Tadpole

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Common frog (Rana temporaria) tadpole RanaTemporariaLarva2.jpg
Common frog (Rana temporaria) tadpole

A tadpole or polliwog (also spelled pollywog) is the larval stage in the biological life cycle of an amphibian. Most tadpoles are fully aquatic, though some species of amphibians have tadpoles that are terrestrial. Tadpoles have some fish-like features that may not be found in adult amphibians such as a lateral line, gills and swimming tails. As they undergo metamorphosis, they start to develop functional lungs for breathing air, and the diet of tadpoles changes drastically.

Contents

A few amphibians, such as some members of the frog family Brevicipitidae, undergo direct 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 adult morphology. 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 tadpole fossils would not exist. However, traces of biofilms have been preserved and fossil tadpoles have been found dating back to the Middle Jurassic. [1]

Tadpoles are eaten as human food in some parts of the world and are mentioned in various folk tales from around the world.

Etymology

The name tadpole is from Middle English taddepol, made up of the elements tadde, 'toad', and pol, 'head' (modern English poll ). Similarly, pollywog / polliwog is from Middle English polwygle, made up of the same pol, 'head', and wiglen, 'to wiggle'. [2]

Tadpoles swimming in a pond in Japan, 2023

General description

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 the Breviceps and Probreviceps genera of frogs) direct development occurs in which the larval stage is confined within the egg. Tadpoles of frogs are mostly herbivorous, while tadpoles of salamanders and caecilians are carnivorous.

Anura

Ten-day-old tadpoles. The external gills will eventually be hidden by a layer of skin. Tadpoles 10 days.jpg
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 by lateral undulation. When first hatched, anuran tadpoles have external gills that are eventually covered by skin, forming an opercular chamber with internal gills vented by spiracles. 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 a notochord which eventually develops into a proper spinal cord.

Metamorphosis of Bufo bufo Bufo metamorphosis.jpg
Metamorphosis of Bufo bufo

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 family Ceratophryidae, 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 as Pipidae and Microhylidae have species whose tadpoles are filter feeders that swim through the water column feeding on plankton. Megophrys tadpoles feed at the water surface using unusual funnel-shaped mouths. [5]

Anatomy of a wood frog tadpole (Lithobates sylvaticus) Anatomy WoodFrog.png
Anatomy of a wood frog tadpole (Lithobates sylvaticus)

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 using apoptosis. 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 inhabit wetlands, 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 family Ranixalidae, whose tadpoles are found in wet crevices near streams. The tadpoles of Micrixalus herrei are adapted to a fossorial 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 strong oral 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 the crab-eating frog can cope with brackish water. [10]

Some anurans will provide parental care towards their tadpoles. Frogs of the genus Afrixalus will lay their eggs on leaves above water, folding the leaves around the eggs for protection. Female Pipa 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 in Pipa 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, usually phytotelma, 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]

Fossil record

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. [14] They are preserved by virtue of biofilms, with more robust structures (the jaw and bones) preserved as a carbon film. [15] 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. [14] Tadpole remains with telltale external gills are also known from several labyrinthodont groups. The oldest unambiguous fossil, a tadpole of the species Notobatrachus deguistioi from the Middle Jurassic, was published on in 2024. [16]

Human use

Tadpoles are used in a variety of cuisines. Tadpoles of the megophryid frog Oreolalax rhodostigmatus are particularly large, more than 10 cm (3.9 in) in length, [6] and are collected for human consumption in China. [17] In Peru Telmatobius mayoloi tadpoles are collected for both food and medicine. [18]

Mythology and history

According to Sir George Scott, in the origin myths of the Wa people in China and Myanmar, the first Wa originated from two female ancestors Ya Htawm and Ya Htai, who spent their early phase as tadpoles ("rairoh") in a lake in the Wa country known as Nawng Hkaeo. [19]

In the Ancient Egyptian numerals, a hieroglyphic representing a tadpole was used to denote the value of 100,000.[ citation needed ]

Related Research Articles

<span class="mw-page-title-main">Amphibian</span> Class of ectothermic tetrapods

Amphibians are ectothermic, anamniotic, four-limbed vertebrate animals that constitute the class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all tetrapods excluding the amniotes. All extant (living) amphibians belong to the monophyletic subclass Lissamphibia, with three living orders: Anura, Urodela (salamanders), and Gymnophiona (caecilians). Evolved to be mostly semiaquatic, amphibians have adapted to inhabit a wide variety of habitats, with most species living in freshwater, wetland or terrestrial ecosystems. Their life cycle typically starts out as aquatic larvae with gills known as tadpoles, but some species have developed behavioural adaptations to bypass this.

<span class="mw-page-title-main">Metamorphosis</span> Profound change in body structure during the postembryonic development of an organism

Metamorphosis is a biological process by which an animal physically develops including birth transformation or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some insects, jellyfish, fish, amphibians, mollusks, crustaceans, cnidarians, echinoderms, and tunicates undergo metamorphosis, which is often accompanied by a change of nutrition source or behavior. Animals can be divided into species that undergo complete metamorphosis ("holometaboly"), incomplete metamorphosis ("hemimetaboly"), or no metamorphosis ("ametaboly").

<span class="mw-page-title-main">Frog</span> Order of amphibians

A frog is any member of a diverse and largely carnivorous group of short-bodied, tailless amphibians composing the order Anura. The oldest fossil "proto-frog" Triadobatrachus is known from the Early Triassic of Madagascar, but molecular clock dating suggests their split from other amphibians may extend further back to the Permian, 265 million years ago. Frogs are widely distributed, ranging from the tropics to subarctic regions, but the greatest concentration of species diversity is in tropical rainforest. Frogs account for around 88% of extant amphibian species. They are also one of the five most diverse vertebrate orders. Warty frog species tend to be called toads, but the distinction between frogs and toads is informal, not from taxonomy or evolutionary history.

<span class="mw-page-title-main">Common frog</span> Species of amphibian

The common frog or grass frog, also known as the European common frog, European common brown frog, European grass frog, European Holarctic true frog, European pond frog or European brown frog, is a semi-aquatic amphibian of the family Ranidae, found throughout much of Europe as far north as Scandinavia and as far east as the Urals, except for most of the Iberian Peninsula, southern Italy, and the southern Balkans. The farthest west it can be found is Ireland. It is also found in Asia, and eastward to Japan. The nominative, and most common, subspecies Rana temporaria temporaria is a largely terrestrial frog native to Europe. It is distributed throughout northern Europe and can be found in Ireland, the Isle of Lewis and as far east as Japan.

<span class="mw-page-title-main">Wood frog</span> Species of amphibian

Lithobates sylvaticus or Rana sylvatica, commonly known as the wood frog, is a frog species that has a broad distribution over North America, extending from the boreal forest of the north to the southern Appalachians, with several notable disjunct populations including lowland eastern North Carolina. The wood frog has garnered attention from biologists because of its freeze tolerance, relatively great degree of terrestrialism, interesting habitat associations, and relatively long-range movements.

<i>Indosylvirana temporalis</i> Species of amphibian

Indosylvirana temporalis, commonly known as the bronzed frog or Günther's golden-backed frog, is a species of true frog found in the riparian evergreen forests of the highlands of southwestern Sri Lanka. They are found abundantly on or close to the ground near water. Individuals are not shy and react by jumping only when provoked. They are important prey of many species of snakes, including the vine snake. Some related species found in the Western Ghats of India were formerly included in this species but were separated in a 2014 study.

<span class="mw-page-title-main">Foothill yellow-legged frog</span> Species of amphibian

The foothill yellow-legged frog is a small-sized frog from the genus Rana in the family Ranidae. This species was historically found in the Coast Ranges from northern Oregon, through California, and into Baja California, Mexico as well as in the foothills of the Sierra Nevada and southern Cascade Range in California. The foothill yellow-legged frog is a Federal Species of Concern and California State Endangered. A federal rule to list four out of six extant distinct population segments (DPS) under the Endangered Species Act was proposed in December 2021.

<span class="mw-page-title-main">Southern toad</span> Species of amphibian

The southern toad is a true toad native to the southeastern United States, from eastern Louisiana and southeastern Virginia south to Florida. It often lives in areas with sandy soils. It is nocturnal and spends the day in a burrow. Its coloring is usually brown but can be red, gray, or black. It is approximately 8 cm (3 inches) long.

<span class="mw-page-title-main">Fletcher's frog</span> Species of amphibian

Fletcher's frog, commonly known as the sandpaper frog or black-soled frog, is a species of nocturnal, terrestrial frog native to eastern Australia. It is primarily found in wet sclerophyll forests along mountain ranges and the coast.

<span class="mw-page-title-main">Italian agile frog</span> Species of amphibian

The Italian agile frog, also known as Lataste's frog, is a species of frog in the family Ranidae. The species is native to southern Europe, primarily found in the Po River Basin of Italy. It is one of the most endangered amphibian species in Europe, with its populations declining sharply in recent years, and has been the focus of multiple conservation plans.

<i>Gastrophryne carolinensis</i> Species of amphibian

Gastrophryne carolinensis, the eastern narrow-mouthed toad, is a species of microhylid frog. It is a relatively small, toad-like amphibian found in damp, shady habitats. The species is highly fossorial, and feeds primarily on ants. These North American microhylids are distinguished from true toads, and other anurans by their moist, smooth skin, their lack of eardrums or tympana, their distinguishable squat body shape, and the unique fold of skin superior to their eyes. It is found in the United States, from southern Maryland to the Florida Keys, west to Missouri and Texas. While not a true toad, it is so called because it is terrestrial.

<span class="mw-page-title-main">Plains spadefoot toad</span> Species of amphibian

The plains spadefoot toad is a species of American spadefoot toad which ranges from southwestern Canada, throughout the Great Plains of the western United States, and into northern Mexico. Like other species of spadefoot toads, they get their name from a spade-like projection on their hind legs which allows them to dig into sandy soils. Their name, in part, comes from their keratinized metatarsals, which are wide instead of "sickle shaped". The species name translates as buzzing leaf shaped. This refers to the species' distinguishing features; its buzzing mating call, and its leaf-shaped digging metatarsals. It was first described by Cope in 1863.

<span class="mw-page-title-main">New Mexico spadefoot toad</span> Species of amphibian

The New Mexico spadefoot toad is a species of American spadefoot toad found in the southwestern United States and Mexico. Like other species of spadefoot toad, they get their name from a distinctive spade-like projections on their hind legs, which enable them to dig in sandy soils. Spea multiplicata can be identified by its wedge-shaped spade. Some sources also refer to the species as the Mexican spadefoot toad, desert spadefoot toad or southern spadefoot toad.

<i>Afrixalus fornasini</i> Species of amphibian

Afrixalus fornasini is a species of frog in the family Hyperoliidae and is native to Africa. Its common name is Fornasini's spiny reed frog or the greater leaf-folding frog

<i>Leptodactylus albilabris</i> Species of amphibian

Leptodactylus albilabris is a species of frog in the family Leptodactylidae.

<i>Zhangixalus viridis</i> Species of frog

Zhangixalus viridis is a species of frog in the family Rhacophoridae. It is endemic to the Ryukyu Islands, Japan, and known from Okinawa, Iheya and Kume Islands of the Okinawa Group. Zhangixalus amamiensis from the Amami Group was formerly included in this species as a subspecies.

<span class="mw-page-title-main">Great Basin spadefoot</span> Species of amphibian

The Great Basin spadefoot is an amphibian in the family Scaphiopodidae. It is 3.8 to 6.3 centimetres long and is usually colored gray, olive or brown. Great Basin spadefoot toads have adapted to life in dry habitats. They use the hard, keratinized spade on each foot to dig a burrow, where they spend long periods during cold and dry weather. They are opportunistic hunters and will eat anything they can subdue. While their tadpoles have numerous predators, adults are able to produce skin secretions that deter enemies.

<i>Calyptocephalella</i> Genus of amphibians

Calyptocephalella is a genus of frogs in the family Calyptocephalellidae. It is represented by a single living species, Calyptocephalella gayi, commonly known as the helmeted water toad, Chilean helmeted bull frog, or wide-mouthed toad. Additionally, there are a few extinct species that are only known from Late Cretaceous and Paleogene fossil remains from Patagonia in South America and the Antarctic Peninsula. The helmeted water toad living today is aquatic to semi-aquatic, and found in deep ponds and reservoirs in central Chile and possibly adjacent west-central Argentina.

<span class="mw-page-title-main">Common Surinam toad</span> Species of frog

The common Surinam toad, the Suriname toad, or star-fingered toad, is a fully-aquatic species of frog, in the family Pipidae, with a widespread range across much of tropical South America and the island of Trinidad. The females of this species are well-known for "incubating" their eggs on their backs, in honeycomb-like depressions directly within the skin, releasing fully-formed froglets after a period of 4–5 months. Pipa pipa is an ambush predator, lying in-wait underwater for prey to inevitably wander too close, swiftly inhaling the unsuspecting creature using suction feeding. Additionally, the Surinam toad's rather flat body shape, combined with rather dark, dull coloration, serves as effective camouflage in the murky waters they inhabit, perfectly mimicking a dead leaf or piece of rotting wood as they await their next meal.

<span class="mw-page-title-main">Gosner stage</span> System of describing stages of development in anurans

Gosner stage is a generalized system of describing stages of embryonal and larval development in anurans. The Gosner system includes 46 numbered stages, from fertilized embryo to the completion of metamorphosis. It was introduced by Kenneth Gosner in 1960. The system is widely used in herpetology to describe exotrophic tadpoles. Gosner stages are based on certain morphological landmarks that allow comparing development in different species that may greatly differ in age or size.

References

  1. ↑ Chuliver, Mariana; Agnolín, Federico L.; Scanferla, Agustín; Aranciaga Rolando, Mauro; Ezcurra, Martín D.; Novas, Fernando E.; Xu, Xing (2024-10-30). "The oldest tadpole reveals evolutionary stability of the anuran life cycle". Nature: 1–5. doi:10.1038/s41586-024-08055-y. ISSN   1476-4687.
  2. ↑ "The Grammarphobia Blog: On tadpoles and pollywogs". 2012-05-01. Archived from the original on 2016-08-22. Retrieved 2016-08-08. 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".
  3. ↑ "North American Tadpoles Spiracle". Archived from the original on 28 December 2016. Retrieved 12 April 2020.
  4. ↑ Pfennig, David (1990). "The adaptive significance of an environmentally-cued developmental switch in an anuran tadpole". Oecologia. 85 (1): 101–107. Bibcode:1990Oecol..85..101P. doi:10.1007/BF00317349. PMID   28310961. S2CID   20616439.
  5. ↑ "Megophryidae". Animal Diversity Web .
  6. 1 2 Li, Cheng; Guo, Xian-Guang; Wang, Yue-Zhao (2011). "Tadpole types of Chinese megophryid frogs (Anura: Megophryidae) and implications for larval evolution". Current Zoology. 57 (1): 93–100. doi: 10.1093/czoolo/57.1.93 .
  7. ↑ 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.
  8. ↑ Crump, Martha L. (2009). "Amphibian diversity and life history" (PDF). Amphibian Ecology and Conservation. A Handbook of Techniques: 3–19. doi:10.1093/oso/9780199541188.003.0001. ISBN   978-0-19-954118-8. Archived from the original (PDF) on 2011-07-15.
  9. ↑ Senevirathne, Gayani; Garg, Sonali; Kerney, Ryan; Meegaskumbura, Madhava; Biju, S. D. (30 March 2016). "Unearthing the Fossorial Tadpoles of the Indian Dancing Frog Family Micrixalidae". PLOS ONE. 11 (3): e0151781. Bibcode:2016PLoSO..1151781S. doi: 10.1371/journal.pone.0151781 . PMC   4814069 . PMID   27027870.
  10. ↑ "Crab-eating frog".
  11. ↑ 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. JSTOR   1566122.
  12. ↑ Zheng, Yuchi; Deng, Duncan; Li, Shuqiang; Fu, Jinzhong (April 2010). "Aspects of the breeding biology of the Omei mustache toad (Leptobrachium boringii): Polygamy and paternal care". Amphibia-Reptilia. 31 (2): 183–194. doi: 10.1163/156853810791069092 – via ResearchGate.
  13. ↑ Brandt, Pröhl, Annely, Heike (April 2002). "Female activity patterns and aggressiveness in the strawberry poison frog Dendrobates pumilio (Anura: Dendrobatidae)". Amphibia-Reptilia. 23 (2): 129–140. doi: 10.1163/156853802760061778 – via ResearchGate.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  14. 1 2 McNamara, 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 .
  15. ↑ McNamara, M. E.; Orr, P. J.; Kearns, S. L.; Alcalá, L.; Anadón, P.; Peñalver-Mollá, E. (2006). Taphonomy of exceptionally preserved tadpoles from the Miocene Libros fauna, Spain: Ontogeny, ecology and mass mortality (PDF). The Palaeontological Association 50th Annual Meeting. The Palaeontological Association. Archived from the original (PDF) on 2011-07-27.
  16. ↑ Chuliver, Mariana; Agnolín, Federico L.; Scanferla, Agustín; Aranciaga Rolando, Mauro; Ezcurra, Martín D.; Novas, Fernando E.; Xu, Xing (2024-10-30). "The oldest tadpole reveals evolutionary stability of the anuran life cycle". Nature: 1–5. doi:10.1038/s41586-024-08055-y. ISSN   1476-4687.
  17. ↑ IUCN SSC Amphibian Specialist Group (2020). "Oreolalax rhodostigmatus". IUCN Red List of Threatened Species . 2020: e.T57600A63861170. doi: 10.2305/IUCN.UK.2020-2.RLTS.T57600A63861170.en . Retrieved 11 November 2021.
  18. ↑ IUCN SSC Amphibian Specialist Group (2017). "Telmatobius mayoloi". IUCN Red List of Threatened Species . 2017: e.T57350A3059558. doi: 10.2305/IUCN.UK.2017-3.RLTS.T57350A3059558.en . Retrieved 11 November 2021.
  19. ↑ Scott, James George, Sir. 1935. The Wa or Lawa: Head-Hunters. In Burma and Beyond. p. 292

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