Clustering of Arcella

[tlansing]

This was a very strange observation that was made a little while ago. I saw this cluster of Arcella, a testate amoeba, as shown in the photo below. It appears that all of the Arcella are alive and of different ages, as indicated by the different shades of the tests of the individuals. I searched some literature to see if this had been reported previously without success. Has anyone else seen this and/or have any information about this phenomenon?

Arcella-1.jpg (103.83 KiB) Viewed 1504 times

The photo below shows a line of Arcella which seem to be connected together. Perhaps this is a precursor to the clustering in the first photo?

Arcella-2.jpg (103.6 KiB) Viewed 1504 times

Photographed using a Canon 1300D camera and an Amscope adapter, 16x Plan achromat, DIC

[richbart]

Very unique. I’ve never seen this happen. I wonder if it could be some type of conjugation.They are both sexual and asexual.

[zzffnn]

I Googled “arcella conjugation” and found that Bill Porter posted about this before. Ferry previously told Bill that it is sharing of plasm (in harsh environment that has limited nutrients), rather than real conjugation.

I think I heard about similar kind of plasm sharing in ciliates or flagellates as well, though I am not 100% I remember it correctly.

[ImperatorRex]

Very interesting, thank you for sharing.

[tlansing]

@richbart, @ImperatorRex: Thanks for your comments

@zzffnn: Thanks for the interesting comment. I had not thought of this. I know that in heliozoa that individual organisms can fuse their cytoplasm in a process called plasmogamy. Perhaps this is a different version of that.

[Bruce Taylor]

I know that in heliozoa that individual organisms can fuse their cytoplasm in a process called plasmogamy. Perhaps this is a different version of that.

Yes, plasmogamy, or cell fusion, is the right term for this phenomenon, which has been observed since at least the 19th century. Quite a few amoebozoans do it. In the case of Cochliopodium, it's been observed that cell fusion is followed by nuclear fusion (karyogamy), so in that genus it is a clearly sexual phenomenon (https://www.sciencedirect.com/science/a ... ZKX5cHvQ_Q). There could be other (non-sexual) reasons for why it occurs in other groups...I don't think anybody knows for sure! In Arcella, cell fusion is sometimes described as a "parasexual" phenomenon, but as far as I know, these fused cells haven't been caught in flagrante delicto, with their nuclei fusing. It's been known since the early 90s that encysted Arcella can undergo meiosis, followed by autogamy (https://onlinelibrary.wiley.com/doi/abs ... cZs2pX1p3w), but I believe the reasons for cell fusion are still mysterious.