Because of the diversity in toxin type and activity, as well
the plethora of regulatory molecules maintaining
homeostatic processes, identical pathologies could be
induced by totally different toxins acting on different
molecular targets. For example, neurotoxicity could be
induced by a three-finger toxin (3FTx) blocking a given
nerve cell receptor, or by a phospholipase (PLA 2 )
breaking down the structural lipids of skeletal muscle
cells – two very different toxins with different precise
targets, but the same pathological outcome: paralysis.
Different roads being driven by different cars, but
arriving at the same destination.
A biochemical weapon.
While the role of venom varies between taxa, the
primary function of venom in snakes is for use in
predation. A snake’s venom does not just have one type
‘it is common for a venom to
be composed of dozens , if not
hundreds , of different toxin
types ’
of toxin. While there are many species whose venom is
dominated by a specific toxin family, it is common for a
venom to be composed of dozens, if not hundreds, of
different toxin types belonging to over a dozen protein
families. These toxins work together, synergistically, to
facilitate efficient prey capture. It is important to note
here that successful predation is reconciled by prey
capture – not prey death. A snake is probably not
perturbed if its meal still has a heartbeat, so long as that
heartbeat is not powering a defensive attack or a bid for
freedom. It just so happens that inducing rapid death is
often an outcome of meeting these criteria. Toxins are
thus likely to be selected for on this basis: the ability to
efficiently immobilise prey, where efficiency is measured
by both predation success and energy conservation. At a
molecular level, efficiency is dictated by the affinity of
toxins for biochemical targets within prey and their
efficacy in disrupting physiological pathways.
The physiological parameters between different animals’
bodies can vary substantially, depending on the organism
and its environment. Blood chemistry, body temperature,
and neurone configuration will differ substantially
between a lizard, a bird, and a fish, for example. This
means that the specific cell types, receptors, and
proteins servicing these body processes will also differ. It
is therefore probable that positive selection would favour
toxins with high affinity and efficacy for their preferred
prey’s molecular physiology.
When looking at the proteome (protein composition) of
snake venoms, there is an observable trend emerging to
suggest that venom composition is indeed evolving to
become more specific to the physiology of the prey taxa
which comprise respective snake species’ diet. Snake
venoms often vary intraspecifically as an apparent
reflection of differences in diet and feeding ecology. For
example, it is not uncommon for the diet - and venom -
of a given snake species to vary between populations,
according to the prey items that are locally available. This
is often observed in species whose distribution covers a
Above: the King Cobra (Ophiophagus hannah) is the longest venomous snake in the
world, and has been documented to reach a total length in excess of 5.5m. Despite a
fearsome reputation, human envenomations are extraordinarily uncommon, as this
species is generally placid and avoids confrontation. Image by Susan Schmitz.