基于代价与效益分析探讨短尾蝮定量注毒行为的进化成因

Snake venom is a chemical weapon and special for advanced snakes, and it cannot be used freely because of very limited yield in venom gland. It is important to study the characteristics and intrinsic mechanisms of snakebite on prey or natural enemy for how to use the snake venom economically, efficiently and constantly, and it would be helpful to interpret the evolution and adaption of snake venom. Conventionally, it was considered that venomous snake will optimize the venom dose that injected into the prey or enemy by venom metering, and thus the venom may become more cost-effective. In addition, excessive injection of venom in a reasonable range would also be help to increase the predation benefit by shorting the death time of envenomated prey. There might be some special components in venom allow the snakes to relocate the envenomated prey effectively, and the predation benefit would also be increased. However, the empirical cases for verifying this hypothesis are relatively scarce. Here, we will use the short-tailed pit viper (Gloydius brevicaudus) to comprehensively detect: (1) metabolic cost, predation behavior and venom metering profiles of the snakes are venom depleted at different levels; (2) the contribution of excessive venom injection and venom components to recognize and relocate the dead prey; and (3) the proteomic and functional profiles of consecutively expelled venom by snakes. This study aims to clarify the metabolic cost of venom regeneration after the snake venom is depleted, and elucidate the characteristics of the trade-off between energy/time cost of venom regeneration and predation effectiveness while snake attacks preys, then to explore the evolutionary causes of venom metering behavior of the short-tailed pit viper.

蛇毒作为新蛇类特有的化学武器，因受其含量有限的制约，无法被随意、过量使用。研究毒蛇咬物注毒的特征及其内在驱动机制是探讨蛇毒如何被节约、高效和持续地用于捕食或御敌的重要环节，更有助于诠释蛇毒的进化适应意义。现行主流观点认同毒蛇在捕食或御敌过程中，会优化使用蛇毒，通过咬物定量注毒行为以提高蛇毒使用的性价比，但与其解释基础有关的研究实例相对匮乏。申请人拟以国产短尾蝮（Gloydius brevicaudus）为对象，系统检测：不同排毒强度下毒蛇的呼吸耗氧量、捕食行为和定量注毒特征的差异，过量注毒对毒蛇捕食效益的影响，蛇毒组分对毒蛇识别死后猎物的贡献，以及定量注毒不同阶段排出毒液的蛋白组构成和功能特征。申请人期望通过阐明毒蛇排毒后毒液再生的能量代价及毒蛇基于毒液再生的能量/时间代价与捕食效益的权衡特征，探讨短尾蝮定量注毒行为的进化成因。

本项目通过检测短尾蝮捕食猎物的行为和注毒量，毒液释放前后的代谢特征，蛇毒组分对猎物识别的贡献以及连续排出毒液的组成与功能特征，探讨短尾蝮定量注毒行为的进化成因。研究发现：（1）短尾蝮明显偏好捕食体重较轻的猎物，其捕食攻击前后对猎物的吐信次数不同，对大规格猎物的吐信次数随捕食次数的增加而增多；其对大的猎物攻击次数较多，但对同规格猎物的攻击次数无批次间差异；其吞食猎物的时间随猎物体重的增大而增加，连续吞食同型猎物所需时间相对稳定。不同规格猎物被注毒后的死亡时间不同，且小规格猎物的死亡时间无批次间差异，大规格猎物的死亡时间与其它规格猎物的差异随捕食次数的增加而扩大；（2）毒液排空短尾蝮捕食攻击前后对猎物的吐信率要低于充盈组，其攻击猎物的次数和猎物死亡时间分别是充盈组的3倍和10倍，攻击并紧咬猎物的比例也高于充盈组；（3）同批次下短尾蝮对中规格猎物的注毒量最多，小规格猎物的注毒量最少，对大规格猎物的注毒量又呈现减少的趋势，其对同规格猎物的注毒量随批次的递进而降低。短尾蝮在捕食过程中，并非一次将毒液注完，其每次平均注毒量不超过总毒量的16%；（4）随着人为过量注射蛇毒剂量的递增，猎物的死亡时间及中毒后持续运动时间均缩短；（5）短尾蝮毒腺毒液排空后至再次充盈引起静息代谢上升，该过程约持续一周，且静息代谢率最大上升11.5%；（6）短尾蝮连续排出毒液中主要毒素组分的相对含量较为稳定，且蛇毒的致死毒性和酶活性无批次间差异。蛇毒去整合素、金属蛋白酶、磷脂酶A2和缓激肽增强肽/利钠肽不影响短尾蝮对猎物的识别率，仅有去整合素能助于短尾蝮快速识别猎物。研究结果表明，蛇毒主要组分的稳定释放可维持其在短尾蝮连续捕食过程中相对稳定的功能，猎物规格与捕食的连续性是影响其捕食行为和注毒量的主因；过量注毒及蛇毒去整合素有助于短尾蝮捕食，但其仍需要权衡毒液再生的代谢耗能。