Ikigai Daily
Menu
WonderAdaptive radiation fact

Lake Victoria's cichlids, small and often colourful fish, split into more than 500 species with different jaws, colours and diets in only about 15,000 years. Much of the raw genetic material came from an ancient cross between two long-separated lineages.

Cichlid

EvolutionBiologyNatureScience

The story behind the card

Lake Victoria dried out almost completely about 17,000 years ago and refilled about 14,700 years ago, as the climate turned wetter. Its cichlids belong to a larger family group of more than 700 closely related species in the region's lakes, which scientists call the Lake Victoria superflock. A genetic study led by Joana Meier, published in 2017, found that the group descends from hybrids between two lineages that had long been apart, one from the upper Nile and one from the Congo basin. The mix gave natural selection a large stock of gene variants to work with as fish specialised in scraping algae, crushing snails, catching insects or hunting other fish. Since Nile perch were introduced to the lake in the 1950s, at least 200 of its cichlid species are thought to have died out.

Türkçe oku
Victoria Gölü'ndeki ciklet balıkları, yalnızca 15 bin yıl kadar bir sürede 500'ü aşkın türe ayrıldı; her birinin çenesi, rengi ve beslenme biçimi farklıdır. Bu çeşitliliğin genetik hammaddesi büyük ölçüde, uzun süre ayrı kalmış iki soyun çok eski bir melezleşmesinden geldi.

Victoria Gölü yaklaşık 17 bin yıl önce neredeyse tamamen kurudu ve iklim yağışlı hâle gelince 14.700 yıl kadar önce yeniden doldu. Gölün cikletleri, bölgedeki göllerde yaşayan ve birbirine çok yakın 700'ü aşkın türden oluşan daha geniş bir grubun parçasıdır; bilim insanları bu gruba “Victoria Gölü süper sürüsü” der. Joana Meier'in yönettiği ve 2017'de yayımlanan bir genetik çalışma, grubun uzun süre birbirinden ayrı kalmış iki soyun melezlerinden türediğini ortaya koydu: biri Yukarı Nil'den, öteki Kongo Havzası'ndan. Bu karışım, doğal seçilime geniş bir gen varyantı dağarcığı sağladı; balıklar da zamanla yosun kazımada, salyangoz kırmada, böcek yakalamada ya da başka balıkları avlamada uzmanlaştı. 1950'lerde göle Nil levreği bırakıldıktan sonra ciklet türlerinden en az 200'ünün yok olduğu düşünülüyor.

Sources and further reading

Background reading: Cichlid
Get the mobile appAbout our cards

Related cards

These cards share a subject or reading mode with the card above.

WonderEvolution

In Hawaii, silverswords, shrubs, cushion plants, vines and trees all descend from a single tarweed, a sticky plant of the daisy family from North America's Pacific coast, that reached the islands millions of years ago.

The ancestor belonged to the tarweeds, sticky, resinous relatives of sunflowers that grow along the Pacific coast of North America. DNA studies suggest it reached Kauaʻi about five million years ago, perhaps as a seed caught in a bird's feathers. With few competitors, its descendants spread into dry scrub, wet forest, bogs and bare lava fields, and today about 34 species in three genera make up what botanists call the silversword alliance. The best known, the silverswords themselves, form globes of silvery, sword-shaped leaves on the high volcanic slopes of Maui and Hawaiʻi Island; some species flower only once, sending up a tall stalk of flower heads before dying. Many members are now endangered, chiefly by grazing animals and invasive plants brought by people.

Silversword allianceRead card
WonderEvolution

Darwin's finches, more than a dozen bird species of the Galápagos Islands, all descend from a single ancestor. Their beaks range from thick nutcrackers for hard seeds to fine tweezers for insects, each suited to the food on its island.

Darwin collected some of these birds in 1835 during the voyage of HMS Beagle but did not realise at the time how closely related they were; the ornithologist John Gould pointed it out after the voyage. Today they are a textbook case of adaptive radiation, in which one ancestral species splits into many, each suited to a different way of life. Despite the name, they are not true finches but belong to the tanager family. Since 1973 Peter and Rosemary Grant have studied them on the small island of Daphne Major. After a severe drought in 1977 left mostly large, hard seeds, birds with bigger beaks survived better, and the next generation's beaks were measurably larger: evolution seen within a few years.

Darwin's finchesRead card
WonderNature

Welwitschia, a plant of the Namib Desert in Namibia and Angola, grows only two leaves in its whole life. They keep growing from their base for centuries, and some plants are thought to be more than a thousand years old.

The Austrian botanist Friedrich Welwitsch came across the plant in southern Angola in 1859; he wrote that he knelt and gazed at it, half afraid that touching it would prove it imaginary. It is a gymnosperm, like conifers, which means its seeds form in cones rather than inside fruit, and male and female cones grow on separate plants. Over the years the wind tears the two leaves into many ribbons, so an old plant looks like a heap of leaves. The Namib is one of the driest places on Earth. The leaves catch fog and dew, which drip onto shallow roots, although a 2019 study suggests that rain soaking into the ground is its main water source. The plant appears on Namibia's coat of arms.

WelwitschiaRead card
WonderNature

The kākāpō, a flightless, night-active parrot of New Zealand, courts with sound: in the rare years when it breeds, males dig shallow bowls in the ground and boom from them through the night, a deep call that can carry for more than a kilometre.

The kākāpō is the world's only flightless parrot and the heaviest, with males weighing up to about 4 kilograms. It once lived across New Zealand, but hunting and the dogs and rats brought by Polynesian settlers, then the cats, stoats and rats that came with Europeans, drove it close to extinction. Today every surviving bird has a name and lives on predator-free islands or in fenced sanctuaries, watched over by the Kākāpō Recovery programme. Females breed only in years when rimu and some other native trees produce a huge crop of fruit, known as masting, which comes every two to four years. In those seasons rangers check nests closely and sometimes raise chicks by hand.

KākāpōRead card
WonderNature

Rafflesia arnoldii lives almost entirely inside a tropical vine as a parasite, emerging briefly to produce a vast carrion-scented flower.

Rafflesia arnoldii grows in the rainforests of Sumatra and Borneo. It is named after Sir Stamford Raffles and the surgeon and naturalist Joseph Arnold, who recorded it in Sumatra in 1818; local people knew it long before. It is a holoparasite: it has no green tissue at all and takes all its water and food from its host, a Tetrastigma vine of the grape family, living as threads of cells inside the vine's stem. A bud swells for many months before opening into a flower up to about a metre across and weighing several kilograms, the largest single flower of any plant. Its smell of rotting meat draws the carrion flies that pollinate it, and the bloom lasts only about a week. Several Rafflesia species are threatened as forests are cleared.

Rafflesia arnoldiiRead card
Next card in the archiveThe Mexican tetra, a small river fish, has colonised caves several times, and cave after cave its populations have evolved tiny or missing eyes and lost their colour, giving biologists natural repeats of the same experiment.Read next →