FNR24150 -- Week 13 Notes

Introduction to Feeding & Food Habits

• Although some exceptions exist, amphibians and reptiles mostly feed on:

  • Frogs & salamanders: insects

  • Turtles: plans & animals (vertebrates & invertebrates)

  • Squamates: animals (vertebrates & invertebrates)

Projectile Tongues

• Commonly found in amphibians (Anurans)

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  • On left:

    • A: projection; mouth opening

    • B: tongue flips forward

    • C: tongue fully extended and turned upside down; dorsal surface of tongue tip encircles prey

    • D: muscles contract and the retract tongue back inside

• Plethodontidae Salamanders

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  • A: minimal protrusion

  • B: Modest protrusion

  • C: free tongue and considerable protrusion

  • D: free tongue and extreme protrusion

  • In some salamander spp., length of tongue = half length of body

• Squamates (Chameleons)

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Hyoid bone: A piece of cartilage that serves as a rigid base of the tongue

Digestive System

Digestive Glands

• Oral cavity

  • Amphibians: Intermaxillary gland

    • Secretes a sticky compound that helps prey adhere to the tip of the tongue

    • Found in both frogs & salamanders

  • Reptiles: venom glands

    • Modified salivary glands

    • Very well-developed

    • Used to subdue and digest

• Opisthoglyph

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  • Rear-fanged snakes (back of maxilla)

  • Fangs not hollow

  • Weak venom

  • Due to location of fangs, snake must move prey to back of mouth before digestion

  • IN: Hognose Snake

• Proteroglyph elapid snakes

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  • Forward-grooved snakes

  • Shortened maxillary bearing fangs with few teeth except for enlarged fangs

  • Fixed fangs with a hollow tube (like a needle/syringe)

  • Many species are some of the most toxic (neurotoxins)

  • Due to the shortened nature of its front teeth, it must hold on momentarily to inject the venom

  • Cobras & Brown Snakes (Australia)

• Solenoglyph Viperid Snakes

  • Most advanced venom delivery method system of any snake

  • Each maxilla reduced to a nub supporting a single hollow fanged tooth

  • Fangs can be as long as half the length of head

  • Gaboon Viper: 2 in long fangs

  • Folded against roof of mouth (hinged)

  • Snake opens mouth 180°

  • Slightly less toxic than proteroglyph; a hemotoxin

  Foraging Modes

  Two general foraging methods

  1. Sit-and-wait (ambush foraging)

     1. Very little investment in time & energy searching for prey

     2. Most energy spent in capturing & handling prey

     3. Users generally have very good eyesight or special organs (pits organ)

     4. Users rely on cryptic coloration

  2. Active foraging (wide foraging)

     1. Predators are moving through the environment in search of prey

     2. Combination of visual & chemical cues

     3. Larger home range

     4. Higher ATR

  3. Likely a continuum of foraging modes from these two extremes

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  • Numerous ecological, behavioural, physiological, and life history parameters that correlate with foraging modes

Factors influencing foraging behaviour

• External factors

  1. Prey availability

  2. Predation risk

  3. Societal interactions

  4. Habitat structure

• Internal factors

  1. How hungry is it?

  2. Amount of learned experiences (coupled with age)

  3. Sex and reproductive state

     1. Males may not forage since they are protecting their territory; females may forage more to produce enough eggs

  4. Genetics

• Phylogenetic factors

  1. Sensory limitations

  2. Morphological characteristics

  3. Physiological constraints

Prey Detection

• Amphibians and reptiles can detect prey using different cues

  • Visual

    • Mostly used by sit-and-wait predators

    • Large, well-developed eyes

    • Discriminate prey based on shape and size

    • Binocular perception

      • Can detect depth & distance

    • Most align heads or entire body axis with that of prey before attacking

  • Chemical

    • Olfaction

      • Prey location identification by sniffing or rapid bugle pumping (frogs inflating their lower mouth)

      • Long-distance detection system

      • Main feeding sense of salamanders & lizards

    • Vomerolfaction (Jacob’s organ)

      • Sensitive to high molecular weight compounds

      • Transported to oral and nasal cavities by the snout or tongue

      • Short-range detection system

      • Main feeding sense in some salamanders & most snakes

        • Snakes have bifurcated tongues (provides directionality of info)

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      1. Tongue flicks and picks up high molecular weight compounds

      2. Snake retracts tongue into set of grooves in upper snout in maxilla

      3. Forks transfer compounds into epithelial cells in Jacobson’s Organ

    • Taste

      • Help distinguish food items from non-food items

  • Tactile

    • Relatively poorly understood

    • Mechanoreceptors in the skin (lateral line in aquatic amphibians)

    • In several spp., flaps of skin are highly innervated and also help in the tactile detection of prey

  • Thermal

    • Infrared light sensed by nerve endings in skin of head which are located inside pit organs

      • Loreal pits in vipers

      • Nasal/upper labial pits in pythons and boas

    • Pits open anteriorly (always face forward) and provide a binocular

    • Most effective for nocturnal spp. that feed on mammals & birds

• Many spp. use some combination of these cues

Prey Capture & Ingestion

Prey Capture

• Biting and grasping

  • Prey typically swallowed whole

• Constriction

  • Common in boas & pythons

• Injected venoms

  • Hemotoxins, neurotoxins

• Filter feeding

  • Tadpoles: large buccopharyngeal cavities

• Suction feeding

  • Prey is vacuumed into mouth

• Projectile tongues

Food Habits

• Specific food habits depend on:

  1. Feeding adaptations of animal

  2. Size of animal and prey-capturing methods

  3. Habitat

  4. Relative abundance and size of prey available at time of feeding

Communication: Types

• Social behaviour

  • An interaction with one or more conspecifics and occasionally with individuals of different species as well

• Communication

  • Transfer of information from a signaler to a receiver

• 4 basic types

  • Visual

    • Distinct colors/body movement

  • Acoustic

    • Vocalization/rubbing body parts together

  • Chemical

    • Odors

    • Well-developed in salamanders, lizards, and some snakes

  • Tactile

    • Individual rubs/presses/hits a body part against another individual

• Advantages for communication

  • Identify & locate mates in a complex environment

Communication: Salamanders

• Chemical cues

  • Salamanders use pheromones

  • Hormones are produced by courtship glands

• Tactical cues

  • Mate location in Plethodontid salamanders aided by nose-tapping

  • Also bite, slap, or rub part of their bodies against each other

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Communication: Frogs

• Acoustic cues

  • Very important

• 4 basic call categories

  1. Advertisement

     1. Attract mates

     2. Deeper = better

  2. Reciprocation

     1. Very rare

     2. Female calls in response to male

  3. Release

     1. Males amplexing other males, so a release call is made by the one being amplexed

  4. Distress

     1. Grasped by predator

• Frogs can make vocalizations by passing air back and forth between lungs, vocal cords, and vocal sacs

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• Visual cues

  • Bright colorations

  • Mostly in diurnal spp.

Communication: Turtles

• Visual cues

  • Headbobs

• Tactile cues

  • Ram, flip, trailing, biting, tickling

• Chemical cues

  • Special glands on bridge of shells

  • Cloacal secretions may also play a role

Communication: Lizards

• Visual cues

  • Coloration of dewlaps, heads and sides of the body in males and bright coloration in females

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• Chemical cues

  • Pheromones (skinks)

• Tactile cues

  • Tongue flicking

  • Neck & body scratching

Communication: Snakes

• Tactile signals very important for snake courtship

• 3 different phases

  1. Tactile phase

     1. A lot of chemosensory sampling of males to determine sex of the individual

  2. Male chases female to copulate

  3. Intromission & copulation

Group Behaviour: Competition

• Competition

  • Interspecific

    • Occasionally occurs among related spp.; frequently congregating spp. partition habitat temporally (especially during breeding)

      • Different spp. in ephemeral ponds organize by spp. and by time of day

  • Intraspecific

    • Occasionally occurs when resources are limited; minimized in larval/juvenile forms

Group Behaviour: Cooperation

• 2 forms

  1. Hibernation

     1. Different spp. of snakes hibernating together to reduce evaporative loss during winter

  2. Breeding Aggregations

     1. Male frogs taking turns to call a female (reduces intraspecific competition)