L9- Amphibians

Darwin was the first to describe amphibians to…

• scientists, but they were known to local communities e.g. Darwin Frog

  • found that those in South America lived in a high diversity of environments but those in Europe all had similar life histories

Shared derived features of amphibians:

1. skin

2. ear

3. vision

4. teeth

5. muscle

1. skin

• have a smooth, moist, permeable skin

• breathe through their skin→ facilitates oxygen uptake and carbon dioxide extraction

  • has a thin epidermis

• suffer high rates of water loss

  → have a semi-aquatic life

2. ear

• use different parts of the inner ear to detect different frequencies (amphibian papilla, basilar papilla)

• have an extra bone→ function is controversial, may be a connector to forelimbs (operculum columella)

3. vision

• rod (light) and cone (colour) photoreceptors are specialised neurons that allow vision and complement each other

• have 4 types of photoreceptors (1 more than usual vertebrates) that allow perceiving light at intensities that other vertebrates cannot

  • are the only vertebrates that can do this

  • has many functions

4. teeth

• are the only group of recent tetrapods to have pedicellate teeth

  • are complex teeth→ function is debated

  • non-calcified connective tissue sandwiched in by two calcified dentine elements

5. muscle

• have a levator bulbi muscle

  • moves the eye as a whole→ retract inside and put back again

  • enlarges buccal cavity

    • is important for feeding→ overcomes the restraint of opening the mouth

There are 3 groups of Amphibians:

1. Anurans→ Frogs and Toads

2. Urodeles→ Newts and Salamanders

3. Gymnophonia→ Caecilians

Caecilians:

• 150 species

• live underground→ difficult to study and find

• have internal fertilisation

• evidence of parental care

caecilians reproductive modes:

• oviparous→ free-living aquatic larvae eggs

• oviparous→ direct development eggs

• viviparous→ terrestrial and aquatic live young

caecilians parental care:

• energy for offspring growth is first supplied by yolk then by mother→ evidence of parental care

  • viviparous→ provided through uterine milk, scrape secretions from the oviduct

  • oviparous→ feed off the skin of the mother, outer epidermal cells have more fat for nutrients

  • young have specialised foetal teeth to feed

Newts and Salamanders:

• 760 species, highly threatened

• mostly internal fertilisation

• paedomorphosis→ adults retain larval traits during adult stage

  • some groups keep traits depending on the environment

internal fertilisation in n and s:

• males deposit their spermatophore in ground that has a sperm cap at the tip, the female uptakes this to fertilise her eggs

• there are many complex courtship behaviours with elaborate secondary sexual characters to make sure the female takes their spermatophore

• pheromones are transferred in many ways e.g. tail fanning, biting, rubbing…

egg laying in n and s:

• most species lay eggs under water that develop into aquatic larvae

• the purely terrestrial species are ovoviviparous/viviparous (produce eggs that hatch inside the body and the young are born live)

  • females retain embryos/eggs until the end of gestation, are fully developed juveniles

Frogs and Toads:

• 5000 species, huge diversity

• all are carnivorous

• have a reduced skeleton with less ossification that is specialised for jumping:

reduced skeleton in f and t:

• elongated hind limbs and pelvis

• reduction or no tail

• urostyle→ shock absorber for the pelvis

• shortened or no ribs→ solid path for transmission of thrust

• tibio-fibula→ tibia and fibula are fused together

Reproductive Modes of Anurans:

• generalised life cycle (eggs, tadpoles, growth)→ only in temperate regions

• is actually very complex and diverse

• traits differ between groups e.g. egg and clutch characteristics, larval development, parental care, site of egg-laying…

there are 2 patterns of the evolution of reproduction:

1. there is higher diversity of reproductive modes in the tropics

2. there is a progression from aquatic to terrestrial reproduction

looked at the selective pressures driving the two patterns of the evolution of reproduction:

• terrestrial reproductive modes are more common in warmer, wetter environments in the tropics

• locations with low precipitation and seasons support aquatic reproductive modes more or have adaptations to resist desiccation

• move from aquatic to terrestrial to reduce predation threat

• however, must now protect young from desiccation and terrestrial predation, so there is a trade off

trade off in eggs:

• terrestrials have less but larger eggs with more water inside→ more costly, need longer development, need parental care, but have higher survival rates

Adaptations for terrestrial reproduction:

1. Foam Nests-

2. Development of eggs on leaves over-hanging water-

3. Some species have ovo/viviparity (produce eggs that hatch inside the body and the young are born live)-

1. foam nests

• are secretions of the oviduct

• protect the eggs from desiccation and predation

• has evolved convergently in 6 lineages, only in tropical continents

2. Development of eggs on leaves over-hanging water-

• when eggs hatch, they will fall into the water

• evolved convergently in 3 groups

• sometimes, male surround leaf to ensure there is no predation

3. ovo/viviparity-

produce eggs that hatch inside the body and the young are born live-

• is present in 2 genera in Africa, 1 in Indonesia and 1 in Puerto Rico

• 1 species has eggs and tadpoles developing in the female oviduct

• some species show true viviparity→ embryos are nourished by secretions

• one species raised tadpoles in their mouth and stomach

• e.g. Darwin’s Frog

e.g. Darwin’s Frog:

• females lay eggs, males remain near until they are ready to hatch

• larvae contract muscles to stimulate males to swallow eggs where they hatch inside and develop and are later expelled

Recent Taxonomic Discoveries:

Amphibians are highly understudied but highly threatened

• a new species found in the south of Ecuador

• a new family was found in 2003

• a new species was found in New York city wetlands