Galápagos Land Iguana

Charles Darwin described the Galápagos land iguanas he observed as "ugly animals, of a yellowish orange beneath, and of a brownish-red colour above: from their low facial angle they have a singularly stupid appearance." The Galápagos land iguana is one of the largest lizards in the world, growing to a length of 0.9 to 1.5 m (3–5 ft), with a body weight of up to 13 kg (29 lb), depending upon which island they are from. Being cold-blooded, they raise their body temperature by basking on volcanic rock or other dark-colored stones that naturally absorb the heat of the sun. By night, they sleep in burrows to conserve their absorbed body heat. These iguanas also enjoy a symbiotic relationship with birds; the birds remove parasites, such as ticks, providing relief to the iguanas and food for the birds.

The Galápagos land iguana is primarily herbivorous; however, some individuals have shown that they are opportunistic omnivores, supplementing their diet with invertebrates, such as centipedes or arachnids, and carrion. Because fresh water is scarce on the islands, the Galápagos land iguana obtains the bulk of its moisture from the prickly-pear cactus (Opuntia sp.), in addition to other Cactaceae species, which makes up nearly 80% of its diet. All parts of the plant are consumed, including the fruit, flowers, pads, and even the sharp spines. During the rainy season, the Galápagos land iguana will drink from temporary vernal pools and other accumulated sources of water, and feast on the blousy, yellow flowers of the perennial succulent genus Portulaca.

The land iguanas of the Galápagos islands (genus Conolophus) vary in morphology and coloration among different populations. In addition to the relatively widespread, well-known Galápagos land iguana (C. subcristatus), there are two other species within Conolophus: the Galápagos pink land iguana (C. marthae), of northern Isabela Island; and the Santa Fe land iguana (C. pallidus), of Santa Fe Island. Based on mtDNA, the ancestors of today's land iguanas and marine iguanas (Amblyrhynchus cristatus) separated about 8–10 million years ago (MYA). Within the land iguana genus, the oldest split (based on mtDNA—about 5.7 MYA) is between C. subcristatus and C. marthae. A more-recent study, which included both mtDNA and nuclear DNA, indicated that the marine iguana split from the land iguana about 4.5 MYA; among the land iguanas, C. subcristatus and C. marthae split from each other about 1.5 MYA. The differentiation between C. subcristatus and C. pallidus is less clear; it has been questioned whether they are separate species. Based on mtDNA and cytochrome b, they fall into three monophyletic groups: C. subcristatus of the western islands (Isabela and Fernandina), C. subcristatus of the central islands (Santa Cruz, Baltra and South Plaza), and C. pallidus. Although the exact pattern is uncertain, it is possible that C. pallidus is closer to one of the C. subcristatus groups than the two C. …