The Factors For Intra- And Inter-specific Variations In Predatory Behavior Of Three Viperid Snakes

Venomous snakes obtain the energy for survival,growth and reproduction by predation,and the predatory behavior might be driven by prey feature,body condition of snake,habitat structure,predation risk,venom toxicity and the resistance of prey to venom.It is inevitable that the venomous snakes have to face the trade-off between the energy cost and benefit during the process of predation.In this study,to investigate the causes for intra-and inter-specific variations in predatory behavior,I used three small sized Viperidae snakes?the short-tailed pit viper Gloydius brevicaudus,the Chinese green tree pit viper Viridovipera stejnegeri and the mountain pit viper Ovophis monticola?to test the effects of habitat height and body condition on the behavior features,the toxic potency and the energy cost of venom replenishment.I used the wireless webcam to record the process of predatory of these snakes,and quantified the behavior features,evaluated the toxic potency by venom yield and median lethal dose(LD₅₀),and also assessed the energy cost and level of venom replenishment based on the RMR?resting metabolic rate?and the venom yield before and after the venom depleted.Following are the main results of this study:Interspecific variations were observed in the number of tongue flicking,attacking times on prey,death time of prey and the means to treat the prey of G.brevicaudus,V.stejnegeri,and O.monticola,but no variations were detected in the initial attacking site on prey and the time of prey swallowing.Except for the success rate of initial attacking,the other features of predatory behavior were not influenced by the habitat height in V.stejnegeri.The attacking times on prey,the death time of prey and the means to treat the prey of G.brevicaudus were affected by the venom reserved in the venom gland,but the number of tongue flicking,the initial attacking site on prey and the time of prey swallowing were not influenced by such factor;the predatory behavior was not affected by fasting level in G.brevicaudus.Except for the initial attacking site on prey,the other features of predatory behavior were not influenced by the fasting level in V.stejnegeri.In addition,there was no significant variation observed in venom depleted and undepleted O.monticola.Venom yield and LD₅₀ were variable among the G.brevicaudus,V.stejnegeri,and O.monticola.The short-tailed pit viper expelled the largest amount of venom?61.7 mg?,which was 2.4-fold and 6-fold of that in V.stejnegeri?24.8 mg?and O.monticola?10.8mg?respectively.The mountain pit viper showed the lowest toxicity on mice with the highest lethality dose of 3.59 mg/kg,it was 2.3-fold and 3-fold of that in G.brevicaudus?1.62 mg/kg?and V.stejnegeri?1.27 mg/kg?respectively.The results suggested that the toxic potency of G.brevicaudus was 2-fold and 13-fold of that in V.stejnegeri and O.monticola,respectively.It was indicated that the venomous snakes with low toxic potency could not attack the prey continuously,and therefore evolved to hold the prey after attacking to reduce the risk of prey losing.The RMR of G.brevicaudus elevated 11.2%on the third day after the venom gland depleted,and subsequently recovered to the level before venom depleting on the eighth day.The RMR of V.stejnegeri increased 18.7%between the third and the forth days after the venom depleted,and subsequently recovered to the level before venom depleting after the eleventh day.The amount of venom in these three Viperidae snakes was replenished at the fourteenth day when compared the venom yield before and after the RMR determination.The results indicated that the venom replenishment of the G.brevicaudus,V.stejnegeri and O.monticola causes the metabolic energy cost,and the venom reserving was replenished as the RMR level fall back to the initial level.