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WonderAnimal origins fact

The closest living relatives of animals are single-celled organisms called choanoflagellates. Their cells look strikingly like certain cells in sponges, and they offer clues to how the first animals evolved from single cells.

Choanoflagellate

BiologyEvolutionScience

The story behind the card

A choanoflagellate beats a single whip-like tail, a flagellum, to draw water through a collar of tiny finger-like projections that trap bacteria to eat. Choanoflagellates are not our ancestors but a sister lineage that split from the animal line hundreds of millions of years ago. Their genomes, first sequenced in 2008, contain genes for proteins such as cadherins, which animals use to stick cells together, and tyrosine kinases, which pass signals between cells. One species, Salpingoeca rosetta, can switch from living alone to forming small rosette-shaped colonies, and in 2012 Nicole King's laboratory at the University of California, Berkeley, found that a molecule released by a particular bacterium triggers the switch.

Türkçe oku
Hayvanların yaşayan en yakın akrabaları, koanoflagellat denen tek hücreli canlılardır. Hücreleri süngerlerdeki bazı hücrelere çarpıcı biçimde benzer ve ilk hayvanların tek hücreli canlılardan nasıl evrildiğine dair ipuçları verir.

Koanoflagellatlar, kamçı denen tek bir ince uzantıyı çırparak suyu, parmak gibi minik çıkıntılardan oluşan bir yakanın içinden geçirir; yakada takılan bakteriler besinleri olur. Bizim atamız değil, hayvan soyundan yüz milyonlarca yıl önce ayrılmış kardeş bir soydur. İlk kez 2008'de okunan genomlarında, hayvanların hücreleri birbirine yapıştırmak için kullandığı kaderinlerin ve hücreler arasında sinyal taşıyan tirozin kinazların genleri bulunur. Salpingoeca rosetta adlı tür, tek başına yaşamaktan küçük, gül biçimli koloniler kurmaya geçebilir. Kaliforniya Üniversitesi Berkeley'den Nicole King'in laboratuvarı 2012'de bu geçişi belirli bir bakterinin salgıladığı bir molekülün tetiklediğini buldu.

Sources and further reading

Background reading: Choanoflagellate
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