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Why do some salamanders keep their gills throughout life?

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Study an amphibious tiger salamander of the mole salamander family Ambystomatidae in its natural habitat — Caudata Tiger salamanders (*Ambystoma tigrinum*) are widespread across much of the United States. Although they are generally black with yellow blotches, bars, spots, or even stripes, some are lighter in colour or have olive markings. Tiger salamanders belong to the mole salamander family, Ambystomatidae.

Some salamanders retain their gills throughout their lives due to a biological phenomenon known as paedomorphosis, in which an organism maintains larval or juvenile characteristics even after reaching sexual maturity.12

In these species, the typical process of metamorphosis—which would normally involve the loss of gills and the development of adult structures—is either partially or completely bypassed. This permanent larval state can be determined by heredity, but in some populations, it may be induced by environmental factors, such as cold temperatures or unfavorable terrestrial conditions like drought.1

By remaining in an aquatic, larval-like state, these salamanders are able to breed while retaining features like external gills. This condition is characteristic of certain families, such as Proteidae (which includes the mud puppy and the olm) and Sirenidae, and is also observed in specific species like the axolotl.123