Marking buds in budding organisms
by jo.irisson translator, scientist
Questions were raised regarding whether to mark buds of doliolids and siphos (as new organisms). Let me try to explain my point of view here. I would welcome remarks from @jessicaluo, @cguigand and anyone else.
The definition of what is an "individual" is actually difficult for asexually reproducing organisms (such as doliolids) and even harder for colonial ones (such as siphos).
In the case of doliolids, the new organisms are just clones, they start growing out of the central stem and share "blood" with the rest of the buds connected to the stem. Actually, the "mother" individual (the big one) is not feeding anymore and just serves for propulsion. It's energy is provided by the small ones that feed. So they kind of live like a colony, with specialised individuals. When do these new buds become actual independent individuals? When they detach from the stem, their life does not change very much...
For siphos, it is even worse. What you see as "one" siphonophore, is actually a colony of "individuals" with very specialised roles. At some point, some some "individuals" grow into independent siphos. See http://blog.planktonportal.org/2014/01/22/tree-map-update-and-budding-siphonophores/ for more details by Jessica.
So, from a purely biological point of view, it would be difficult to define clear criteria on when to mark buds or not. From an ecological point of view, the role of these organisms in the ecosystem, in terms of the amount of food they consume, of carbon they fix, of food they can represent for others, of reproductive output, etc. depends quite strongly on their size. One small doliolid is not the same as one big doliolid. So the number of marks is not a direct predictor of the ecological significance of a group. The biomass would be. Once we have the marks from PP, we will post-process the frames and measure all organisms (you previously did this yourselves, for that very reason: size is important; we streamlined the process because we figured we could get that information after the fact quite reliably). So, as long as organisms are somewhat connected to each other, or close enough, we will detect them, and measure them, as one entity. So it is enough to mark the main part of the sipho or doliolid, because we will associate the area of the whole thing with this ID. Marking it several times may actually make our life difficult afterwards (we may count the same whole thing several times).
Of course the information that an organism is reproducing is important and interesting, but this is something we may extract from size (by looking at the largest ones in each category, which should not be that numerous). Plus, as I explained above, it would be quite difficult to define clear criteria on what to mark or not to mark exactly.
So, that's my point of view and the reason why I would recommend not marking buds in siphos or doliolids separately from the main part (of course if you only see the buds, put a mark on them --one mark-- as you would for any other partial organism). What do others think?
Thank you very much, Jean-Olivier. It really makes sense not to mark any buds. And it also makes sense not to mark both -house and larvacean- as long as the larvacean is inside the house but do mark both when the larvacean has escaped. Am I right?
by jo.irisson translator, scientist
Yes, for similar reasons. Larvaceans filter particles out of the water through their mucus house. When you see a larvacean free, out of its house, we know it will rebuild one within minutes. So larvaceans with or without house have a similar role (because a larvacean without house is a soon-to-be larvacean with house). The house itself, with no animal in it, is just an inert mass, sinking. It has a different ecological role.
by yshish moderator, translator
I've found nice diagrams of reproduction of Salps and Doliolids!
[Source in German] I bet the site is full of interesting stuff and useful information but I don't understand the language 😦
Here is a diagram of reproduction cycle at Rocket-ship Siphonophores for a comparison:
Hope you find it helpful and not confusing 😃