Editing Frog (section)

===Skin===
A frog's skin is protective, has a respiratory function, can absorb water, and helps control body temperature. It has many glands, particularly on the head and back, which often exude distasteful and toxic substances ([[Skin|granular glands]]). The secretion is often sticky and helps keep the skin moist, protects against the entry of moulds and bacteria, and makes the animal slippery and more able to escape from predators.<ref>{{cite book |title=A Natural History of Amphibians |last=Stebbins |first=Robert C. |author-link1=Robert C. Stebbins |author2=Cohen, Nathan W. |year=1995 |publisher=Princeton University Press |isbn=978-0-691-03281-8 |pages=10–14 }}</ref> The skin is shed every few weeks. It usually splits down the middle of the back and across the belly, and the frog pulls its arms and legs free. The sloughed skin is then worked towards the head where it is quickly eaten.<ref>{{cite journal |jstor=2456779 |pages=530–540 |last1=Frost |first1=S. W. |title=Notes on feeding and molting in frogs |volume=66 |issue=707 |journal=The American Naturalist |year=1932 |doi=10.1086/280458 |bibcode=1932ANat...66..530F |s2cid=84796411 }}</ref>

Being cold-blooded, frogs have to adopt suitable behaviour patterns to regulate their temperature. To warm up, they can move into the sun or onto a warm surface; if they overheat, they can move into the shade or adopt a stance that exposes the minimum area of skin to the air. This posture is also used to prevent water loss and involves the frog squatting close to the substrate with its hands and feet tucked under its chin and body.<ref name=BandN>{{cite book |title=Frogs |last=Badger |first=D. |author2=Netherton, J. |year=1995 |publisher=Airlife Publishing |isbn=978-1-85310-740-5 |page=27 }}</ref> The colour of a frog's skin is used for thermoregulation. In cool damp conditions, the colour will be darker than on a hot dry day. The [[Grey Foam-nest Treefrog|grey foam-nest tree frog]] (''Chiromantis xerampelina'') is even able to turn white to minimise the chance of overheating.<ref>{{cite book |title=Amphibians and Their Ways |last=Smyth |first=H. R. |year=1962 |publisher=Macmillan |isbn=978-0-02-612190-3 }}</ref>

Many frogs are able to absorb water and oxygen directly through the skin, especially around the pelvic area, but the permeability of a frog's skin can also result in water loss. Glands located all over the body exude mucus which helps keep the skin moist and reduces evaporation. Some glands on the hands and chest of males are specialised to produce sticky secretions to aid in [[amplexus]]. Similar glands in tree frogs produce a glue-like substance on the adhesive discs of the feet. Some arboreal frogs reduce water loss by having a waterproof layer of skin, and several South American species coat their skin with a waxy secretion. Other frogs have adopted behaviours to conserve water, including becoming [[nocturnal]] and resting in a water-conserving position. Some frogs may also rest in large groups with each frog pressed against its neighbours. This reduces the amount of skin exposed to the air or a dry surface, and thus reduces water loss.<ref name=BandN/> [[Woodhouse's toad]] (''Bufo woodhousii''), if given access to water after confinement in a dry location, sits in the shallows to rehydrate.<ref>{{cite book |title=The Frog Book: North American Frogs and Toads |last=Dickerson |first=M. C. |year=1969 |publisher=Dover Publications |isbn=978-0-486-21973-8 |url=https://archive.org/details/frogbooknorthame00dick_0 }}</ref> The male [[hairy frog]] (''Trichobatrachus robustus'') has [[dermal papillae]] projecting from its lower back and thighs, giving it a bristly appearance. These contain blood vessels and are thought to increase the area of the skin available for respiration.<ref>{{cite web |url=http://amphibiaweb.org/cgi-bin/amphib_query?where-genus=Trichobatrachus |title=''Trichobatrachus robustus'' |author=Blackburn, D. C. |date=November 14, 2002 |publisher=AmphibiaWeb |access-date=August 18, 2012}}</ref>
[[File:Hip-pocket Frog - Assa darlingtoni.jpg|thumb|alt=Frog barely recognisable against brown decaying leaf litter.|[[Pouched frog]] (''Assa darlingtoni'') camouflaged against leaf litter]]
[[File:WoodFrog DarienLakesStatePark 2020-06-16 (02).jpg|thumb|[[Wood frog]] (''Lithobates sylvaticus'') uses [[disruptive coloration]].]]

Some species have [[Osteoderm|bony plates]] embedded in the skin, a trait that appears to have evolved independently several times.<ref>{{cite journal |author1=Ruibal, Rodolfo |author2=Shoemaker, Vaughan |year=1985 |title=Osteoderms in Anurans |journal=Journal of Herpetology |volume=18 |issue=3 |pages=313–328 |jstor=1564085 |doi=10.2307/1564085}}</ref> In certain other species, the skin at the top of the head is compacted and the connective tissue of the dermis is co-ossified with the bones of the skull ([[exostosis]]).<ref>{{cite book |title=Herpetology: An Introductory Biology of Amphibians and Reptiles |last1=Vitt |first1=Laurie J. |last2=Caldwell |first2=Janalee P. |year=2013 |publisher=Academic Press |isbn=9780123869203 |page=50  |url={{Google books|Gay9N_ry79kC|page=50|plainurl=yes}} }}</ref><ref>{{cite journal |author1=Jared, C. |author2=Antoniazzi, M. M. |author3=Navas, C. A. |author4=Katchburian, E. |author5=Freymüller, E. |author6=Tambourgi, D. V. |author7=Rodrigues, M. T. |year=2005 |title=Head co-ossification, phragmosis and defence in the casque-headed tree frog ''Corythomantis greeningi'' |journal=Journal of Zoology |volume=265 |issue=1 |pages=1–8 |doi=10.1017/S0952836904005953  |s2cid=59449901 }}</ref>

[[Camouflage]] is a common defensive mechanism in frogs. Features such as warts and [[skin fold]]s are usually on ground-dwelling frogs, for whom smooth skin would not provide such effective camouflage. Certain frogs change colour between night and day, as light and moisture stimulate the pigment cells and cause them to expand or contract.<ref name=Observer>{{cite book |title=The Observer's Book of British Wild Animals |last=Burton |first=Maurice |year=1972 |publisher=Frederick Warne & Co |isbn=978-0-7232-1503-5 |pages=204–209 }}</ref> Some are even able to control their skin texture.<ref>{{Cite journal|last1=Guayasamin|first1=Juan M.|last2=Krynak|first2=Tim|last3=Krynak|first3=Katherine|last4=Culebras|first4=Jaime|last5=Hutter|first5=Carl R.|date=2015|title=Phenotypic plasticity raises questions for taxonomically important traits: a remarkable new Andean rainfrog ( Pristimantis ) with the ability to change skin texture: Phenotypic plasticity in Andean rainfrog|journal=Zoological Journal of the Linnean Society|language=en|volume=173|issue=4|pages=913–928|doi=10.1111/zoj.12222|doi-access=free}}</ref> The [[Pacific tree frog]] (''Pseudacris regilla'') has green and brown morphs, plain or spotted, and changes colour depending on the time of year and general background colour.<ref>{{cite journal |author1=Wente, W. H. |author2=Phillips, J. B. |year=2003 |title=Fixed green and brown color morphs and a novel color-changing morph of the Pacific tree frog ''Hyla regilla'' |journal=The American Naturalist |volume=162 |issue=4 |pages=461–473 | jstor=10.1086/378253 |doi=10.1086/378253 |pmid=14582008 |bibcode=2003ANat..162..461W |s2cid=25692966 }}</ref> The [[Wood frog]] (''Lithobates sylvaticus'') uses [[disruptive coloration]] including black eye markings similar to voids between leaves, bands of the dorsal skin (dorsolateral dermal plica) similar to a leaf [[midrib]] as well as stains, spots and leg stripes similar to fallen leaf features.