tadpole

A tadpole, polliwog (also pollywog, polliwig, polwig, or purwiggy), or pollywiggle (also polliwiggle, polwiggle, or porwiggle) is the wholly aquatic larval stage in the life cycle of an amphibian, particularly of a frog or toad.

Appellation

The name "tadpole" is from Middle English taddepol, made up of the elements tadde, "toad", and pol, "head" (modern English "poll"). Similarly, "polliwog" and "pollywiggle" are from Middle English polwigle, made up of the same pol and wiglen, "to wiggle".

General description

Metamorphosis of Bufo bufo.

Tadpole stage of Haswell's Frog.

Tadpoles are young amphibians that live in the water. During the tadpole stage of the amphibian life cycle, most respire by means of autonomous external or internal gills. They do not usually have arms or legs until the transition to adulthood, and typically have dorsal or fin-like appendages and a tail with which they swim by lateral undulation, similar to most fishes.

As a tadpole matures, it most commonly metamorphosizes by gradually growing limbs (usually the legs first, followed by the arms) and then (most commonly in the case of frogs) outwardly absorbing its tail by apoptosis. Lungs develop around the time of leg development, and tadpoles late in development will often be found near the surface of the water, where they breathe air. During the final stages of external metamorphosis, the tadpole's mouth changes from a small, enclosed mouth at the front of the head to a large mouth the same width as the head. The intestines shorten to make way for the new diet.^[1] Tadpoles are consumers.Most tadpoles are herbivorous, subsisting on algae and plants. Some species are omnivorous, eating detritus and, when available, smaller tadpoles.^[2] However, other tadpoles are normally safe from cannibalistic predation because all tadpoles in a given body of water are the same age and, therefore, the same size.

An exception to the rule of distinct differences between the tadpole (juvenile) and adult (frog, toad, salamander etc) stages is the axolotl. Axolotls exhibit a property called neoteny, meaning that they reach sexual maturity without undergoing metamorphosis.

Fossil record

Remarkably, despite their soft-bodied nature and lack of mineralised hard parts, fossil tadpoles (around 10 cm in length) have been recovered from Upper Miocene strata.^[3] They are preserved by virtue of biofilms, with more robust structures (the jaw & bones) preserved as a carbon film.^[4] In Miocene fossils from Libros, Spain, the brain case is preserved in calcium carbonate, and the nerve cord in calcium phosphate. Other parts of the tadpoles' bodies exist as organic remains and bacterial biofilms, with sedimentary detritus present in the gut. ^[3]

References

External links

• Media related to Tadpole at Wikimedia Commons
• The Wiktionary definition of tadpole
• Video of Hundreds of Tadpoles
• How to Raise Tadpoles
• Raising Tadpoles to Adulthood (University of California Berkeley)