Worm Breeder's Gazette 15(5): 25 (February 1, 1999)

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Humidity affects the behavior of worms

Catharine H. Rankin

Department of Psychology, University of British Columbia, 2136 West Mall, Vancouver, BC. V6T 1Z4

The take-home message from these observations is that the behavior of worms can be influenced by environmental variables not previously considered important. Consistency of conditions and controls for environmental effects are necessary in all behavioral studies. We routinely keep detailed records of time of day, temperature, and humidity for each worm that we test. Despite having a new environmental control system in the lab we now always pair an experimental and control worm and run them at as close to the same time and in same conditions as possible.

The response that we study is backward movement in response to a mechanical tap to the NGM agar filled dish on which the worm sits. It is important to note that we do our testing with the lids off of the plates, so ambient environment can influence behavior. The temperature in my lab is relatively constant (range 19 to 21.5 degrees C) but prior to purchasing a new environmental control system the relative humidity ranged from ~35% to 75%. We found no consistent effect of time of day or of temperature on the magnitude of the reversal response, however we did find a significant effect of humidity. Higher humidity produced larger responses- especially when humidity exceeded 50%. For example, when humidity was 44% the mean response magnitude was 142.9 +/- SEM 22.16 pixels (on the monitor) - when the humidity was 56% the mean response magnitude was significantly larger at 199.5 +/- SEM 18.4 (t(15)= 1.84, p=.04). In another experiment a shift from 40% to 50% relative humidity led to a doubling of response magnitude. We hypothesize that changes in humidity affect the properties of the agar such that humidity above 50% makes worm movement easier, thus responses to tap are larger.

Humidity also affects another aspect of worm behavior. We have been working for several years to show context conditioning with habituation (paper now submitted). This is associative learning in which worms learn the pairing of a chemical cue (NaCH3COO) with habituation training to tap - in later tests worms remember more of the training in the presence of the chemical cue than when there is no cue. This has been replicated 6 times (each with groups of at least 40 worms) when the relative humidity is below 50%, but has not, thus far been replicated when the humidity is over 50% (~4 tries). It may be that some aspect of either chemoreception or associative larning is also affected by changes in humidity.