Neoteny and Paedogenesis | Zoology Optional Notes for UPSC PDF Download

Introduction

In this comprehensive exploration, we delve into the intriguing phenomena of neoteny and paedogenesis within the amphibian realm, specifically focusing on their manifestation in the Vertebrate class Chordata. Through an elucidative discussion supported by a relevant diagram, we unravel the complexities and implications of these developmental processes.

Neoteny in Amphibia

Amblystoma Genus (Urodele):

• Some individuals reach sexual maturity while remaining in the larval condition.
• Notable example: Siredon, the axolotl.
• Lack of metamorphosis characterizes this unique state.

Genus Triton:

• Occasional instances of neoteny observed, extending beyond the Amblystoma genus.
• Phylogenetic adaptability demonstrated within Triton.

Necturus and Amphiuma (Obligate Neoteny):

• These species exhibit neoteny as a physiological adaptation.
• Thyroxine T4 fails to induce metamorphosis in these cases.

Facultative Neotenes:

• Axolotl and certain Amblystoma individuals experience facultative neoteny.
• Thyroxine T4 typically triggers metamorphosis in these cases.

Underlying Factors:

• Neoteny is attributed to a low level of thyrotropin-releasing hormone (TRH).
• Genetic predisposition and environmental factors contribute to this phenomenon.

Paedogenesis in Amphibia

Definition:

• Paedogenesis involves the reproduction of a sexually mature descendant in a pre-adult form.

Evolutionary Influence:

• Garstang suggests paedogenesis has played a significant role in the evolution of certain animal types.

Axolotl as a Classical Case:

• Mexican Axolotl frequently engages in paedogenesis, breeding in the gilled or larval state.

Experimental Induction of Metamorphosis:

• Administration of thyroxin, especially in early developmental stages, prompts the loss of gills, lung development, and emergence in an adult form.
• Reduction of water levels, hindering gill respiration while facilitating pulmonary respiration, also induces metamorphosis.

Term Application:

• The term "Axolotl" appropriately applies to the branchiate stage of this intriguing biological phenomenon.

In summary, this exploration not only sheds light on the intricacies of neoteny and paedogenesis in amphibians but also underscores their significance in the broader context of evolutionary biology within the class Chordata.