Week 2 - lizards and snakes Flashcards
Describe why lizards are not a natural group?
natural group is a particular phylogenetic concept where they are each other’s closest relatives - lizards to the exclusion of snakes
Describe the selection pressures that lead to the multiple independent evolutions of setae in geckos and how we known that this is not a basal feature?
convergent evolution lead to adhesive toe pads - the underlying mechanics vary.
evolving to selection pressures, climbing up something might required different textures ( mechanically different solution - overall function is the same)
basal - terrestrial and not able to climb but due to convergent evolution they developed independent characteristics such as sticky pads.
describe the spines of spiny-tail geckos and what they are used for
unique among geckos - defensive secretes out of spines with an associated gland
can shoot secretes
sticky and smells bad - repels any predator away.
describe what features distinguish legless lizards from snakes
limb reduced, morphology is similar to snakes - leglessness is a convergent condition.
evolved 25 time
long tail - above ground
short tail - below grow
pelvic girdle
may have eyelids - reduced eyes
external earholes
evolved from geckos
well ossified skulls
describe the two basic morphotypes of legless lizards and niche each morphotype evolves to fill and why one type is more species-rich than the other
short tail - burrow
short tail - highly evolved for a particular soil, mechanically push through the soil - required different skull morphology. Requires a different head shape for different types of soils.
describe the venom system of anguimorpha lizards such as varanids
describe why the bacteria as a weapon hypothesis in komodo dragons invalid
Describe the predatory strategy of pythons and how they subjugate their prey
They don’t kill by suffocation - the constriction increases the blood pressure = Dramatic rise in blood pressure which can have two effects.
- Less blood flow, therefore less oxygen being supplied to brain and body (respiratory failure death).
- Rise in blood pressure can be very dramatic - back pressure can cause heartattack.
Ability to swallow large prey - lower jaw bones are not fused.
Describe the predatory strategy of file snakes, how they subjugate their prey,
and what morphological features aid in prey handling
scales - use constriction to suffocating fish - wrapping around the head of the fish and preventing the gills from opening. Thus, the fish cannot filter oxygen = death. Scales help with the traction of this grip on the scales.
Describe what site snake venom neurotoxins bind to and what kind of paralysis
they produce
neuromuscular junction in a nerve - acetylcholine is released as a messenger.
Snake venom alpha-neurotoxins bind to the postsynaptic nicotinic acetylcholine receptor to produce flaccid paralysis.
Toxins targets different channels, such as potassium channels, Sodium Channels nicotinic receptors calcium channel.
Distinguish between procoagulant, pseudo-procoagulant, and classic
anticoagulant venoms in regards to the action on fibrinogen and the type of
fibrin clot formed
Procoagulant - indirect action on fibrinogen to form strong stable clots. Generation of endogenous thrombin by activation of factor X or prothrombin. Therefore due to the body size in humans it
produces small little blood clots - but they consume all of the clotting factors and therefore the body cannot make a blood clot which ultimately causes internal bleeding.
Pseudo- procoagulant
There is a depletion of
Classic Anticoagulant - kill be hemorrhagic shock- instantaneous bleeding within the body, decreasing the blood pressure.
- depletion of fibrinogen levels by non-clotting proteolysis of fibrinogen
- depletion of fibrinogen levels by pseudo-procoagulant cleavage of fibrinogen resulting in very weak, short-lived, fibrin clots that rapidly degrade.
Describe how lethal Australian coagulotoxic snakes like brown snakes or
taipans act on the blood: what are the biochemical characteristics of the
toxins, where do they act, and how are prey animals affected differently than
humans and why
Taipans: prey is mammals and have coagulopathic venom - long distance striking and large amount of venom (they often go for something bigger and more dangerous)
Brown snake:
Kill by induction of stoke in a prey animal and human victims bleed out.
They cause conversion of fibrinogen into fibrin clots by activation of upstream element - prothrombin activators.
Venom evolved - overdose scenario - activated clotting enzymes. Toxin are essential mutated to form blood clotting factors (factor Xa and Va)
Describe what selection pressures have led to the differences in juvenile vs
adults in brown snakes vs taipans
baby taipans - act like adults. and venom potency is identical.
Brown snake adults and juveniles are different - babies are nocturnal (specialise on sleeping lizards and neurotoxin) , adult active during the day and specialist on mammals - coagulopathic venom.
Describe the relationship between pain inducing defensive toxins in hooding
snakes and warning colouring/patterns
local painful wounds - evolved with hodding not spitting.
Egyptian cobra - no markings on hood - horizontal bar, venom has wounding toxins
Indian cobra - eye catching marking - non spitting cobra - massive wounding venom. increase in wounding colours, increase in venom severity (wound inflecting)
The convergent evolution of aposematic warning banding patterns is
linked in each case to further increases in the levels of cytotoxic 3FTx.
