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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  </p>

  • 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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  </p>

  • 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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  </p>

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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

  • <br />

  </p>

  • %%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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  </p>

  • 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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  </p>

  • 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)
    • 
    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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  • 
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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)

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