Hidden Riches Buried in the Sand of the Orinoco
From Cal Poly Pomoma College of Science News Letter, Fall 2001, by Laura Moore

Dr. Jonathan Baskin, Professor of Biological Sciences at Cal Poly Pomona, along with Dr. Scott Schaefer, a curator of fishes at the American Museum of Natural History in New York, and Professor Francisco Provenzano of Universidad Central de Venezuela, recently trekked up a section of the Orinoco river in Venezuela in pursuit of missing pieces in a global phylogenetic puzzle. Their quarry? A primitive and poorly understood species of catfish.

The landscape of the upper Orinoco is amazing, beautiful, and illusory. The horizon gives the impression of rolling hills, which are actually Tepuis; high, flat-topped mesas created over hundreds of thousands of years as channels erode in the bedrock of which the continent is composed. They are similar to buttes and mesas of the North American Southwest but are covered with a lush, tropical flora and fauna, and are so remote that they are only recently being explored via helicopter.

The ecology of this part of the upper Orinoco is not like the dense, rich-soiled rainforests further south. This section of river flows over exposed bedrock, and what little soil there is comes from sand and the decaying vegetation from the processes of succession-- ferns and algae take hold on the bare rock and die, creating decaying matter that forms a substrate for the next set of colonizing plants.

Because of the physically demanding nature of visiting and collecting in these extremely remote areas, ichthyologists have only a few examples of these rare fishes to study, and must work with sparse information gathered mostly during the early 19^th century. Even samples that were gathered as late as the 1970's by anthropologist Standford Zent of Universidad Simon Bolivar in Caracas, had brought back only a single specimen of the catfish species they were looking for.

After a series of delays brought about by the difficulty of obtaining permits, the expedition finally got under way, but this was only the beginning of a series of difficulties that plagued the team and tested their resolve. It was well into the dry season when the expedition began, their progress now hindered by particularly low water-levels. At shallow rapids, the team was forced to get out and walk the boats upriver. Deeper sections of the river were well-known for large whirlpools. Stories circulated of an abnormally strong whirlpool created by a hole in the bedrock, down which a native woman had recently disappeared, emerging downstream alive.

All of this trouble seems a lot to go through for a catfish. Dr. Baskin smiles ruefully at this point, but is clearly passionate about the reasons for his efforts.

"Besides the fact that I love South America," he says wryly, "Is that catfish are so compelling."

"Back when I was a student at the University of Miami, I was discouraged by the fact that everyone and their grandmother was studying the same subject I was-- Marine Biology. Not only that, but I discovered that I got deathly seasick! It happened that I took a course in ichthyology and noticed that despite their diversity and potential as a subject of study, nobody was really looking at catfishes."

"While I was at the marine lab, I got an opportunity to study marine fishes in Brazil, and on the way back, I was at a city on the Amazon in the fishmarket and discovered tables and counters covered with all of these bizarre fishes of all sizes and shapes and colors, like something from another planet-- they were catfishes. At that moment, it sort of just clicked with me-- I thought, this is what I want to do. And better yet, no one else was doing it!"

Catfish compose a large group of scaleless fishes of the order Silariformes, suborder Nematognathi, characterized by feelers around the mouth called barbels, somewhat like a cat's whiskers. They are omnivorous scavengers, and are able to use the swim bladder to produce sounds. Catfish range across the globe and vary in size from less than 2 inches* to 13 feet and a weight of 400 pounds. South American catfishes show a great diversity: there are small, delicate species armored with bony plates; parasitic types that live in the gills of other fish, and one catfish of the Andes in which the pelvic fins are modified to enable it to cling to rocks. Some tropical South American catfish survive dry seasons by burrowing into the mud or by crawling overland in search of water. Catfishes have over 3,000 species and 25 families of representatives, some armored, some stinging or bloodsucking, and some that even eat wood or swim up the urethras of unsuspecting mammals.

"Beyond just the pure fascination with catfish," Dr. Baskin points out," Is that they are a very useful fish to study in terms of phylogenetic biology. They are an extremely diverse group of species that are found all over the world, and yet have very clear characteristics, which make them a perfect tool for understanding the evolutionary history of species."

Phylogenetics is the study of the history or course of evolution, and is sometimes confused with classification of species. It differs from taxonomy however, in that it is not so much about "naming" species, as about examining the relationships between related species in order to form a better understanding of their evolution, and the evolution of the entire planet. Akin to a complex jigsaw puzzle, phylogenetics involves the study of not only flora and fauna, but geological history as well. Because of plate tectonics, or the movement of continents, scientists can extrapolate how and when (through studying both the fossil record and living organisms) different species evolved from a common ancestor. Catfish in particular lend themselves to this study because they are extremely diverse in some areas, and have retained primitive characteristics in others.

"The area of South America where the upper Orinoco wends its way is a perfect place for the study of phylogenetics," Dr. Baskin explains. "It is a clear water river that runs over a part of the ancient part of the continent from the Pre-Cambrian period. This piece of rock, which forms a big chunk of South America north of the Amazon, was once part of a much larger landmass in geological history that encompassed parts of what is now Africa. By looking at the fossil records, at great masses of rock in Africa and South America that were once a single slab in an original "supercontinent", we can get an idea of how long it has taken species to evolve, how long ago they shared a common ancestor, and the time periods involved."

"I had seen these specimens from other parts of Venezuela," Dr. Baskin explains, "But the area we were attempting to reach had been explored very little from the standpoint of ichthyology. We feel it is important to map this group of fishes that are poorly understood and rare, because they are probably the primitive relatives of other large groups of species, which make them important in terms of reconstructing the evolutionary history of related fishes."

Biogeography and Phylogenetics Take a Two-Dimensional Idea of Species' Distribution and Interpret It As a Three-Dimensional 'Tree of Life' Which Has Branched Out Over a Long Evolutionary History

"A common misconception when we try to visualize how evolution works is that these so-called 'primitive' fishes are actually the ancestors of the fish who have evolved-- a kind of 'missing link' in an evolutionary backwater. But this is not the case. Every living thing has had an equally long evolutionary history," Dr. Baskin says, grabbing a piece of scrap paper and drawing a rough diagram of a tree with a single trunk and many diverging branches.

"What we are doing is comparing the branches and leaves at the tips of the tree," he says. "That is where every living species is-- way out on the branches. Even if they have retained primitive characteristics, they have still been evolving as long as everyone else has. We cannot look at living examples of the trunk of the tree, because they no longer exist."

Dr. Baskin and his colleagues are in essence, helping to gather the pieces of a giant puzzle that lets us trace the history of waves of time and evolution on the earth-- the movements of continents, the history of the organisms that live and have lived.

Unfortunately, even with these ideas and hopes driving the expedition, there were tangible limits. Having reached the final village they needed to pass through, Drs. Baskin, Schaefer and Provenzano realized they would have to turn back.

"We were exhausted and disappointed," Dr. Baskin admitted. "We had come so close to our goal, but we had no choice-- we were running out of time and supplies."

"As a last-ditch effort, we sent our guides ahead into the village with a description of the species we were looking for, and where to find them-- on the outside chance that they would be given a chance to look. Then we packed up and headed home."

Just a few hours later, their guides caught up with them bearing specimens of the fish they had been looking for, and reports of where they had been found. Unable to obtain permission for the entire party to pass through, the guides had been allowed to look for the fish themselves.

"We were ecstatic. Sure we had wanted to see the places for ourselves, but that was secondary. We had found what we came for... and, there was an unexpected bonus as well."

"During the time we spent hanging around in the sandy areas, waiting for our guides, we identified three new species of fishes that had never been documented. Even the native people did not know about them. They are very tiny fish, perhaps the smallest vertebrate in the world, that live buried in the sand-- and they are catfish."

So maybe being stuck behind, either as a scientist or a species, isn't always such a bad thing.

*Specimens of new catfish species brought back from this expedition are less than an inch long.

Follow these links for more information on:

Dr. Jonathan Baskin
Catfish
Phylogentic Trees and Biogeography