The Galapagos by Henry Nicholls

Author:Henry Nicholls
Language: eng
Format: epub
Publisher: Profile Books

FIGURE 7.2. Land iguana. Conolophus subcristatus is the most common of three species of land iguana in the Galápagos. Reproduced from Thomas Bell, ‘Part 5. Reptiles,’ in The Zoology of the Voyage of H.M.S. Beagle, ed. Charles Darwin (London: Smith, Elder and Co., 1838–1843), 22.

Of the ones Darwin saw (C. subcristatus), he described their belly, legs and head as being ‘Saffron’ and ‘Dutch orange’ in colour. The land iguanas of Santa Fé (C. pallidus) are judged to be a different species owing to their lighter skin tone and a few other characteristics. More recently, in 1986, rangers from the Galápagos National Park Service discovered that Wolf Volcano on Isabela is home to a pink variety, but with the pressures of other work, it took almost twenty years before a dedicated expedition went in search of this by then nearly mythological beast. In 2005, park wardens found four pink iguanas. The following year, they located a further thirty-two. These expeditions resulted in the formal description of a new species (C. marthae).

Apart from its striking colouration, this new species has several other notable differences from its yellow and pallid cousins. Whereas C. subcristatus and C. pallidus both have pretty prominent spines on their heads and down their backs, these are almost absent on C. marthae. In addition, each form has its own distinctive head-bobbing routine, a display that the land iguanas of Santiago appear to have performed for Darwin in 1835. ‘When attentively watching an intruder they curl their tails, & raising themselves as if in defiance on their front legs, vertically shake their heads with a quick motion,’ he wrote in his Zoology Notes. This head-bobbing display is a common feature in iguanas, used in territoriality and courtship.

But the result of the genetic analysis is the most intriguing, strongly suggesting that C. marthae has descended from an ancient lineage that split away from the other land iguanas some 5.7 million years ago. If this is the case, it’s weird that C. marthae is confined to Wolf Volcano and is not found on any of the older islands.

One possibility is that the arrival of humans and other introduced species has, for some reason, taken a disproportionate toll on the pink iguana, though given that the pink iguana does not show up in any of the many historical accounts of Galápagos fauna, this seems a little unlikely. Another possibility is that it’s been usurped by C. subcristatus. Whatever the explanation for its incredibly confined distribution (it’s thought to occupy no more than 25 km2), there’s a serious danger that it could soon disappear altogether. Only one in every three of the pink iguanas discovered during the 2006 expedition was female, and there were no signs of juveniles. A more recent expedition, in 2012, found evidence that reproduction is still occurring, with a youngster estimated to be around four years old, but clearly the situation is touch-and-go. If the Galápagos National Park Service gets an inkling that the population is about to vanish, it

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