Might be a good idea to draft long comments locally, then cut & paste to comment posting site. Sorry about your comments.

Thos are some very interesting alternative explanations. I am really quite new to endosymbiosis, so I cannot provide a good critique of yours vs. Moustafa’s suggestions. To be fair, I don’t think Moustafa, nor I ever suggested these were separate events: just that the green one may have occurred earlier, as you suggested with tertiary endosymbiosis. (Well, first there was red, then temporary green, then red only again: so temporary green did occur earlier than *current* red).

But since I actually bothered to dig out the relevant citations, in pt form:

– chromalveolate hypothesis – common red algal plastid origin for stramenopiles (incl diatoms), alveolates and ‘crhaptophytes’. Even if not true, still most parsimonious to assume common origin for ochrophyte plastid, especially since some of the non-photosynthetic basal stramenopiles have evidence of plastids in their past. This common endosymbiosis. was red; green makes no sense. Separate endosymbiosis for diatom original plastid would be unparsimonious…

(for good review + diagram of plastid endosymbioses in euk history: Keeling 2004 Am J Bot)

- karlodinium (dinoflagellate) had tertiary endosymb with haptophyte; thereby having hapto plastid. It lost original plastid, but interestingly the new plastid-targetting genes are chimeric, mixed dino and hapto origin. (Patron, Waller & Keeling 2006 J Mol Biol)

-> perhaps in diatoms something similar happened, but in reverse: original plastid red algal, then temporary green algal tert. endosymbiont w partial gene transfer, then loss of green plastid?

Could be BS though, as I’m not a molecular biologist… >_>

Glad to see someone else write stuff about protists!

Cheers,

-Psi-

(hopefully this thing won’t eat my comment this time…not at this insane hour of the night anyway… grr!)