Famine's mark

Some of the marine iguanas from the Galapagos Islands have a secret hidden in their DNA: the signature of an environmental disaster. In 1997 and 1998, the area was hit by an intense El Niño. The periodic warming of the sea surface caused a famine among iguanas, vegetarians that live primarily on seaweed. In some places, 90 percent died.

In 2004, Yale ecologist Gisella Caccone and her colleagues sampled 11 different Galapagos iguana populations. When the team compared these with DNA samples taken before the El Niño, they found varying degrees of a drop in genetic diversity. The biggest reduction occurred on Marchena, an island that experienced a devastating volcanic eruption several years before the El Niño. Its iguanas have yet to recover, Caccone reports in the December Public Library of Science One."Multiple stressors may have a synergistic effect on population,” she says.