The effects of water availability on the life history of the desert snail,Trochoidea seetzeni : An experimental field manipulation.

In the Negev desert of Israel, the pulmonate land snailTrochoidea seetzeni is active, grows and reproduces in the month following the torrential winter rains. Thereafter, these snails estivate until the following year's rains. By experimental supplementation of water in the field, we examined the ability of these snails to alter their life histories. Specifically, we measured changes in feeding activity, overall activity levels, movement patterns and reproductive output. We found that snails on artificially-watered plots stopped feeding on higher plants and fed on soil-surface algae growing as a result of increased water availability. Most snails moved onto the watered plots, and reduced the total amount of movement once there, in response to increased food availability. Snails on the watered plots grew more and remained active for a longer period into the summer months than did snails on control plots. However, we found little evidence for the ability of these snails to alter their reproductive outputs in response to increased water (and hence food) availability. There was also no carry-over effect of high water availability in one season enhancing reproduction in the following season. We postulate that the low level of phenotypic plasticity recorded here is a consequence of an adaptive conservative strategy to maintain a high reproductive output under extremely unpredictable desert conditions.