Resistance of the Common Spiny Mouse to theVenom of the Saw-Scaled Viper (Echis coloratus)

A. Bouskila, S. Weissenberg (Open University), T. Dayan (Tel-AvivUniversity) and A. Elbar

Resistance to snake venoms is known among animals of various taxonomic groups and may have an ecological-evolutionary significance. Occasional observation revealed that spiny mice (Acomys cahirinus) did not die afterone strike by the saw-scaled viper (Echis coloratus) or by the hornedviper (Cerastes cerastes),and that they died only after receiving additional strikes. The relative protection of spiny mice from venomous snakes could be provided either mechanically, by the spiny cover of the body and/or by a physiological mechanism of resistance.

To test the contribution of the spines as a mechanical barrier, snake were allowed to strike a mouse (shaved or non shaved) only once, and were separated from the mouse right after the strike. A single Echis strike did not kill any of the spiny mice, shaved or not. To test the physiological resistance, the LD50 of the venom was determined in spiny mice and in laboratory mice. The spiny mice were resistant to an amount of E. coloratus venom that was 38 times larger than the LD50 of lab mice.

These results indicate that the common spiny mouse is physiologically resistant to E. coloratus venom, and that this resistance does not dependend on the presence of the spines. The results raised additional questions regarding the ecological-evolutionary significance of this resistance, and some of these were investigated by Alon Elbar in a large outdoor enclosure. He found that the resistance to one strike is enough to save the spiny mice, because (1) the snakes rarely followed the envenomated prey, and (2) when the snakes followed, the spiny mice were alert enough to escape and avoid a second strike. The study will continue to test whether there are ecological implications of the resistance on predator prey relationships, microhabitat selection, foraging behavior,etc.