Incredible cross-sea species migration

Today, the ancestors of wild bactrian camels in the desert of Central Asia came from North America, while Australian marsupials arrived there from America through the South Pole. This kind of animal migration is not difficult to understand. After all, there are land links between Asia and North America, the United States and Australia. However, some animals without the ability to fly can cross the vast ocean and reach distant islands. How did they do it?

Great migration of species

In the East Pacific Ocean, about 1000 km from the South American continent, there is a volcanic archipelago with an area of 7,500 square kilometers. Because of its diverse climate and long-term isolation, it has become a paradise for animal and plant reproduction. Today, there are about 700 species of higher plants inhabiting this archipelago, 40% of which are endemic to this area. There are more than 80 species of birds and many unique large reptiles, such as terrestrial iguanas and Galapagos tortoises. This island is the Cologne Islands. The amazing diversity of Darwin's finches in the Cologne Islands even inspired Darwin and made a "contribution" to his theory of natural selection.

However, even this archipelago, which is famous for its species diversity, was a lifeless barren land when it was just formed. About100000 to 5 million years ago, the Cologne Islands "surfaced" for the first time, about 600 kilometers from Ecuador, in the middle of the Pacific Ocean. This means that at the beginning, this volcanic archipelago exposed to water was completely free of plants and animals. Now all plants and animals on the island must be "immigrants". However, how can they cross the sea of 600 kilometers?

Low-grade spore plants such as ferns, mosses, lichens and spores, as well as feathery and lighter seeds such as Taraxaceae can reach the island by wind, and small animals such as snails and bats can also reach the island by wind. Marine animals such as sea lions, turtles and penguins can swim to this sunny island by means of ocean currents.

But some land reptiles on the island, such as giant turtles, are land animals and can't swim at all. It is incredible that they can colonize this remote island. Seabirds can fly to this island easily, but terrestrial birds with weak flying ability can't. However, now 80% of the birds on this island are terrestrial birds.

The mysterious migration of land reptiles across the sea is not only in the Cologne Islands. Today, Madagascar is famous for its unique lemurs, and there are more than 60 species of lemurs living here. This primate has eyes like foxes, tails like raccoons and walks like cats. It is very cute.

Although lemurs are endemic to Madagascar, their ancestors were actually African immigrants. DNA shows that they came to Madagascar from Africa about 60 million years ago. However, Madagascar was separated from the African continent about 65438+600 million years ago. How did the ancestors of lemurs cross mozambique channel? Other Malagasy animals whose ancestral home is in Africa, such as the island hedgehog, have also crossed mozambique channel in some way.

Flood sweeping theory

There are many explanations for this seemingly impossible animal migration. The most common is the theory of flood sweeping. People who hold this view believe that when there is a flood in the habitat of these animals, the flood will uproot the trees and vegetation along the coast. Animals also washed away by the flood, if they are lucky enough to "ride" on these floating objects on the water surface and can endure the state of no water and no food for a long time, may use ocean currents to go to a new island.

Although it is unlikely that this form will successfully colonize the island, there are indeed such examples in real life.

1In September 1995, Gua Derippe Island in the eastern Caribbean was hit by two hurricanes. Less than two weeks after Hurricane Marilyn, Hurricane Louis appeared again. The double attack flooded the habitat of the island's unique green iguana. After the storm, researchers found that there were 15 green iguanas among the uprooted trees floating in the sea. Green iguanas are cold-blooded reptiles. They can get heat from sunlight, so they don't need much food. Rainfall can provide them with drinking water. Therefore, although they drifted for three weeks, these green iguanas drifted safely to Anguilla 200 meters away with the floating vegetation and began to breed there within two years. There were no green iguanas in Anguilla before.

There is more than one way.

Although the example of green iguana drifting once again confirms the correctness of the flood sweeping theory. However, this view does not explain everything. In particular, animals must live near the coast to be swept away by the flood. So, how did inland animals get caught in the sea and drift to the new island?

On La Palma Island at the northwest end of the Canary Islands in Spain, there is a weevil. This beetle has a long nose and mouth, like the elephant trunk in the zoo, hence its name. However, this nose is actually the mouth of an insect.

The weevil has average flying ability and feeds on plants. After testing the DNA of the weevil in La Palma Island, the researchers found that the DNA of these weevils is almost the same as that of the weevil in Tenerife Island, especially in the northern port of Sol, Delacruz. Tenerife Island is 0/20km away from La Palma Island/Kloc. More importantly, weevils live in the port of Sol, Delacruz at an altitude of more than 700 meters. It is obviously impossible for weevils to reach La Palma from Tenerife because they were involved in the flood. How did they cross the ocean?

Recently, Spanish researchers put forward a brand-new view: large-scale geological movements can promote this seemingly impossible trip. This geological movement is a landslide.

About 600 thousand years ago, a large-scale landslide occurred on the north coast of Tenerife Island. Within a few minutes, nearly 1.30 square meters of land on the north coast of Tenerife Island slipped into the Atlantic Ocean. Researchers speculate that this huge geological activity may lead hundreds of millions of plants, animals and invertebrates to start a difficult "migration" journey. Then, lucky animals, including weevils, passed through floating vegetation and followed the direction of ocean currents, and arrived at La Palma Island after 4~ 13 days.

Compared with floods that only allow a few animals to migrate, large-scale landslides can "migrate" more animals and plants at a time, improve their genetic diversity, and then improve the reproductive rate. It seems that landslide, a catastrophic event that is very terrible for human beings, can also help the earth achieve biodiversity.

This article is from the fifth issue of Great Science and Technology 20 17.