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The polka-dot tree frog (''Boana punctata''), also known as the dotted tree frog, is a frog species in the family Hylidae found in much of South America and also in Trinidad and Tobago. It is fairly small with a snout–to– vent length of .
Its natural habitats are
In 2017, several polka-dot tree frogs collected in the Santa Fe Province in Argentina were the first
subtropical or tropical dry forest
The tropical and subtropical dry broadleaf forest is a habitat type defined by the World Wide Fund for Nature and is located at tropical and subtropical latitudes. Though these forests occur in climates that are warm year-round, and may receive ...
, subtropical or tropical moist lowland forest
Tropical and subtropical moist broadleaf forests (TSMF), also known as tropical moist forest, is a subtropical and tropical forest habitat type defined by the World Wide Fund for Nature.
Description
TSMF is generally found in large, discont ...
, subtropical or tropical swamp
A swamp is a forested wetland.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p. Swamps are considered to be transition zones because both land and water play a role in ...
s, subtropical or tropical moist montane forest, swamps, freshwater marshes, intermittent freshwater marshes, rural gardens, urban areas, and heavily degraded former forests. It is not considered threatened by the IUCN
The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...
.
Pigmentation and skin fluorescence
In 2017, several polka-dot tree frogs collected in the Santa Fe Province in Argentina were the first amphibian
Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...
, amongst more than 6,000 species of frog, identified as naturally fluorescent. Among land-living vertebrates, it had only been confirmed earlier in certain parrots (as opposed to fish and invertebrates where fluorescence is relatively widespread). A few months later, fluorescence was discovered in the closely related ''Hypsiboas atlanticus
''Boana atlantica'' is a small-sized species of tree frog in the family Hylidae. It is endemic to the Atlantic Forest from Pernambuco to Bahia in northeastern Brazil. It is a very abundant species inhabiting primary and secondary forest and fores ...
'', and in 2019 it was discovered in the distantly related pumpkin toadlet
The pumpkin toadlet (''Brachycephalus ephippium''), or Spix's saddleback toad, is a small and brightly coloured species of frog in the family Brachycephalidae. This diurnal species is endemic to southeastern Brazil where it is found among leaf ...
(''Brachycephalus ephippium'') and red pumpkin toadlet
''Brachycephalus pitanga'', the red pumpkin toadlet, is a small and brightly coloured species of anuran in the family Brachycephalidae. It is endemic to Atlantic rainforests in São Paulo state of southeastern Brazil, and only known from four lo ...
(''B. pitanga''). In 2020, it was confirmed that fluorescence is relatively widespread among frogs and other amphibians.
When exposed to ultra-violet light
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...
, the skin of the polka-dot tree frog emits a bright green fluorescent glow. The discovery was made accidentally when the researchers checked the skin secretions of the frog under UV light. They expected only a faint red fluorescence, because the frog skin contains biliverdin
Biliverdin (latin for green bile) is a green tetrapyrrolic bile pigment, and is a product of heme catabolism.Boron W, Boulpaep E. Medical Physiology: a cellular and molecular approach, 2005. 984-986. Elsevier Saunders, United States. It is the pi ...
, a green tetrapyrrolic bile
Bile (from Latin ''bilis''), or gall, is a dark-green-to-yellowish-brown fluid produced by the liver of most vertebrates that aids the digestion of lipids in the small intestine. In humans, bile is produced continuously by the liver (liver bile ...
pigment responsible for its dull mottled browny-green colour. The surprising green fluorescence is attributed to hyloin compounds, mainly hyloin-L1, hyloin-L2 and hyloin-G1. These fluorescent molecules, in the dihydroisoquinolinone family and derived from the isoquinoline (a benzene ring fused to a pyridine ring), in an alkaloid protecting mucous membrane, have been identified in the lymph tissue, skin and glandular secretions of the frog. Because it is linked to secretions from skin glands, they can also leave fluorescent markings on surfaces where they have been.
The fluorescence intensity represents about 18−29% of the luminosity under twilight conditions and is suspected to play a possible role in the communication, camouflage and mating of the frog.
References