Chelonoidis abingdonii

Chelonoidis abingdonii
Lonesome George at the Charles Darwin Research Station in 2006, the last known individual of his species of Galápagos tortoise
Estado de conservación
Ficheiro:Status IUCN3.1 EX gl.svg Extinto
Clasificación científica
Xénero: Chelonoidis Especie: abingdonii
Map of the Galápagos Islands indicating species' locations Map of the Galápagos Islands indicating species' locations

Chelonoidis abingdonii é unha especie de tartaruga xigante dos Galápagos propia da illa Pinta do arquipélago das Galápagos , que probablemente está extinta.

Evolución

The origin and systematic relationships are still unresolved today, it even captivated Charles Darwin himself. Scientists used DNA sequencing and decided to collect a few tortoises from the Pinta Island in 1906.^{[Cómpre referencia]} With DNA sequencing as their method, their results show that the three best candidates for the closest living relative of the Galapagos tortoises are all located in South America. It is the yellow-footed tortoise (Geochelone denticulata), the red-footed tortoise (Geochelone carbonaria), and the Chaco tortoise (Geochelone chilensis). These 3 species are known as extant species.

Comportamento e ecoloxía

During their time on the island, the Galapagos Tortoise, including the Pinta Island species, was observed many times and it was concluded that the tortoises rest about 16 hours a day.^{[Cómpre referencia]} The Galapagos tortoises are herbivores who feed primarily on greens, grasses, native fruit, and cactus pads. These tortoises also drink heavy quantities of water which they can then store in their bodies for long periods of time and utilize later. They can reportedly survive up to six months without any food or water.^{[Cómpre referencia]}

For breeding, the tortoises are most active during the "hot season" (January to May) and then during the cool season (June to November), female tortoises migrate to nesting zones in order to lay out their offspring.

The effort to conserve species to increase biodiversity is a very important aspect of life involving economic, social and cultural values with phylogenetic, biogeographic, ecological and demographic indulgence. Galapagos giant tortoises provide a great example of this as they represent the top mega-herbivores that aid in shaping Galapagos ecosystems. They provide critical ecosystem services by seed dispersing and by being ecological engineers through herbivory and nutrient cycling. Due to the extinction of many of these large herbivores, ecosystem functioning has diminished worldwide.

Dispersión de sementes

On the Island of Santa Cruz near the geographic center of the Galapagos, there was a study done by Blake et al. on seed dispersal by Galapagos tortoises. In order to determine the number of seeds spread, they identified and counted intact seeds from 120 fresh dung piles in both the agricultural and natural park land. To obtain the distance seeds were moved by tortoises they used an estimated digesta retention time from captive tortoises as a proxy for retention times of wild tortoises and data for the tracking of the tortoises was obtained from GPS telemetry. Germination trials were administered for five plant species to determine whether germination success was influence by tortoises. In the results, it was found that there were over 45 plant seeds still intact. On average tortoises defecated 464 (SE 95) and 2.8 (SE 0.2) species per dung pile. Seeds were found over long distances where turtles had transported them. However, there was no evidence found that tortoise ingestion or the presence of dung influenced the success of seed germination. In conclusion, it was discovered that Galapagos tortoises are colossal seed dispersers, regularly transporting a vast amount of seeds over distances. More extensive research is needed to quantify germination success, demography of plants under natural conditions, with and without tortoise dispersal to determine the seed dispersal effectiveness of Galapagos tortoises.

Relacións cos humanos

Esforzos de conservación

In 1958, goats immigrated to Pinta Island, Galápagos began eating much of the herbs and shrubs to the detriment of the natural habitat. A prolonged effort to exterminate the goats was initiated. As the goat populations declined, the vegetation underwent an amazing recovery. Small trees began regenerating from the stumps left by the goats. Highland shrub species, forest tree seedlings, Opuntia cactus, and other endemic species increased. In 2003, Pinta Island was declared "goat-free".

In addition to current conservation efforts such as the elimination of goat populations in the Galápagos, there has been a new effort to revive a number of species of Galápagos tortoise. There is new information which states that from 12 females and 3 male tortoises there came around 1700 offspring which now live in the Galápagos area. Many of these offspring also coincide with many species of Galápagos tortoise, such as the vital Pinta Island Galápagos tortoise. The statistics also show that compared to a 3% hatching rate in 2004, in 2007 there was a 24% hatching rate which gave an unprecedented rise in tortoise population. This also shows that the number of animals in a species can rise despite genetic variation.

Xurxo o Solitario (Lonesome George)

Artigo principal: Xurxo o Solitario.

Lonesome George at the Charles Darwin Research Station

The last known individual of the species was a male named Lonesome George (castelán: El Solitario Jorge/George), who died on 24 June 2012. In his last years, he was known as the rarest creature in the world. George served as a potent symbol for conservation efforts in the Galápagos and internationally.

George was first seen on the island of Pinta on 1 December 1971 by Hungarian malacologist József Vágvölgyi. Relocated for his safety to the Charles Darwin Research Station on Santa Cruz Island, George was penned with two females of a different species. Although eggs were produced, none hatched. The Pinta tortoise was pronounced functionally extinct as George was in captivity.

Over the decades, all attempts at mating Lonesome George had been unsuccessful, possibly due to the lack of females of his own species.

On 24 June 2012, at 8:00 am local time, Director of the Galápagos National Park Edwin Naula announced that Lonesome George had been found dead by his caretaker of 40 years, Fausto Llerena. Naula suspects that the cause of death was heart failure consistent with the end of the natural lifecycle of a tortoise.

Posibles individuos superviventes

In 2006, Peter Pritchard, one of the world’s foremost authorities on Galápagos tortoises, suggested that a male tortoise residing in the Prague Zoo might be a Pinta Island tortoise due to its shell structure. Subsequent DNA analysis, however, revealed it was more likely to be from Pinzón Island, home of the species C. duncanensis.

Whalers and pirates of the past used Isabela Island, the central and largest of the Galápagos Islands, as a tortoise dumping ground. Today, the remaining tortoises that live around Wolf Volcano have combined genetic markers from several species. In May 2007, analysis of genomic microsatellites (DNA sequences) suggested that individuals from a translocated group of C. n. abingdonii may still exist in the wild on Isabela. Researchers have identified one male tortoise from the Volcano Wolf region, which has half his genes in common with George's species. This animal must be a first-generation intergrade between the species of the islands Isabela and Pinta. A pure Pinta tortoise possibly lives among the 2,000 tortoises on Isabela.

The identification of eight individuals of mixed ancestry among only 27 individuals sampled (estimated Volcano Wolf population size 1,000–2,000)… suggests the need to mount an immediate and comprehensive survey… to search for additional individuals of Pinta ancestry.

A recent trek to Isabela by Yale University researchers revealed that there are 17 first-generation hybrids living at Wolf Volcano. The researchers plan on returning to Isabela in the spring of 2013 to look for surviving Pinta and to try to collect hybrids in an effort to start a captive selective-breeding program and to hopefully reintroduce Pintas back to their native island. -->

Notas

• Caccone, Adalgisa; Gibbs, James P.; Ketmaier, Valerio; Suatoni, Elizabeth; Powell, Jeffrey R. (1999-11-09). "Origin and evolutionary relationships of giant Galápagos tortoises". Proceedings of the National Academy of Sciences 96 (23): 13223–13228. ISSN 0027-8424. PMC 23929. PMID 10557302. doi:10.1073/pnas.96.23.13223. 
• Nicholls, Henry (2004-06-03). "Tortoise conservation: One of a kind". Nature 429 (6991): 498–500. ISSN 0028-0836. doi:10.1038/429498a. 
• Giant Tortoises, Galapagos Conservancy
• Recovery of a nearly extinct Galápagos tortoise despite minimal genetic variation., Wiley Online Library

Véxase tamén

Outros artigos

• Lista de especies de tartarugas dos Galápagos

Ligazóns externas

• Naked Scientists audio discussion of Lonesome George
• Article on Lonesome George The giant tortoise of Galapagos Island.
• Lonesome George, by Vicki Seal
• "Team of Veterinarians Prepare Hybrid Tortoises for Release on Pinta Island in 2010" (Nota de prensa). Galapagos Conservancy. February 3, 2010. Arquivado dende o orixinal o February 8, 2010. 
• Garrick, Ryan C.; Benavides, Edgar; Russello, Michael A.; Gibbs, James P.; et al. (2012). "Genetic rediscovery of an 'extinct' Galápagos giant tortoise species". Current Biology 22 (1): R10–1. PMID 22240469. doi:10.1016/j.cub.2011.12.004.