Introduction to Herpetology - JH

Vision Range

Effective over short to mid-range.

Signal Quality

Instantaneous signals; quality influenced by environment (e.g., blurred in rainforests).

Tetrachromats

Can see UV and millions of colours (e.g., chameleons, tortoises).

Rods (Photoreceptor Type)

• Specialized photoreceptor cells in the retina responsible for vision in low light conditions.
• Sensitive to a broad spectrum of light, enabling black and white vision.
• Predominantly used by nocturnal species for night vision.

Cones (Photoreceptor Type)

• Photoreceptor cells in the retina that function in bright light conditions, enabling color vision.
• Respond to narrow ranges of light wavelengths, facilitating color mixing and perception.
• Predominantly used by diurnal species for daytime vision.

Scleral Ossicles in Lizard Vision

Maintain eye shapes in most lizards, absent in snakes.

Oil Droplets in Lizard Vision

Filter light, enhancing colour vision.

UV Reflection in Lizard Vision

Visual traits reflect UV for marking territory, invisible to mammals.

Diurnal Lizard Vision Traits

• Broad field of view, dual fovea
• All-cone retina = poor night vision
• Sensitive to jerky motion and sun angle

Nocturnal Lizard Vision Traits

Large eyes dominate skull shape. Geckos have only cones - 4x larger than in day geckos. Eye structure optimised for twilight activity.

Parietal Eye Function 1

Detects light intensity; no image-forming function.

Parietal Eye Function 2

Regulates circadian rhythm and thermoregulation.

Parietal Eye Function 3

Connects to non-visual brain areas.

Tortoise Vision

Tetra chromatic - UV vision

example - Hermans tortoise prefers yellow - linked to quality in diet

Fossorial - Amphisbaenians

Simplified eyes under head scales

Fossorial - Amphisbaenians

Iris fused with ciliary bodies

Fossorial - Amphisbaenians

Detect only light levels and vague shapes

Amphibian Vision - Photoreceptors

Frogs have 4 photoreceptors (2 in rods)

Amphibian Vision - Color Vision

Amphibians can see color in complete darkness

Amphibian Vision - Fossorial Caecilians

Even fossorial caecilians retain functional eyes

Amphib

Aquatic adaptations resemble reptiles

Snake Vision - Complexity Reduction

How is snake vision less complex than other species? Snakes lack ciliary muscles and oil droplets.

Snake Vision - Focusing

How do snakes focus their vision? They move the lens within the eye.

Snake Vision - Dichromatic Vision

What type of color vision do most snakes have? Most are dichromatic, meaning they see two colors.

Snake Vision - Opsin Genes

What are the key Opsin genes in snake vision? LWS (yellow-orange), SWS1 (UV blue), RH1 (low light).

Snake Vision - Blind Snakes

What is the vision capability of blind snakes? They have grayscale vision only.

Diurnal Snakes - Activity

When are diurnal snakes active? They are active in daylight and rely on basking for thermoregulation.

Diurnal Snakes - Color Vision and Depth Perception

How is the color vision and depth perception of diurnal snakes considered? They have good color vision and depth perception.

Diurnal Snakes - Reflexes and Coloration

What are the characteristics of diurnal snake reflexes and coloration? They have fast reflexes and are often brightly colored.

Diurnal Snakes - Example

Give an example of a diurnal snake and its special traits. Ahaetulla: horizontal pupils, sharp motion/depth perception.

Infrared Vision in Snakes

Which snakes have infrared detecting abilities? Pit vipers, pythons, and boas.

Wavelength Sensitivity of Pit Vipers

What wavelength of infrared light can pit vipers sense? 1.5µm.

RC (raticularis caloris)

What is the function of the RC (raticularis caloris) neural pathway? It processes infrared signals.

LLTD (lateral descending trigeminal tract)

What is the role of the LLTD (lateral descending trigeminal tract)? It carries infrared signals to the brain.

Integration of IR Signals

Where do infrared signals integrate with vision in the snake brain? In the optic tectum for thermal imaging.

Loreal Pit Location

Where is the loreal pit located on infrared-detecting snakes? Between the eye and nostril.

TRPA1 Channel Function

What is the function of the TRPA1 channel in snake pit organs? It detects heat.

Pit Membrane Characteristics

Describe the pit membrane. It is thin, vasculated, and innervated.

TG Fibers Function

What is the role of TG fibers in infrared detection? They transmit IR signals quickly to the brain.

Mechanorecprtion - vibration detection

air = hearing

water = lateral line/tactile detection

ground = somatic conduction e.g snakes

airborne vibration = hearing

Early tetrapod hearing

• Tiktaalik (375mya) - lateral dominant line'; little airborne hearing

• Itchyostega (365mya) - beginning of middle ear; detects low frequencies

Anurans

• amphibian papilla (low frequencies)

• Basiliar papilla (high frequencies)

Anurans vocal production

• vocal scar; air from lungs over vocal chords

• both sexes vocalise'; males have enhanced larynx and large vocal muscles

• call types - territorial, mating, species recognition, distress, warning, release, response

• ultrasound - some frogs e.g concave eared torrent frog ca;; up to 38kHZ