How the Cobra Got Its Flesh-Eating Venom: Cytotoxicity as a Defensive Innovation and Its Co-Evolution with Hooding, Aposematic Marking, and Spitting.
The cytotoxicity of the venom of 25 species of Old World elapid snake was tested and compared with the morphological and behavioural adaptations of hooding and spitting. We determined that, contrary to previous assumptions, the venoms of spitting species are not consistently more cytotoxic than those of closely related non-spitting species. While this correlation between spitting and non-spitting was found among African cobras, it was not present among Asian cobras. On the other hand, a consistent positive correlation was observed between cytotoxicity and utilisation of the defensive hooding display that cobras are famous for. Hooding and spitting are widely regarded as defensive adaptations, but it has hitherto been uncertain whether cytotoxicity serves a defensive purpose or is somehow useful in prey subjugation. The results of this study suggest that cytotoxicity evolved primarily as a defensive innovation and that it has co-evolved twice alongside hooding behavior: once in theHemachatus + Najaand again independently in the king cobras (Ophiophagus). There was a significant increase of cytotoxicity in the AsianNajalinked to the evolution of bold aposematic hood markings, reinforcing the link between hooding and the evolution of defensive cytotoxic venoms. In parallel, lineages with increased cytotoxicity but lacking bold hood patterns evolved aposematic markers in the form of high contrast body banding. The results also indicate that, secondary to the evolution of venom rich in cytotoxins, spitting has evolved three times independently: once within the AfricanNaja, once within the AsianNaja, and once in theHemachatusgenus. The evolution of cytotoxic venom thus appears to facilitate the evolution of defensive spitting behaviour. In contrast, a secondary loss of cytotoxicity and reduction of the hood occurred in the water cobraNaja annulata, which possesses streamlined neurotoxic venom similar to that of other aquatic elapid snakes (e.g., hydrophiine sea snakes). The results of this study make an important contribution to our growing understanding of the selection pressures shaping the evolution of snake venom and its constituent toxins. The data also aid in elucidating the relationship between these selection pressures and the medical impact of human snakebite in the developing world, as cytotoxic cobras cause considerable morbidity including loss-of-function injuries that result in economic and social burdens in the tropics of Asia and sub-Saharan Africa.
Venom Evolution Lab, School of Biological Sciences, University of Queensland, St. Lucia, QLD 4072, Australia. nadya.panagides@gmail.com.
Nadya
N
Panagides
Venom Evolution Lab, School of Biological Sciences, University of Queensland, St. Lucia, QLD 4072, Australia. tnwjackson@gmail.com.
Timothy N W
TN
Jackson
QIMR Berghofer Institute of Medical Research, Herston, QLD 4049, Australia. maria.ikonomopoulou@qimrberghofer.edu.au.|School of Medicine, The University of Queensland, Herston, QLD 4002, Australia. maria.ikonomopoulou@qimrberghofer.edu.au.
Maria P
MP
Ikonomopoulou
Department of Biosciences, College of Science, Swansea University, Swansea SA2 8PP, UK. kevin.arbuckle@swansea.ac.uk.
Kevin
K
Arbuckle
Venom Evolution Lab, School of Biological Sciences, University of Queensland, St. Lucia, QLD 4072, Australia. rp1990@gmx.at.
Rudolf
R
Pretzler
Monash Venom Group, Department of Pharmacology, Monash University, Clayton VIC 3800, Australia. daryl.yang@monash.edu.
Daryl C
DC
Yang
Venom Evolution Lab, School of Biological Sciences, University of Queensland, St. Lucia, QLD 4072, Australia. dr.syedabidali@gmail.com.|HEJ Research Institute of Chemistry, International Centre for Chemical and Biological Sciences (ICCBS), University of Karachi, Karachi 75270, Pakistan. dr.syedabidali@gmail.com.
Syed A
SA
Ali
Venom Evolution Lab, School of Biological Sciences, University of Queensland, St. Lucia, QLD 4072, Australia. jcoludar@gmail.com.
Ivan
I
Koludarov
Venom Evolution Lab, School of Biological Sciences, University of Queensland, St. Lucia, QLD 4072, Australia. james.dobson@uqconnect.edu.au.
James
J
Dobson
Venom Evolution Lab, School of Biological Sciences, University of Queensland, St. Lucia, QLD 4072, Australia. brittany.sanker@uq.net.au.
Brittany
B
Sanker
Venom Evolution Lab, School of Biological Sciences, University of Queensland, St. Lucia, QLD 4072, Australia. angelique.asselin@uq.net.au.
Angelique
A
Asselin
Venom Evolution Lab, School of Biological Sciences, University of Queensland, St. Lucia, QLD 4072, Australia. renancassant@gmail.com.
Renan C
RC
Santana
Venom Evolution Lab, School of Biological Sciences, University of Queensland, St. Lucia, QLD 4072, Australia. iwanhx@yahoo.com.
Iwan
I
Hendrikx
Working Group Adder Research Netherlands, RAVON, 6525 ED Nijmegen, The Netherlands. info@eyecreations.nl.
Harold
H
van der Ploeg
Working Group Venomous Bites Netherlands, RAVON, 6525 ED Nijmegen, The Netherlands. jeremie@ratelslangen.nl.
Jeremie
J
Tai-A-Pin
Naturalis Biodiversity Center, 2333 CR Leiden, The Netherlands. rovdbergh@me.com.
Romilly
R
van den Bergh
Institute of Biology Leiden (IBL), Leiden University, Sylviusweg 72, 2333 BE Leiden, The Netherlands. h.m.i.kerkkamp@biology.leidenuniv.nl.
Harald M I
HM
Kerkkamp
Naturalis Biodiversity Center, 2333 CR Leiden, The Netherlands. freek.vonk@naturalis.nl.
Freek J
FJ
Vonk
Snakebite Assist, Pretoria ZA-0001, South Africa. afnaude@worldonline.co.za.
Arno
A
Naude
Department Pharmacology, University of Pretoria, Pretoria ZA-0001, South Africa. morne.strydom@synexus.com.|SYNEXUS Clinical Research SA Pty Ltd., Pretoria ZA-0001, South Africa. morne.strydom@synexus.com.
Morné A
MA
Strydom
Zoology Department, University of Pretoria, Pretoria ZA-0001, South Africa. louissnakes@gmail.com.
Louis
L
Jacobsz
Venom Supplies, Tanunda, South Australia 5352, Australia. nathan@venomsupplies.com.
Nathan
N
Dunstan
Planet Exotica, 5 Avenue des Fleurs de la Paix, 17204 Royan, France. marc.jaeger@bluewin.ch.
Marc
M
Jaeger
Monash Venom Group, Department of Pharmacology, Monash University, Clayton VIC 3800, Australia. wayne.hodgson@monash.edu.
Wayne C
WC
Hodgson
QIMR Berghofer Institute of Medical Research, Herston, QLD 4049, Australia. John.Miles@qimrberghofer.edu.au.|School of Medicine, The University of Queensland, Herston, QLD 4002, Australia. John.Miles@qimrberghofer.edu.au.|Australian Institute of Tropical Health and Medicine, James Cook University, Cairns, QLD 4878, Australia. John.Miles@qimrberghofer.edu.au.
John
J
Miles
Venom Evolution Lab, School of Biological Sciences, University of Queensland, St. Lucia, QLD 4072, Australia. bgfry@uq.edu.au.
Bryan G
BG
Fry
D000818:Animals; D001522:Behavior, Animal; D005075:Biological Evolution; D002460:Cell Line; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D002645:Chickens; D004546:Elapid Venoms / Q000633:toxicity; D017815:Elapidae / Q000502:physiology; D006801:Humans; D018482:Muscle, Skeletal / Q000294:innervation; D009469:Neuromuscular Junction / Q000187:drug effects; D009498:Neurotoxins / Q000633:toxicity; D010858:Pigmentation
D004546:Elapid Venoms; D009498:Neurotoxins
Elapidae; Hemachatus; Naja; Ophiophagus; antipredator defense; cobra; cytotoxin; evolution