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Chameleons born in Africa, rafted to Madagascar

AFP-JIJI

Chameleons took to the waves to migrate from Africa to Madagascar about 65 million years ago, says a study that seeks to resolve a roiling biological debate.

Chameleons are famous for the extraordinary ability of some species to change color, and for a lightning-fast talent to catch prey with their tongue. Biologists, though, are bemused by a wider question: Where on Earth did chameleons come from?

The vast majority of the 195 chameleon species today are found in Africa and Madagascar, both once part of a supercontinent called Gondwana that broke apart some 120 million years ago. During that split, Africa and Madagascar became separated by a sea trough that today is 400 km wide.

Fossil evidence suggests the first chameleons only showed up after the breakup — but scientists have long disagreed about where.

The new study, published on Wednesday, was based on a genetic analysis of 174 chameleon species and says the migration came from Africa. It was led by lizard pioneers that probably hitched a ride on rafts of floating debris washed downstream in big African rivers during floods, the authors suggested.

“What we did was estimate the time period when various related chameleons on Africa and Madagascar diverged,” said lead author Krystal Tolley at the South African National Biodiversity Institute in Cape Town.

“We found out this was probably first, in the late Cretaceous, 65 million years ago, and then again in the Oligocene Period, about 45 million years ago,” Tolley said . “We concluded that (both dispersal events were) more likely to be from Africa to Madagascar, but we then also backed this up by using information on the direction of oceanic currents in those very same time periods.”

During the late Cretaceous and the Oligocene, currents flowed from Africa toward Madagascar, the opposite of today’s flow, a discovery that was “the icing on the cake, as far as we were concerned,” she said.

Another study on chameleon origins, published in 2002, concluded the lizards originated in Madagascar. Ancestral lizards crossed the present-day Mozambique Channel to Africa, where they underwent species differentiation, evolving in habitat niches that were shaped by climate and landscape change, the study said.

Those findings were based on DNA analysis of about 40 percent of chameleon species and used a technique called the molecular clock to estimate the pace of evolution and reconstruct the ancient family tree.

“(We) were a bit suspicious of this line of thought, and decided to investigate their origins more closely,” said Tolley.

Raft dispersion by animals and plants, sometimes across hundreds of kilometers, is a known if rare phenomenon, she added. “It would be a difficult journey, so it probably does not happen often, and the currents have to be in the right direction, too. For chameleons, it has likely occurred only a few times. Between African and Madagascar, we think it only has occurred twice.”

Elsewhere in the Indian Ocean, chameleons traveled from Africa to the Seychelles Islands on one occasion, and in the Atlantic they managed to make it to Bioko Island in the Gulf of Guinea, Tolley said. Latin America and the southeast U.S. also have lizards that are called chameleons, but they are actually from a family called anoles, which are more closely related to iguanas than to chameleons.