Q.27 Neoteny is exhibited by :-
(1) Axolotl larva
(2) Zoea larva
(3) Bipinnaria larva
(4) Planula larva
What is Neoteny?
Neoteny is a form of paedomorphosis where juvenile traits (e.g., gills, fins) are retained into sexual maturity, skipping full metamorphosis. It allows reproduction in a larval-like form, often due to thyroid hormone changes. Common in salamanders, neoteny aids survival in stable environments. This concept is crucial for evolutionary biology and exams like NEET.
Correct Answer: Neoteny is Exhibited by Axolotl Larva (Option 1)
The correct answer is (1) Axolotl larva.
The axolotl (Ambystoma mexicanum), a salamander from Mexico, shows classic neoteny. Its aquatic larva retains external gills, a finned tail, and larval body shape into adulthood, becoming sexually mature without metamorphosing into a terrestrial adult. Under iodine-rich conditions, it can metamorphose, proving neoteny is physiological, not fixed.
Key feature: Obligate neoteny in natural habitats like Lake Xochimilco.
Explanation of All Options
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(1) Axolotl larva: Exhibits neoteny—reaches sexual maturity with larval features (gills, aquatic form). Example: Breeds while gill-bearing.
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(2) Zoea larva: Crustacean larva (crabs, lobsters) with spines and swimming appendages. Undergoes normal metamorphosis to megalopa; no neoteny.
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(3) Bipinnaria larva: Echinoderm larva (starfish, sea urchins) with ciliated bands for feeding. Metamorphoses to adult via brachiolaria stage; standard development.
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(4) Planula larva: Cnidarian larva (jellyfish, corals) with free-swimming, ciliated form. Settles and metamorphoses to polyp; no neoteny.
| Larva Type | Group | Exhibits Neoteny? | Development Pattern |
|---|---|---|---|
| Axolotl | Salamander | Yes | Paedomorphic adult |
| Zoea | Crustaceans | No | Metamorphosis |
| Bipinnaria | Echinoderms | No | Metamorphosis |
| Planula | Cnidarians | No | Metamorphosis |
Significance of Neoteny in Evolution
Neoteny drives evolution by retaining youthful traits, seen in human skull shapes or axolotl regeneration. It contrasts with normal larval metamorphoses in options 2-4, emphasizing heterochrony (timing shifts in development).
Explore more on paedomorphosis or amphibian life cycles in our developmental biology series.
