Evolutionary history of free-swimming and sessile lifestyles in urochordates as deduced from 18S rDNA molecular phylogeny
Open Access
- 1 September 1998
- journal article
- research article
- Published by Oxford University Press (OUP) in Molecular Biology and Evolution
- Vol. 15 (9) , 1189-1194
- https://doi.org/10.1093/oxfordjournals.molbev.a026026
Abstract
Whether the ancestral chordates were free-swimming or sessile is a longstanding question that remains to be settled. Vertebrates and amphioxi are free-swimming, but the most basal chordate subphylum (the urochordates) includes both sessile and free-swimming species. Here, 1 report molecular phylogenetic analyses of 18S rDNA of urochordates to deduce which lifestyle is ancestral. This revealed a close relationship between salps and doliolids and paraphyly of the ascidians. An early divergence of larvaceans, which show a tadpole-like body plan throughout life, is also supported by the analyses. Based on this phylogeny, a free-swimming ancestor for chordates is more parsimonious than a sessile ancestor. The evolutionary history of various lifestyles of chordates from this ancestral form is proposed.Keywords
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