Snakes Exam

1. Burrowing Lizard hypothesis: all snakes are limbless or virtually so, lack external tympana, and have peculiar eyes that appear to be reconstructed from leftovers following a period of degeneration

2. Aquatic mosasaur hypothesis: Fused, transparent eyelids of snakes evolved to combat marine conditions, and the external ears were lost though disuse in an aquatic environment

What are the two hypotheses for the origin of snakes?

33%

What % of all reptiles are snakes?

1. Terrestrial: fast active foragers; sit-and-wait predators

2. Fossorial: small body size; narrow head; reduced eye; skull reinforcements; pale coloration

3. Arboreal: long, thin body; thin tail; reduced eye; skull reinforcements; pale coloration

4. Aquatic: valves on nostrils; freshwater ecomorphs often look pretty terrestrial; eyes & nostrils shifted towards dorsal surface

Name & describe the 4 ecomorphs

Lateral undulation

What is the primary locomotion for snakes?

1. Concertina - employed on low-friction, tight spaces, or while climbing trees; one portion of body is anchored while another part moves

2. Rectilinear - draws body forward in straight line (for heavy-bodied snakes)

3. Sidewinding - sand-dwelling snakes; body is only touching the ground in two spots; creates parallel lines

4. Gliding

5. Diving - elapids

Name the types of movements and explain them

Cutaneous respiration (breathing through the skin)

Type of respiration that marine snakes have, but terrestrila do not

1. Sit-and-wait: sedentary, ambush predators

2. Tail luring: some sit-and-wait predators use parts of their bodies as lures

3. Heat-sensitive pits: sense infrared heat radiating from mammalian prey

Types of prey acquisition specialized morphology

1. Constriction

2. Envenomation

What are the two primary mechanisms of larger snakes to acquire prey?

Cranial kinensis

What is the term that allows snakes to completely open their jaw wider?

“Comb-like” teeth

What kind of teeth do molluschivory snakes have?

1. Aglyphous: homodont

2. Opisthoglyphous: rear-fanged

3. Proteroglyphous: “fixed” front-fanged

4. Solenoglyphous: “hinged” front-fanged

What are the 4 kinds of teeth types? (Homodont)

Male location

What is the biggest determinant of male reproductive success?

Mostly maternal, but can be biparental (seen in rattlesnakes)

What does parental care look like in snakes?

Shivering thermogenesis; can be incredibly metabolically expensive

Type of egg incubation

Reproductive activity; allocation to reproduction reduces both growth and survival; tradeoff between reproduction and survival

The reduction of an individual’s future fitness is caused by:

Pace-of-life hypothesis; short-lived & long-lived

What is the life history hypothesis that says there is a tradeoff between reproduction and survival that is driven by physiological linkage to metabolism?

Garter snakes

What kind of snake hibernate together in tens of thousands and mate immediately in giant balls in the spring?

Internal using hemipenes (using only 1 at a time)

How does fertilization work w/ snakes?

Specialized mechanoreceptors on the surface of the scales

What are ‘scale sensilla’?

1. Chemosensory (most)

2. Acoustic

3. Visual anti-predator displays

What are the types of communication?

In species with intense male-male combat

When are males larger?

Death-feigning: parasympathetic nervous system response co-opted as anti-predator defense

What is the main visual anti-predator display?

By following pheromone trails

How do males find females?

Keratiin

What are rattlesnake rattles made of?

• Poison: passively absorbed or ingested

• Venom: is actively injected; prey acquisition or predator defense

What is the difference between poisonous and venomous?

At least 3 times

How many times have the front fangs evolved?

Chemosensory & utilizes large lipid molecules

What is the primary communication method & what they use?

1. Neurotoxin: attacks neuromuscular junctions - leading to respiratory or circulatory failure

2. Hemotoxin/necrotoxin/myotoxin: essentially “digests” and necrotizes tissue; often results in amputation: more common in vipers

What are the two types of venom types & effects?

1. Assess proteins: Run “gland juice” through a column, “things” separate based on size and type

2. Sequence all RNA: tells you everything that is being transcribed within that gland at that time point

How is venom variation assessed?

Grace Wiley

Who was the woman who owned snakes and then later died from a snake bite?

Diet

What did they look at that determines appearance of venom in colubrids?

1. Mullerian mimicry: multiple dangerous species converge on the same warning phenotype

2. Batesian mimicry: one species has a warning phenotype which is deceitfully imitated by harmless species

What are the tow types of visual mimicry?

1. Copied from Coral snakes

2. Colubrines and Dispadines

What snake is famous for being copied in terms of the Batesian mimicry?

Wallace’s Three Laws (1867)

1. Must be found in the same geographical region

2. Mimicry confined to a few groups (rare phenotype)

3. Imitators must be less abundant than models

What are the rules for mimicry?

1. Mimics can’t be outside the range of models

2. Way too many mimics

What are the violations for the mimicry rules?