Comments (7)
I am not sure, but I think UPARSE is quite strict and eliminates clusters that have a low abundance or low quality sequence. It also removes chimeras as far as I know. That may be a reason why it ends up with fewer clusters.
from swarm.
If I am not mistaken, the ITS sequences of fungi (if that's what you are studying) often have highly variable length gaps when aligned. That may cause Swarm to split groups more than other algorithms.
from swarm.
@torognes is right. Swarm does only one thing: it makes clusters of sequences; whereas UPARSE also applies aggressive filters to remove rare sequences, low quality sequences, and chimeras.
In my own analyses I use swarm --difference 1 --fastidious
, and I apply all these somewhat arbitrary filters after clustering, rather than before. The idea is that applying filters is less harmful once the clusters are defined.
Other filters that can efficiently reduce the number of clusters:
- eliminating clusters present in only one technical replicate,
- eliminating low-abundant clusters present in only one biological replicate,
- eliminating clusters dissimilar to any known reference sequence
from swarm.
Thank you @torognes and @frederic-mahe
I think it is possible, I do eliminate singletons in UPARSE and it is true that removes chimeras automatically.
I can try to remove chimeras before using SWARM, remove singletons after generating the clusters.
I am not sure about the reference based approach but it may be another more conservative option.
What if I increase --difference
to e.g. 3 or more?
Gian
from swarm.
I suggest to eliminate chimeras after clustering and after removing singletons.
Increasing the --difference
value will indeed reduce the number of clusters, but it will also reduce the resolution (you will not be able to distinguish taxa with only a few differences in your molecular marker).
In my own projects, using the high resolution --difference 1
has always been a greater advantage. The final number of clusters is an issue only if you are trying to get absolute alpha diversity values (and in that case having a lot of replicates is the prefered solution). For normal comparative diversity studies, the total number of clusters doesn't really matter.
from swarm.
thanks a lot for the explanation. I will follow your advice and let you know what I get.
Gian
from swarm.
I am going to close that issue. Please feel free to re-open if need be.
from swarm.
Related Issues (20)
- Incorrect results with long sequences, very high gap penalties, and d>1 HOT 9
- Roadmap HOT 9
- table formats for making OTU table from swarm results HOT 2
- documentation: maximal input sequence length HOT 9
- Link to new swarm 3 paper HOT 3
- Issues with plotting: OTU not found HOT 3
- OTU table without abundance values HOT 6
- Compiling fails on Windows HOT 3
- maximal header length HOT 1
- uc file question HOT 7
- Invalid numeric argument for option -t or --threads HOT 8
- integer division might be one byte too small in some cases HOT 14
- Seeds not in same order as clusters in output files HOT 2
- Option to exclude seeds or clusters with low abundance HOT 1
- risk of silent 8-bit unsigned integer overflow in score matrix HOT 5
- fastidious boundary applies to the consolidated cluster mass? HOT 1
- Option to output cluster member ids/sequence id? HOT 3
- swarm terminates if any sequence in the input fasta file has an N HOT 2
- Refactor Bloom filter code
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