An end at the beginning: the tale of the Galápagos Tortoises

The Galápagos Islands

Most who know of the name “Darwin” will be familiar with the Galápagos. These relatively

uninviting islands protrude harsh, crashing waves like spears of mountainous rock, formed

through millions of years of fierce volcanic activity. Even Charles Darwin himself thought

life could not be sustained in such a remote and harsh environment, writing in his 1835

Journal of Researches:

Little did the 22-year-old university graduate know at the time, these rugged islands would spark the most pivotal and influential theory in the field of modern biology.

Due to the Hawaiian archipelago’s unique volcanic origins, the cluster of islands have grown jagged and fractured, with some islands showcasing altitudes as low as a few meters above sea level to others flexing spaces over 5000 feet above sea level. These extremely diverse habitats enable the observation of vastly different sub-populations of the same (or closely related) species*, exhibiting differing adaptations to their unique environments. These morphological distinctions lead to Darwin’s infamous 1859 book ‘On the Origin of Species’, detailing his evidence for the theories of evolution. 

*This article may refer to the Galápagos Tortoises as different subspecies or species

interchanagably, as this remains a contentious area.

The giant tortoises

One most apparent examples of evolution that Darwin noted were the Galapagos tortoises, Chelonoidis niger, of which there were at least  15 subspecies. Darwin devoted almost four pages of his Journal of Researches to the Galapagos tortoise, more than he did to any other Galápagos species. These captivating reptiles can grow up to 5 feet in length and weigh over 220kg, making them the largest tortoises in the world. This miraculous species can survive over a year without food or water, able to store tremendous volumes of liquid in their bladders in periods of drought - one of the many adaptive characteristics that enable them to routinely live well over 150-years-old.

Darwin notably observed the species’ two unique primary shell morphologies - saddleback

and domed. Some subspecies, such as the Pinta Island Tortoise (Chelonoidis niger

abingdonii), have saddle-shaped shells which raise at the front, making it easier for the neck to stretch upwards to feed on taller vegetation on hotter, more arid islands. Whereas the populations with the dome-shaped shells, including the Chelonoidis niger porteri, occupy islands where there’s an abundance of flora lower to the ground, making upward stretching of the neck unnecessary to feed. Features such as these are well documented in Darwin’s evidence for evolutionary adaptation throughout the islands. 

Torment and tragedy

Only two centuries ago, the Galápagos Islands were rife with life, with an estimated 250,000 giant tortoises. Today, multiple species are extinct, with only around 10% of the individuals surviving. The dramatic decline of the Galápagos tortoises has been characterised by frequent human failure, and in some instances, human design. 

Between the 1790s and 1800s, whalers began operating around the Galápagos, routinely

taking long voyages to explore the Pacific Ocean. With whaling voyages lasting about a year, the tortoises were selected as the primary source of fresh meat for the whalers, with each taking 200 to 300 tortoises aboard. Here, in a ship’s hold, the hundreds of tortoises would live without food or water for months, before being killed and consumed. Documentation regarding how many tortoises were taken aboard by whalers is scarce, however estimates place the number between 100,000 and 200,000 by 700 whaling ships between 1800 and 1870. 

This initial decimation via over-consumption was then followed by the introduction of

harmful invasive species. In the years since, multiple foreign species have been introduced to the archipelago, mainly for farming, including pigs (a lot of which are feral), dogs, cats, rats, goats and donkeys. These non-native species are an enduring threat to the giant tortoise populations, preying on their eggs and hatchings, whilst also providing fierce and unprecedented competition for food. 

Furthermore, increasing temperatures attributed to climate change are thought to trigger

atypical migrations. These migrations have the potential to reduce tortoise nesting success, further adding to the list of threats these species have had to endure.

The Pinta giant tortoise, Chelonoidis nigra abingdonii, a species of the unique saddleback shell variety, was thought to be extinct since the early 20th century. But then, in 1971, József Vágvölgyi, a Hungarian scientist on Pinta island made a special discovery – Lonesome George. Seemingly a sole survivor of his kind, Lonesome George became an icon of the sparking conservation movement surrounding the Galápagos species. This lone Pinta individual could have been wandering the small island for decades in search for another member of his species - a search that would unfortunately never bear fruit. Despite selective breeding efforts, on June 24, 2012, at 8:00 A.M. local time, Lonesome George would pass away without producing any offspring, found by park ranger Fausto Llerena who had looked after him for forty years.

Hope and the future

Despite all the devastation the Galápagos tortoises have endured, not is all lost. Just like the story of Lonesome George, a microcosm of this larger crisis, there is a small light at the end of the tunnel. Just prior to George’s passing a remarkable discovery was made. During 2008, research conducted by the Ecology and Evolutionary Biology Department of Yale University on neighbouring Isabela Island, set out to genetically sequence the local giant tortoise population. Over 1,600 tortoises were tagged and sampled for their DNA, with analyses revealing an astonishing number of tortoises with mixed genetic ancestry. Within this sample, 17 individuals contained DNA from the Pinta tortoise species (and more contained DNA from the also extinct Floreana species). Retrospective study of old whaling logbooks seems to indicate that, in order to lighten the burden of their ships, whalers and pirates dropped large numbers of tortoises in Banks Bay, near Volcano Wolf, Isabela Island, likely accounting for these hybrids. This miracle discovery opens the door to selective breeding efforts, pathing a future of reintroduction of the previously-extinct Pinta Island species. 

While only a fraction of their original numbers remain, the Galápagos tortoises continue to

personify evolution’s stunning intricacies and persist as a bright beacon of hope for the

greater world of conservation. It is vital that we do our part as human beings to correct the

errors of our past and to respect and nurture these gentle giants and all that they represent in this world we call home.

Written by Theo Joe Andreas Emberson

Related articles: Conservation of marine iguanas / 55 years of vicuna conservation / Conserving the Californian condor

REFERENCES

Sulloway FJ. Tantalizing tortoises and the Darwin-Galápagos legend. J Hist Biol.

2009;42(1):3-31. doi:10.1007/s10739-008-9173-9

Patrick J. Endres. AlaskaPhotoGraphics.com