Trophi in bdelloid rotifer carcass

[hans]

I have not yet found living rotifers but have seen quite a few things I suspected were dead rotifers. This is the first one with the trophi so clearly visible. Seems a bit small, 100 um by 80 um, perhaps shrunk after death? Trophi are 17 um long with 500 nm spacing between the finer teeth.

[75RR]

Nice detail of the trophi - don't think it is dead, most probably encysting

[hans]

Thanks 75RR, I think it was lucky, without any intentional preparation, to find one with the trophi pressed so close to and parallel with the cover glass and without too much diffusive material behind it to get good resolution and contrast. With all the other ones I have seen and suspected as rotifers, if they are deeper in the sample or angled slightly differently then I only occasionally see faint hints of fine structure that might be trophi passing through the focal plane as I scan up and down.

I had not even considered it might be encysted. I said carcass because I was thinking it looked like it was filled with green algae and/or cyanobacteria and not normal rotifer organs.

[Rapidray]

Great photo - and a really nice find.

[hans]

Thanks Rapidray.

I wonder, if there are encysted rotifers or eggs in this sample, what might help revive them? The sample has been indoors with some water added for three days now, and I added a couple grains of rice as suggested recently. I am seeing some new algae growth and more moving nematodes but not much other activity. There were some very small cilliates (I think, never got a good look) when I first got the sample but I haven't seen any recently.

[75RR]

.
If they become active then this link might help with an ID

https://www.researchgate.net/publicatio ... d_Rotifers

[hans]

Found an active one, images should be direct links to video files, please let me know if there is any difficulty viewing these:

[MZsarko]

Beautiful pictures. Well done!

[hans]

Thanks MZsarko, excited to have found a convenient rotifer source right next to the house.

Curious if anyone know what this small part is, toward the right side in this video, that remains active when they are dormant? (Not sure if this one is actually encysted?) The trophi are not visible in this video but I did see them at one point and they look the same as in the active rotifer in the previous set of videos.

[Michael Müller]

Hi hans,

the whirling little structure in your video is an so called "flame cell", which is part of the protonephridial system. It pumps fluid into a tube. Normally, these tubules drain into a urinary bladder that leads to a cloaca. The protonephridial system is used for excretion and osmoregulation.

Best regards

Michael

[hans]

the whirling little structure in your video is an so called "flame cell", which is part of the protonephridial system. It pumps fluid into a tube. Normally, these tubules drain into a urinary bladder that leads to a cloaca. The protonephridial system is used for excretion and osmoregulation.

Thank you, Michael, very interesting. The slide dried out overnight and the rotifer that was active is now in the same state. I added back water and can now see four flame cells active as well as some other motion. Hopefully it will revive soon.

[75RR]

The slide dried out overnight and the rotifer that was active is now in the same state. ]

If you place the slide overnight in a Slide Mailer it will prevent it drying out.

[hans]

If you place the slide overnight in a Slide Mailer it will prevent it drying out.

I will try this with the next slide. I assume these rotifers must be used to it, though, since the ones that became active I found in an even drier location than the A/C condensate discharge I was talking about recently. They are from a spot on the other side of the house that is watered only by dew dripping from the roof at night which gets direct sun for probably 30 minutes to an hour and I believe dries out completely most days. The area was fairly wet when I took the photo this morning because the first rain of the season just happened last night, but there had been no rain before I collected the sample.

[Michael Müller]

Bdelloid rotifers are tough little beasts! They can dry out for month or even years and get active again if the conditions are favorable. The only sign, that the animals are still alive in the contracted state are the active flame cells.

[hans]

Bdelloid rotifers are tough little beasts! They can dry out for month or even years and get active again if the conditions are favorable. The only sign, that the animals are still alive in the contracted state are the active flame cells.

Good to know, this is something I was not clear on from the limited reading I have done so far. Would it be accurate to say there are only three states in which they remain viable: extended and active, contracted with only flame cells active, and egg? In particular, if I see one that is extended but showing no signs of activity, can I conclude that it is permanently deceased? I come across extended, inactive ones fairly regularly and so far have not seen one revive. I have been guessing that they died due to something like bacterial infection or a change in the environment that happened too quickly for them to properly enter the contracted state?

[Rapidray]

Bdelloid rotifers are tough little beasts! They can dry out for month or even years and get active again if the conditions are favorable. The only sign, that the animals are still alive in the contracted state are the active flame cells.

Active flame cells??? I had to google that one. Thanks - always enjoy learning new thing’s.

[Michael Müller]

Good to know, this is something I was not clear on from the limited reading I have done so far. Would it be accurate to say there are only three states in which they remain viable: extended and active, contracted with only flame cells active, and egg? In particular, if I see one that is extended but showing no signs of activity, can I conclude that it is permanently deceased?

Expanded animals should be active if alive. I suppose, that most bdelloids die contracted, but the increasing osmotic pressure (without active flame cells) causes the carcass to expand somewhat. After some days, there should be only an empty cuticle with the trophi left.
BTW: not all bdelloids lay eggs - you already showed alive offspring.

[hans]

BTW: not all bdelloids lay eggs - you already showed alive offspring.

Are there species that can do both, depending on conditions or something? All the bdelloids I am seeing look very similar but I see quite a few eggs also, I think. (I have been planning to photograph a few and post here to confirm.) The first one that ruptured I wasn't sure if the live offspring was normal, but last night I saw another one with similarly-developed (mastax clearly visible and operating) offspring inside.

[Michael Müller]

All rotifers produce eggs - the difference is, whether the eggs are disposed before the embryo develops or if the egg is kept inside the mother until the juvenile animal is fully developed. So you may find eggs in every species but developing embryos only in a few species.
Some years ago I published a photo sequence of the birth of a bdelloid rotifer on the German forum for microscopy. If you are interested: https://www.mikroskopie-forum.de/index. ... ic=29342.0

[hans]

Thanks for all the information, those are very nice photos with a clearer view on the offspring than I have gotten with bright field. Must have taken a lot of patience to capture that.

In the species that have the ability to carry the offspring to maturity, do these species also have the option of disposing of the egg early and the offspring can still develop and survive? Or is it necessary for them to carry the offspring all the way to maturity? I wonder because so far all the bdelloids I see look very similar, but I think I am seeing both immature eggs alone and also fully developed offspring being carried. Could the free eggs and live offspring both be the same species? Or would this indicate I have two different species in the sample?

[Plasmid]

Rotifers are the instant pancake of the microworld.......Just add water
Here is a video of one I found in toilet water.....dont ask how it got there, the toilet had been removed from the base while I was remodeling my bathroom floor, 3 days later there was a bio film around the water that was left inside the toilet and in it I found this little fella. They can remain in a cystic state for days.
https://youtu.be/9YCZ5k-ksBI

[Michael Müller]

They can remain in a cystic state for days.

A friend told me. that his record for a dried and revived bdelloid is more than 3 dry years! Bdelloids have been found in permanent filters inside coffee makers!

In the species that have the ability to carry the offspring to maturity, do these species also have the option of disposing of the egg early and the offspring can still develop and survive? Or is it necessary for them to carry the offspring all the way to maturity? I wonder because so far all the bdelloids I see look very similar, but I think I am seeing both immature eggs alone and also fully developed offspring being carried. Could the free eggs and live offspring both be the same species? Or would this indicate I have two different species in the sample?

I never heard of this for bdelloid rotifers ...
But anyway you may see immature eggs inside the mother until the offspring "hatches" inside the animal. Sometimes you even see active offspring and a new egg simultaneously in bdelloids,

[hans]

I did eventually see one that looked somewhat different than the ones I am seeing more frequently sometimes with offspring inside, so perhaps these are responsible for the free eggs. It moved around a lot more quickly while feeding, overall body shape a bit different without the obvious lengthwise ridges, head looks different, and the internal thing with dark outline and uneven joint in the middle I had not seen before:

[hans]

I think this is a rotifer egg? It is 26 by 17 um and appears to have a fairly thick (maybe ~1 um, hard to tell) transparent coating.

[Michael Müller]

Looks like a egg, but as long as you don't see any embryo, it is impossible to say anything of its origin. It is very small, so I don't believe, it's from a bdelloid. The size of the trophi from your first post was already 17µm, so it would fill the egg totally. As trophi don't grow this would be impossible.

The only way to decide the species is to observe what hatches (or to see, who deposited the egg). One possibility for this is, to separate a single egg in a slide and store this slide in a wet chamber (a tight box with some water or wet tissue in it to saturate the air in it with moisture). The slide will not dry out and you can check the development of the egg and eventually see the hatched animal.

[hans]

Interesting, about the trophi not growing. You are probably right about that one not being from a bdelloid. I got some better video of one carrying an egg and the trophi in the egg are indeed about the same size as the mother's:


I also looked at drops of sample with no cover slip so I could try to separate out an egg as you suggested and eventually found one with the trophi clearly visible. I pushed it out to the edge of the droplet with a needle then soaked up most of the drop and other debris with a tissue leaving the egg reasonably cleanly separated in a small amount of water, looking like this:

DSC_9301.jpg (43.25 KiB) Viewed 9313 times

This one is 70 by 45 um and the trophi roughly 15-20 um long. I let the remaining water evaporate leaving the egg stuck to the slide and marked the location, figuring that would be a reasonable way to store it while deciding what to do next. The image quality in the initial photos of the egg (including the one above using 40x 0.66 objective) suffered a bit due to the lack of cover glass and residual water so a few hours later I decided to try to get better photos under cover glass. The rotifer remained somewhat shrunk after drying out while the casing quickly rehydrated back to the original size:

DSC_9303.jpg (43.84 KiB) Viewed 9313 times

After about 10 minutes messing with photos I went to take the cover glass back off and the outer casing had burst leaving the bdelloid floating freely but still in the contracted state:

DSC_9306.jpg (77.5 KiB) Viewed 9313 times

Another 10 minutes or so and there was some movement and eventually it extended. It is lacking the pinkish-orange color and the stomach looks fairly empty. Perhaps that color comes from something they eat? Otherwise it appears to be behaving normally:


The cut in the video is where I added a bit more water to the slide and the flow washed the rotifer away, took me a minute or two to find it again.

[Michael Müller]

Hi, hans - great, you hit the mark!

You observed the hatching of a bdelloid rotifer. I'm not sure, whether it was somehow accelerated by your procedure, but the young girl seems to feel quite good. I never had the luck to see something like this!

The trophi are not growing because they do not consist of cells. They are a mineral structure (like our teeth) and obtain their full size during the development of the embryo.

Well done!

[hans]

Thanks Michael.

I'm not sure, whether it was somehow accelerated by your procedure, but the young girl seems to feel quite good.

Yeah, I suspect it was not a coincidence since it happened so quickly. Possibly pressure from the cover glass but the casing was intact when I first rehydrated it, not much time had passed, and there was still enough water for the rotifer to be floating freely after out of the casing. Or maybe there is some intentional mechanism for the eggs to hatch soon after being rehydrated? If I find another one in a drop I will try isolating and drying it in the same way, then rehydrating later without cover glass, and see if that still triggers hatching.

[Rapidray]

That was interesting...watching stuff like that is alway an unexpected surprise.

[Plasmid]