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shocko61
this worm is outside the food area for the entire period and is the first time I have seen this happen . Usually the worm gets back to the food area very quickly . It would be interesting to know if the worm went outside of it's own accord or was it put thereby the scientist . Cheers , Ian
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Quia
moderator
I have seen a few worms move out of the food area on their own and had the video end with them out in the empty area, so I can verify that sometimes they do leave the food area of their own volition.
I wonder how long their memory is? Would this worm still remember where the last food it found was, or is it going to have to rediscover it?
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DZM
admin
Do they even have "memory?" They're such simple organisms...
Would certainly be interested in a scientist's explaining more about this!
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Quia
moderator
They do! http://learnmem.cshlp.org/content/17/4/191.long
Prior experience with high-quality food made L1 worms more likely to explore when placed on a lawn of low quality food (nonpathogenic, but hard-to-eat bacteria) (Shtonda and Avery 2006). This suggests that worms remember not only the smell of pathogens but also the satiation status associated with previous conditions.
I've read the experimental setup for the worms in Worm Watch Lab, they are moved to a dish with a much thinner layer of food to make clearer recordings. While they're left alone in their new home to habituate for a while before the recording starts, it's possible these worms that wander outside the 'poor food' area are searching for the higher concentration of food that they remember.
Here are a few more interesting tidbits
Work with C. elegans confirms the importance of learning and memory to survival: Even this relatively small organism shows a large number of degrees of freedom in adapting its behavior to reflect its experience. Thus far, the only limit to worm learning in the laboratory seems to be the creativity of researchers in designing assays to evaluate performance.
Zhang et al. (2005) demonstrated that worms could learn to avoid odors associated with pathogenic bacteria, preferring those associated with familiar nonpathogenic strains. Given a choice between a lawn of pathogenic bacteria and a lawn of nonpathogenic bacteria at opposing sides of an assay plate, naïve worms preferentially migrated to the lawns of some strains of pathogenic bacteria, but this changed with experience.
Under the appropriate training regime, worms show long-term memory for tap habituation (Beck and Rankin 1997). Adult worms given four blocks (each separated by 1 h) of 20 taps at a 60-sec ISI had decremented TWRs when tested 24 h after training
In worms, Lee et al. (2009) found that chronic exposure to ethanol during development resulted in an even stronger preference for ethanol in adulthood. Thus, early experience can alter behavioral preference for odorants and intoxicants.
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aexbrown
scientist
Quia's beaten me to it, but yes, they do have memory. They can form a variety of associations between food and temperature or smells and they also remember their feeding history. One thing that's not clear though is whether they have any spatial memory. That is, whether they know something like "I left the food patch three waves ago and then turned to the right, so if I reverse and turn right again I should get back to the food." This is one paper on C. elegans solving mazes which would seem to require something like that, but I admit I'm still skeptical! http://www.ncbi.nlm.nih.gov/pubmed/17268620
To answer Ian's original question, they do leave of their own volition and it's actually very interesting to think about why. There are some genes that are known to affect their propensity to leave. The question's also really interesting for male worms. If they haven't found a hermaphrodite on a patch of food then they leave with high probability because if they don't mate they'll never pass their genes on. On the other hand, if they have previously found a hermaphrodite on a patch of food, they're much less likely to leave.
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Quia
moderator
I am constantly amazed by how much there is to learn. Yesterday I wondered if c. elegans had any memory, now I'm wondering if they might be able to remember a maze.
We're looking at all hermaphrodites here, right? Can't imagine any males laying eggs! All the worms(tiny sample size, I know) that I've seen leaving have been very mobile and active... If they're very efficient at eating food, might they have excess energy in order to risk going out and finding a better source?
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aexbrown
scientist
Yes, these are all hermaphrodites (unless a rare male managed to sneak in!). For these experiments we used fairly thin lawns of bacterial food so they're eating pretty much constantly. One of the reasons they're more active when they leave is just that they can sense they're no longer on food so they move faster until they find the food again.
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Quia
moderator
That makes sense! Speaking of senses, what kind of range can they detect things like 'food' through chemosensory/olfactory senses? I ask because I watched a worm leave the food area, and then move parallel to the curvature of the edge of the food, about half a body length away, for about 10 seconds before the video ended. I wouldn't be surprised it was coincidence, but it made me wonder!
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aexbrown
scientist
There isn't really a fixed range. Following an odour depends on the presence of a gradient. In an undisturbed petri dish with a spot of food in the middle I would say there's a followable gradient pretty much everywhere so that even if they're at the edge of a 5 cm plate they can find the patch in the middle.
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Quia
moderator
Surprised by a little 1mm long worm, again! I thought they might get lost wandering around, but no, they've got amazing 'noses' in that tiny little body.
Thank you so much for answering my questions! I try and find published literature when I'm curious but sometimes it's really hard to figure out what terms to look for.
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