Week 15 - Evolution and diversity of vertebrates 2

When did amphibian orders first orginate?

220-250 million years ago.

What is modern amphibian classification based on?

1 mitochondrial gene (16S rRNA) and 4 nuclear genes.

What is the order of the 3 clades, and what is each orders common name?

Clade	Order	Common Name
I	Apoda (Gymnophiona)	Caecilians
II	Urodela (Caudata)	Salamanders & Newts
III	Anura (Salientia)	Frogs & Toads

What is the shared morphology of Clade I (Order: Apoda, Common name: Caecilians)?

• They elongate without limbs or limb girdles

• Their body is segmented by annular grooves.

• Are highly specialized for burrowing (heavily ossified compact skulls) and recessed mouths

• Have no ear openings

How does Clade I eat and detect prey (Order: Apoda, Common name: Caecilians)? Are they carnivorous?

Are carnivorous (eat earthworms and other ground dwelling invertebrates).

Because they have no ear openings, they use their retractable tentacles to sense prey and mates. The tentacles carry chemical cues from the environment to the nasal cavity. This allows for detection.

They can grip prey and spin to process.

They can then use their venom glands in tissue next to teeth in upper and lower jaw to finish consumption.

How do Clade I (Order: Apoda, Common name: Caecilians) reproduce?

Via internal fertilization.

How do primitive, advanced and the most advanced Clade I (Order: Apoda, Common name: Caecilians) reproduce?

• Primitive: Oviparous (eggs) with aquatic eggs and larvae.

• Advanced: Oviparous with direct development of terrestrial eggs.

• Most advanced: Viviparous (live birth). Direct development of terrestrial eggs. Larvae use specialized teeth for matrotrophy (scraping the oviduct to obtain nutrients secreted by oviduct cells).

What is the shared morphology of Clade II (Order: Urodela, Common name: Salamanders & Newts)?

• Possess a distinct tail

• Limbs are more or less equal length

How do Clade II (Order: Urodela, Common name: Salamanders & Newts) reproduce?

Fertilisation is external in some; mostly internal fertilization without copulation. Males produce spermatophores (sperm packets), which females pick up via the cloaca (where sperm is stored). Eggs are laid on land or water. On hatching, some species have larvae, while other species skip the larval stage entirely.

What is padeomorphosis (neoteny)?

Retention of larval traits (like gills) in adults (after maturity). 

Where is paedomorphosis seen in Clade II (Order: Urodela, Common name: Salamanders & Newts)?

The Axolotl (Ambystoma mexicanum) stays aquatic but can be induced to metamorphose via thyroid stimulation. It:

• Keeps its external gills

• Remains fully aquatic

• Still becomes sexually mature and reproduces

What are the 3 UK native species of Clade II (Order: Urodela, Common name: Salamanders & Newts)?

• Palmate newt (Triturus heveticus)

• Smooth newt (Lissotriton vulgaris)

• Great crested newt (Triturus cristatus)

What are the 3 UK non-native species of Clade II (Order: Urodela, Common name: Salamanders & Newts)?

• Fire salamander (Salamandra salamandra)

• Alpine newt (Triturus alpestris)

• Italian crested newt (Triturus carnifex)

What is the shared morphology of Clade III (Order: Anura, Common name: Frogs & Toads)?

• Lack a tail when adult.

• Legs are always present in adults

• Have hindlimbs larger than fore limbs, as well as webbed toes (making them highly adapted for locomotion-jumping).

How do Clade III (Order: Anura, Common name: Frogs & Toads) efficently communicate within themselves?

Short term aggregations (visual and auditory) are important for communication in breeding.

Large vocal sacs amplify male mating calls.

How do Clade III (Order: Anura, Common name: Frogs & Toads) reproduce?

Fertilization is mostly external (bar a few species).

• Most are oviparous with aquatic eggs and larvae

• Some are oviparous, but with direct development of terrestrial eggs

• Some are viviparous (mostly lecithotrophy – nutrients supplied by yolk)

What are the 4 UK native species of Clade III (Order: Anura, Common name: Frogs & Toads)?

• Common frog (Rana temporaria)

• Common toad (Bufo bufo)

• Natterjack toad (Bufo calamita)

• Pool frog (Pelophylax lessonae)

What are the 8 UK non-native species of Clade III (Order: Anura, Common name: Frogs & Toads)?

• Midwife toad (Alytes obstetricans)

• Yellow-bellied toad (Bombina variegata)

• East Iberian painted frog (Discoglossus pictus)

• European tree frog (Hyla arborea)

• Marsh frog (Pelophylax ridibunda)

• Edible frog (Pelophylax esculenta)

• American bullfrog (Rana catesbeiana)

• African clawed toad (Xenopus sp.)

What is the diversification and development of different amphibian families related to?

Distribution of amphibian families is closely linked to continental drift.

Families started to diversify after fragmentation.

The evolution and diversification of different amphibians continued into the Cretaceous, as a result of the evolution and development of flowering plants.

How do major amphibian families differ in their evolution and geographic distribution?

• Dendrobatidae

Evolved 20–50 MYA

Restricted to South America

• Mantellidae

Evolved ~50 MYA

Restricted to Madagascar

• Bufonidae

Evolved ~50 MYA

Found on all continents except Australia & Antarctica

• Microhylidae

Evolved ~70 MYA

Found on all continents except Australia & Antarctica

What percentage of all amphibians live in forests?

82%

Are amphibians ectothermic or endothermic? What does this mean?

Amphibians are ectothermic vertebrates. They typically have a body temperature close to that of their immediate surroundings.

How does an amphibian’s body temperature compare to its environment?

It is usually very close to the surrounding temperature.

Do amphibians produce their own body heat? What happens because of this?

No, they produce very little internal heat.

This is then quickly lost to the environment.

How does temperature affect an amphibian’s metabolism?

Higher temperature increases metabolism; lower temperature decreases it.

Why can amphibians survive a long time without food when cool?

Their metabolism slows down, so they use less energy.

How do some amphibians regulate their body temperature behaviourally? Give an example.

Some amphibians (anurans) warm themselves by basking in the sun, but they do this less than reptiles. For example, Anaxyrus debilis basks on open slopes, where it gets warmer than it would in the shade.

What does it mean for an amphibian to bask?

For an amphibian to bask means:

👉 to sit or rest in a warm place (usually in the sun) to raise its body temperature

What problem do amphibians face when basking? Why is this?

They lose water through evaporation. Tis happens because they have highly permeable, well-vascularised skin.

How do some amphibians reduce water loss while basking?

Some bask in water instead of on land.

How do land-basking amphibians heat up efficiently? How do they stay cool in to counteract this?

They have dark skin, which absorbs heat quickly.

They use evaporative cooling to lower their body temperature.

How does the Rhinella marina regulate its temperature?

During the day, it stays cooler than the environment using evaporative cooling; at night, its body temperature matches the surroundings.

What temperature range do salamanders typically live in? What about frogs and toads?

Salamanders: About -2°C to 30°C.

Frogs and toads: About -3°C to 36°C.

What determines the lower lethal temperature of an amphibian species?

The environment it lives in.

What is the lowest lethal temperature?

Lower lethal temperature = the lowest temperature an organism can survive.

How do amphibians from higher latitudes differ from those in lower altitudes?

They can tolerate colder temperatures.

How do amphibians survive extreme seasonal conditions?

They enter dormancy (hibernation) and reduce their metabolic rate to save energy.

What is special about some amphibians in very cold environments?

Some are freeze-tolerant.

Give an example of a freeze-tolerant amphibian.

The Rana sylvatica (North American wood frog).

How do amphibians obtain and manage water in their bodies?

Body is 70–80% water.

Adults do not drink.

Water is absorbed through permeable skin from the environment.

Water is lost through skin, urine, faeces and respiration.

How is amphibian skin adapted for gas exchange and what are the consequences?

Skin is highly permeable and well-vascularised

Used for gas exchange (plus buccal cavity)

Skin has little keratin → thin and delicate

Must stay moist → restricts amphibians to moist environments

How do amphibians prevent dehydration?

Have many mucus glands

Mucus keeps skin moist

Prevents drying out and maintains gas exchange

How does nitrogenous waste excretion differ in amphibians?

Aquatic species: excrete dilute urine

Terrestrial species: excrete urea or uric acid to conserve water

This is energy expensive but effective

How do amphibians store and use water?

Urinary bladder acts as a water reservoir

Stored water can be released to body tissues when needed

What are the 5 behavioural adaptations exhbited by amphibians to avoid water loss?

• Avoid exposure to the sun

• Hide in moist shelters

• Live in locations with water availability

• Reduce surface area by compacting resting posture

• Aggregate to reducec exposed surface area.

Where do spadefoot toads live and how do they survive dry conditions?

• Live in arid habitats (southern Canada → Mexico, where rainfall is unpredictable (may not occur for years)

• Burrow underground (~1 m deep) using hardened hind feet (“spades”)

• Enter hibernation underground

• Emerge when rain vibrations are detected

How are spadefoot toads adapted for rapid reproduction?

• Breed only after rain

• Eggs laid in temporary pools

• Tadpoles develop very quickly (~30 days)

• Adults are nocturnal during rain and hide during the day to avoid heat.

What do spadefoot toads eat and when do they feed?

• Feed during brief active periods after rain

• Eat desert invertebrates, including termites

How do spadefoot toads conserve water in extreme environments?

• Do not drink → absorb water through skin when buried

• Urinary bladder stores water (up to ~50% body weight)

• Store urea in tissues → increases osmotic gradient to absorb water

• Can lose ~40% body water and survive

What are the growth patterns and lifespan of spadefoot toads?

• Growth occurs in bursts during wet periods (like tree rings)

• Can live ~10 years on average, up to 17 years

What is the advantage of amphibians having distinct larval and adult stages?

Reduces intraspecific competition (less competition for food/resources)

How do diets differ between larval and adult amphibians?

Adults: exclusively carnivorous (mainly arthropods), eat live moving prey

Tadpoles: omnivorous or herbivorous

• Some are filter feeders

• Some can be cannibalistic

How do amphibians detect prey at different life stages?

• Adults: rely mainly on vision → suited to sit-and-wait strategy

• Larvae (tadpoles): have lateral lines for detecting movement in water

How are the tongues of lungless salamanders adapted for feeding?

They have ballistic tongues that can shoot out rapidly, powered by muscles originally used for lungs.

How are prey items generally caught by amphibians?

Using their sticky tongue.

Tongue can be propelled by muscular activity, or a flip-type action (or both).

What anti-predator defenses do amphibians use?

• Crypsis: Concealing or disruptive coloration (e.g., mid-dorsal lines).

• Flash Colors: Hidden bright colors (e.g., Barred leaf frog) that confuse predators during movement.

• Aposematism: Bright warning colors signaling toxicity (Poison dart frogs).

• Body Inflation: Making themselves too large to swallow (Common toad).

• Risk Management: Tungara frogs reduce calling/ripples when bats are near, as bats detect water ripples.

How are colour and physical traits used in amphibian competition?

Bright colours can signal aggression and social status (brighter males = more dominant if same size)

Strong male–male competition leads to fighting adaptations, including:

• Spines (hand = pre-pollical, arm = humeral)

• Jaw spines (moustached toad)

• Teeth (tusked frog)

What are the 3 main parental core strategies?

1 - Lay aquatic eggs, develop into larvae (tadpoles), metamorphose into small versions of adults

or

2- Lay terrestrial eggs, eggs hatch as small adults (direct development)

or

3- Viviparous (give birth to live young)

What reproductive strategy does the Foam Nest Tree Frog use?

• Overhanging nests

• Builds bubble nests on branches

• Larvae fall into water after hatching

How does the Midwife Toad care for its offspring?

• Female expels a strand of eggs in which a male externally fertilizes.

• Paternal carrying

• Male carries fertilised eggs on legs

• Skin warts on their back produces strong smelling for protection for both the adult and larvae.

What is unique about Rheobatrachus reproduction?

• Gastric brooding

• Larvae develop in the stomach

• Species is extinct (since mid-1980s)

How do poison frogs transport their young?

• Adults carry eggs on their backs

• Move them between water pools

How do marsupial frogs reproduce?

• Use a brood pouch on the back (dorsal brood pouch)

• Eggs are fertilised and develop inside this pouch

• Pouch is vascularised (provides oxygen) (eggs are next to the vascular tissue, providing oxygen).

What is unique about reproduction in Nectophrynoides?

• They are the only anurans that do not lay true, external eggs.

• Viviparous (live-bearing)

• Internal fertilisation

• Eggs develop in oviduct in a female

• Feed on uterine milk (secreted by the oviduct) after yolk is used up.

• Thus it shows mammal-like characteristics.

What are anurans?

Anuran refers to any tailless amphibian belonging to the order Anura, specifically frogs and toads (Clade III)

How does habitat loss and fragmentation threaten amphibians?

• Agriculture:

  • Irrigation dries out wetlands

  • Fertilisers cause chemical pollution

• Fragmentation:

  • Separates adult habitats from larval breeding sites

  • Leads to higher mortality during migration between habitats

How does climate change impact amphibian populations?

• Drought:

  • Rising temperatures cause permanent wetland drying

  • Leads to major population and distribution declines (e.g., Yellowstone National Park)

• Sex ratios:

  • In species with temperature-dependent sex determination (e.g., Tuatara)

  • Warming causes skewed sex ratios, which can threaten survival

What is chytrid fungus and what conditions favour it?

• Disease: Chytridiomycosis

• Caused by Batrachochytrium dendrobatidis

• Infects keratinised skin

• Optimal temperature ~23°C

• Climate change has made new areas suitable, especially previously cooler regions

What are the symptoms and how does chytrid fungus spread?

• Symptoms:

  • Skin sloughing

  • Hind leg paralysis

  • Death

• Spread:

  • Motile zoospores swim in water and penetrate skin

  • Spread via global amphibian trade

  • Carriers include American bullfrog and Axolotl

  • Likely originated in South Korea

Where is chytrid fungus most impactful and why?

• Most severe in Central and South America

• Especially affects riparian (river) habitats

• Regions with high amphibian diversity are most affected

Which early amphibians gave rise to amniotes, that lay eggs on dry land?

Early “labyrinthodont” amphibians gave rise to ‘amniotes’ that lay eggs on dry land.

What type of eggs do amphibians have? How does this differ from amniotes?

Shell-less eggs that need water to survive/reproduce.

Amniotes (sister clade to living amphibians) evolved the Amniotic egg, allowing reproduction away from water (advantageous).

Do amphibians have a larval stage?

Yes, their young (like tadpoles) undergo metamorphosis into adults

Do amniotes have a larval stage?

No, the young resemble miniature adults.

How do different amniotes protect and develop their eggs?

Birds: Hard, calcareous shell

Reptiles: Leathery, flexible shell

Mammals: Most have no eggshell; embryo develops inside mother’sbody