Aldabrachelys gigantea hololissa
Giant tortoises are among the longest-lived animals on the planet. Some individual Aldabra giant tortoises are thought to be over 200 years of age, but this is difficult to verify because they tend to outlive their human observers. Adwaita was reputedly one of four brought by British seamen from the Seychelles Islands as gifts to Robert Clive of the British East India Company in the 18th century, and came to Calcutta Zoo in 1875. At his death in March 2006 at the Kolkata (formerly Calcutta) Zoo in India, Adwaita is reputed to have reached the longest ever measured life span of 255 years (birth year 1750). Today, Jonathan, a -year-old, Saint Helena-dwelling Seychelles giant tortoise, is thought to be the oldest living terrestrial animal on Earth since the 2006 death of Harriet; a 176 year old Galapagos giant tortoise who lived at Australia Zoo. Coming in second to Jonathan is Esmeralda, at years old. Esmeralda is an Aldabra giant tortoise that lives in the Galapagos Islands.
Alcedo Volcano
In a 2003 study of the subspecies of Galapagos tortoise on Alcedo, "Geochelone nigra vandenburghi" the genetic diversity was shown to be much lower than would be expected in a population of its size, currently estimated to be approximately 4000. The Alcedo tortoise has the largest wild populations in the Galapagos Islands, however, the genetic diversity was 3-5 times less than that of other sub species of Galapagos tortoise. This low diversity is believed to be caused by a massive reduction in the population approximately 100,000 years ago. The reduction in population to only a few individuals is believed to have been caused by a large eruption of Alcedo volcano. The Alcedo tortoise has managed to rebuild its population since that time. Since the islands discovery by man it has come under new pressure, as have other Galapagos tortoises. They were hunted by early sailors to the islands as tortoises provided a food source on subsequent voyages. The introduction of non-native species also affected the habitat of the tortoise and other fauna and flora on Alcedo.