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The polka-dot tree frog (''Boana punctata''), also known as the dotted tree frog, is a
In 2017, several polka-dot tree frogs collected in the
frog
A frog is any member of a diverse and largely carnivorous group of short-bodied, tailless amphibians composing the order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-frog" ''Triadobatrachus'' is ...
species in the family
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
Hylidae
Hylidae is a wide-ranging family of frogs commonly referred to as "tree frogs and their allies". However, the hylids include a diversity of frog species, many of which do not live in trees, but are terrestrial or semiaquatic.
Taxonomy and ...
found in much of South America and also in Trinidad and Tobago
Trinidad and Tobago (, ), officially the Republic of Trinidad and Tobago, is the southernmost island country in the Caribbean. Consisting of the main islands Trinidad and Tobago, and numerous much smaller islands, it is situated south of ...
. It is fairly small with a snout–to–vent
Vent or vents may refer to:
Science and technology Biology
*Vent, the cloaca region of an animal
* Vent DNA polymerase, a thermostable DNA polymerase
Geology
*Hydrothermal vent, a fissure in a planet's surface from which geothermally heated wate ...
length of .
Its natural habitat
In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...
s are subtropical or tropical dry forest, subtropical or tropical moist lowland forest, subtropical or tropical swamps, subtropical or tropical moist montane forest
Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures fall as elevation increases, causing the ecosystem to stratify. This stratification is a crucial ...
, swamps, freshwater marsh
A marsh is a wetland that is dominated by herbaceous rather than woody plant species.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p Marshes can often be found a ...
es, intermittent freshwater marshes, rural gardens, urban area
An urban area, built-up area or urban agglomeration is a human settlement with a high population density and infrastructure of built environment. Urban areas are created through urbanization and are categorized by urban morphology as cities ...
s, and heavily degraded former forests. It is not considered threatened by the IUCN.
Pigmentation and skin fluorescence
In 2017, several polka-dot tree frogs collected in the Santa Fe Province
The Province of Santa Fe ( es, Provincia de Santa Fe, ) is a province of Argentina, located in the center-east of the country. Neighboring provinces are from the north clockwise Chaco (divided by the 28th parallel south), Corrientes, Entre R ...
in Argentina were the first amphibian, amongst more than 6,000 species of frog, identified as naturally fluorescent
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, ...
. Among land-living vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...
s, it had only been confirmed earlier in certain parrot
Parrots, also known as psittacines (), are birds of the roughly 398 species in 92 genera comprising the order Psittaciformes (), found mostly in tropical and subtropical regions. The order is subdivided into three superfamilies: the Psittacoide ...
s (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 for ...
'', and in 2019 it was discovered in the distantly related pumpkin toadlet (''Brachycephalus ephippium'') and red pumpkin toadlet (''B. pitanga''). In 2020, it was confirmed that fluorescence is relatively widespread among frogs and other amphibians.
When exposed to ultra-violet light, the skin
Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation.
Other animal coverings, such as the arthropod exoskeleton, have different de ...
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 ...
, a green tetrapyrrolic bile pigment
A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compou ...
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
Isoquinoline is a heterocyclic aromatic organic compound. It is a structural isomer of quinoline. Isoquinoline and quinoline are benzopyridines, which are composed of a benzene ring fused to a pyridine ring. In a broader sense, the term isoqu ...
(a benzene
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms ...
ring fused to a pyridine
Pyridine is a basic heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with a ...
ring), in an alkaloid
Alkaloids are a class of basic, naturally occurring organic compounds that contain at least one nitrogen atom. This group also includes some related compounds with neutral and even weakly acidic properties. Some synthetic compounds of similar ...
protecting mucous membrane
A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It i ...
, have been identified in the lymph
Lymph (from Latin, , meaning "water") is the fluid that flows through the lymphatic system, a system composed of lymph vessels (channels) and intervening lymph nodes whose function, like the venous system, is to return fluid from the tissues ...
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