I’m having trouble scoring for worm mortality on a variety of stress assays. I’m finding that my method of simply prodding and watching for movement is flawed
at best. In worms that have lost motility, there is a very small amount of movement in the head that I am unsure of as a sign of life. I cannot confirm that this movement is a sign of
life and believe that it may be caused as a direct result of my prodding. I believe this due to the fact that the worms head/pharynx shrivels inward after prodding and no movement
is attainable from from further prodding. Is this worm dead, or just desensitized to prodding?
a few things spring to mind here as I munch on my Mozzarella and Tomato Roll (+ balsamic Vinegar).
Stop stabbing them in the head and try another site.
Extracting the ‘confesion’ (signs of movement) requires patience and subtlety. Beating the Jesus out of the worms instead of gradually increasing the intensity of your prodding loses valuable information about the stress effect.
Can/do the worms recover from your stress test when placed in a non-stressful environment?
i just finished my rittersport and (possibly due to the chocolaty after-effects) have a bit more sympathy for djd.
i’m not an aging expert, but i have tried a few lifespan assays on plates and i saw the same thing when the worms were getting really old.
you touch a worm on the head (or tail, or midsection) and it appears to undergo body muscle contraction - it moves! but if it doesn’t do anything more after that - no spontaneous
motion and no repeat flinch performance, then it is very likely to be dead. i don’t know what the initial “response” results from but i guess even a dead will bounce.
The head movement you see is likely a sign of life.
Worms will adhere to the bacteria and sort of shrivel internally. Prodding them will break the adhesion and cause them to shorten after they’ve been immobile for a while. Sometimes they’re still alive after this so pay close attention to the head region. If they swivel it side to side after a few seconds after they they shrink I usually score them as alive. If they’re not dead yet, they will be soon (in my experience).
I think this is due to the bacteria growing slightly around the worm since it’s not nearly as active. The worms also tend to shrink as they age so both of these in combination keep the worm in a stretched state and prodding them releases them from the bacteria. These are only my observations doing lifespans so take it for whatever it’s worth.
Gently tap their tail and give them a second or two to respond. Depending on how impatient you are you can score them as dead or give them a few more seconds to respond. It’s somewhat subjective but as long as you’re consistent then it should be okay.
If other people are doing survival scoring in your lab it helps to have a session where multiple people score the same plate and compare results to make sure the lab is getting consistency in their results.
Lastly, based on what you’ve described I would score that worm as dead. I haven’t run into a situation where the worm has been desensitized to prodding. It could happen, and maybe it does, but I haven’t noticed it.
there…following Eric’s advice…i have just eaten a muffin and feel much better.
Of course, the cuticle of an old worm is much much thicker, so this might also play a role in the ‘spring back’ effect mentioned by the last poster and also perhaps the lower sensitivity to prodding?