TY - JOUR

T1 - Unexpected lack of specialisation in the flow properties of spitting cobra venom

AU - Avella, Ignazio

AU - Barajas-Ledesma, Edgar

AU - Casewell, Nicholas R.

AU - Harrison, Robert A.

AU - Rowley, Paul

AU - Crittenden, Edouard

AU - Wüster, Wolfgang

AU - Castiglia, Riccardo

AU - Holland, Chris

AU - van der Meijden, Arie

PY - 2021/4/7

Y1 - 2021/4/7

N2 - Venom spitting is a defence mechanism based on airborne venom delivery used by a number of different African and Asian elapid snake species (‘spitting cobras’; Naja spp. and Hemachatus spp.). Adaptations underpinning venom spitting have been studied extensively at both behavioural and morphological level in cobras, but the role of the physical properties of venom itself in its effective projection remains largely unstudied. We hereby provide the first comparative study of the physical properties of venom in spitting and non-spitting cobras. We measured the viscosity, protein concentration and pH of the venom of 13 cobra species of the genus Naja from Africa and Asia, alongside the spitting elapid Hemachatus haemachatus and the non-spitting viper Bitis arietans. By using published microCT scans, we calculated the pressure required to eject venom through the fangs of a spitting and a non- spitting cobra. Despite the differences in the modes of venom delivery, we found no significant differences between spitters and non-spitters in the rheological and physical properties of the studied venoms. Furthermore, all analysed venoms showed a Newtonian flow behaviour, in contrast to previous reports. Although our results imply that the evolution of venom spitting did not significantly affect venom viscosity, our models of fang pressure suggests that the pressure requirements to eject venom are lower in spitting cobras than in non-spitting cobras.

AB - Venom spitting is a defence mechanism based on airborne venom delivery used by a number of different African and Asian elapid snake species (‘spitting cobras’; Naja spp. and Hemachatus spp.). Adaptations underpinning venom spitting have been studied extensively at both behavioural and morphological level in cobras, but the role of the physical properties of venom itself in its effective projection remains largely unstudied. We hereby provide the first comparative study of the physical properties of venom in spitting and non-spitting cobras. We measured the viscosity, protein concentration and pH of the venom of 13 cobra species of the genus Naja from Africa and Asia, alongside the spitting elapid Hemachatus haemachatus and the non-spitting viper Bitis arietans. By using published microCT scans, we calculated the pressure required to eject venom through the fangs of a spitting and a non- spitting cobra. Despite the differences in the modes of venom delivery, we found no significant differences between spitters and non-spitters in the rheological and physical properties of the studied venoms. Furthermore, all analysed venoms showed a Newtonian flow behaviour, in contrast to previous reports. Although our results imply that the evolution of venom spitting did not significantly affect venom viscosity, our models of fang pressure suggests that the pressure requirements to eject venom are lower in spitting cobras than in non-spitting cobras.

KW - Cobra

KW - Venom

KW - Rheology

KW - Viscosity

KW - Concentration

KW - pH

KW - toxinology

KW - Herpetology

U2 - 10.1242/jeb.229229

DO - 10.1242/jeb.229229

M3 - Article

VL - 224

JO - Journal of Experimental Biology

JF - Journal of Experimental Biology

SN - 0022-0949

IS - 7

M1 - jeb229229

ER -