The functional morphology of hooding in cobras

Abstract

SUMMARYMany snakes, particularly cobras, form as part of a defensive display, a hood, an active lateral expansion of their neck skin and underlying musculature and ribs. We identified muscle groups possibly involved in hooding based on their attachments on the specialized ribs of the neck. We then used a combination of morphology, kinematic analysis, morphometrics, electromyography and muscle stimulation to test hypotheses about the functional basis of hooding. We confirmed that hood protraction and erection is an active process that begins cranially and extends caudally, often in stages, through the combined action of several sets of muscles. One set of axial muscles (levator costae and supracostalis lateralis superior) coursing along a line of action to rib displacement are the prime erectors acting to lift the hood. However, a second set of muscles connecting ribs to skin primarily keep the skin taut, rather than to displace the ribs relative to the vertebrae. A third set of muscles coursing between ribs function primarily to transmit forces between adjacent ribs rather than to move ribs. The maintenance of the erect hood requires continued muscle activity. Hood relaxation is due to both active muscle contraction of a fourth set of axial muscles and to passive recoil events in the costovertebral ligaments. The shape of the fully erect hood is reflective of the morphometrics of the underlying ribs, while the duration and kinematics of hood erection and relaxation are related to the behavioral context of the display.

How animals glide: from trajectory to morphology

“…The mechanism of flattening has been hypothesized by to involve the same suite of muscles as used for hooding in cobras (Young and Kardong 2010), but an anatomical study is needed. In Chrysopelea paradisi, the aerial cross-section at midbody can be considered as a rounded triangle, with two ventrally-projecting lips at the lateral edges.…”

How the Cobra Got Its Flesh-Eating Venom: Cytotoxicity as a Defensive Innovation and Its Co-Evolution with Hooding, Aposematic Marking, and Spitting

“…Most prior research has focussed on the spitting behavior itself, treating it as a peculiar oddity in nature without investigating associated evolutionary trends (e.g., venom composition) [16], and it has been described at the morphological [17,18], mechanical [12,19,20] and behavioural levels [13,21]. Hooding is a distinctive characteristic of the genera Hemachatus , Naja and Ophiophagus and members of these genera are found in Africa and Asia [22].…”

El uso de señales aposemáticas en serpientes: contra advertencia no hay engaño

“…Considerando que hasta un 18% de las especies de serpientes neotropicales pueden mimetizarse con los coralillos (figuras 1b, 1c y 1d), e incluso tener cierta toxicidad (Brodie lll y Brodie, 2004;De la Torre-Loranca et al, 2006), es necesario evaluar otras características para corroborar la honestidad de sus señales visuales y con ello su identidad. Otro ejemplo bien conocido de señales de advertencia en elápidos lo constituye la conducta del despliegue de la capucha en cobras y su capacidad para erguirse más de un tercio de su tamaño corporal cuando son amenazadas (Young y Kardong, 2010).…”