When venomous snakes are born they already possess the
apparatus and venom to deliver a toxic bite. It is an essential ability in
order for the young to feed and defend themselves immediately as this is when
they are most susceptible to predation. As growth from young to old is closely
linked to preferential prey it is likely a that this change corresponds to more
accurately target its prey at that age (Gibbs et al. 2011).
Venoms are an efficient and targeted tool to aid in feeding, this specialisation of venoms leads to the diverse forms we see today. As the diet of the snakes change so must its venom to ensure it is effective. Investigations into the composition shifts in venoms over a snakes lifetime has been carried out on many species particularly the Crotaline snakes (rattle snakes and relatives). Many of these snakes feed on frogs or small lizards when young. In the case of Crotalus oreganus a higher percentage of myotoxins are found in the venom of older snakes that have progressed to feeding on small mammals.The younger specimens showed more neurotoxic venom while still at a similar overall toxicity to the adults (Mackessy et al. 2003).
This adaptation can cause greater difficulty in producing an effective treatment for bites. The most effective antivenom, polyvalent antivenom, is produced to target specific component of the venom.Should the venom be varied due to ontogenetic shifts a bite from a juvenile may not be effectively treated by an antivenom produced for adults venom. Natural variation in populations and between populations in different localities and conditions also presents the same concern (McCue. 2006).
References
Mackessy, S.P., Williams, K. and Ashton, K.G., (2003). “Ontogenetic variation in venom composition and diet of Crotalus oreganus concolor: a case of venom paedomorphosis?.” Copeia, Vol: 2003 No: 4, pp.769-782.
McCue M.D. (2006). “Cost of Producing Venom in Three North American Pitviper Species.” Copeia, Vol: 2006, No: 4, pp. 818-825.
Gibbs, H.L., Sanz, L., Chiucchi, J.E., Farrell, T.M. and Calvete, J.J., (2011). “Proteomic analysis of ontogenetic and diet-related changes in venom composition of juvenile and adult Dusky Pigmy rattlesnakes (Sistrurus miliarius barbouri).” Journal of proteomics, Vol: 74 No:10, pp.2169-2179.
Image
http://www.stuartdahnephotography.com/keyword/crotalus%20tigris%20the%20tiger%20rattler/i-xttv4cn accessed: 13/4/16
Are ontogenetic shifts common to all species or do some species retain their same venom profile throughout their lifetime? Does venom have to change with age because of the specific peptides within that the venom that target specific parts of the prey (i.e. something that kills an insect may not skill a mammal)?
ReplyDeleteInformation on these venom shifts is not overly wide ranging but certainly many species of snake have shown ontogenetic shifts in venom composition in at least three families.
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