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WonderCave evolution fact

The 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.

Mexican tetra

EvolutionBiologyScience

The story behind the card

About 30 cave populations are known in a limestone region of San Luis Potosí and southern Tamaulipas in north-eastern Mexico, while their eyed relatives still live in rivers nearby. Genetic studies suggest the caves were entered at least five separate times, and that the cave forms are recent, less than about 20,000 years old. When fish from two different caves are crossed, some offspring can see, a sign that eye loss happened partly through different genes. Cave life brought other changes too: taste buds all over the head, a very sensitive lateral line (the row of pressure sensors along a fish's side), and bodies that store about four times more energy as fat, which helps them survive long gaps between meals.

Türkçe oku
Küçük bir nehir balığı olan Meksika tetrası mağaralara birkaç kez yerleşti. Her mağarada balıkların gözleri küçüldü ya da tamamen kayboldu, renkleri de uçtu; biyologlar böylece aynı deneyin doğada kendiliğinden tekrarlandığı örnekler buldu.

Kuzeydoğu Meksika'da, San Luis Potosí ile Tamaulipas'ın güneyindeki kireçtaşı bölgesinde yaklaşık 30 mağara topluluğu bilinir; gözlü akrabaları ise hâlâ yakındaki nehirlerde yaşar. Genetik çalışmalar, mağaralara en az beş ayrı kez girildiğini ve mağara biçimlerinin yeni olduğunu, 20 bin yıldan genç olduğunu düşündürüyor. İki ayrı mağaranın balıkları çiftleştirildiğinde yavruların bir kısmı görebiliyor; bu da gözlerin kısmen farklı genler yoluyla kaybolduğunu gösteriyor. Mağara hayatı başka değişiklikler de getirdi: başın her yanına yayılmış tat tomurcukları, balığın iki yanı boyunca uzanan basınç algılayıcıları dizisi olan yanal çizginin çok duyarlı hâle gelmesi ve normalin dört katı kadar enerjiyi yağ olarak depolayan bir beden. Bu yağ, uzun açlık dönemlerini atlatmalarını sağlar.

Sources and further reading

Background reading: Mexican tetra
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