Heart rate and hemocyte number as stress indicators in disturbed hibernating vineyard snails, Helix pomatia

In humans and other vertebrates, mental or physical stressors may trigger a variety of symptoms generally referred to as the fight/flight response (Cannon 1929). The processes also include variability of the heart frequency as well as leukocytosis. We monitored both body responses in disturbed hibernating vineyard snails, H. pomatia, to obtain information on the stress sensitivity of these "sleeping" invertebrates. The first mild stressor, a 100 meter transport of hibernating snails from the cold room to the laboratory, caused cardiac arrhythmia in the animals. This reaction could have been provoked by mechanical disturbances and/or by raising the body temperature to room temperature. But a change in the ambient temperature did not trigger an abnormal heart rhythm. Different from this observation, we recorded instant heart rate changes in response to knocking on the shell and a very irregular heartbeat occurred when a hole was punched in the shell. With a short time delay upon damaging the shell, a large increase in the number of circulating cells also occurred. This was not observed after knocking on the shell or when snails were adapted to different temperatures for each 48 h. Thus, hibernating snails sense environmental variations which cause an immediate change of the heart frequency and an elevated stimulus level initiates in addition leukocytosis which occurs at a post-stimulus latency. This disparity could indicate the activity of two different stress regulation pathways. Furthermore, the assays demonstrate an increasing linear relation between rising temperature and frequency of heart pulsations (y=1.01x-2.1); but the results do not indicate a correlation between heartbeat frequency and the number of cells in circulation. Consequently, neither temperature nor heart frequency seems to influence the number of circulating cells in hibernating H. pomatia.