Were vertebrates octoploid?

Abstract

It has long been suggested that gene and genome duplication play important roles in the evolution of organismal complexity. For example, work by Ohno proposed that two rounds of whole genome doubling (tetraploidy) occurred during the evolution of vertebrates: the extra genes permitting an increase in physiological and anatomical complexity. Several modifications of this 'two tetraploidies' hypothesis have been proposed, taking into account accumulating data, and there is wide acceptance of the basic scheme. In the past few years, however, several authors have raised doubts, citing lack of direct support or even evidence to the contrary. Here, we review the evidence for and against the occurrence of tetraploidies in early vertebrate evolution, and present a new compilation of molecular phylogenetic data for amphioxus. We argue that evidence in favour of tetraploidy, based primarily on genome and gene family analyses, is strong. Furthermore, we show that two observations used as evidence against genome duplication are in fact compatible with the hypothesis: but only if the genome doubling occurred by two closely spaced sequential rounds of autotetraploidy. We propose that early vertebrates passed through an autoautooctoploid phase in the evolution of their genomes.

Timing and mechanism of ancient vertebrate genome duplications – the adventure of a hypothesis

“…For example, in two closely spaced rounds of genome duplications, where the second round occurred before the diploidization of the first round is complete [11], the topology of the duplicates will not reflect the sequence of duplication. If the two rounds of duplications are the result of autopolyploidy then the grouping of duplicates on a phylogenetic tree will be random [71]. This happens because the duplicates are not well-resolved, which translates into a similar phylogenetic distance between them.…”

Chromosome inheritance in triploid Pacific oyster Crassostrea gigas Thunberg

“…Polyploidization has clearly occurred in some invertebrate and lower vertebrate taxa (White, 1978;Schultz, 1980;Komaru et al, 2000). It has been suggested recently that two rounds of genome duplication (or tetraploidization) have occurred during the evolution of vertebrates (Furlong and Holland, 2002;Spring, 2002). There is renewed interest in the biology and evolutionary significance of polyploid animals, which is poorly understood at this time.…”

Major events in the genome evolution of vertebrates: Paranome age and size differ considerably between ray-finned fishes and land vertebrates

“…Still others reject whole-genome duplications in vertebrates all together and only accept a continuous rate of gene duplication (10,11). As a consequence, the 2R hypothesis of vertebrate genome evolution is still vividly debated, and opinions range from strong belief (12)(13)(14) to strong skepticism (15)(16)(17).…”