Atadpole orpolliwog (also spelledpollywog) is thelarval stage in thebiological life cycle of anamphibian. Most tadpoles are fullyaquatic, though some species of amphibians have tadpoles that areterrestrial. Tadpoles have somefish-like features that may not be found in adult amphibians, such as alateral line,gills and swimmingtails. As they undergometamorphosis, they start to develop functionallungs for breathing air, and the diet of tadpoles changes drastically.
A few amphibians, such as some members of thefrog familyBrevicipitidae, undergodirect development – i.e., they do not undergo a free-living larval stage as tadpoles – instead emerging from eggs as fully formed "froglet" miniatures of the adultmorphology. Some other species hatch into tadpoles underneath the skin of the female adult or are kept in a pouch until after metamorphosis. Having no hard skeletons, it might be expected that tadpolefossils would not exist. However, traces ofbiofilms have been preserved and fossil tadpoles have been found dating back to theMiddle Jurassic.[1]
Tadpoles are eaten ashuman food in some parts of the world and are mentioned in variousfolk tales from around the world.
The nametadpole is fromMiddle Englishtaddepol, made up of the elementstadde, 'toad', andpol, 'head' (modern Englishpoll). Similarly,pollywog /polliwog is from Middle Englishpolwygle, made up of the samepol, 'head', andwiglen, 'to wiggle'.[2]
The life cycle of all amphibians involves a larval stage that is intermediate between embryo and adult. In most cases this larval stage is a limbless free-living organism that has a tail and is referred to as a tadpole, although in a few cases (e.g., in theBreviceps andProbreviceps genera of frogs)direct development occurs in which the larval stage is confined within the egg. Tadpoles of frogs are mostly herbivorous, while tadpoles ofsalamanders andcaecilians are carnivorous.
Ten-day-old tadpoles. The external gills will eventually be hidden by a layer of skin.
Tadpoles of frogs and toads are usually globular, with a laterally compressed tail with which they swim bylateral undulation. When first hatched, anuran tadpoles have external gills that are eventually covered by skin, forming anopercular chamber with internal gills vented byspiracles. Depending on the species, there can be two spiracles on both sides of the body, a single spiracle on the underside near the vent, or a single spiracle on the left side of the body.[3] Newly hatched tadpoles are also equipped with a cement gland which allows them to attach to objects. The tadpoles have a cartilaginous skeleton and anotochord which eventually develops into a proper spinal cord.
Anuran tadpoles are usually herbivorous, feeding on soft decaying plant matter. The gut of most tadpoles is long and spiral-shaped to efficiently digest organic matter and can be seen through the bellies of many species. Though many tadpoles will feed on dead animals if available to them, only a few species of frog have strictly carnivorous tadpoles, an example being the frogs of the familyCeratophryidae, their cannibalistic tadpoles having wide gaping mouths with which they devour other organisms, including other tadpoles. Another example is the tadpoles of the New Mexico spadefoot toad (Spea multiplicata) which will develop a carnivorous diet along with a broader head, larger jaw muscles, and a shorter gut if food is scarce, allowing them to consume fairy shrimp and their smaller herbivorous siblings.[4] A few genera such asPipidae andMicrohylidae have species whose tadpoles arefilter feeders that swim through the water column feeding onplankton.Megophrys tadpoles feed at the water surface using unusual funnel-shaped mouths.[5]
As a frog tadpole matures it gradually develops its limbs, with the back legs growing first and the front legs second. The tail is absorbed into the body usingapoptosis. Lungs develop around the time as the legs start growing, and tadpoles at this stage will often swim to the surface and gulp air. During the final stages of 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 as they transition from a herbivorous diet to the carnivorous diet of adult frogs.
Tadpoles vary greatly in size, both during their development and between species. For example, in a single family,Megophryidae, length of late-stage tadpoles varies between 3.3 centimetres (1.3 in) and 10.6 centimetres (4.2 in).[6] The tadpoles of the paradoxical frog (Pseudis paradoxa) can reach up to 27 centimetres (11 in),[7] the longest of any frog,[8] before shrinking to a mere snout-to-vent length of 3.4–7.6 cm (1.3–3.0 in).
While most anuran tadpoles inhabitwetlands,ponds,vernal pools, and other small bodies of water with slow moving water, a few species are adapted to different environments. Some frogs have terrestrial tadpoles, such as the familyRanixalidae, whose tadpoles are found in wet crevices near streams. The tadpoles ofMicrixalus herrei are adapted to afossorial lifestyle, with a muscular body and tail, eyes covered by a layer of skin, and reduced pigment.[9] Several frogs have stream dwelling tadpoles equipped with a strongoral sucker that allows them to hold onto rocks in fast flowing water, two examples being the Indian purple frog (Nasikabatrachus sahyadrensis) and the tailed frogs (Ascaphus) of Western North America. Although there are no marine tadpoles, the tadpoles of thecrab-eating frog can cope with brackish water.[10]
Some anurans will provide parental care towards their tadpoles. Frogs of the genusAfrixalus will lay their eggs on leaves above water, folding the leaves around the eggs for protection. FemalePipa frogs will embed the eggs into their backs where they get covered by a thin layer of skin. The eggs will hatch underneath her skin and grow, eventually leaving as either large tadpoles (such as inPipa parva) or as fully formed froglets (Pipa pipa). Female marsupial frogs (Hemiphractidae) will carry eggs on her back for various amounts of time, with it going as far as letting the tadpoles develop into tiny froglets in a pouch. Male African bullfrogs (Pyxicephalus adspersus) will keep watch over their tadpoles, attacking anything that might be a potential threat, even though he may eat some of the tadpoles himself.[11]
Males of the Emei mustache toads (Leptobrachium boringii) will construct nests along riverbanks where they breed with females and keep watch over the eggs, losing as much as 7.3% of their body mass in the time they spend protecting the nest.[12] Male midwife toads (Alytes) will carry eggs between their legs to protect them from predators, eventually releasing them into a body of water when they are ready to hatch. Poison dart frogs (Dendrobatidae) will carry their tadpoles to various locations, usuallyphytotelma, where they remain until metamorphosis. Some female dart frogs such as the strawberry poison dart frog (Oophaga pumilio) will regularly lay unfertilized eggs for the developing tadpoles to feed on.[13]
Despite their soft-bodied nature and lack of mineralised hard parts, fossil tadpoles (around 10 cm in length) have been recovered from UpperMiocene strata.[14] They are preserved by virtue ofbiofilms, with more robust structures (the jaw and bones) preserved as acarbon film.[15] In Miocene fossils fromLibros, Spain, thebrain case is preserved incalcium carbonate, and the nerve cord incalcium phosphate. Other parts of the tadpoles' bodies exist as organic remains and bacterial biofilms, with sedimentarydetritus present in the gut.[14] Tadpole remains with telltale external gills are also known from severallabyrinthodont groups. The oldest unambiguous fossil, a tadpole of the speciesNotobatrachus deguistioi from theMiddle Jurassic, was published on in 2024.[1]
Tadpoles are used in a variety of cuisines. Tadpoles of themegophryid frogOreolalax rhodostigmatus are particularly large, more than 10 cm (3.9 in) in length,[6] and are collected for human consumption in China.[16] In PeruTelmatobius mayoloi tadpoles are collected for both food and medicine.[17]
According toSir George Scott, in theorigin myths of theWa people inChina andMyanmar, the first Wa originated from two female ancestorsYa Htawm andYa Htai, who spent their early phase as tadpoles ("rairoh") in a lake in theWa country known asNawng Hkaeo.[18]
^"The Grammarphobia Blog: On tadpoles and pollywogs". 2012-05-01.Archived from the original on 2016-08-22. Retrieved2016-08-08.The word is a compound of the Middle English tade or tadde (toad) and, apparently, the noun "poll" (head or roundhead), Oxford says. [...] Its earliest appearance in writing—spelled "polwygle"—is from 1440, the OED says. That very odd-looking word was originally derived, Oxford says, from "poll" plus "wiggle".
^Altig, Ronald; McDiarmid, Roy W.; Nichols, Kimberly A.; Ustach, Paul C."North American Tadpoles: Spiracle".Tadpoles of the United States and Canada: A Tutorial and Key. USGS Patuxent Wildlife Research Center. Archived fromthe original on 28 December 2016. Retrieved12 April 2020.
^Bokermann, W.C.A. (1967). "Girinos de anfíbios brasileiros—3: sôbre um girino gigante de Pseudis paradoxa (Amphibia, Pseudidae)".Revista Brasileira de Biologia.27:209–212.
^Cook, C. L.; Ferguson, J. W. H.; Telford, S. R. (June 2001). "Adaptive Male Parental Care in the Giant Bullfrog, Pyxicephalus adspersus".Journal of Herpetology.35 (2):310–315.doi:10.2307/1566122.JSTOR1566122.
^abMcNamara, M. E.; Orr, P. J.; Kearns, S. L.; Alcalá, L.; Anadón, P.; Peñalver-Mollá, E. (2009). "Exceptionally preserved tadpoles from the Miocene of Libros, Spain: ecomorphological reconstruction and the impact of ontogeny upon taphonomy".Lethaia.43 (3):290–306.doi:10.1111/j.1502-3931.2009.00192.x.hdl:10261/141680.
