Venom

Lecture exam 2

Venom evolution

it used to be claimed venom evolved once and was lost in some lineages

now evidence points to venom evolving multiple times

3 finger toxins (3ftx)

very specialized for certain taxa

Gila monster

venom is thought to be defensive because bulk of diet is eggs

Birth-death model of venom evolution

all the genes can duplicate and go wild in glands, some will degrade a little, some degenerate entirely, and some mutate and undergo neofunctionalization 

Venom Variation

1. within population

2. sexual dimorphism

3. geographic

4. ontogenetic

5. seasonal

6. interspecific

7. hybridization

8. convergent evolution

9. prey specificity

10. venom resistance

venom variation within a population

Venoms can vary among individuals within a single population (i.e. cobras)

venom variation: sexual dimorphism

venoms can vary between sexes

geographic venom variation

venom can vary across species ranges

ontogenetic venom variation

venom can vary across different ages

seasonal venom variation

venom can vary between seasons

interspecific venom variaion

venom can vary across different species

hybridization-induced venom variation

hybrids can have different venom than both the parents

convergent evolution venom variation

many species converged on a few optimal venom formulations

venom prey specificity

Probably underlying all of these and having the most effect on venom

venom resistance variation

A lot of prey (i.e. opossums) can gain adaptations to make them resistant to venom 

biochemical ecology

Ecological interactions (e.g., predation) that are chemically meditated via natural toxins in one or both parties

Western diamndback rattlesnake venom variation

venom variation is minor

Mojave rattlesnake venom variation

venom variation is major across geographic range

prairie rattlesnake venom variation study

Two spatially-discreet venom phenotypes

• Myotoxin a dominated Northern Phenotype

• SVMP dominated Southern Phenotype

Venom phenotypes are under strong selection from various interacting biotic and abiotic factors

Myotoxin a is a taxon-specific toxin for mammals, the first prey-specific toxin identified from a rattlesnake

Van Valen’s Red Queen Hypothesis

Idea that reciprocally interacting organisms are coevolving to remain competitive

Prey-Predator venom interaction study

• Rattlesnake venoms are locally adapted for

some prey species

• Several rodents possess strong resistance

to rattlesnake venoms

• North American raptors are not resistant to

SVMPs

• The venom resistance landscape is complex

and everchanging