On the day I conceived this article, I was shocked to receive news that the "Darwin Arch" had collapsed due to the erosion of perennial waves. As a famous landmark of the Galapagos Islands, the arch named Darwin witnessed the birth of the theory of evolution here and the spread of species extinction here. The Galapagos tortoise is perhaps the most widely known species in the Galapagos Islands. Coincidentally, on a small island in the Indian Ocean thousands of miles away, there is also a group of giants of the turtles, the Aldabra tortoise.
The former genus name Dipochelys of the Aldabra tortoise means "giant tortoise" is not enough, and the species name gigantea also means "great shore, huge". Indeed, as a male with an average shell length of up to 120 centimeters and an average weight of more than 250 kilograms, the huge body of the Aldabra tortoise gave people a huge visual impact at that time.
Aldabra tortoise | Xjschx / Wikimedia Commons
<h1 class="pgc-h-arrow-right" data-track="6" > Why are tortoises so big? </h1>
Everyone understands the truth, but why is the Aldabra tortoise so big? This brings us to a controversial concept – the "island effect". In 1964, a biologist named J. Bristol Foster published a paper proposing that small animals tend to evolve into larger sizes after settling on islands, a corollary known to posterity as the "island effect" or "Foster's law."
Is the sheer size of the Aldabra tortoise also a consequence of the law of the islands? Molecular biology studies have found that the closest thing to this taxa of aldabra tortoises is a group of cobwebs distributed in Madagascar, a small tortoise with a shell length of no more than 15 centimeters.
These small tortoises entering desert islands rapidly grow in size in the absence of competition and predators, and their larger bodies allow them to cope with harsher and more unstable island climates, while obtaining a wider source of food, which is undoubtedly very beneficial on isolated islands with relatively poor food. The ancestors of the Aldabra tortoises grazed on the island carefreely, bred and even learned to swarm in caves to avoid the harsh weather until they became the behemoths they are today.
Jonathan, the Aldabra tortoise, the longest-living land vertebrate, was born in 1832 and is still alive | Xben911 / Wikimedia Commons
However, megascaling is not endless, mega-engineering is often limited by environmental constraints such as food climate, and when a certain equilibrium threshold is reached, mega-scaling tends to stagnate, which is why, despite the huge size of the Aldabra tortoise, it is still inferior to many large animals on the continent.
Interestingly, animals entering the island are not all mega,000, and when large animals such as elephants, tigers, and even humans enter the island from the rich continent, instead of becoming larger, they appear "dwarfized". Smaller requires fewer resources such as food, shorter reproductive cycles and easier adaptations. In addition, mega-phylloscopy tends to take a relatively long time, while dwarfism undergoes major changes in morphology in just a few thousand years, and the two phenomena tend to exist in an island ecosystem at the same time.
Fossil skulls of Flores, a humanoid species that live on the island of Flores, are only 1.1 meters tall | Daderot / Wikimedia Commons
<h1 class="pgc-h-arrow-right" data-track="52" > super long standby, drifting the world</h1>
Since galapagos and Aldabra tortoises look so similar, are they close relatives? Judging from the results of molecular evolution, both types of tortoises originated independently in the archipelago, and their kinship is roughly equivalent to that of our Homo sapiens and Australopithecus australis. The reason for such a similar morphology is precisely because the climate and other environmental factors in the archipelagos (Galapagos and Seychelles) in which the two types of tortoises live are very similar, and biology calls this phenomenon convergent evolution.
Interestingly, the Galapagos tortoise on an arid island, with the front half of its back upturned like a saddle, has become more slender in limbs and necks, able to eat higher vegetation like a giraffe and get more food in harsh environments. In the Seychelles Archipelago, thousands of miles away, Seychelles tortoises, which live on drier islands, have also evolved saddle-shaped dorsal carapace. Originally not a class, but a and b with certain kinship, after further evolution, similar appearances aa and bb appeared, this phenomenon is called parallel evolution.
Saddle-backed Galapagos tortoise, note its upturned shell and long neck | Paul Krawczuk / Flickr
How did the ancestors of these giant turtles come to the isolated island? Although long-term land evolution has made tortoises less adept at swimming, this does not mean that aldabra tortoises are dry ducks. On the one hand, the tortoise's wide back armor can provide enough buoyancy to drift along the waves for a long time, and even stick its head out of the water to eat; on the other hand, the tortoise has super endurance and can "standby" for 6 months or even longer without fresh water. Coupled with the lifespan of giant tortoises of hundreds of years, it laid a solid foundation for this strange way of drifting and spreading, so that there are all kinds of behemoths in the Galapagos and Seychelles Islands today.
<h1 class="pgc-h-arrow-right" data-track="53" > victim of human appetite</h1>
Large size, long lifespan, and less difficult reproduction mean that tortoises can do whatever they want on the archipelago? However, the truth is very cruel, many species of giant tortoises have slid into the abyss of extinction, almost all of which are due to human activities that have destroyed the fragile ecological balance of the island.
Before the Age of Discovery, there were 18 species of giant tortoises, including the Aldabra tortoise, living on small islands in the Western Indian Ocean and in madagascar. But European navigators found that giant tortoises not only provide a lot of fresh meat, but also survive for a long time without feeding, and their back armor can also be used as a container, which is an ideal meat supply, and people call them live cans. Thus, in the 16th and 19th centuries, every ship passing through islands in the Indian Ocean was loaded with a large number of giant turtles (in 1842, a fleet of ships loaded 1200 giant turtles at a time, and Darwin also captured tortoises on the island of Canada as food supplies for the Beagle), and only a small part of these giant turtles were brought to captivity around the world, and most of them were reduced to human rations.
In 1776, a Hololissa subspecies Adabra tortoise was given to a Mauritian military camp by the French explorer Marion de Fresne, where it lived for 118 years | Wikimedia Commons
The tortoise colony in the Seychelles archipelago is left with only the last remnants of al-Idabra Atoll. It is not that the human hands are merciful, but because there is no fresh water in The Aldabra Atoll, humans will not come here to replenish the supply. The Seychelles giant turtle and the Seychelles saddleback turtle, which were later discovered, are descendants of captive individuals scattered around the world, and the wild population has long been extinct.
Adabra tortoise stamp from Seychelles | Wikimedia Commons
Today, due to proper protection, the number of tortoises on Aldabra Atoll has reached more than 100,000, which can be said to be a temporary escape from the haze of extinction. The giant tortoises scattered around the world also continue in their respective villages, no longer have to worry about the fate of food one day, and some of these artificially bred individuals will circulate between trade channels of various countries.
However, it should be noted that the Aldabra tortoise belongs to the species of Appendix II of the Washington Convention, which is prohibited by individuals according to The laws of our country, and the institution needs relevant procedures and legal domestication certificates. Due to the huge size and food intake of the Aldabra tortoise, most families cannot meet the conditions for raising it, so abandonment or even poor care has led to the death of the tortoise. If you really love it, let it live happily in your homeland, and don't bring home the greed that humanity has endured for centuries.
Although it looks cute, please do not imitate this behavior | Chuckupd / Wikimedia Commons
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