lect 8 - venom

Question 1

poison

Answer 1

a substance toxic when swallowed

Question 2

venom

Answer 2

substance produced in a specialized gland and injected into a wound to produce a toxic effect

Question 3

snake skull

Answer 3

• mandible = lower jaw
• maxilla = outer upper jaw
• palatine + pterygoid = inner upper jaw

Question 4

4 dentitation types

Answer 4

• aglyphous
• opisthoglyph (rear-fanged)
• proteroglyph (fixed front-fanged)
• solenoglyph (hinge-fanged)

Question 5

aglyphous

Answer 5

all maxillary teeth solid, without grooves
eg. grass snakes

Question 6

opisthoglyph (rear-fanged)

Answer 6

enlarged posterior maxillary fangs with grooves (external groove not encased)
eg. african vine snake

Question 7

proteroglyph (fixed-front fanged)

Answer 7

tubular fangs at front of immobile maxilla with internal venom canal
eg. cobra (Elapidae family)

Question 8

solenoglyph (hinge-fanged)

Answer 8

long tubular fangs on mobile maxilla with venom conducting tube
- venom gland surrounded by compressor muscle
eg. viper

Question 9

Duvernoy’s gland

Answer 9

toxin-secreting gland present behind the eye in many snakes with aglyphous dentition

Question 10

snake biting

Answer 10

1. muscles pull palatine-pterygoid ball
2. ball pulls forward and pushes maxilla forward
3. maxilla rotates against prefrontal
4. prefrontal rotates against rest of the skull
   = fangs swing forward

Question 11

origin of snake venom apparatus

Answer 11

more derived delivery system evolved multiple times independently

Question 12

toxin evolution

Answer 12

gene duplication of “housekeeping” gene, followed by neofunctionalization
(further duplication -> multigene families)

Question 13

venomous lizards

Answer 13

venom apparatus in lower jaw
- assumed non-homologous to snake
(evolved independently)

Question 14

Fry’s single early origin hypothesis

Answer 14

suggests venom evolved once in the ancestor of Toxicofera

Question 15

what level does venom composition vary

Answer 15

within individuals, between individuals/populations, between species

Question 16

3 main drivers of venom variation

Answer 16

1. gene flow
2. phylogeny
3. natural selection (diet related)

Question 17

Overkill hypothesis

Answer 17

snakes produce more venom than needed, possibly reducing selection pressure

Question 18

example of prey specific venom in coral snakes

Answer 18

Micrurus venom is significantly more lethal to its natural prey

Question 19

significance of coevolution in venom systems

Answer 19

leads to specialized toxins and resistance