Oh, that's neat

...huh.

What puzzles me is what would drive the radical growth/compression of a genome

usually we think of evolutionary genetics being very gradual changes, but doubling or tripling the length or more (or reducing it by the same amount) implies to me either a very different mode of mutation, or something very strange about their transcription method that it's prone to either adding or excising large segments from one generation to another

in particular, I guess there may be a (modest) preference toward shorter genomes--all else being equal, a shorter genome presumably implies faster cell division and thus (marginally) faster gestation which I guess is a (very small) survival advantage, but unless they shed hundreds of thousands of base pairs all at once it would be a really tiny difference...

...and I can't think of any survival advantage in a longer genome.

especially not like 2-3 times longer, that's very weird, especially since it sounds like they're many repeating intron sequences, which... as far as my limited understanding of genetics, that's like flicking a genetic switch on and off and on and off???

I guess it could be like a really clunky way to deliberately slow down some stages of gestation for some reason...?

hrm... with a little background reading it seems that some kinds of environmental shocks can cause polyploidy (production of more than two chromosome sets) by throwing off the normal process of cell division, so I wonder if it might be something like that...