Why must I spoil the plot by peeking into advance online publications instead of waiting for the damn issue to come out, like normal people do? Especially with an 8am class coming up so soon...
Anyway, apparently Ceratium ranipes, a photosynthetic dinoflagellate, decided to grow plastid-stuffed 'fingers' during daylight:
(Pizay et al. 2009 Protist, in press; light period)
And retracts them back in for the night:
(Pizay et al. 2009 Protist, in press; dark period)
In case you're not convinced these are the same organism:
(Pizay et al. 2009 Protist, in press; sequence from a single individual removed from light, T measures minutes of darkness) (a video of that would be so awesome...!)
Chloroplasts fluoresce red when hit by UV light (see my own example with a diatom); take a look at those fingers:
(Pizay et al. 2009 Protist, in press. Left: formalin-preserved C.ranipes with a daytime morphology; the inset shows UV autofluorescense of the plastids: note their concentration in the 'fingers'. The bluish/whitish subinset shows Calcofluor White staining, which indicates the presence of thecal plates on the fingers. Right: transitional morphology at the end of the day: note how the plastids migrated inwards away from the fingers.)
This raises some cell biology-related questions: how is plastid movement coordinated and regulated? What does the genetic developmental pathway look like for those fingers, and how does it interact with whatever immediately respond to light? More importantly, why does this thing seemingly waste its time growing and retracting fingers, when it could have just kept them protruded during dark hours?
Could be just a low cost glitch in the system, or perhaps there is something to it. After all, perhaps it wouldn't take much to lose the finger retraction ability - so is there some cost when that happens, thereby keeping this process going? Sinking may have something to do with it - many planktonic algae sink for the night and float back up during the day. Fingers may drastically slow down the sinking speed. However, there's no data yet showing any vertical migration in C.ranipes (Pizay et al. 2009 Protist). Could be a relic from an ancestor that did sink, but then why hasn't this behaviour been found earlier, and in more dinos?
Another idea in the same paper is that the fingers get in the way of directed swimming; during daylight hours, you sacrifice your swimming ability for a larger photosynthetic capacity, but it may be advantageous to put away the tackle in the absense of light.
This reminds me of two things: 1) plant leaves - increasing the surface area exposed to surroundings for gas exchange, as well as the area exposed to light. Sort of a convergence. 2) Many 'radiolaria' have algal symbionts they use for photosynthesis, and they too spread them out towards the tips of the host's filopodia during daytime, and retract them inwards for the night. So whatever you do, don't dangle your plastids in plain view when they're not in use.
Pizay, M., Lemée, R., Simon, N., Cras, A., Laugier, J., & Dolan, J. (2009). Night and Day Morphologies in a Planktonic Dinoflagellate Protist DOI: 10.1016/j.protis.2009.04.003