Study Guide questions

Familiarize yourself with the phylogenetic tree depicting the relationships of the following sarcopterygiian groups: Coelacanthiformes, Dipnoi, †Eusthenopteron, †Panderichthys, †Tiktaalik, †Ventastega, †Acanthostega, †Ichthyostega, Amphibia, and Amniota.  Be sure to label to following monophyletic groups: Tetrapodomorpha, Elipsostegalia, and Tetrapoda.

Draw a phylogenetic tree depicting the phylogeny of the tetrapods. Be sure to label the following monophyletic groups: Gymnophiona, Urodela, Anura, Lissamphibia, Sphenodontidae, Squamata, Lepidosauria, Testudines, Crocodilia, Aves, Archosauria, Sauropsida, Mammalia. This is the phylogeny you should commit to memory for the exam.

Distinguish between the following sarcopterygian lineages: Coelacanthiformes, Dipnoi, Ceratodontiformes, and Lepidosireniformes, citing characteristics of each.

• Habitats

  • Coelacanthiformes: marine environments

  • Dipnoi, Ceratodontiformes, Lepidosireniformes: freshwater

• Appearance

  • Coelacanthiformes

    • lobe-finned appendages that resemble limbs

  • Dipnoi

    • possess one or two lungs, which are modified swim bladders

  • Ceratodontiformes

    • tooth plates used for crushing hard-shelled prey

  • Lepidosireniformes

    • elongated eel-like body, fins reduced in size, smoother skin with less pronounced scales

• Coelacanthiformes

  • behavior: predators that hunt small bony fishes, squids and other invertebrates

• Dipnoi

  • survival adaptations: can survive dry periods by burrowing into mud and breathing air

• Ceratodontiformes

  • evolutionary significance: closest living relatives of tetrapods

Why is the discovery of the coelacanth considered the greatest animal discovery of the 20^th century? Argue for the significance of this fish.

1. living fossil: until its discovery in 1938, they were thought to be extinct

2. evolutionary link: helps to understand the transition from aquatic to terrestrial life

3. biological insights: it has unique features such as its lobed fins and rostral organ for electro-sensory perception

Outline examples of permanent and temporary secondary sex characteristics in fishes. What is the function of these various features?

• permanent secondary sex characteristics

  • gonopodium in male guppies

    • a modified anal fin used for transferring sperm to females

  • bright coloration in male cichlids

    • males use vibrant colors to attract females and assert dominance

• temporary secondary sex characteristics

  • nuptial tubercles in male minnows

    • small, hard bumps that appear on the head and body during the breeding season for better grip on females

  • kype in male salmon

    • hooked jaw that develops during breeding season for fighting other males

Hermaphrodism has evolved multiple times in fishes. Describe the various manifestations of hermaphrodism, citing specific examples of each.

• simultaneous hermaphroditism

  • individuals possess both male and female reproductive organs at the same time

  • ex. hamlets

• protandry

  • individuals start life as males and later change to females

  • ex. bluehead wrasses

• protogyny

  • start as females and change to male

  • ex. California sheephead

• bidirectional sex change

  • change sex more than once

  • ex. blackspot tuckfish

Some fishes can be categorized as ‘parasitic hybrids’ based on their reproductive strategy. Explain why these fishes are considered ‘parasitic’ and describe both hybridogenesis and gynogenesis as reproductive strategies. A well-labeled diagram may be useful to illustrate your answer.

Considered parasitic because their reproductive strategies exploit the genetic material and energy of their host species without contributing genetically to their offspring.

• hybridogenesis

  • the hybrid’s egg retains only its maternal genetic material and then the hybrid mates with a male from the host species to restore the discarded genome. The offspring are essentially clones of the mother

• gynogenesis

  • the egg of the hybrid requires stimulation from the sperm of the host species to develop, but the sperm’s genetic material is not incorporated into the offspring

An otophysic connection between the gas bladder and inner ear has evolved several times in teleost fishes. Describe these different otophysic connections, citing specific examples.

• Weberian Apparatus

  • a series of small bones connect the anterior part of the swim bladder to the inner ear, acting like an ear drum, important for hearing sensitivity especially lower frequencies

  • found in carps and their relatives

• Anterior swim bladder extensions

  • extensions of the swim bladder come into contact with the inner ear, transmitting sound vibrations directly, important for enhancing auditory capabilities

  • found in some cichlids

• Labyrinth Fishes

  • the swim bladder is closely associated with the inner ear, allowing sound ways to be transmitted efficiently, contributes to improved hearing

  • found in Japanese rice fish

Electroreception and electrogenesis have evolved several times in fishes. Discuss categories and functions of electroreception and electrogenesis in fishes, citing specific examples.

• Electroreception: helps with object location like locating prey (ex. sharks), navigation and orientation in environment (ex. catfish) and communication like social interactions and mating behaviors (ex. mormyrids)

  • passive electroreception

    • detects electric fields generated by other organisms or natural sources

  • active electroreception

    • fish generate their own electric fields and detect distortions caused by objects in the environment

• Electrogenesis: prey detection and capture by using electrical discharge to locate and incapacitate prey (ex. electric eels), defense by shocking (ex. electric eels), communication done by weakly electric fish

  • weakly electric fish

    • generate weak electric fields for navigation and communication

    • mormyridae (elephantfish) and gymnotiformes (knifefish)

  • strongly electric fish

    • generate strong electric fields for stunning prey or defense

    • electric eel

Drag acts to oppose the forward motion of fishes in water. Discuss types of drag that affect fish locomotion and the strategies that different fishes employ to overcome it using specific examples from class where appropriate.

• viscous drag

  • resistance caused by the friction between the fish’s body and the water. It is primarily influenced by the water's viscosity and the surface area of the fish.

  • most significant at lower speeds, affected by the shape and texture of the fish's body. Streamlined, smooth surfaces reduce viscous drag.

  • ex. Eels (Anguilla spp.) exhibit elongated, slender bodies minimize surface area, reducing viscous drag during swimming and they make subtle body movements that allow them to glide through water

• inertial drag

  • result of separation of boundary layer

  • influenced by the shape of the fish; blunt shapes create more turbulence and higher pressure drag, while streamlined shapes minimize it.

  • ex. Tuna (Thunnus spp.) have a streamlined, fusiform shape that reduces inertial drag, allows them to swim at high speeds with minimal energy expenditure. Their muscular bodies and powerful tails help them maintain speed and agility

• strategies to overcome

  • streamlined body shape

    • ex. tuna have fusiform body that reduces pressure drag by allowing water to flow smoothly over their surface

  • mucus secretion

    • ex. parrotfish secrete mucus to reduce viscous drag

  • fin modification and tail shapes

    • ex. mackerels have stiff narrow caudal fins

  • undulatory motion and body flexibility

    • ex. eels use anguilliform locomotion

  • behavioral adaptations

    • flying fish will leap out of the water and glide through the air since the air has less drag

  • creating microturbulence

    • helps to stop boundary layer from separating

Locomotory strategies of fishes are the result of undulatory and/or oscillatory movements of the body or fins. Compare and contrast different locomotory strategies used by fishes including fin-based and caudal/trunk based and the relative importance of oscillation and undulation to each strategy.

• Caudal based locomotion

  • undulatory movement

    • anguilliform

      • used by eels, whole body wave like movement

      • allows high maneuverability and movement through tight spaces

    • subcarangiform and carangiform

      • used by trout and mackerels, waves are generated mostly in rear part of body

      • balances speed and maneuverability

    • thunniform

      • used by tuna and some sharks, undulation confined mostly to the tail

      • maximizes speed and efficiency for long-distance swimming

  • Oscillation: The tail fin oscillates back and forth, providing thrust. This is the primary mode of movement for many pelagic fish (e.g., tunas and mackerels)

• Fin-based locomotion

  • labriform

    • involves the pectoral fins, used by wrasses and parrotfish

    • allows for precise movements and effective maneuvering in reefs

• Comparison

  • caudal: primarily involves undulatory movements, they emphases speed, agility and a mix of both

  • fin-based: prioritize maneuverability, stability and precision, primarily uses oscillation but can use a mix of both

The fossil record indicates tetrapods are derived from extinct sarcopterygian fishes. Present the evidence for this, citing specific examples from the fossil record. What characters that we traditionally associate with tetrapods likely evolved in the aquatic environment and how may they have been useful in that environment?

Evidence from fossils

1. Tiktaalik: often referred to as a "fishapod" due to its intermediate features. It had both fish-like characteristics (scales, fins) and tetrapod-like features (robust ribcage, limb bones).

2. Panderichthys: This fossil shows a mix of aquatic and terrestrial traits, with limb bones suggesting the ability to support its body out of water.

3. Acanthostega and Ichthyostega: These early tetrapods had limbs with multiple digits, indicating a transition from fin to limb.

Characters evolved in aquatic environments

1. Limb-like Fins: Early sarcopterygians like Panderichthys and Tiktaalik had fins with bones similar to tetrapod limbs, which likely helped them navigate through shallow waters and muddy environments.

2. Robust Ribcage: A stronger ribcage provided support for the body, which would be crucial for movement in shallow waters.

3. Lungs and Air Breathing: Some sarcopterygians, like lungfish, had primitive lungs, allowing them to breathe air when oxygen levels in water were low.

4. Modified Skull and Jaw: Changes in the skull and jaw structure, such as the development of choanae (internal nostrils), facilitated air breathing.

Utility in aquatic environments

• Limb-like Fins: Allowed for better maneuverability in shallow, vegetated waters, aiding in feeding and avoiding predators.

• Robust Ribcage: Provided structural support, enabling these fishes to move in environments where buoyancy was less reliable.

• Air Breathing: Enabled survival in oxygen-poor waters, giving these fishes an edge in diverse environments.

Argue for the importance of the fossil ‘fishapod’ †Taktaalik to our understanding of tetrapod evolution. In what ways was †Tiktaalik fish-like? Tetrapod-like?

Importance of Tiktaalik in Tetrapod Evolution

1. Intermediate Form: bridges the gap between fish and early tetrapods, showing a mix of features from both groups. This makes it an excellent example of evolutionary transition.

2. Evolutionary Milestone: highlights the gradual adaptations needed for life on land, such as limb development and changes in respiration.

3. Functional Morphology: structure reveals how early vertebrates might have used their limbs and body to move and support themselves in shallow water and on land.

• Fish-like Features of Tiktaalik

  • Scales: had scales covering its body, typical of fish.

  • Fins: possessed fin rays similar to those in fish, indicating its aquatic nature.

  • Gills and Lungs: had both gills for underwater respiration and primitive lungs for breathing air.

• Tetrapod-like Features of Tiktaalik

  • Limbs: limb-like pectoral fins with bones resembling a wrist, elbow, and shoulder, indicating the beginnings of weight-bearing limbs.

  • Ribs: more developed ribcage compared to fish, providing support for the body and aiding in respiration.

  • Neck: had a mobile neck, allowing it to move its head independently of its body, which is crucial for terrestrial movement and predation.

Outline how modifications to the support system helped tetrapods adapt to life in a terrestrial environment. Consider both axial and appendicular systems.

• Axial System Modifications

  • vertebral column

    • Strengthened and Interlocked Vertebrae: supports the body's weight against gravity, the vertebrae became more robust and interlocked, providing a strong, flexible backbone.

    • Development of Zygapophyses: interlocking processes between vertebrae enhanced stability and mobility, greater support and flexibility on land.

  • ribs

    • Expanded Ribcage: additional support for the body and aided in lung ventilation, helped prevent the body from collapsing under its own weight and assisted in breathing by expanding and contracting the thoracic cavity.

  • neck

    • Development of a Mobile Neck: Allowed tetrapods to move their head independently of their body, crucial for feeding, sensory perception, and interacting with the environment.

• Appendicular System Modifications

  • limbs

    • Transformation of Fins to Limbs: Fins evolved into stronger, jointed limbs with digits, provided the support and mobility for walking on land.

    • Strengthened Limb Girdles: pectoral and pelvic girdles became more robust, allowing for the attachment of muscles needed for terrestrial locomotion.

  • pectoral girdle

    • Loss of Direct Connection to the Skull: change reduced the shock transmitted to the head when walking, improving balance and movement.

  • pelvic girdle

    • Enlargement and Fusion of Bones: pelvic girdle became larger and more robust, with fused bones providing a strong anchor for the hind limbs, crucial for supporting the body’s weight and enabling powerful locomotion.

• functional significance

  • Weight Support: allowed tetrapods to support their body weight on land, overcoming the lack of buoyancy.

  • Movement and Locomotion: Jointed limbs with digits enabled walking, climbing, and running, facilitating exploration of diverse terrestrial habitats.

  • Breathing and Feeding: Enhanced ribcage and neck mobility improved lung ventilation and enabled more effective feeding strategies.

Discuss the evolution of respiratory systems from aquatic to terrestrial vertebrates. You should include a phylogenetic tree and mention the role of axial and cranial musculature in both buccal and aspiration pump systems.

• Evolutionary Path of Respiratory Systems

  • Early Vertebrates (Fish)

    • Gills: respiratory organs in fish, allowing for efficient gas exchange in water.

    • Buccal Pumping: cranial musculature creates pressure differences, forcing water over their gills.

  • Lobe-finned Fish (Sarcopterygii)

    • Lungs and Gills: Some lobe-finned fish, like lungfish, developed lungs in addition to gills, using both for respiration.

    • Buccal Pumping: use of cranial muscles to pump air into the lungs, especially in oxygen-poor environments.

  • Early Tetrapods

    • Lungs: Dominant respiratory organs, with gills becoming less significant.

    • Buccal Pumping: used buccal pumping to ventilate their lungs, similar to modern-day amphibians.

  • Amniotes (Reptiles, Birds, Mammals)

    • Aspiration Pumping: Transition to using axial musculature (rib cage and diaphragm) to create negative pressure and draw air into the lungs, a more efficient mechanism for terrestrial life.

Phylogenetic Tree

         ┌────────── Agnathans (Jawless Fish)
         │
    ┌────┴─────── Chondrichthyes (Cartilaginous Fish)
    │
    │     ┌────── Actinopterygii (Ray-finned Fish)
    │     │
    │ ┌───┴────── Sarcopterygii (Lobe-finned Fish)
    │ │           └─── Lungfish
    │ │
    │ └────────── Tetrapods
    │                ├─── Early Tetrapods (Buccal Pump)
    │                │
    │                └─── Amniotes (Aspiration Pump)
    │                      ├─── Reptiles
    │                      ├─── Birds
    │                      └─── Mammals

• Role of axial and cranial musculature

  • Buccal Pump System

    • Cranial Musculature: create positive pressure, forcing air into the lungs, less efficient but sufficient for early tetrapods and amphibians.

    • Ex: Frogs inflate their lungs by lowering the floor of their mouth, creating negative pressure and then raising it to push air into the lungs.

  • Aspiration Pump System

    • Axial Musculature: rib cage and diaphragm create negative pressure, pulling air into the lungs, greater control and efficiency in breathing.

    • Ex: Mammals use the diaphragm to expand the thoracic cavity, drawing air into the lungs.

How did the differing properties of air and water select for modifications to the sensory systems of terrestrial vertebrates? Your response should consider each sensory system and its specific modifications.

• Vision

  • Water: Light is absorbed and scattered differently, reducing visibility and color perception.

    • Eyes moved to the top of the head in early tetrapods to look above the water's surface, like in Tiktaalik.

    • More rounded lenses to focus light effectively in air.

    • Enhanced color vision evolved in some lineages due to the increased range of light wavelengths in air.

• Hearing

  • Water: Sound travels faster and more efficiently, but with less directionality.

    • Development of the middle ear ossicles (stapes in amphibians, later malleus and incus in mammals) improved sound transmission.

    • External ears, evolution of pinnae in mammals to funnel sound waves and improve directional hearing.

• Olfaction

  • Water: Olfactory receptors detect waterborne chemicals.

    • Nasal passages: more complex nasal structures to detect airborne odors.

    • Vomeronasal organ: Some tetrapods retain this organ to detect pheromones in the air

• Touch

  • Water: Water pressure and movement can be detected through mechanoreceptors.

    • Enhanced skin sensitivity: specialized receptors in the skin to detect air currents, vibrations, and surface textures.

    • Whiskers: In some mammals, like rodents and cats, whiskers (vibrissae) evolved to sense their surroundings

• Taste

  • Water: Taste buds distributed over the body, especially around the mouth.

    • Concentration in the mouth: Taste buds became concentrated in the oral cavity to detect chemicals in food more effectively.

• Lateral Line System

  • Water: Detects water movements and vibrations.

    • Reduction or loss: Most terrestrial vertebrates lost the lateral line system as it became less useful in air.

• Electroreception

  • Water: Detects electrical fields generated by other organisms.

    • Reduction or loss: Electroreception became less significant for most terrestrial vertebrates.

How do the thermal properties of air affect terrestrial vertebrate thermoregulatory strategies differently than aquatic vertebrates?

• Thermal Properties of Air vs. Water

  • Heat Capacity: Water has a higher heat capacity than air, meaning it can absorb and retain more heat without a significant change in temperature.

  • Heat Conductivity: Water conducts heat more efficiently than air, leading to more rapid heat loss or gain for aquatic organisms.

  • Thermal Stability: Aquatic environments tend to have more stable temperatures, while terrestrial environments experience greater fluctuations in temperature.

• Aquatic Vertebrates

  • Convection and Conduction: Since water has high heat conductivity, aquatic vertebrates experience rapid heat exchange with their environment. This makes maintaining a stable body temperature challenging.

  • Ectothermy: Most aquatic vertebrates are ectothermic (cold-blooded), relying on the water’s temperature to regulate their body heat.

  • Counter-Current Heat Exchange: Some fish, like tuna and sharks, have evolved this system to retain body heat by transferring it between blood vessels flowing in opposite directions.

• Terrestrial Vertebrates

  • Insulation: Feathers, fur, and fat layers provide insulation, helping to retain body heat in a cooler environment or reduce heat absorption in a hotter one.

  • Endothermy: Many terrestrial vertebrates, like birds and mammals, are endothermic (warm-blooded), generating their own heat through metabolic processes.

  • Behavioral Adaptations: Seeking shade, basking in the sun, and changing activity patterns based on the time of day or season.

  • Evaporative Cooling: Sweating, panting, or other forms of evaporative cooling help dissipate excess body heat.

• Hibernation and Torpor: Some animals enter states of reduced metabolic activity to survive extreme temperatures.

List and describe the synapomorphies of the Lissamphibia.

Lissamphibia is a clade that includes all modern amphibians: Anura (frogs and toads), Urodela (salamanders), and Gymnophiona (caecilians).

1. Pedicellate Teeth: Teeth with a crown separated from the base by a pedicel.

2. Middle Ear Structure: Presence of a columella (stapes) and an operculum, which are not homologous to fish structures.

3. Fat Bodies Development: Fat bodies develop from the germinal ridge.

4. Skin Glands: Skin contains both mucus and poison glands.

5. Specialized Retinal Cells: Presence of specialized receptor cells in the retina called green rods (except in caecilians).

6. Levator Bulbi Muscle: A sheet of muscle under the eye called the levator bulbi, allowing the raising of the eyes.

7. Cutaneous and Buccopharyngeal Respiration: Ability to respire through the skin and the lining of the mouth and throat.

8. Two Occipital Condyles: Two occipital condyles at the base of the skull.

9. Radial Condyle: The radius and ulna articulate with the humerus at a single point called the radial condyle.

10. Skull Fenestration Patterns: Shared fenestration patterns and loss of certain skull bones with Paleozoic tetrapods.

Draw a phylogenetic tree illustrating the evolutionary relationships of the Lissamphibia. Discuss the characteristics of each group.

Where on the globe is amphibian diversity highest? Lowest? What is responsible for this pattern?

• highest in tropical regions. These areas provide the warm, moist environments that amphibians thrive in. Conversely, amphibian diversity is lowest in arid and polar regions, such as deserts and the polar ice caps, where conditions are too harsh for most amphibians to survive.

• Factors Responsible for This Pattern:

  • Climate: ectothermic (cold-blooded) and rely on external temperatures to regulate their body heat. Warm, humid climates are ideal for their survival and reproduction.

  • Habitat Availability: Tropical regions offer abundant water bodies and diverse habitats, which are essential for amphibian life cycles that often include both aquatic and terrestrial stages.

  • Biodiversity Hotspots: Tropical regions are biodiversity hotspots, meaning they have a high number of species and a large variety of ecosystems, which support a wide range of amphibian species.

  • Evolutionary History: These regions have been relatively stable over geological time, allowing for the evolution and diversification of many amphibian species.

Compare and contrast courtship in the rough skinned newt, Taricha granulosa, with the courtship displays of newts such as Triturus cristatus.

• Courtship in Rough-Skinned Newt (Taricha granulosa)

  • engage in simple courtship behavior. Males perform a tail undulation display to attract females. During this display, the male swims with his tail moving side to side, which helps to release pheromones that signal his readiness to mate. Once a female is interested, the male will grasp her with his cloacal lips in a behavior known as amplexus, and fertilize her eggs externally.

• Courtship in Crested Newt (Triturus cristatus)

  • have a more elaborate courtship display. Males perform a series of visual and tactile displays, including waving, fanning, quivering, and creeping. These behaviors are often accompanied by the male's crest, which is a jagged ridge along his back that becomes more prominent during the breeding season. The male also deposits a spermatophore on the substrate, which the female picks up with her cloaca to fertilize her eggs.

• Comparison

  • Simplicity vs. Complexity: Rough-skinned newts have a simpler courtship display compared to the more complex and varied displays of crested newts14.

  • Pheromones vs. Visual Displays: Rough-skinned newts rely more on pheromones released during tail undulation, while crested newts use a combination of visual signals (crest display) and tactile signals (spermatophore deposition)14.

  • Amplexus vs. Spermatophore: In rough-skinned newts, amplexus is the primary method of fertilization, whereas in crested newts, spermatophore deposition plays a crucial role

What evolutionary trends in courtship rituals are important in newt lineages?

1. Visual and Olfactory Signals: Many newts use a combination of visual displays (like tail fanning and crest displays) and olfactory signals (pheromones) to attract mates. This dual approach increases the chances of successful mating by engaging multiple senses.

2. Spermatophore Deposition: In many newt species, males deposit a spermatophore (a packet of sperm) on the substrate, which the female picks up with her cloaca. This method of internal fertilization is a significant evolutionary trend that distinguishes newts from other amphibians like frogs and toads.

3. Complex Courtship Displays: Newts often perform elaborate courtship rituals that involve specific movements and behaviors to entice females. These displays can include tail undulations, body arching, and even creeping movements.

4. Temporal Patterns: Courtship activities are often timed to coincide with specific environmental conditions, such as the onset of the breeding season or the presence of suitable water bodies. This timing ensures that mating occurs when conditions are optimal for egg development and survival.

5. Sexual Dimorphism: Many newt species exhibit sexual dimorphism, where males and females have different physical characteristics, such as crests or coloration, which play a role in courtship and mate selection.

How are both internal and external modes of fertilization expressed in all three major amphibian lineages? Use examples of particular species or groups to illustrate your response.

• Anura (Frogs and Toads)

  • External Fertilization:

    • Common in Frogs and Toads: Most anurans, like the common frog (Rana temporaria), use external fertilization. During amplexus, the male grasps the female and releases sperm over the eggs as the female lays them in water. This ensures that the sperm fertilizes the eggs externally.

  • Internal Fertilization:

    • Rare but Present: Internal fertilization occurs in some species like the tailed frog (Ascaphus truei), which has a specialized structure called the "tail" (actually an extension of the cloaca) used to transfer sperm directly to the female.

• Urodela (Salamanders)

  • External Fertilization:

    • Primitive Salamanders: In species like the Cryptobranchidae (giant salamanders), fertilization is external. Males and females release their gametes into the water, where fertilization occurs.

  • Internal Fertilization:

    • Spermatophore Deposition: Many salamanders, such as the spotted salamander (Ambystoma maculatum), exhibit internal fertilization through spermatophore deposition. The male deposits a spermatophore on the ground, and the female picks it up with her cloaca to fertilize her eggs internally.

• Gymnophiona (Caecilians)

  • Internal Fertilization:

    • Universal: All known caecilians use internal fertilization. Males have an intromittent organ called a phallodeum, which they use to transfer sperm into the female during copulation. For instance, the common caecilian (Ichthyophis glutinosus) exhibits this behavior.

While parental care among amphibians is not common, maintaining offspring or eggs outside the reproductive tract has evolved multiple times in several amphibian lineages. Citing specific examples, describe the manner in which each lineage maintains their offspring or eggs.

• Anura (Frogs and Toads)

  • Darwin's Frog (Rhinoderma darwinii)

    • Method: Males keep the fertilized eggs in their vocal sacs. Once the eggs hatch, the tadpoles remain in the sac until they metamorphose and are released as miniature frogs.

  • Surinam Toad (Pipa pipa)**

    • Method: Females embed their fertilized eggs into their back skin. The skin then grows over the eggs, forming protective pockets. The embryos develop within these pockets until fully formed young toads emerge.

  • Gastric-Brooding Frogs (Rheobatrachus spp.)

    • Method: Females swallow their fertilized eggs, and the embryos develop in the stomach. During this period, the frog's digestive system shuts down to avoid harming the developing young, which are eventually regurgitated as froglets.

• Urodela (Salamanders)

  • Alpine Salamander (Salamandra atra)**

    • Method: Females give live birth to fully developed young. The embryos develop inside the female’s body, nourished by yolk and, in later stages, by secretions from the mother.

  • Hellbenders (Cryptobranchus alleganiensis)**

    • Method: Males guard the eggs after external fertilization. They create nests under rocks in streams and protect the eggs from predators and debris until they hatch.

  • Red-Backed Salamander (Plethodon cinereus)**

    • Method: Females guard their terrestrial egg clusters. They coil around the eggs to keep them moist and protect them from predators until they hatch.

• Gymnophiona (Caecilians)

  • Caecilians (Ichthyophis spp.)**

    • Method: Females lay eggs in moist soil and then coil around them, keeping them hydrated and protected until they hatch.

  • Live-Bearing Caecilians (e.g., Typhlonectes compressicauda)

    • Method: Some caecilians give live birth. The embryos develop inside the mother’s body, nourished initially by yolk and later by specialized uterine secretions.

What are reasons we might expect life histories that involve a larval phase that is dramatically different from the adult, requiring a metamorphic transformation, would be favored by natural selection?

• Niche Differentiation

  • Reduced Competition: Larvae and adults occupy different ecological niches, minimizing competition for resources. For example, tadpoles often feed on algae in water, while adult frogs eat insects on land.

• Survival Strategies

  • Dispersal: Larval stages can aid in dispersal, spreading offspring over a wider area and reducing competition among siblings. Many amphibian larvae are aquatic and can be carried by water currents to new locations.

  • Specialized Adaptations: Different life stages can have specialized adaptations for survival in their respective environments. Larvae may be adapted for rapid growth and feeding, while adults focus on reproduction.

• Predation Pressure

  • Predator Avoidance: Different life stages face different predators. For instance, aquatic tadpoles may avoid terrestrial predators that adult frogs encounter, and vice versa.

• Resource Utilization

  • Efficiency: Metamorphosis allows organisms to take full advantage of resources available at different life stages. For example, caterpillars are specialized for feeding and rapid growth, while adult butterflies are adapted for reproduction and dispersal.

• Environmental Adaptation

  • Seasonal Timing: Larval and adult stages can be timed to exploit seasonal variations in the environment. Amphibians may breed during rainy seasons when water bodies are abundant for their larvae, and adults may be more active in other seasons.

Having a highly specialized aquatic larval phase (i.e. tadpole) is a derived character within the Anura. Describe alternate life histories in amphibians that circumvent the aquatic larval phase, citing specific examples of each.

1. Direct Development: Some species develop directly from egg to juvenile without a free-living larval stage. An example is the Surinam toad (Pipa pipa), where eggs are embedded in the mother’s back and develop into fully formed toads, avoiding a tadpole stage altogether. Similarly, the Iberian ribbed newt (Pleurodeles waltl) can also develop directly, depending on environmental conditions.

2. Terrestrial Egg Laying: Certain frogs, like the Darwin's frog (Rhinoderma darwinii), have a unique reproductive strategy where the male carries the developing young in his vocal sac. The eggs hatch directly into miniature frogs rather than tadpoles, enabling them to avoid aquatic environments.

3. Hatching into Juveniles: Some species hatch as small versions of adults. The Brachycephalus (bracheycephalid frogs) exhibit this behavior, where they lay eggs in leaf litter that develop directly into tiny frogs, completely bypassing the tadpole phase.

4. Gilled Larval Stage but Terrestrial: In some cases, like the Axolotl (Ambystoma mexicanum), individuals can remain in their larval form with gills (a condition called neoteny) while still living in a terrestrial environment, though they can also undergo metamorphosis if conditions change.

Some amphibians are capable of surviving extremely low temperatures by allowing large portions of their bodies to freeze. Explain the adaptations that allow them to accomplish this, citing specific examples

• Cryoprotectants:

  • Example: Wood Frog (Lithobates sylvaticus): Wood frogs can produce high concentrations of glucose and urea, which act as cryoprotectants. These substances help prevent ice formation in their cells, allowing them to tolerate body freezing while maintaining cellular integrity.

• Controlled Freezing:

  • Example: The Boreal Chorus Frog (Pseudacris maculata): This frog can survive freezing by allowing ice to form in its extracellular spaces while keeping its cells unfrozen. It uses specific proteins to manage ice formation, directing it outside of vital organs.

• Antifreeze Proteins:

  • Some amphibians produce antifreeze proteins that inhibit ice crystal growth within their bodies. These proteins bind to small ice crystals, preventing them from growing larger and causing cellular damage.

• Supercooling:

  • Example: Some salamander species (e.g., Ambystoma): Certain salamanders can supercool their bodily fluids, allowing them to remain in a liquid state below freezing temperatures. This helps them avoid ice formation entirely under specific conditions.

• Behavioral Adaptations:

  • Many amphibians will seek out microhabitats, such as burrows or leaf litter, to avoid exposure to extreme cold. By positioning themselves in these sheltered areas, they can reduce the risk of freezing.

• Metabolic Rate Reduction:

  • During freezing conditions, amphibians significantly lower their metabolic rates. This adaptation minimizes energy expenditure and reduces the need for oxygen, allowing them to survive in a dormant state until temperatures rise again.

Compare and contrast anuran and urodelean larvae.

• Anuran Larvae (Tadpoles)

  • Morphology:

    • Body Shape: Generally more streamlined and oval, facilitating swimming.

    • Tail: Tadpoles have long, flattened tails that are primarily used for propulsion in water.

    • Limbs: Tadpoles typically lack limbs in the early stages; legs develop later during metamorphosis.

  • Feeding Habits:

    • Diet: Most tadpoles are herbivorous or detritivorous, feeding on algae, plant matter, and organic debris. Some species, particularly in later stages, may become carnivorous.

    • Mouth Structure: Tadpoles have a rounded mouth with specialized structures (like keratinized mouthparts) for grazing on plant material.

  • Respiration:

    • Gills: Tadpoles possess external gills early in their development, which later transform into internal gills or disappear as they transition to lungs during metamorphosis.

  • Development:

    • Aquatic Lifestyle: Tadpoles are entirely aquatic and undergo a metamorphosis that includes significant morphological changes (e.g., loss of tail, development of limbs, lung formation).

• Urodelean Larvae (Salamander Larvae)

  • Morphology:

    • Body Shape: Urodelean larvae typically have a more elongated and cylindrical body shape.

    • Tail: Their tails are generally more rounded than those of tadpoles and may have lateral fins.

    • Limbs: Salamander larvae usually have well-developed limbs early in life, allowing for a more versatile mode of locomotion.

  • Feeding Habits:

    • Diet: Salamander larvae are generally carnivorous, preying on small invertebrates, including insects and other larvae.

    • Mouth Structure: They have a more pronounced jaw structure with teeth for capturing prey.

  • Respiration:

    • Gills: Most urodelean larvae possess external gills throughout their larval stage, which remain prominent until metamorphosis or in some cases, throughout their lives if they are neotenic.

  • Development:

    • Aquatic or Terrestrial: Urodelean larvae can be either aquatic or terrestrial, depending on the species. Some remain aquatic throughout their lives (e.g., axolotls), while others undergo metamorphosis into terrestrial adults.

Describe the 3 major phases of metamorphosis in anurans. Outline each phase and describe adaptive reasons why some phases are shorter or longer than others.

1. Pre-Metamorphosis Phase

Overview: This initial phase occurs while the organism is still in the larval stage (tadpole). During this time, the tadpole grows and develops basic physiological structures.

• Key Changes:

  • Growth in size and development of the tail for swimming.

  • Development of gills for respiration in water.

  • Accumulation of energy reserves in preparation for later stages.

Adaptive Reasons for Duration:

• Environmental Factors: The duration of this phase can be influenced by environmental conditions such as temperature, food availability, and habitat quality. Longer pre-metamorphosis may allow for better growth and energy accumulation, enhancing survival chances during the more vulnerable metamorphic phases.

• Species Variation: Different species have adapted to varying lengths of this phase depending on their specific ecological niches and reproductive strategies. For example, species that face predation may develop more quickly to reduce vulnerability.

2. Prometamorphosis

Overview: This phase involves significant morphological and physiological changes as the tadpole prepares for transformation into an adult.

• Key Characteristics:

  • Development of Limbs: Hind limbs develop first, followed by front limbs. The body begins to change shape as it prepares for terrestrial life.

  • Resorption of Tail: The tail starts to be absorbed, gradually reducing the size of the tail fin.

  • Lung Development: Transition from gills to lungs occurs, allowing for air breathing.

  • Dietary Shift: Tadpoles begin to shift from herbivorous diets to a more carnivorous diet as they prepare for adult life.

Adaptive Reasons for Duration:

• Physiological Readiness: The duration of this phase can vary based on the readiness of the tadpole to undergo these significant changes. Environmental factors, such as temperature and food availability, can influence growth rates and the speed of limb development.

• Predation Pressure: In environments with high predation risk, a shorter prometamorphic phase can be advantageous, allowing tadpoles to transition to a less vulnerable adult form more quickly.

3. Metamorphic Climax

Overview: This final phase marks the completion of metamorphosis, resulting in a fully formed adult anuran.

• Key Characteristics:

  • Final Body Restructuring: The tail is fully resorbed, and limbs are fully developed, completing the transition to an adult form.

  • Skin Changes: Development of skin adaptations for terrestrial living, including moisture retention mechanisms and a more complex skin structure.

  • Behavioral Adjustments: New behaviors emerge, including foraging techniques, mating calls, and territory establishment.

Adaptive Reasons for Duration:

• Habitat Requirements: The length of this phase can depend on habitat stability. Species that need to mature quickly to breed in seasonal ponds may have a shorter climax phase, while those in stable environments might take longer to establish their new life patterns.

• Survival Strategies: Longer periods in this phase can allow individuals to acclimate to their new terrestrial environment, improving survival rates before reaching reproductive maturity.

1. The skin is a very important component of amphibian anatomy.  Discuss the major functions of amphibian skin.

1. Respiration

• Gas Exchange: Amphibians have permeable skin that allows for the exchange of gases, enabling them to absorb oxygen and release carbon dioxide directly through their skin. This is especially important in aquatic environments where their lungs may not be as effective.

• Supplementing Lung Function: In many species, particularly when active or during times of stress, cutaneous respiration (skin breathing) can significantly contribute to their overall respiration needs.

2. Moisture Regulation

• Water Absorption: Amphibians often live in environments where moisture is critical. Their skin can absorb water directly, which is vital for hydration, especially in dry conditions.

• Prevention of Desiccation: The skin acts as a barrier to minimize water loss in terrestrial habitats, although it remains permeable to gases. Amphibians often need to maintain skin moisture to facilitate respiration and other physiological processes.

3. Protection

• Physical Barrier: The skin serves as a protective barrier against physical injuries, pathogens, and parasites. It can help shield internal tissues from abrasions and external threats.

• Toxin Production: Many amphibians produce toxic secretions through their skin (e.g., poison dart frogs). These toxins can deter predators and provide a means of defense against threats.

4. Thermoregulation

• Temperature Regulation: Although amphibians are ectothermic and rely on external sources to regulate body temperature, their skin can help moderate heat absorption and loss. The skin's moisture content also plays a role in thermoregulation.

• Behavioral Thermoregulation: Amphibians can change their behavior (e.g., seeking shade or moisture) based on skin moisture and temperature, enhancing their ability to regulate body temperature in variable environments.

5. Sensory Function

• Tactile Sensation: The skin is rich in sensory receptors, allowing amphibians to detect changes in their environment, such as temperature, pressure, and humidity. This sensory information is crucial for behavior, feeding, and social interactions.

• Chemical Sensing: Amphibians can also detect chemical signals through their skin, aiding in communication with other individuals and helping them identify suitable habitats or potential mates.

6. Coloration and Camouflage

• Adaptation to Environment: Amphibian skin can change color due to the presence of chromatophores (pigment cells), helping them blend into their surroundings and avoid predators.

• Social Signaling: Coloration can also play a role in mating displays and social interactions, signaling health and reproductive status to potential mates.