More support for my hypothesis that introns facilitate the evolution of metazoans from: Kim E, Magen A, Ast G. 2007. Different levels of alternative splicing among eukaryotes. Nucleic Acids Research 35:125-131.
Here, the researchers compared levels of alternative splicing in eight different organisms: human, mouse, rat, chicken, sea squirt, fruit fly, worm, and plant. Here is a figure from their paper that reports the core finding:
And here are a couple of key excerpts:
In this study we compare the level of alternative splicing among eight different organisms. By employing an EST independent approach we reveal that the percentage of genes and exons undergoing alternative splicing is higher in vertebrates compared with invertebrates.
The difference in the level of alternative splicing suggests that alternative splicing may contribute greatly to the mammal higher level of phenotypic complexity, and that accumulation of introns confers an evolutionary advantage as it allows increasing the number of alternative splicing forms.