Observations that obligatory imply the presence of another species

I would be curious to hear some thoughts on this: An observation of one species that inherently implies the presence of another species - when I think about this complex, there seems no simple rule to when it makes sense and when it does not make sense to record both species. I think for lichen it is rather simple and easy to say, that these kinds of observations just cause redundancy, and might not be “false”, since for specific mycobionts a special photobiont is implied, but at the same time could be considered “unnecessary”, since there is no additional information. But since it also is not false, it might make sense to still collect these kinds of observations, depending on your objective of using inaturalist. Is recording the observation of the Dinocampus coccinellae paralysis virus also a redundancy or not - the wasp Dinocampus coccinellae can not complete its lifecycle without it, (if I understand it correctly @jameskdouch ). When it comes to wheat is possible to record with the help of which “tool” (one could use a microscope) , it does not make the discussion easier, it just adds another level of complexity. I think generally using different tools can clarify a symbiosis in case you are not sure if the symbiosis really is an obligatory one, but if one observation really implies the other species, I do not know if we have to “make it visible”, in the case that the observation of the context (the other species, or traces of something) already implies the presence of a second species for sure. If this is possible I would rather use the non-invasive method if I am doing work in environmental education, while for a research project, I want to make sure that I double-check the species, so I make sure that I collect the specimen (e.g. in case of the obligatory connection between the two species being not as obligatory as people thought and has to be revised in the future).

(Background of these thoughts is the discussion about photosymbionts of lichen here: https://www.inaturalist.org/observations/154762568#activity_comment_f22ba371-a1eb-4bb2-80f2-5e343f41c71f and here https://www.inaturalist.org/observations/154762374#activity_comment_f4a4c138-eafe-4858-a6a1-9d37d3f72b58)

In some cases, it’s probably just up to the observer whether they want to make a duplicate observation for the other symbiont/host species or not - some might want to take the time, some might not.

I think that in terms of any researcher who wants to use iNat data, if there is an obligate relationship, they would know enough to search for both species. So I don’t think that not creating an observation for both species would have a major cost. This would almost certainly be the case with lichens.

A couple other thoughts:

If any observation doesn’t have any photographic evidence of the “other” obligate species (like just microphotos of one species), it might not be ideal to make an observation of it if it could cause weird CV-training issues.

More broadly, while we might think that some species are obligates, that isn’t always the case! Someone might discover a new host/symbiont, but, if we just assume the presence of the known host/symbiont based on the presence of the first species, we could completely miss this discovery. It’s a fairly rare scenario, but one reason why it might be good to not always assume the presence of another species.


I’d say record what you can see and don’t make assumptions about what you can’t. So many times DNA work shows that systems we’d thought were simple are much more complex, so what was one species is now many. You risk introducing errors into the data set if you assume we know what’s going on in these cases.


Posting observation for both species is valuable and a specific object of interest for various projects, like this one.

I see a lot of observations displaying the CV icon for Hornworm Parasitoid Wasp Bracovirus (Cotesia congregata bracovirus) from new(-ish) users. Almost undoubtedly, they are actually interested in the ID of either the caterpillar or the wasp cocoons.

But I may do a series of three observations: one each for the caterpillar, the wasp, and the virus (generally 1st time only). I do this mostly so I can reference iNat for the name of the virus when I can’t think of it off the top of my head.

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In the cases of parasitic plants that are species-specific (they have just one known host).
Few examples: Orobanche artemisiae-campestris-Artemisia campestris; Orobanche picridis-Picris hieracioides; Phelipanche lavandulacea-Bituminaria bituminosa. .

Where there is Azolla (a floating fern) there is Anabena living in pockets in the fern. I wouldn’t post the Anabena, though, unless I squeezed some out and used a microscope. Which I have done.

If the relationship is obligate, researchers can find both members of the relationship without our posting the two separately. I’d say, post only what you can post photos for.


Speaking of specific plant parasites…now I’m wondering if I should duplicate some of my gall observations to create observations for the host plant.

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If you look through viruses, you will see a lot of pictures of the “Gold Dust” Japanese aucuba identified as Genus Badnavirus. So many, in fact, that I have been told that the CV identifies such pictures as the virus rather than the plant. And while it is true that the"Gold Dust" effect that makes this tree popular in horticulture is, indeed, a symptom of viral infection, some of the comments on such observations have questioned whether it is at all useful to observe so heavily a virus that after all has a range essentially exactly matching the cultivation of an ornamental plant. When have you ever seen a cultivated Japanese aucuba that wasn’t the “Gold Dust” (infected) variety?

This is certainly never a bad idea, and interesting, too, to see which gall-formers are more generalistic and which ones more specific. But it makes sense to have the host-observation in mind already when you look at the gall, so that you can make sure to take a photo of the essential traits of the host.

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Some mycorrhizal fungi are partner-specific.

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