Metamorphosis

Metamorphosis

development of amphibian larva into adult

caecilians — most direct development

salamanders — tadpoles resemble adults

anurans — tadpoles different from adults

why

• 2 habitats for two diets/lifestyles

• reduces adult - young competition

Duration

temporary habitat = fast change

stable = long

Size

specific size required

• good resources = later metamorphosis b/c similar sized young

• poor resources = sooner metamorphosis b/c varial sizes

maximum larval size = metamorphosis

low current growth rates/poor resources = metamorphosis

if there are good resources, larger size may be attained before metamorphosis occurs —> usually young will try to grow to max larval size before morphing

Mechanism

2 phases — growth and differentiation

• environment cues

• hypothalamus — corticotropin hormone triggers hormones in pituitary gland

• pituitary

  • prolactin for additional growth which inhibits morphing

  • TSH — thyroid makes T4 keeps tadpole but if converted to T3 by corticosterone then metamorphosis

  • Adrenocorticotropic hormone (ACTH) — interrenal creates corticosterone to convert T4 to T3 and a positive feedback loop to hypothalamus

Salamander vs Frog Tadpoles

Tadpoles

• thin, vascular skin

• cartilage skeleton

• lidless eyes

• finned tail

• gills

• specialized mouth parts

• GI tract

• Limbless

Salamander

• same skin but thicker, glands

• bone skeleton

• eyelids

• keep tail but loses fin

• pharyngeal slits, external gills in tadpoles

• change teeth

• no/little GI change

• front limbs appear first

Frog

• same skin but thicker, glands

• bone skeleton

• eyelids

• loses tail

• “covered” gills in tadpoles

• replace with adult teeth/jaw

• shortens intestines

• rear limbs first while front develop hidden in operculum