trefaut Rodrigues, of the Institute of  Bio-sciences (IB) and director of the Zoology Museum of the University of São Paulo (USP), traveled round the Santo Inácio (population: 200) area for the first time in 1980 as part of a group of botanists. “It was all new”, he says. He came back with a species of lizard of about 30 centimeters and exclusive to the area – Tropidurus amathites.

Four years later, Rodrigues walked down the mountains of the Chapada Diamantina (Diamond Plateau) and found in the sands on the opposite side, examples of a similar Tropidurus and still not described, that he called Tropidurus divaricatus. From then on, he never stopped making new discoveries: to date, more than 20 species and four types.

From a more recent journey, he brought back two new discoveries: a lizard (Ameiva sp) and a two-headed snake (Amphisbaena sp) of 50 centimeters. One month previously, an ex-student of Rodrigues, Flora Acunã Juncá, professor of the State University of Feira de Santana (Uefs), Bahia, found in the dunes of the left bank, a burrowing snake from 40 to 50 centimeters, the right bank sister species of which, Rodrigues had described as Typhlops yonenagae. The new Typhlops completed the fifth pair of vicarious species – close to one another philogenetically, but separate geographically. “I am sure that there are more endemic species and other vicarious pairs”, says Rodrigues, who coordinates the Studies on the Ecology and Differentiation of the Reptile Fauna of the Middle São Francisco River (Lepidosauromorpha, Squamata), kicked off in 1997 and financed by FAPESP.

Indeed, the labyrinth of islands along this stretch of river is really little explored. It was in June on the island of Gado Bravo, the largest of the São Francisco, near to the city of Xique-Xique, that Rodrigues discovered a new lizard of the Ameiva type. The closest species, the Ameiva ameiva which is known in English ad the green ameiva or jungle runner, is one of the most aggressive colonizers of open countryside or country which has been cleared by man. Given its ability to move across large areas, its populations show little appreciable difference except in the case of the dunes. Hence, the discovery on the island of Gado Bravo, of a new species of Ameiva with a very distinct coloring, is an indication of effective isolation when compared to the adjacent margins of the river where the Ameiva ameiva can be found with a color pattern which is standard throughout Brazil.

Another case involving adaptation to the environment is the Proechimys yonenagae – a kind of spiny rat, 20 centimeters in length which has a tuft of hair on its tail and big ears, lives in deep burrows and hops, supporting its body weight primarily on its back paws. Only in the deserts of the USA and African are similar examples to be found. This rat was discovered by Pedro Luís Rocha, ex-student of Rodrigues who now teaches at the Federal University of Bahia (UFBa), in Salvador. Also in this particular area of the São Francisco only, can be found the nighthawk Nyctriprogne vielliardi, a bird of nocturnal habits with a height of about 20 centimeters.

A recent survey has indicated areas in the Caatinga either with an accentuated endemicity or which should be closer studied (see box). This is the case of the Negra and Cavalos hill ranges in the state of Pernambuco and Baturité in the state of Ceará and the Chapada do Araripe (Araripe Plateau), on the state border between Pernambuco, Piauí and Ceará. They  are areas covered with dense jungle – the refuges – and extremely rich in wildlife: the fauna and flora of these  ‘islands’ have accumulated differences in relation to the same species of the Atlantic Rain Forests and the Amazon Basin, areas which were previously connected before the formation of the Caatinga.

The zoologist, Paulo Emílio Vanzolini and the geographer, Aziz Ab’ Saber, both from USP, identified these biological refuges in the seventies. Ab’Saber was one of the first scientists to classify the dunes as paleo-desert, an assertion in which he was supported by the geomorphologist, Jean Tricart, of the Louis Pasteur University of Strasbourg.

The dunes also have a special flora. There are clumps of quipá (Opuntia inamoena) and macambira (Bromelia laciniosa), intermingled with generally isolated bushes. In lower lying and humid areas, it is commonplace to find carnauba palm (Copernicia cerifera) and the Poligonacea ruprechtia bush which is protected from ants by the trunk: “When a branch is cut, the ants attack”, tells Luciano Paganucci, professor at Uefs who visits the dunes every year. He has identified in the area the endemic leguminous Pterocarpus monophyllus, a tree about 4 meters high with very hard wood, and seed dispersal adapted to water and, something rare, non-divided leaves.

The plants are generally low and have very small leaves of a deciduous nature (the leaves fall in the dry season). But the most significant sign of adaptation to the environment is invisible. These are the roots: deep and widely spread, they use the available nutrients in the dry soil to the maximum.

History of the dunes
The history of the dunes explains the bio-diversity of the area. Geologist, Alcina Magnólia Franca Barreto, of the Federal University of Pernambuco (UFPE), studied the transformation of the area in her Ph.D. at the Institute of Geo-Sciences of   USP with funding from FAPESP (the project is entitled “Morphologies and Probable Ages of the Fossil Dunes System of the Middle São Franscisco River, State of Bahia”). “The dunes have already been in existence for the past 11 thousand years”, she says, “although a little different from what they are today.”

By studying the sediments together with other vegetal remains (peat deposits) collected from the banks of the Icatu River, a tributary of the São Francisco, Alcina deduced the changes. There have been forests in the region for example. Dating tests on the organic material and sand reveal that there have been phases with different temperatures and humidity. More than 11 thousand years ago, the climate was arid or semi-arid, but with lower temperatures. Thereafter, it became progressively very humid and cold, humid and hot, dry and hot, humid and hot and finally dry and hot again – the existing semi-arid conditions. “For about the last 4,000 years, the vegetation, climate and temperature conditions have been little different to those currently prevailing”, she says.

The origin of the sand dunes is uncertain, since they are deep (up to 150 meters) and Alcina only collected samples from the uppermost layers. But there are two hypotheses. The first supposes a lake formed by the waters of the present São Franscisco, prior to reaching sufficient volume to force an outlet to the sea. The second is that the river could have flowed in another direction – flowing out to the west and not the east. The certainty is that over time, the river changed its course and water volume. During drier phases, there could have been more space for the animals to live together and share the evolutionary process. During the more humid periods, freedom of access no longer existed and the river formed a natural barrier between areas previously joined together.

DNA studies
Until the middle of the seventies, the dunes remained intact. However, in 1975, deep changes occurred due to the Sobradinho dam, which flooded extensive areas.  But the vicarious species survived on the two banks, an example being the Tropidurus amathites lizard on the right bank only and its sister species, Tropidurus divaricatus, on the left.

Isolation produced distinguishing characteristics. “Evolution rates are not the same for species that become separated”, explains Rodrigues, the supposition being that evolution has not been linear. It is necessary to discover whether there have been jumps or fast changes as it has been suggested by the comparative study of the species Calyptommatus and  Nothobachia, that diverged two or three million years ago at the most.

And why in some cases does the same species inhabit both sides of the river? It is possible in these cases that the species has such a powerful dispersal capacity that it has been able to break the barriers of isolation. It is also probable that there has not been time enough for differences to appear or the species have remained equal on both sides for some unknown historical reason.

The research into the genetic differences between vicarious species of the area and related species is done by Maria Lúcia Benozzati, of the Institute for Bio-Sciences of USP, on the basis of DNA studies (deoxyribonucleic acid) of the cellular mitochondria. The sequencing of fragments of mitochondrial DNA done by Maria Lúcia has confirmed Rodrigues’s morphological analysis: as we move up the ladder from the more primitive types of a lizard group to typical species of the dunes, we notice the reduction in body members and the lengthening of the body. For example, Nothobachia and Calyptommatus, the most recent types of the group and the most adapted to dune life, have fore-members that are either so discreet or absent that they look like a snake to the point that they crawl sinuously covered with a fine coating of sand.

By July 2001, when the project is expected to come to an end, Rodrigues expects to have reached some clearer conclusions on what determines the difference between these species. Besides this, he believes that it is necessary to focus urgently on an aspect that still remains pending: the cataloguing and computerization of the zoological collections that are held at the research centers and museums of Brazil.For Rodrigues, this would be enough for a leap forward in the knowledge of Brazilian bio-diversity, identify areas that deserve more intensive study and discover other treasures – rare species such as those of the dunes of the São Francisco.

The surprising diversity of the Caatinga

The bio-diversity of the Caatinga – the only exclusively Brazilian ecosystem, that covers nearly all the Northeast plus the north of the state of Minas Gerais – is surprising. A study which encompassed around 150 research scientists showed that in the oldest occupied ecosystem in Brazil, there are 327 species of endemic animals, nearly double the 183 that were previously known. Typical of the area, for example, are 13 species of mammal, 23 lizards, 20 fish and 15 birds. There are 323 endemic species although only around 190 were listed.

Meeting in Petrolina, State of Pernambuco at the Biodiversity Workshop for the Caatinga, the scientists looked into other environmental factors (soil, climate, topography and hydrology) and the living conditions (education, health and the human development index) of the local communities. More surprises: about half the area has suffered some form of environmental damage at the hands of man and, in the case of between 15% and 20%, this had reached a high degree (with the risk of desertification).

“The region lost its natural resources without generating wealth for the local population, still one of the poorest in the country”, says biologist  José Maria Cardoso da Silva, of the Federal University of Pernambuco (UFPE), that coordinated the workshop. “The lack of water is perhaps the consequence of the poor uses of the biological resources of the Caatinga in the past.”

Two maps show what can be done: one outlines important areas for conservation due to the high degree of bio-diversity and the endemicity of its species, and the other, little known areas for priority studies. Part of the scientific team was responsible for policies for the recovery or preservation of the area: each municipality for example can adopt as a symbol, a local species which it would care for its conservation, well as its habitat.

The study, which was prepared by the UFPE, the Conservation International of Brazil, the Foundation Biodiversitas and Embrapa Semi-Arid, included a controversial theme: the use of the São Francisco River for irrigation. The study suggests that before anything else, priority should be given to the use of rain or artesian water for irrigation. Only, as a last resort, should the option to withdraw river water be examined and only after discussions with specialists and through the intermediary of environmental impact studies.

The biologist, Ana Maria Giulietti, of the State University of Feira de Santana (State of Bahia), was responsible for the vegetative inventory. >From the very beginning, she noted the richness of the Caatinga in unique areas, or enclaves, which varied from dense jungle to sand, each with its own flora and fauna. She discovered a leguminous species which, was named Anamaria heterophila: in her honor: this is a grass that grows to 30 centimeters and has a life span of two months at the most, since it depends for its survival on the level of the water in the lakes which appear during the rainy season. The 20 types of listed endemic plants are double those that were previously known. “When an endemic type is involved, the need for conservation is much greater’, she says.

Early warning signals from the ants
Carlos Brandão, of USP, coordinated a study of  the still-little known invertebrates of the Caatinga, as part of the content of his project, “ Social Insects in the Formations of  the North-East region of Brazil: Surveys of Fauna and Behavioral Ecology,” and concluded in 1991 with FAPESP financing. Besides recording areas with endemic species, he confirmed the possibility of using ants as ecological indicators: they are a more precise indication of the state of conservation of the natural spaces than other animals. A more conserved area of the Caatinga can shelter about 200 species of ant while in the more environmentally damaged areas, the species amount only to between 30 to 40.

The study of the Caatinga concludes the cycle of seminars on the conservation of the Brazilian ecosystems. The first comprising the Cerrado (wooded savanna) and the Pantanal (swampland ), was held in March 1998.Then,  meetings on the Atlantic Rain Forest and the Southern Plains in August, the Amazon Region in September and the Coastal and Seabed Zone in October followed.

The report on the Cerrado and the Pantanal in November 1999, identified 70 priority areas for conservation and 21 for research. It was discovered that 67% of the environment in the Center-West has been altered. “We could never have imagined this result”, says Luiz Paulo de Souza Pinto from the state of Minas and coordinator for the Conservation projects. The survey indicated that there are 6,387 species of trees  (40% endemic), 837 birds (3% exclusive to the region) and 809 bees (51% endemic) living in the region. On the basis of this, the region of the Cerrado was included among the 25 hotspots (critical areas) of the world. “The Caatinga stands a good chance of being put into the same category”, he says.

There are good arguments to justify this. The Brazilian bird, which is most threatened by extinction, the blue macaw, (Anodorhynchus spix), has its habitat in the Caatinga, where only one male has so far been found. Also found in the region, is the second most threatened species, the lear’s macaw, “arara-azul-de-lear” (Anodorhynchus leari): which is found in the surrounding areas of  the city of Canudos in the state of Bahia. Here, there are less than 150 individuals, one tenth of the ideal population in for this kind of birds which are slow to reproduce.

• Miguel Trefaut Urbano Rodrigues, 47, graduated in biology at the Université de Paris VII, France, in 1978. Obtained a Ph.D. in 1984 at the Bio-Sciences Institute of USP, where he has taught since 1986, and is director of the Zoological Museum.
Project: Studies and Differentiation of Fauna and Ecology of Reptiles of the Middle São Francisco River Dunes (Lepidosauromorpha, Squamata)
Investment: R$ 76,700 and US$ 115,307.01

• Alcina Magnólica Franca Barreto, 42, graduated in Geology at UFPE and obtained a masters degree and Ph.D. from the Bio-Sciences Institute of USP. She has been professor of the Geology Department of UFPE since 1997.
Project: Morphologies and Probable Ages of the Fossil Dune Systems of the Middle São Franscisco River, State of Bahia
Investment: R$ 21,229.79

• Carlos Roberto Ferreira Brandão, 47, graduated and obtained a Masters Degree and Ph.D. from the Zoology Department of the Bio-Sciences Institute of USP. He has worked in the Zoology Museum at USP since 1991, where he has been head professor and technical Director of the Scientific Division since 1997
Project: Social Insects in the Formations of the North-East region of Brazil: Surveys of Fauna and Behavioral Ecology
Investment: R$ 105,344.55