Study guide- Amphibians

Human-mediated dispersal example?

Bullfrogs spreading due to farming/escape

What is the main reproduction type in amphibians?

sexual reproduction

Other amphibian reproduction types?

Unisexual + hybridization

Protogyny

Sex change from female → male

What is the most common fertilization type in amphibians?

External

Internal fertilization occurs in which amphibians?

Caecilians + most salamanders

• Ascaphus truei

  • tail→ extension of the male cloaca

Phallodeum

The specialized copulatory organ of caecilians

What are the 3 types of reproductive modes in amphibians?

• Oviparity (most amphibians) or Viviparity (some caecilians→ evolved at least four times)

• Deposition Sites

• Developmental Pathways (direct vs indirect)

What are some Frog egg deposition sites?

• Water→ bubble or foam nests

• Land→ Terrestrial / arboreal or Eggs on Ground or Rocks or Burrows

Indirect development

Larva → metamorphosis → adult

Direct development

terrestrial eggs hatch directly into tiny, fully formed froglets or salamanders

• allowing species to thrive without standing water

What triggers the production of gametes?

• Environmental Stimuli

• Hormonal Regulation

What are some of the Environmental Stimuli that triggers the production of gametes?

Rainfall, temperature, day length

What is the Hormonal Regulation pathway that triggers the production of gametes?

GnRH → pituitary → gonads

• nervous system releases GnRH → 

• stimulates pituitary gland to produce gonadotropins (hormones) →

• act on testes/ovaries to produce sperm/eggs =>

• drive reproductive behaviors

What is the main Costs and Energy Investment in reproduction?

• Parent investment

• Parental Care

• Nutritional Support

• Larval investment

Parent investment

• Reproductive episodes

• Number of eggs / Size of eggs

  • produce many small eggs or a few large ones

What does parental Care do?

increases the chances of larval survival

What is the cost of parental care?

• Very costly for the adult

  • ~increasing predation risk and reducing the parent's ability to feed or reproduce again

Nutritional Support

Matrotrophy vs patrotrophy

Larval investment

numerous small eggs with minimal yolk

• massive energetic burden of development→ larvae

• must consume enough energy from the environment → grow and survive

-Development (& metamorphosis)

-Survival

What are the most common types of reproductive modes of frogs?

• Fertilization mode-> external

• Egg deposition site→ water/land

• Larval stage or not

• Feeding or non-feeding larvae

• presence and type of parental care

What are the most common types of reproductive modes of Salamanders?

• Fertilization external

  • oviparity-> eggs = aquatic-> indirect development

• Fertilization internal

  • Oviparity

    • Eggs aquatic-> indirect

    • Eggs terrestrial-> 

      • indirect-> aquatic/terrestrial

      • Direct

  • Viviparity-> birth-> neonates terrestrial

    • Lecithotrophy

    • Matrotrophy -> oviduct histophagy/ oophagy or adelphophagy

What are the most common types of reproductive modes of Caecilians?

• Fertilization internal

  • Oviparity→ terrestrial

    • indirect

    • direct

  • Viviparity→ Birth→ Neonates

    • terrestrial

    • aquatic

What are some of the adaptations for osmoregulation of amphibians?

• Have highly permeable skin and are better adapted to moist environments.

• They rely on moisture absorption through the skin and use the bladder as a significant water storage reservoir

What are two ways Terrestrial amphibians osmoregulate?

skin absorption and urinary bladder water storage to maintain their water balance

• (1) decrease their water loss, and/or

• (2) increase water uptake

What are the Three major categories of adaptations?

• Behavioral Adaptations

• Structural Adaptations

  • skin, urinary bladder, lymph sacs

• Physiological Adaptations

  • waterproofing and nitrogen excretion

What is the main route of water loss for amphibians?

Through the Skin

• Rate of loss can be 50X that of a lizard of the same size

What are the structural adaptations for water intake of salamanders?

Costal grooves draw water up onto skin through capillary action

What are the structural adaptations for water intake of Frogs?

• Ventral pelvic region

  • specialized for the uptake of water

  • skin is thinner and more vascularized in terrestrial species

What are some behavioral adaptations for osmoregulation?

• Movement to Osmotically Favorable Environments

  • Calling→ max loss

    • (done during wet nights)

  • Crouched→ min loss

    • (done during dry nights)

• Burrowing

What are some Physiology adaptations for osmoregulation?

• Excretion of uric acid in some frog species

  • Rhacophoridae and Hyperoliidae

  • Several South American Tree Frogs

• elevate the osmotic concentration of their body fluids

  • Urea retention

  • May also increase plasma concentrations of sodium and chloride

• maintains a favorable osmotic gradient for water uptake

What is one reason most terrestrial amphibians are nocturnal?

• Temperatures are lower and humidity is higher at night.

• Animals spend the day in diurnal retreats

Why do amphibians not tolerate salt (or the beach)?

• It makes them lose water to the environment quickly

  • some species do tolerate salinity

What are some species examples of tolerating salt (or the beach)?

• Dicamptodon tenebrosus (larvae / tidal)

• Taricha granulosa (tidal)

• Pseudacris regilla (beach and cliff pools in spray zone)

  • I have heard them at Sue Meg (wedding rock)

• Anaxyrus boreas (beach, saline lakes)

What are some Structural / Water Storage adaptations for osmoregulation?

1. Enlarged urinary bladders

• Bladder water

  • Terrestrial frogs and salamanders can hold up to 20-50% of body mass

  • can be absorbed over time to maintain suitable levels of plasma solutes

2. Subcutaneous lymph sacs

What are some Physiology / Waterproofing adaptations for osmoregulation?

• Cocoon

  • Covers the body during long dormant periods

    • allow frog to withstand long periods without much water loss

• Waxy coating

  • During the day, when the animal is inactive

  • Coating reduces evaporative water loss

• Water holding frogs→ bladder water

  • Produces a cocoon

  • Lives off stored fat

  • Recycles urea into useful proteins to avoid self-poisoning

Examples of frogs that evolved waxy coatings

• Phyllomedusea

  • Coating reduces evaporative water loss by 90-95% relative to most other frogs

  • Rate of EWL from a resting P. sauvagei is nearly as low as that of a desert iguana

• Hylidae

  • Litoria coerulea (AUS)

  • Several spp in florida (exhibit higher rates of EWL than true waterproof frogs)

• Rhacophoridae (india)

  • Polypedates maculatus