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WonderParallel evolution fact

Three-spined sticklebacks, small fish of northern seas, have moved into lakes and rivers again and again. Each time they tend to evolve lighter armour, often using a gene variant their sea-going ancestors already carried.

Three-spined stickleback

EvolutionBiologyScience

The story behind the card

Sea-going sticklebacks carry 30 to 40 bony plates along each side, protection against predatory fish; most freshwater populations have between none and a dozen. A single gene called Eda (ectodysplasin) largely decides how many plates grow, and the low-armour version survives at low frequency in sea populations, ready whenever fish settle in fresh water. The change can be fast. In 1982, Loberg Lake in Alaska was poisoned to clear it for trout and salmon, and sea-going sticklebacks recolonised it. In the twelve years from 1990, the fully armoured form fell from the whole population to about one fish in ten, while a low-plate form rose to three in four. Because thousands of lakes were colonised separately after the last ice age, the same change has happened independently again and again.

Türkçe oku
Kuzey denizlerinde yaşayan küçük üç dikenli dikence balıkları defalarca göllere ve nehirlere geçti. Her seferinde zırhları hafifledi; bunun için çoğu zaman denizdeki atalarının zaten taşıdığı bir gen varyantını kullandılar.

Denizde yaşayan dikence balıklarının her iki yanında, avcı balıklara karşı koruyan 30 ila 40 kemik plaka bulunur; tatlı su topluluklarının çoğunda ise hiç plaka yoktur ya da en fazla on iki kadardır. Kaç plaka çıkacağını büyük ölçüde Eda (ektodisplazin) adlı tek bir gen belirler. Az zırhlı varyant denizdeki topluluklarda da düşük oranda yaşamayı sürdürür ve balıklar tatlı suya geçtiğinde hazırda bekler. Değişim çok hızlı olabilir. Alaska'daki Loberg Gölü 1982'de alabalık ve somon yetiştirmek için zehirlenerek balıklardan arındırıldı, ardından göle denizden dikence balıkları geldi. 1990'dan sonraki on iki yılda tam zırhlı balıklar bütün topluluktan onda bire indi, az plakalı biçim ise dörtte üçe çıktı. Son buzul çağından sonra binlerce göle ayrı ayrı yerleşildiği için aynı değişim defalarca, birbirinden bağımsız olarak yaşandı.

Sources and further reading

Background reading: Three-spined stickleback
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