Chile’s Altiplano: why do African ostriches, camels and flamingos have Chilean relatives?

July 25, 2012 update: Rémi Wattier, author of a recent paper on phylogeny of American flamingos (see citation at end of post), said: "Unpublished molecular phylogenies are pointing out that Greater, American and Chilean flamingos are closely related while being divergent from the three last species (Adean, Puna and Lesser flamingos) which are also related together. Therefore speciation before inter-continental migration is the most likely scenario." A visit to Chile last month (November 2009) gave me a chance to consider questions of biogeography that had been bothering me since I first read Charles Darwin’s Voyage of the Beagle. Darwin saw what he called “ostriches,” now classified as rheas, but so closely related that they look almost identical and live in similar flat, dry habitats. One bears his name, Darwin’s Rhea. How could the ostrich of Africa be so closely related to the rhea of South America, with ratite relatives also in Australia (Emus) and New Zealand (Cassowaries)? How is it that three species of flamingo live in the two-mile high deserts of northern Chile, Bolivia and Argentina, while the world’s other three species are scattered from the Americas through the Mediterranean and Africa ? Darwin also recognized vicuñas and guanacos (and of course their domesticated descendants the alpaca and llama) as relatives of camels: what biological or geological forces of nature caused camelids to occur in South America and Africa/Arabia and nowhere in between? Finally, what combinations of geology and evolution caused these disparate groups—ratites, camelids and flamingos—to have the same disjunct distribution?
Usually, when mountains rise up, forced by tectonic forces deep in the earth at rates of only millimeters per year, the water running off them finds its way down to lower levels and eventually to the sea, cutting rills that become canyons and then wide valleys along the way. But in the Andes Mountains of northern Chile, western Argentina, Bolivia and southern Peru, something different happened. The land rose as one over a vast area, creating not sharp mountains and deep valley but a high plain, the Altiplano. The land folded a little, creating north-south ridges that prevented the water from running to the oceans, either Pacific or Atlantic. Instead, what little water there was pooled in the depressions and evaporated in the dry air. These eventually filled with silt, creating many broad salt flats. No matter how salty the flats are, the springs feeding them ensure that there is always a gradient of fresh to brackish water. The less salty parts are filled with plants and animals. The plants are microscopic algae and the animals include such tiny arthropods as brine shrimp, brought to each isolated salt flat on the legs of wading birds. These are the habitats of the flamingo and another wading bird unique to Altiplano salt flats, the Andean Avocet.
Although the Altiplano kept rising for so many millennia that it reached heights unequalled anywhere outside of the Himalayas, not all of its rise was gradual. Through this high plain burst volcanoes, not one or two, but hundreds. They showered the land with ash and cinders, colouring it in reds, greys and yellows as if by an artist gone mad.
Although inland from the Atacama desert, where it may not rain for years at a time, the Altiplano is high enough to get a little moisture. Driving from the airport at Calama to my base at San Pedro de Atacama, I passed through one of the driest deserts on Earth. Hardly a living plant grew there and I saw no birds, not even a lizard. The ancient oasis town of San Pedro, still built of mud brick despite the bustle of adventure tourism, is watered by a network of tiny canals running through the town, although the San Pedro River itself was dry when I was there.
North and East of San Pedro, the roads climb to the Altiplano. Unlike the desert drive from Calama, there is some little vegetation—even a patch of trees—but still the land is parched, dry and grey, with shades of brown and red from the volcanic cinders and the dry vegetation. Suddenly at around 3000 meters, the colours dramatically change. Here there is enough moisture for grass and the land suddenly changed from grey and brown to yellow. And what a yellow! The clear air and strong sunlight made this the brightest yellow I have ever seen in a grass. Its brilliance contrasted with the deep blue of the sky and the reds of the volcanoes. I can only imagine what it looks like in spring when the grass is green. This vast grassland is the habitat of the guanacos of middle elevation and vicuñas and rheas of high elevation—we crossed one pass at 5000 meters. I had been afraid that I might go all this way and not see guanacos, vicuñas, rheas or the three species of flamingos, but they were all there in abundance, as well as two dozen other species of birds found nowhere else and unique mammals including the Andean fox, highland tuco-tuco (a relative of the guinea pig), and mountain viscacha (in the chinchilla family).
And everywhere loom volcanoes, many above 6000 meters, most with a little snow, and some even with glaciers. Their melt water sometimes cuts deep canyons before disappearing into the ground, but then it reappears as springs at the edges of the salt flats.
A little research answered some of the biogeography questions. These ratites, camelids, and flamingos diverged from their African counterparts too recently for their disjunct populations to have resulted from the tectonic separation of Gondwana Land into the eastern and western hemispheric land masses we know today, about 100 million years ago (MYA). The rheas and ostriches diverged a mere 65 MYA, much too late for the South America-Africa split, but while Australia, Antarctica and Madagascar were still connected. DNA analysis showed the emus to be the base of the ratite tree, and the high diversity of tinamous, a sister clade to the ratites that occurs only in South America, suggests a long history there. Ostrich ancestors may have gone from there (or Australia) to Antarctica, and thence to Madagascar, where ratite relatives (Elephant Birds) have also been found.
The camelids have a different story: their family evolved in North America and then dispersed to South America and Asia, thence to central Asia (the Bactrian Camel) and Arabia/Africa (the Dromedary) after which, during the Pleistocene, all North American and east Asian species went extinct.
The flamingo story has not yet been unravelled. They are one of the most ancient of avian lineages, having separated from (probably) grebe ancestors in the Middle Eocene around 40 MYA. Currently they are classed in two genera, Phoenicopterus, with two species in Africa and two in the Americas, and Phoenicoparrus, the two species of which (Andean Flamingo and Puna or James’ Flamingo) are restricted to the Altiplano. One can imagine how the migratory Chilean Flamingo, Phoenicopterus chilensis, might have reached Chile: it is closely related to Africa’s Greater Flamingo, Phoenicopterus roseus, and the American Flamingo, Phoenicopterus ruber, which occurs from the Caribbean to the Galapagos. From there it is a few short hops following the coastal lagoons and Altiplano lakes loaded with brine shrimp and other macroscopic animals to Chile. Once there, during Pleistocene glacial advances, it may have gotten isolated and diverged a little from its American counterpart. But the Andean and Puna Flamingos? They are quite different: although nomadic within the Altiplano, they do not migrate to the coast like the Chilean Flamingos. Their bills are differently constructed and they are vegetarians, filtering diatoms and other microscopic algae and blue-green algae from the water. In this they are unlike every other flamingo except the Lesser Flamingo, which I had previously seen in Namibia and feeds in flat, briny lakes in eastern and southern Africa. It also feeds on algae and blue-green algae. The Lesser Flamingo, although currently classed as a Phoenicopterus species, was formerly classed in a third genus, Phoeniconaias because of morphological differences that are different from other Phoenicopterus species, but similar to the two Phoenicoparrus species. Is its morphological and dietary similarity to the Andean and Puna Flamingos a coincidence of evolutionary convergence? Or are they more related to each other than to the Greater and American species? This is not known, but if so, it would imply two dispersals: one that populated both the Americas and Africa with ancestral flamingos, and a later one that saw a lineage evolve to filter microscopic plants instead of macroscopic animals, with a subsequent dispersal from Africa to South America or vice-versa. This is speculation. No one knows. It is why science is so exciting: so many mysteries still to explore.
Travel Notes
I stayed at the Hotel Tambillo, http://www.hoteltambillo.cl/, tambillo@sanpedroatacama.com. A great, inexpensive hotel with a shady courtyard surrounded by high adobe walls. It has a restaurant and the proprietor, Veronica, is full of helpful information about the town and all the roads and places of interest. I hired a mountain guide (Ivan Mery, rutacien@gmail.com) for one day to reach a place near the Bolivian border that I doubted that I could find by myself, and am glad I did.
Key References
Darwin, C. R. (1839). Narrative of the surveying voyages of His Majesty's Ships Adventure and Beagle between the years 1826 and 1836, describing their examination of the southern shores of South America, and the Beagle's circumnavigation of the globe. Journal and remarks. 1832-1836. London, Henry Colburn.
Haddrath, Oliver and Allen J. Baker (2001). "Complete mitochondiral DNA sequences of extinct birds: ratite phylogenetics and the biogeographical vicariance hypothesis." Proc. Royal Society B 268(939-995).
Kadwell, M., M. Fernandez, et al. (2001). "Genetic analysis reveals the wild ancestors of the llama and the alpaca." Proc. of The Royal Society B 268: 2575-2584.
Cui, Peng, Rimutu Ji, et al. (2007). "A complete mitochondrial genome sequence of the wild two-humped camel (Camelus bactrianus ferus): an evolutionary history of camelidae." BMC Genomics 8: 241.
Olson, Storrs L. and Alan Feduccia (1980). Relationships and Evolution of Flamingos (Aves: Phoenicopteridae). Washington D.C., Smithsonian Institution Press.
Morgan-Richards, Mary, Steve a Trewick, et al. (2008). "Bird evolution: testing the Metaves clade with six new mitochondrial genomes." BMC Evolutionary Biology 8: 20. Geraci, J., Béchet, A., Cézilly, F., Ficheux, S., Baccetti, N., Samraoui, B., and Wattier, R. Greater flamingo colonies around the Mediterranean form a single interbreeding population and share a common history. Journal of Avian Biology.