Mountain Yellow-legged Frog (Rana muscosa) Fact Sheet: Reproduction & Development

Reaching sexual maturity

• Females mature between 1.73 and 1.97 inches (44 and 50 mm) in length (Zweifel 1955)
• First breeding at about 2 years of age

Breeding

• At lower elevations, breeding occurs between April and May
• Eggs laid late spring to early summer (Natalie Calatayud, personal communication, 2016)
  • Often laid on undersides of leaves or other horizontal structures

Egg (The Mountain Yellow Legged Frog Site 2015; Vredenburg 2005; Zweifel 1955)

• Number of eggs: 40-300 per egg mass
  • Egg size about 1.9-2.3 mm
• Time to hatch
  • Depends on environmental conditions
  • In the wild: not well-understood
  • In managed care: 5-6 weeks (Natalie Calatayud, peronsonal communication, 2016, citing Michelle Curtis and Nicole Gardner, personal communications, 2016)
  • Eggs hatch into free-living larvae
• Timing of metamorphosis (time elapsing from fertilization of egg to frog)
  • • At lower elevations: same season as eggs are laid
    • At higher elevations: usually occurs the next summer
      • May not occur until the fourth summer at the highest elevations

Tadpole

• One of largest tadpoles of any North American frog
  • Up to 3 inches long
• Produces mucous to anchor itself to plants
• Feeds off residual yolk from yolk sac
• Develops long tail, external gills, working mouth parts, and long digestive tract
• Metamorphosis in the wild
  • May occur within 6 months, but may take up to 2-3 years, depending on environmental conditions
    • Most frog species only need one season
• Metamorphosis in managed care
  • Occurs before winter
• Metamorphosis: changes in body structure
  • Tadpole increases in size
  • Eyes more noticeable, mouth is wider
  • Hindlimbs and forelimbs develop
  • Tail becomes shorter; reabsorbed
  • Gills become smaller; fold of skin grows over external gills
    • Breathes exclusively through internal gills as external gills disappear
    • Lungs develop
      • Tadpole breathes by gulping air from surface
  • Young frog can move to land
  • Diet becomes carnivorous

Wild populations

• Approx. 12–15 years (Natalie Calatayud Crump, personal communication, 2023)

Managed care

• No AZA estimates

Female Mountain Yellow-Legged Frog (Rana muscosa) with eggs.

Image credit: © San Diego Zoo Wildlife Alliance. All rights reserved.

Development of a tadpole.

Image credit: © San Diego Zoo Wildlife Alliance. All rights reserved.

Zweifel (1955)
Livezey and Wright (1945)
Stebbins (1951)
Mathews and Miaud (2007)
Vredenburg (2005)
The Mountain Yellow Legged Frog Site