RUI: Functional Convergence in the Venom Delivery System of Snakes

RUI：蛇毒液输送系统的功能融合

• 批准号: 0129805
• 负责人: Bruce Young
• 金额: $ 16.72万
• 依托单位: Lafayette College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-07-01 至 2005-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0129805&HistoricalAwards=false
• 关键词: RUI; Functional; Convergence; Venom; Delivery

Snakes have one of the most specialized feeding mechanisms among vertebrate animals. One of the key aspects of snake feeding is the presence of a venom delivery system in roughly one-fifth of the living snakes. Molecular and anatomical studies suggest that a venom delivery system has evolved independently in at least four snake lineages. The Viperidae (including pit-vipers and true vipers), the Elapidae (cobras and sea snakes), the Atractaspidae (Stiletto snakes from Africa), and several taxa - such as the boomslang - within the Colubridae have all evolved venom delivery systems. In recent years a suite of techniques were developed to study the mechanics of venom injection in one representative viper, the western diamondback rattlesnake (Crotalus atrox). The purpose of this grant is to apply these same techniques to the mechanics of venom delivery in representative elapids. This will be the first experimental analysis of venom expulsion in an elapid, and a comparison with the earlier studies will highlight the degree of functional convergence among snake venom delivery systems. The venom delivery system will be examined through four integrated projects on the kinematics, neuro-muscular control, functional morphology, and behavioral ecology of venom injection. The kinematics of venom expulsion will be studied using high-speed digital videography and computer-based image analysis techniques to document the degree to which the monocled cobra (Naja kaouthia) modulates its strike depending on such factors as the size of the target and the behavioral context of the strike. The kinematics of venom "spitting" by the red spitting cobra (N. pallida) will also be documented. In snakes the venom is expulsed through skeletal muscle contraction; by regulating the contractile state of the muscle the snake could control the amount of venom injected. The extrinsic venom gland musculature will be studied in N. kaouthia using anatomical techniques to document the gross and microscopic structure of the muscle and its innervation. Subsequent experimental analyses will combine muscle stimulation with measurements of venom flow and pressure to document any spatial functional specialization within the muscle, and the motor units within the muscle will be mapped using glycogen depletion. In cobras venom forced from the venom gland by muscle contraction flows through the venom duct into a series of soft tissue chambers which are surrounded by the fang sheath, a drape of connective tissue and epithelium. The functional morphology of this region will be studied in both N. kaouthia and N. pallida using gross and microscopic anatomy, radiopaque tracers (used to document venom barriers), cannulation experiments, and recordings of venom pressure. The behavioral ecology of venom injection will be studied by chronically implanting transonic flow probes onto the venom duct of N. kaouthia. Venom flow (measured with flow probes) will be synchronized with high-speed digital videography while the cobra strikes a variety of defensive and predatory targets. This will document the kinematics of venom flow during the strike and reveal the extent to which cobras inject differential volumes of venom depending on target size or behavioral context.

在脊椎动物中，蛇有着最特殊的进食机制。喂蛇的一个关键方面是大约五分之一的活蛇都有毒液输送系统。分子和解剖学研究表明，毒液输送系统至少在四种蛇的谱系中独立进化。蝰蛇科（Viperidae）（包括坑蝰蛇和真蝰蛇）、眼镜蛇科（Elapidae）（眼镜蛇和海蛇）、非洲细刺蛇科（Eustaspidae）（非洲的细刺蛇）和几个分类群（如非洲树蛇）都进化出了毒液输送系统。近年来，一套技术被开发出来，以研究毒液注射在一个代表性的毒蛇，西部菱背响尾蛇（响尾蛇）的力学。这项资助的目的是将这些相同的技术应用于有代表性的眼镜蛇的毒液输送机制。这将是第一个实验分析毒液驱逐眼镜蛇，与早期的研究比较将突出蛇毒输送系统之间的功能趋同程度。毒液输送系统将通过四个综合项目的运动学，神经肌肉控制，功能形态学和毒液注射的行为生态学进行检查。毒液排出的运动学将使用高速数字摄像和基于计算机的图像分析技术进行研究，以记录单目眼镜蛇（Naja kaouthia）根据目标的大小和罢工的行为背景等因素调整其罢工的程度。红吐毒眼镜蛇（Red Spitting Cobra，N. pallida）也将被记录。蛇的毒液是通过骨骼肌收缩排出的;通过调节肌肉的收缩状态，蛇可以控制注射毒液的量。外源性毒腺肌肉组织将在N. kaouthia使用解剖技术来记录肌肉及其神经支配的大体和显微结构。随后的实验分析将结合联合收割机肌肉刺激与测量毒液流量和压力，以记录肌肉内的任何空间功能专业化，肌肉内的运动单位将使用糖原消耗映射。在眼镜蛇中，毒液通过肌肉收缩从毒腺中流出，通过毒液导管流入一系列被尖牙鞘（结缔组织和上皮细胞的褶皱）包围的软组织腔室。该区域的功能形态将在N. kaouthia和N.苍白球使用大体和显微解剖学，不透射线示踪剂（用于记录毒液屏障），插管实验和记录毒液压力。本研究将利用跨音速探针长期植入中华白蛉的毒管，探讨其注射毒液的行为生态学。kaouthia。当眼镜蛇攻击各种防御和捕食目标时，毒液流（用流量探针测量）将与高速数字摄像同步。这将记录在罢工期间毒液流的运动学，并揭示眼镜蛇根据目标大小或行为背景注射不同体积毒液的程度。