Galapagos land iguana

Galapagos land iguana
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Suborder: Iguania
Family: Iguanidae
Genus: Conolophus
Species: C. subcristatus
Binomial name
Conolophus subcristatus
(Gray, 1831)
C. pallidus endemic to Santa Fe Island

The Galapagos land iguana (Conolophus subcristatus) is a species of lizard in the family Iguanidae. It is one of three species of the genus Conolophus. It is endemic to the Galápagos Islands (Ecuador), in the dry lowlands of Fernandina, Isabela, Santa Cruz, North Seymour, Baltra, and South Plaza.[1][2][3]

Taxonomy

The land iguanas in the Galápagos vary in morphology and coloration among different populations.[4] In addition to the relatively widespread and well-known Galapagos land iguana (C. subcristatus), there are two other species of Conolophus: the pink land iguana (C. rosada) from northern Isabela Island and the Santa Fe land iguana (C. pallidus) from Santa Fe Island.[4][5] Based on genetic evidence, the land iguanas and marine iguana diverged about 8–10 million years ago.[6][7] Within the land iguana genus, the oldest split, about 5.7 million years old, is between C. subcristatus and C. rosada.[7][8] The differentiation between the last two species, C. subcristatus and C. pallidus, is less clear and it has been questioned if they are separate species.[4] Based on mtDNA and cytochrome b, they fall into three monophyletic groups: C. subcristatus of western islands (Isabela and Fernandina), C. subcristatus of 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. subcristatus groups are to each other.[8]

Its generic name, Conolophus, is derived from two Greek words: conos (κώνος) meaning "spiny" and lophos (λοφος) meaning "crest" or "plume", denoting the spiny crests along their backs. Its specific name subcristatus is derived from the Latin words sub meaning "lesser" and cristatus meaning "crested", and refers to the low crest of spines along the animal's back which is not as tall as in most iguanas.

Anatomy and morphology

Charles Darwin described the Galapagos land iguana 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."[9] The Galapagos land iguana grows to a length of 3 to 5 ft (0.9–1.5 m) with a body weight of up to 25 lb (11 kg), depending upon which island they are from.[10][11] Being cold-blooded, they absorb heat from the sun by basking on volcanic rock, and at night sleep in burrows to conserve their body heat.[10] These iguanas also enjoy a symbiotic relationship with birds; the birds remove parasites and ticks, providing relief to the iguanas and food for the birds.[2][12]

Diet and longevity

Feeding
Feeding on fallen cactus branches

Land iguanas are primarily herbivorous; however, some individuals have shown that they are opportunistic carnivores supplementing their diet with insects, centipedes and carrion.[2] Because fresh water is scarce on the islands it inhabits, the Galapagos land iguana obtains the majority of its moisture from the prickly-pear cactus that makes up 80% of its diet: fruit, flowers, pads, and even spines.[2][10] During the rainy season it will drink from available standing pools of water and feast on yellow flowers of the genus Portulaca.[10][12]

It is estimated that the Galapagos land iguana has a 50 to 60-year lifespan.[2][11]

Reproduction

Basking

Galapagos land iguanas become sexually mature anywhere between eight and fifteen years of age, depending on which island they are from.[2] Mating season also varies between islands, but soon after mating, the females migrate to sandy areas to nest, laying 2–20 eggs in a burrow about 50 cm (20 in) deep.[2] The eggs hatch anywhere from 90 to 125 days later.[2][11]

On South Plaza Island, where the territories of marine iguanas and land iguanas overlap, the two sometimes interbreed, resulting in a hybrid iguana that shows a mixture of features from each species.[2] The most likely unions tend to be between male marine iguanas and female land iguanas. Despite their long separation time and their being two distinct species from different genera, the offspring are viable, although likely sterile.[2][4]

Population

It is estimated that between 5,000 and 10,000 land iguanas are found in the Galapagos.[2] These iguanas were so abundant on Santiago Island at one time that naturalist Charles Darwin remarked when it was called King James Island that "...when we were left at James, we could not for some time find a spot free from their burrows on which to pitch our single tent".[10][13] In the years since then, entire populations (including all the animals on Santiago Island) have been wiped out by introduced feral animals such as pigs, rats, cats, and dogs.[2][10]

Evolutionary history

Researchers theorize that Galapagos land iguanas and marine iguanas evolved from a common ancestor since arriving on the islands from South America, presumably by rafting.[14][15] The marine iguana diverged from the land iguana some 8 million years ago, which is older than any of the extant Galapagos islands.[6] It is therefore thought that the ancestral species inhabited parts of the volcanic archipelago that are now submerged. The two species remain mutually fertile in spite of being assigned to distinct genera, and they occasionally hybridize where their ranges overlap.

Recovery efforts

Male
Yellow land iguana at the Charles Darwin Research Station
Galapagos land iguana on North Seymour Island.

Beginning in the early 1990s, the Galapagos land iguana has been the subject of an active reintroduction campaign on Baltra Island. These animals became extinct on Baltra by 1954, allegedly wiped out by soldiers stationed there who shot the iguanas for amusement.[2][12] However, in the early 1930s, William Randolph Hearst had translocated a population of land iguanas from Baltra to North Seymour Island, a smaller island just a few hundred metres north of Baltra because he could not understand why no iguanas were present there. Hearst's translocated iguanas survived, and became the breeding stock for the Charles Darwin Research Station captive breeding program that has successfully reintroduced the species to Baltra and a number of other areas.[2] Visitors today frequently see iguanas on both the runway of the Baltra airport or while they cross the road.

References

  1. 1 2 World Conservation Monitoring Centre (1996). "Conolophus subcristatus". IUCN Red List of Threatened Species. IUCN. 1996: e.T5240A11121212. doi:10.2305/IUCN.UK.1996.RLTS.T5240A11121212.en.
  2. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 "Land iguanas" (PDF). Charles Darwin Research Station Fact Sheet. Charles Darwin Foundation for the Galapagos Islands. 2006. Archived from the original (PDF) on 2007-06-06. Retrieved 2007-10-14.
  3. ↑ Swash, A.; and R. Still (2000). Birds, Mammals & Reptiles of the Galápagos Islands. Yale University Press. pp. 118–119. ISBN 0-300-08864-7.
  4. 1 2 3 4 Rassmann, Kornelia; Markmann, Melanie; Trillmich, Fritz; Tautz, Diethard (2004), "Tracing the Evolution of the Galapagos Iguanas", Iguanas: Biology and Conservation, California: University of California Press, pp. 71–83, ISBN 978-0-520-23854-1
  5. ↑ Gentile, Gabriele; Anna Fabiani; Cruz Marquez; Howard L. Snell; Heidi M. Snell; Washington Tapia; Valerio Sbordonia (2009). "An overlooked pink species of land iguana in the Galapagos". Proceedings of the National Academy of Sciences of the United States of America. National Academy of Sciences of the United States of America. 106 (2): 507–11. PMC 2626733 Freely accessible. PMID 19124773. doi:10.1073/pnas.0806339106.
  6. 1 2 "Explaining the Divergence of the Marine Iguana Subspecies on Espa". amnh.org.
  7. 1 2 Black, Richard (5 January 2009). "Pink iguana rewrites family tree". BBC News. BBC. Retrieved 20 May 2017.
  8. 1 2 Gentile; Fabiania; Marquez; Snell; Snell; Tapia;and Sbordonia (2009). "An overlooked pink species of land iguana in the Galápagos". Proceedings of the National Academy of Sciences of the United States of America. National Academy of Sciences of the United States of America. 106 (2): 507–511. PMC 2626733 Freely accessible. PMID 19124773. doi:10.1073/pnas.0806339106.
  9. ↑ Darwin, Charles (1989), The Voyage of the Beagle: Charles Darwin's Journal of Researches, New York: Penguin Classics, p. 401, ISBN 978-0-14-043268-8
  10. 1 2 3 4 5 6 Rogers, Barbara (1990), Galapagos, New York: Mallard Press, p. 51, ISBN 978-0-7924-5192-1
  11. 1 2 3 Rosenthal, Ellen (1997), "Days and nights of the iguana: in the Galapagos, a devoted pair work to save land iguanas", Animals
  12. 1 2 3 Kricher, John (2006), Galapagos: A Natural History, New Jersey: Princeton University Press, pp. 9,51,91,200, ISBN 978-0-691-12633-3
  13. ↑ Darwin, Charles (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., London: Henry Colburn, p. 488
  14. ↑ Rassmann, K.; Tautz, D.; Trillmich, F.; Gliddon, C. (1997). "The micro – evolution of the Galápagos marine iguana Amblyrhynchus cristatus assessed by nuclear and mitochondrial genetic analysis". Molecular Ecology. 6 (5): 437. doi:10.1046/j.1365-294X.1997.00209.x.
  15. ↑ Marine Iguana. marinebio.org.
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