NEOTENY IN AMPHIBIA
Dr Anita Kumari
Dept. Of Zoology
L .S.College
Neoteny is defined as the failure or delay of larva to metamorphose while becoming sexually
mature. It is character of some amphibians.
The best example is axolotl larva of Ambystoma. It is aquatic. It has gills. It develops
gonads. It lays eggs and attains large size. Ambystoma on the other hand, is terrestrial and
without gills. It was considered the axtolotl as a separate genera in the beginning, with the
administration of thyroxine, axtlotl lost its gills and develops lungs. It metamorphosed into the
adult. Metamorphosis of axolotl can be induced by reducing the water level.
Proteus. and Necturus are permanently neotenous forms. They retained the larval features
and reproduce sexually like a mature animal.
Two terms, paedogenesis and neoteny ,coined by Kollwann and are often used as synonyms
which is not correct. Neoteny refers to the retention of a larval or embryonic trait in the adult
body. Familiar examples are retention of embryonic cartilaginous skeleton in adult in
Chondrichthyes; and the larval gills in some adult salamanders.
Paedogenesis or paedomorphosis refers to development of gonads and/or production of
young ones by an otherwise immature, larval or preadult animal. The examples are scattered
in several groups or animals (e.g. gall fly, liver fluke, and salamanders). Thus, whereas
neoteny emphasizes the retention of embryonic or larval features in the adult body and
paedogenesis stresses precocious development of gonads in larval body
Axolotl. Classical and most informative examples of neoteny and paedogenesis among
Amphibia (vertebrates) are furnished by Ambystoma. A. tigrinum (tiger salamander) in high
altitudes of Colorado (North America). Ordinarily they go through typical gilled aquatic
larval stages, then metamorphosis, to transform into adult air-breathing land forms. However,
under certain circumstances, the larvae do not metamorphose, retain their gills and aquatic
habitat but become sexually mature. This sexually mature but morphologically immature,
larva Stage with external gills is called an axoiotl. Thus, neoteny emphasizes the retention of
embryonic or larval features in the adult body and paedogenesis stresses precocious
development of gonads in larval body. Amphibian examples. Some aquatic larval urodeles
delay or fail to metamorphose.
Environmental factors affecting neoteny. The significance and causes of neoteny are not
properly understood. Environmental factors affect metamorphosis in several ways.
Abundance of food, cold temperature or insufficient iodine (a component of thyroxin
hormone that induces amphibian metamorphosis) may cause failure of metamorphosis and
retention of larval features. This is indicated by the fact that drying up of swamps, lack of
Dr Anita Kumari
Dept. Of Zoology
L .S.College
Neoteny is defined as the failure or delay of larva to metamorphose while becoming sexually
mature. It is character of some amphibians.
The best example is axolotl larva of Ambystoma. It is aquatic. It has gills. It develops
gonads. It lays eggs and attains large size. Ambystoma on the other hand, is terrestrial and
without gills. It was considered the axtolotl as a separate genera in the beginning, with the
administration of thyroxine, axtlotl lost its gills and develops lungs. It metamorphosed into the
adult. Metamorphosis of axolotl can be induced by reducing the water level.
Proteus. and Necturus are permanently neotenous forms. They retained the larval features
and reproduce sexually like a mature animal.
Two terms, paedogenesis and neoteny ,coined by Kollwann and are often used as synonyms
which is not correct. Neoteny refers to the retention of a larval or embryonic trait in the adult
body. Familiar examples are retention of embryonic cartilaginous skeleton in adult in
Chondrichthyes; and the larval gills in some adult salamanders.
Paedogenesis or paedomorphosis refers to development of gonads and/or production of
young ones by an otherwise immature, larval or preadult animal. The examples are scattered
in several groups or animals (e.g. gall fly, liver fluke, and salamanders). Thus, whereas
neoteny emphasizes the retention of embryonic or larval features in the adult body and
paedogenesis stresses precocious development of gonads in larval body
Axolotl. Classical and most informative examples of neoteny and paedogenesis among
Amphibia (vertebrates) are furnished by Ambystoma. A. tigrinum (tiger salamander) in high
altitudes of Colorado (North America). Ordinarily they go through typical gilled aquatic
larval stages, then metamorphosis, to transform into adult air-breathing land forms. However,
under certain circumstances, the larvae do not metamorphose, retain their gills and aquatic
habitat but become sexually mature. This sexually mature but morphologically immature,
larva Stage with external gills is called an axoiotl. Thus, neoteny emphasizes the retention of
embryonic or larval features in the adult body and paedogenesis stresses precocious
development of gonads in larval body. Amphibian examples. Some aquatic larval urodeles
delay or fail to metamorphose.
Environmental factors affecting neoteny. The significance and causes of neoteny are not
properly understood. Environmental factors affect metamorphosis in several ways.
Abundance of food, cold temperature or insufficient iodine (a component of thyroxin
hormone that induces amphibian metamorphosis) may cause failure of metamorphosis and
retention of larval features. This is indicated by the fact that drying up of swamps, lack of
