Herpetology Unit 2

·      Diets, foraging, and predation

-       Most herps are carnivorous. Carnivores assimilate 90% of vertebrate prey’s energy.

-       Carnivores have short digestive tracts.

-       Herbivores assimilate 30-60% of energy available.

-       Salamanders feed selectively on soft-bodied inverts but will head chitinous insects during dry periods

-       Texas thorny devils are spiny with tank-like bodies, peg-like teeth, and cryptic coloration, and tank-like body handles large quantities of invert prey.

-       Dendrobatid tadpoles eat unfertilized eggs (oophagy).

-       Hawksbills eat sponges and leatherback jellyfish.

-       Snail eaters: Upper jaw strongly braced with braincase to pull out snails or just crush shells with strong jaws.

-       Cannibalism common in amphibians due to limited resources. Common in tiger salamanders and spadefoots. Some triggers induce jaw muscle enhancement and predation, can be crowding or ingestion of shrimp/tadpoles!

-       Adult tuataras eat their hatchlings 

-       Specialized herbivores have gut flora for fermentation and high bite force for size!

-       Herbivores include anuran tadpoles, tortoises, green sea turtles, iguanas, and some agamids.

-       Herbivore teeth are robust and blade-like with a long, enlarged colon.

-       Specialized herbivores typically tend to be large and live in warmer climates.

-       Omnivory is most common in lizards and turtles.

-       Lizards can act as important pollinators on islands without high nectarivorous bird densities.

-       Feeding preferences can vary in sexually dimorphic species.

-       Innate vs learned behaviors. Amphibians who actively search for prey that move continuously, ambush predators look for small, compact prey that exhibit jerky quick movements.

-       Experiences are adaptive, novel experiences can inform about palatability and danger.

-       Volmerofaction: Important sense for squamates. Uses tongue to sample non-volatile molecules. Ventral side of tongue delivers to Jacobson’s organ.

-       Infrared radiation- Thermal cues: Pit vipers, boas, pythons.

-       Lateral line system: Mechanoreceptors and electroreceptors.

-       Tympanic membranes: Frogs and crocs sense air/substrate vibrations.

-       Foraging strategies:

-       Ambush: use vision and more likely to consume chemically dubious prey. Tend towards short and stout features and cryptically colored. Low reward but low cost.

-       Active foraging: Move frequently and fairly fast and search for hidden prey. Vomerolfaction. Long and lean features are common.

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-       Caudal autonomy: Tail dropping.

-       Compensatory suction: Prevents a pressure wave that pushes prey away and uses negative pressure. Head snaps forward with open mouth and expands buccalpharyngeal cavity, creates negative pressure that causes prey to be sucked into mouth. Often associated with larger cavity for more force!

-       Inertial suction: Accommodates water and creates an inward flow of water by expansion of long neck.

-       Neustophalia: Skim small floating items like pollen and algae from water’s surface.

-       Terrestial turtles have akinetic skulls, no teeth but sharp edges, and can generate considerable bite force.

-       The two primary weaknesses of turtle feeding include a large middle ear and a small head for retraction. They have compensated by evolving a trochlear process that acts as a pulley to change direction of the muscle with minimum loss of force. Adductor muscle curves around trochlear process.

-       Pterygoid bone (Pleurodirans) and quadrate bone (Cryptodirans) processes .

-       Tortoises grind food down.

-       Larval and some paedomorphic salamanders, and some larval Caecillians can create one-way flows of water. They do this by using labial lobes to seal the sides of the mouth, preventing water and prey from escaping.

-       Anuran tadpoles are primarily scraping algae-eaters.

-       Gill filters filter food in Anuran tadpoles. Some also use keratinous mouth structures to scrape algae.

-       Pipid frogs feed via negative suction and shoving food in their mouth with their forelimbs.

-       Burrowing modifications of caecilians have placed constraints on feeding adductor mandibulae muscles. They compensate by having a long retroarticular process with an enlarged interhytoid muscle extending far back along sides of the neck, attaching to retroarticular process from below.

-       Caecilians utilize rotational feeding when targeting a large prey item.

-       Crocodilians feed by opening their mouths by simply lifting their heads!

-       Generalist crocodilians have shorter, rounder jaws, sacrificing some speed for strength.

-       Small prey of crocodilians can be crushed against the roof of their mouth with their tongue.

-       Some crocodilians will lure birds with appetizing sticks.

-       Projectile tongues: Frogs/salamanders/chameleons. Almost all rely on the concept of elastic energy storage released into the tongue.

-       Salamanders use lingual prehension: Tongue is slapped onto prey.

-       Plethodontids make use of space produced by loss of lungs for hyobrachial tongue feeding system.

-       Specialized tongue projector muscles contract around the arms of the Y-shaped hyobranchial skeleton, firing the tongue out rapidly.

-       Mechanical pulling: Some frogs utilize contracting muscles to draw their tongue out and back. During protraction, the tongue shortens and projects only slightly beyond the tip of the lower jaw. Projection slow and usually include lunging at prey and use forelimbs to stuff it into their mouths. Found in basal frogs sucg as Hylids.

-       Inertial elongation: Tongue is flung forward and downwards like a catapult, muscles stiffen at the front of the tongue.

-       Hydrostatic elongation: Tongue functions as a muscular hydrostat that can be projected in multiple directions, but does not extend passed the jaw. Tongue has a fixed volume but muscles can act to make it longer, shorter, and narrower and wide. Lack independent skeletal systems, characteristic of myrmecophages.

-       Chameleons possess an accelerator muscle and sticky pad.

-       Lizards have lost the lower temporal arch so the quadrate can move forward and back around.

-       Inertial feeding occurs in monitors and tegus. These lizards have deeply forked tongues for chemoreception. Food is held in jaws, jaw is held back.

-       Scolecophidians- Feed on large quantities of small prey. Short jaws and small gape. Consume much ant and termite larvae.

-       Alethinophidians- Feed on fewer large individuals. Alternating jaw movements progressively move prey down mouth. Streptostylic quadrate allows jaws to move sideways.

-       Unilaterally feeding: Prey is transported via left and right undulating jaw movements.

-       Snail-eaters extract snails with long mandible excursions that are laterally compressed with comb-like teeth. Can trigger different directions in snail coils on the population level.

-       Many Alethinophidians restrain prey by pressing it against substrate.

-       True constriction requires squeezing of bodily coils around prey.

-       Venom immobilizes, kills, digests, and can also serve as a defense tool.

-       Colubrids: Duvernoy’s gland and posterior maxillary teeth. Fang grooves conduct venom.

-       Front fangs: Enclosed tube for venom conduction. Large glands; venom is expelled via pressure exerted by a compressor muscle. Includes Elapids (coral snakes, cobras, sea snakes, taipans) with short non-retractable fangs and neurotoxic venom, and Viperidae with long fangs that are retractable and non-rotatable and tissue-toxic venom.

-       Helodermatids: Venom gland lies along the lateral surface of each mandible. Venom is secreted through ducts to deep grooves in teeth.

Tissue destruction or nervous disruption are the primary venom strategies