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: