The moor frog (''Rana arvalis'') is a slim, reddish-brown,

semiaquatic In biology, semiaquatic can refer to various types of animals that spend part of their time in water, or plants that naturally grow partially submerged in water. Examples are given below. Semiaquatic animals Semi aquatic animals include: * Ve ...

amphibian native to

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located entirel ...

and

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...

. Moor frogs are known for their ability to freeze solid and survive

thawing Melting, or fusion, is a physical process that results in the phase transition of a substance from a solid to a liquid. This occurs when the internal energy of the solid increases, typically by the application of heat or pressure, which ...

. The frog makes use of various

cryoprotectant A cryoprotectant is a substance used to protect biological tissue from freezing damage (i.e. that due to ice formation). Arctic and Antarctic insects, fish and amphibians create cryoprotectants ( antifreeze compounds and antifreeze proteins) in ...

s i.e.

antifreeze An antifreeze is an additive which lowers the freezing point of a water-based liquid. An antifreeze mixture is used to achieve freezing-point depression for cold environments. Common antifreezes also increase the boiling point of the liquid, all ...

that decreases its internal freezing temperature. The species is distributed over a large range, covering a significant portion of

Eurasia Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelago ...

. Male moor frogs are known to turn blue temporarily during the height of mating season. This coloration is assumed to signal a mate's fitness. Moor frogs typically mate through multimale

amplexus Amplexus (Latin "embrace") is a type of mating behavior exhibited by some externally fertilizing species (chiefly amphibians and horseshoe crabs) in which a male grasps a female with his front legs as part of the mating process, and at the same ...

a form of

polyandry Polyandry (; ) is a form of polygamy in which a woman takes two or more husbands at the same time. Polyandry is contrasted with polygyny, involving one male and two or more females. If a marriage involves a plural number of "husbands and wives ...

. The moor frog spawns its eggs in large batches in still bodies of acidic waters. Human-caused pollution is causing excessive

acidification Acidification may refer to: * Ocean acidification, decrease in the pH of the Earth's oceans * Freshwater acidification, atmospheric depositions and soil leaching of SOx and NOx * Soil acidification, buildup of hydrogen cations, which reduces the ...

of habitat which harms egg health. The moor frog's habitat is also under destruction due to a variety of other anthropogenic means. The species has an IUCN listing of Least Concern. However, a majority of European states independently consider the conservation status of the moor frog to be unfavorable. The moor frog, like other members of ''Rana,'' is

omnivorous An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nut ...

and will consume anything that it can physically ingest.

Description

The moor frog is a small bog frog, characterized by a solid belly, a large, dark ear spot, and often a pale stripe down the centre of the back. The species is reddish-brown, but can also be yellow, grey, or light-olive. Common traits include white or yellow pigmentation on its underside and black stripes from its nostrils along the sides of its head. The Moor frog ranges from 5.5 to 6.0 cm (2.2 to 2.4 in) long, but can reach up to 7.0 cm (2.8 in) in length. Their heads are more tapered than those of the

common frog The common frog or grass frog (''Rana temporaria''), 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 ...

(''Rana temporaria''). The skin on their flanks and thighs is smooth, and their tongue is forked and free. Pupils are horizontally oriented, feet are partially webbed, and back legs are shorter than those in the same family of frogs. Males, unlike females, have nuptial pads on their first fingers and paired guttural

vocal sac The vocal sac is the flexible membrane of skin possessed by most male frogs and toads. The purpose of the vocal sac is usually as an amplification of their mating or advertisement call. The presence or development of the vocal sac is one way ...

Taxonomy

The family the moor frog belongs to, Ranidae, is a broad group containing 605 species. The family contains ranoid frogs that do not belong to any other families and are found on every continent but

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...

. The moor frog belongs to genus ''Rana'', which includes species found in Europe and Asia. The moor frog is not found in the

Americas The Americas, which are sometimes collectively called America, are a landmass comprising the totality of North and South America. The Americas make up most of the land in Earth's Western Hemisphere and comprise the New World. Along with th ...

. The moor frog's scientific name, ''Rana arvalis,'' means "frog of the fields". It is also called the Altai brown frog because frogs from the Altai Mountains in Asia have been included in the ''R. arvalis'' species. The Altai frogs have some different characteristics such as shorter shins, but currently there is no official distinction and all frogs are known as one species—''Rana arvalis''. The moor frog was first reported by Nilsson in volume 3 of ''Skandinavisk fauna'' with a moderate muzzle and prominent first cuneiform bone.

Distribution and habitat

The moor frog can be found in a large majority of Europe and Asia. The species' east-west range extends from northeastern France and northern Belgium all the way to the

Lena Lena or LENA may refer to: Places * Léna Department, a department of Houet Province in Burkina Faso * Lena, Manitoba, an unincorporated community located in Killarney-Turtle Mountain municipality in Manitoba, Canada * Lena, Norway, a village in ...

River in

Siberia Siberia ( ; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive region, geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a ...

. The north-south range extends as far north as the 69th parallel in

Finland Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of B ...

and as far south as the

Pannonian basin The Pannonian Basin, or Carpathian Basin, is a large basin situated in south-east Central Europe. The geomorphological term Pannonian Plain is more widely used for roughly the same region though with a somewhat different sense, with only th ...

in Central Europe. The moor frog can be found in a wide range of altitudes. In the western region of its range, the moor frog can be found as high up as 900

meters above sea level Height above mean sea level is a measure of the vertical distance (height, elevation or altitude) of a location in reference to a historic mean sea level taken as a vertical datum. In geodesy, it is formalized as ''orthometric heights''. The com ...

, and in the eastern portion, the moor frog can be found as high up as 2000 meters in the Altai. Within this geographical range, the moor frog is often found in bodies of still water with

littoral The littoral zone or nearshore is the part of a sea, lake, or river that is close to the shore. In coastal ecology, the littoral zone includes the intertidal zone extending from the high water mark (which is rarely inundated), to coastal a ...

vegetation and pH below 6. The diversity of habitats demonstrates the frog's plasticity. Moor frogs can live in

tundra In physical geography, tundra () is a type of biome where tree growth is hindered by frigid temperatures and short growing seasons. The term ''tundra'' comes through Russian (') from the Kildin Sámi word (') meaning "uplands", "treeless mou ...

forest A forest is an area of land dominated by trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations' ...

forest steppe A forest steppe is a temperate-climate ecotone and habitat type composed of grassland interspersed with areas of woodland or forest. Locations Forest steppe primarily occurs in a belt of forest steppes across northern Eurasia from the eastern ...

s, steppes, forest edges, glades, semideserts, swamps, meadows, fields,

bushland In Australia, bushland is a blanket term for land which supports remnant vegetation or land which is disturbed but still retains a predominance of the original floristics and structure. Human survival in bushland has a whole mythology evolving ...

s, and gardens. They prefer areas untouched by humans, such as damp meadows and bogs, but are able to live in agricultural and urban areas. Moor frogs provide a good model for studying local adaptation as they experience a wide range of environments and are relatively limited in their movements. Their restriction in movements implies limited gene flow and facilitates evolution through adaptive genetic differentiation among populations. The species has been successfully bred in captivity in the UK and a reintroduction has been proposed as part of Celtic Reptile & Amphibian's

rewilding Rewilding may refer to: *Rewilding (conservation biology), the return of habitats to a natural state **Rewilding Europe Rewilding Europe is a non-profit organisation based in Nijmegen, Netherlands, working to create rewilded landscapes through ...

plans.

Historical distribution

The earliest fossil record of the moor frog extends back to between the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Early Pleistocene found in Dvorníky-Včeláre, Slovakia. Other fossil records of the moor frog from the early

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...

were found on land inside the modern range of the moor frog. Fossil records from the

middle Pleistocene The Chibanian, widely known by its previous designation of Middle Pleistocene, is an age in the international geologic timescale or a stage in chronostratigraphy, being a division of the Pleistocene Epoch within the ongoing Quaternary Period. Th ...

demonstrate the range extended as far south as south-central France and as far west as the eastern coast of

Great Britain Great Britain is an island in the North Atlantic Ocean off the northwest coast of continental Europe. With an area of , it is the largest of the British Isles, the largest European island and the ninth-largest island in the world. It i ...

. Records from the late Pleistocene show the range extended as far south as

Bosnia and Herzegovina Bosnia and Herzegovina ( sh, / , ), abbreviated BiH () or B&H, sometimes called Bosnia–Herzegovina and often known informally as Bosnia, is a country at the crossroads of south and southeast Europe, located in the Balkans. Bosnia and H ...

and

Azerbaijan Azerbaijan (, ; az, Azərbaycan ), officially the Republic of Azerbaijan, , also sometimes officially called the Azerbaijan Republic is a transcontinental country located at the boundary of Eastern Europe and Western Asia. It is a part of t ...

Distribution in Romania

The moor frog is found in three regions in

Romania Romania ( ; ro, România ) is a country located at the crossroads of Central, Eastern, and Southeastern Europe. It borders Bulgaria to the south, Ukraine to the north, Hungary to the west, Serbia to the southwest, Moldova to the east, and ...

. The first is the Transylvanian region which includes the Western Plains (with the largest Romanian population of moor frogs), the

Transylvanian Plateau The Transylvanian Plateau ( ro, Podișul Transilvaniei; hu, Erdélyi-medence) is a plateau in central Romania. The plateau lies within and takes its name from the historical region of Transylvania, and is almost entirely surrounded by the East ...

, and the

Eastern Carpathians Divisions of the Carpathians are a categorization of the Carpathian mountains system. Below is a detailed overview of the major subdivisions and ranges of the Carpathian Mountains. The Carpathians are a "subsystem" of a bigger Alps-Himalaya Sy ...

. The second region is the northern part of Romanian Moldavia. The third and smallest region is the

Tisa River The Tisza, Tysa or Tisa, is one of the major rivers of Central and Eastern Europe. Once, it was called "the most Hungarian river" because it flowed entirely within the Kingdom of Hungary. Today, it crosses several national borders. The Tisza b ...

Basin—north of

Maramureș or Marmaroshchyna ( ro, Maramureș ; uk, Мармарощина, Marmaroshchyna; hu, Máramaros) is a geographical, historical and cultural region in northern Romania and western Ukraine. It is situated in the northeastern Carpathians, alon ...

. Most populations of moor frog in Romania are isolated and not contiguous due to the

edge effects In ecology, edge effects are changes in population or community structures that occur at the boundary of two or more habitats. Areas with small habitat fragments exhibit especially pronounced edge effects that may extend throughout the range. As ...

of human developments. Each population typically has 200-400 adults; however, exceptional populations of 2000 adults have been found as well. Most Romanian populations of moor frog can be found between 108-414 meters above sea level; exceptional populations have been found to exist at 740 meters above sea level. In Romania, the moor frog is known to live in humid habitats that border land with human activity, such as flooded agricultural fields, ditches on the side of roads, small canals and streams, and human settlements. The moor frog is sparingly found in habitats with little human activity. Swamps are one of the few habitats with little human activity that host moor frogs.

Diet

An adult moor frog's diet consists of any mobile and

terrestrial animal Terrestrial animals are animals that live predominantly or entirely on land (e.g. cats, dogs, ants, spiders), as compared with aquatic animals, which live predominantly or entirely in the water (e.g. fish, lobsters, octopuses), and amphibian ...

s that they can physically ingest. Moor frogs most commonly consume

beetle Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...

s; however, other insects from the orders hemiptera (true bugs), hymenoptera, and diptera (flies) are consumed as well. Moor frogs also consume non-insect invertebrates from the orders gastropoda (snails and slugs),

arachnid Arachnida () is a class of joint-legged invertebrate animals (arthropods), in the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegar ...

a, and

myriapoda Myriapods () are the members of subphylum Myriapoda, containing arthropods such as millipedes and centipedes. The group contains about 13,000 species, all of them terrestrial. The fossil record of myriapods reaches back into the late Silurian ...

(centipedes and millipedes). Beetles make up the majority of the moor frog's diet due to their abundance. Large moor frogs do appear to have a preference for beetles because they are larger than most other insect prey. Large moor frogs tend to consume large prey and small moor frogs consume small prey. This behavior is assumed to have evolved to reduce competition between moor frogs or to maximize net energy gained from feeding, as large moor flogs consuming both large and small prey would leave little food for smaller moor frogs. Aside from size preferences, individual moor frogs do not appear to prefer more energetically favorable prey over less energetically favorable prey of equal size. The moor frog will ingest any animal that it is able to swallow. Moor frogs are opportunistic predators that wait for prey to appear before consuming them, as opposed to intentional predators that actively hunt for prey. More mobile prey are more often consumed by the moor frog because of their opportunistic nature. Plant matter and inedible objects such as pebbles are also found to be consumed by the moor frog. Plant matter is found to be consumed in greater quantities when more prey has been consumed, which suggests that plant matter is consumed accidentally during the capture of prey. The moor frog's shed skin is also consumed; however, it is unknown whether consumption of shed skin is accidental or intentional in nature.

Mating

Multimale

, in which multiple males mate with a single female, is the predominant method of mating that the moor frog performs. The sperm of male moor frogs compete in the female reproductive tract for fertilization of the female's egg. Female frogs do not appear to prefer males of a particular size. Instead, they tend to prefer to mate with males that have successfully helped produce offspring with them in the past. Long thumb length is correlated with poor sperm quality, and short thumb length is correlated with higher sperm quality. Males with higher quality sperm breed progeny with greater chances of survival. Despite this correlation, female individuals do not appear to prefer thumb length or be able to detect variation in thumb length.

Blue coloration

Male moor frogs turn a conspicuous blue during the mating season, but only for a few days during peak reproductive activity. Females remain brown during this time. While the blue is conspicuous to human vision, the greatest color change in male moor frogs occurs in the

ultraviolet 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 ...

region from 350-450 nm, invisible to human vision. Males who have mated appear bluer and have been recorded as having higher body temperatures. Blue reflectance may be a form of intersexual communication. It is hypothesized that males with brighter blue coloration may signal greater sexual and genetic fitness; however, studies have only revealed tadpoles fathered by bright blue individuals had greater chances of survival when pitted against large beetle larvae than when fathered by dull individuals.

Ecology

Hibernation

Moor frogs hibernate sometime between

September September is the ninth month of the year in both the Julian and Gregorian calendars, the third of four months to have a length of 30 days, and the fourth of five months to have a length of fewer than 31 days. September in the Northern H ...

and June, depending on their latitude. Frogs in southwestern

plain In geography, a plain is a flat expanse of land that generally does not change much in elevation, and is primarily treeless. Plains occur as lowlands along valleys or at the base of mountains, as coastal plains, and as plateaus or uplands ...

habitats will hibernate (around November or December) and wake earlier (February). However, frogs in cold, polar areas will hibernate sooner (in September) and wake later (in June).

Breeding

The mating season takes place between March and June, right after the end of hibernation. Males form breeding choruses that may sound similar to air escaping from a submerged empty bottle, similar to those of the agile frog ''Rana dalmatina''. Males can also develop bright-blue coloration for a few days during the season. Spawning happens quickly and is completed in 3 to 28 days. The spawn of each frog is laid in one or two clusters of 500-3000

egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...

s in warm, shallow waters.

Effects of acidification on population

Environmental plasticity

Increased acidity levels in breeding areas may be problematic for moor frog populations, as it reduces survival and growth of the aquatic embryos and

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. ...

e. When exposed to acidity, moor frogs have been shown to be able to adapt relatively rapidly (within 16–40 generations). Local adaptation to acidity is also possible in survival during the embryonic stage, during which frogs are most sensitive to severe acidity. Moreover, compared to those from neutral sites, acidic origin populations have higher embryonic and larval acid tolerance (survival and larval period were less negatively affected by low pH), higher larval growth but slower larval development rates, and larger metamorphosing size. Divergence in embryonic acid tolerance and metamorphic size correlates most strongly with breeding pond pH, whereas divergence in larval period and larval growth correlates most strongly with latitude and predator density, respectively. Moor frogs can adapt to the various effects of

through long-term selection causing genetic change or spontaneous behavioral changes mediated by hormonal responses. Stressors that demand immediate solutions, such as a sudden shift in temperature or appearance of a predator, demand that an individual can respond appropriately, such as moving to a more temperate location or evading or fighting off a predator. The extent to which an individual can adapt to respond to a new situation is referred to as an individual's

phenotypic plasticity Phenotypic plasticity refers to some of the changes in an organism's behavior, morphology and physiology in response to a unique environment. Fundamental to the way in which organisms cope with environmental variation, phenotypic plasticity encompa ...

. These plastic adaptations can be quantitatively analyzed through the measurement of hormones that spike when individuals are under stress, such as cortisol. Moor frog tadpoles use and understand a variety of chemicals that signal stressors, and acidification can chemically disrupt a tadpole's ability to receive and send signals, thus making an individual tadpole unable to respond to environmental stressors. Acid-tolerant Moor frogs are larger and more active than Moor frogs that have not acclimatized to acidification. Acid-tolerant moor frogs also exhibit stronger hormonal responses to immediate dangers like the presence of a predator, which, in turn, creates a stronger behavioral response to evade those predators. Some acid-tolerant Moor frogs have lower levels of sodium, which may be an adaptation to acidification.

Maternal effects

Frogs from acidic environments may favor different reproductive strategies than those in more benign environments. Compared to neutral-origin females, acid-origin females tend to invest relatively more in

fecundity Fecundity is defined in two ways; in human demography, it is the potential for reproduction of a recorded population as opposed to a sole organism, while in population biology, it is considered similar to fertility, the natural capability to pr ...

than in egg size, invest more in their offspring than in self-maintenance, and increase their reproductive effort as their residual reproductive value decreases. Consequently, acid origin females increase the clutch size and total reproductive output with age, while neutral origin females only increase egg size but not clutch size or total reproductive output with age. RanaArvalisMatingPlusSpawn

Environmental acidification has various reproductive impacts: decreased maternal investment, selection for investment in larger eggs at a cost to fecundity, hindered reproductive output, altered relationship between female phenotype and maternal investment, and strengthened egg-size-fecundity trade-off. High habitat acidity often imposes great costs to survival, which may lead to the culling of Moor frogs. High acidity imposes stress on eggs; when a habitat is acidic enough, embryos often exhibit developmental defects and become inviable. Egg coats are maternally derived structures that surround Moor frog eggs to protect them. Egg coats can buffer the low pH of the Moor frog's acidic habitats; however, drastic decreases in habitat pH caused by human-made pollution affects an egg coat's function. High habitat acidity causes thinning and a loss in the egg coat's ability to attract water. Thinned egg coats are more tacky and opaque. These eggs are more susceptible to drying out, pathogen infection, UV light degradation, and poor

gas exchange Gas exchange is the physical process by which gases move passively by diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liquid, a gas-permeable membrane, or a ...

. The disabling of the egg coat leaves an embryo defenseless and tremendously susceptible to developmental defects. Moor frogs that are more easily killed by acidic waters are less fit and their genes are lost from the gene pool. Acidification is strong enough to cause rapid adaptation due to the high selection pressure it places on the Moor frog. As a result, certain highly acidic habitats have seen the development of Moor frogs that are less sensitive to the stress of highly acidic waters. Eggs of acid-tolerant frogs have coats with a greater negative charge. This suggests glycans give the egg coat its

hydrophilic A hydrophile is a molecule or other molecular entity that is attracted to water molecules and tends to be dissolved by water.Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon'' Oxford: Clarendon Press. In contrast, hydrophobes are ...

properties. Acid-tolerant eggs also have egg coats that are more acidic which suggests a greater concentration of negatively charged glycans as compared to typical Moor frogs. High acidity is able to reduce an egg coat's attraction to water because high proton concentration in acidic water is able to protonate the coat, thus neutralizing a glycan's charge. This is also why high habitat pH causes egg coat glycans to

deprotonate Deprotonation (or dehydronation) is the removal (transfer) of a proton (or hydron, or hydrogen cation), (H+) from a Brønsted–Lowry acid in an acid–base reaction.Henry Jakubowski, Biochemistry Online Chapter 2A3, https://employees.csbsju.ed ...

which restores the egg coat's negative charge/attraction to water.

Physiology

Cold tolerance

Moor frogs are renowned for their ability to tolerate freezing temperatures because most frog species live in hot and humid tropical environments. Many frogs that do live in cold climates will attempt to

overwinter Overwintering is the process by which some organisms pass through or wait out the winter season, or pass through that period of the year when "winter" conditions (cold or sub-zero temperatures, ice, snow, limited food supplies) make normal acti ...

in bodies of water because ambient temperatures are moderated by water. In these cases, temperatures only reach a few degrees below freezing. The moor frog is only known to overwinter on land. They overwinter in pits of leaf litter and between tree stumps. Moor frogs from European Russia and Western Siberia are able to tolerate freezing to temperatures as low as -16℃. Moor frogs from Denmark are only able to survive freezing temperatures as low as -4℃ for 3 to 4 days. The minimum freezing temperatures at which frogs are able to survive with 0% mortality is different between frog populations. Minimum freezing temperatures with some chance of survival appears to decrease from Western Europe to Western Siberia. However, in the aforementioned Siberian and Danish populations mitochondrial DNA testing revealed that they were closely related. The supercooling point (SCP) is the lowest temperature at which an organism can be cooled to (below freezing) before ice crystals form (cold-tolerant animals often use

s that decrease the freezing temperature to prevent the formation of ice). Freeze-tolerant frogs may see up to 65% of their body freeze solid during winter. Moor frogs, like many frogs, are particularly susceptible to freezing solid because of their skin which is thin and porous—permeable to the exchange of gases and liquids. Formation of ice crystals externally can act as nucleation sites for the formation of crystals inside the moor frog. When temperatures reach below the SCP a moor frog's skin darkens, muscles become rigid, eyes dull, and solid ice can be readily felt through touch. At temperatures between 0℃ and 1℃ frogs assume normal behavior but still respond to external stimuli i.e. frogs will leap away if disturbed. At temperatures immediately below freezing frogs assume an overwintering posture with their limbs adducted. When touched at below-freezing temperatures, frogs are only capable of slight movements of the limbs and body. Siberian populations exhibit 0% mortality at -8℃, 25% mortality at -10℃, and 50% mortality at -12℃. A few members from a population from Karasuk were able to freeze solid to -16℃, thaw, and survive. The time a frog spends frozen does not seem to affect mortality rather the absolute minimum temperature they experience has the greatest effect on mortality. Frogs have been recorded to spend around 3 months in this frozen state with the potential to survive thawing.

Cryoprotectants

Freezing temperatures impose tremendous stress on the moor frog; breathing stops, circulation stops, ice forms in the tissues, and cells are severely dehydrated. To tolerate these tremendous stressors the moor frog and many other ice-tolerant animals greatly subdue metabolic processes, produce antioxidants, and use other biochemical means to make freezing tolerable i.e. cryoprotectants (anti-freeze). Moor frogs are known to utilize

glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...

as a cryoprotectant which is formed through gluconeogenesis—a natural process in livers. Because gluconeogenesis is generally restricted to the liver and glycolysis (the breakdown of glucose) continues through wintering, it is presumed there are cryoprotectants other than glucose at play in other parts of the body i.e. the muscles.

Glycerol Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...

is found in much greater concentrations in the liver and muscles of frozen moor frogs.

Mannose Mannose is a sugar monomer of the aldohexose series of carbohydrates. It is a C-2 epimer of glucose. Mannose is important in human metabolism, especially in the glycosylation of certain proteins. Several congenital disorders of glycosylation ...

, maltose, and

maltitol Maltitol is a sugar alcohol (a polyol) used as a sugar substitute. It has 75–90% of the sweetness of sucrose (table sugar) and nearly identical properties, except for browning. It is used to replace table sugar because it is half as energetic, ...

are also known to be in higher concentrations in the liver and muscles of frozen moor frogs; however, the change in concentration is not as drastic as the change in concentration of glycerol between frozen and non-frozen moor frogs. Freezing temperatures directly increase the rate at which glucose is broken down. The manufacture of these products all requires the use of glucose, which is stored in a

polymer A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...

ic form, glycogen, in the muscles. As expected, the production of these cryoprotectants and continued metabolism (even though it is slowed) consumes a great quantity of glycogen that is not replenished as the frog is not feeding during the winter. Lactate and

ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...

are found in higher concentrations in frozen moor frogs. The moor frog is the only known terrestrial vertebrate to produce ethanol as a product of glycolysis. These two molecules are products of anaerobic processes which is to be expected because breathing/aerobic processes drastically slow down to the point of stopping when the moor frog is in a frozen state. Products of the breakdown of DNA are found in higher concentrations in frozen moor frogs suggesting that freezing is a highly stressful process for the frog. Frozen moor frogs also have greater concentrations of antioxidants; which are presumably made in anticipation of the

oxidative stress Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage. Disturbances in the normal ...

when aerobic respiration resumes after thawing.

Metabolism during freezing

Moor frogs still exhibit aerobic respiration at temperatures immediately below 0℃ i.e -0.5℃ to -1℃. However, the amount of oxygen consumed exponentially decreases with each decrease in degree Celsius. The majority of glucose degradation still occurs through anaerobic processes. Glycogen content in muscles reaches 35% in males, 20% in females, and 25% in juveniles by mass in autumn before wintering. Glycogen in the muscles also decrease much more over winter than in the liver as limbs freeze before the core does. The mass of glycogen in the liver decreased by 10 times in females and up to 30 times in males. In a study, female Moor frogs lost 82% in mass of body fat after wintering and males lost 81%.

Conservation

Population threats

It is currently classified as

Least Concern A least-concern species is a species that has been categorized by the International Union for Conservation of Nature (IUCN) as evaluated as not being a focus of species conservation because the specific species is still plentiful in the wild. T ...

by the International Union for Conservation of Nature ( IUCN). However, the moor frog may soon be impacted by the destruction and pollution of breeding sites and adjacent habitats, mostly through urbanization, recreational use of waterside areas, and intensive agriculture. The species does not appear to be notably susceptible to

chytridiomycosis Chytridiomycosis ( ) is an infectious disease in amphibians, caused by the chytrid fungi '' Batrachochytrium dendrobatidis'' and '' Batrachochytrium salamandrivorans''. Chytridiomycosis has been linked to dramatic population declines or extinc ...

, although the fungus has been detected in frogs in Germany. The 2009

IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is the world's most comprehensive inventory of the global conservation status of biol ...

status of the moor frog does not properly reflect the current declining nature of the moor frog. There is a general lack of research on the conservation status of the moor frog in many EU member states and in-range countries. However, a European Habitats Directive performed in 2013 revealed that 19 of the 28 member states of the time reported that the conservation status of the moor frog was unfavorable. 11 of the 19 said that their status was in decline as well. It is known that existing populations in Europe are small in number which indicates a significant loss of genetic diversity. This lack of genetic diversity threatens the current stability of populations and long-term survival because of the increased risk of

inbreeding Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are closely related genetically. By analogy, the term is used in human reproduction, but more commonly refers to the genetic disorders and o ...

. 12 helminth and nematode species are known to parasitize the moor frog. Trematode infection can cause the formation of

cyst A cyst is a closed sac, having a distinct envelope and division compared with the nearby tissue. Hence, it is a cluster of cells that have grouped together to form a sac (like the manner in which water molecules group together to form a bubble) ...

s in larvae; particularly at areas undergoing metamorphosis. These cysts can cause the formation of extra limbs, deformation to the vertebral skeleton. Frogs with these deformations are particularly susceptible to predation by the trematode's final and definitive hosts.

Conservation status in France

The moor frog is considered nearly extinct in France where the western limit of the moor frog range extends. As of 2020, there are only four isolated populations in France. These four were once a contiguous metapopulation. In France, moor frog habitats are limited and of poor quality due to significant human development that encroaches on and destroys moor frog habitats.

Edge effects In ecology, edge effects are changes in population or community structures that occur at the boundary of two or more habitats. Areas with small habitat fragments exhibit especially pronounced edge effects that may extend throughout the range. As ...

of human developments also fragment and degrade remaining habitats. Mild inbreeding greatly reduces the moor frog fitness due to the small number of individuals in these isolated populations.

Conservation efforts

Acidification Acidification may refer to: * Ocean acidification, decrease in the pH of the Earth's oceans * Freshwater acidification, atmospheric depositions and soil leaching of SOx and NOx * Soil acidification, buildup of hydrogen cations, which reduces the ...

eutrophication Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytopla ...

, and other forms of water pollution negatively affect the aquatic habitats of moor frogs. Moor frogs normally enjoy acidic environments; however,

peat bogs A bog or bogland is a wetland that accumulates peat as a deposit of dead plant materials often mosses, typically sphagnum moss. It is one of the four main types of wetlands. Other names for bogs include mire, mosses, quagmire, and muskeg ...

which produce these acidic conditions have poor buffering properties that make them susceptible to drastic decreases of pH even below 4.5. There are various conservation practices being initiated in order to remediate these pH driven effects. Liming of peat bogs by adding chalk can increase pH. Acidification of freshwater aquatic habitats has the detrimental effect of reduced biodiversity. One study showed in highly acidic waters, pH 4.2, eggs of the moor frog were especially susceptible to fungal infection. Many eggs were infected and those that were had a mortality rate of 50%. Organic sediment is removed from pools before the addition of limestone particles (<3mm) to prevent eutrophication. Before liming of acidic waters, moor frog eggs can expect to be infected with fungi 75-100% of the time. Liming treatment is able to reduce the presence of fungal infection to 0-25% of the time by increasing pH to 5-6. While this method may allow for moor frog reproduction to occur in the short-term, the effect is only temporary and acidification will ultimately reoccur. Protection and addition of

riparian zone A riparian zone or riparian area is the interface between land and a river or stream. Riparian is also the proper nomenclature for one of the terrestrial biomes of the Earth. Plant habitats and communities along the river margins and banks a ...

s by preventing grazing and replanting

vegetation aids the rewetting process of drained land. Drainage of land for agriculture is especially dangerous to the moor frog because they are prone to desiccation. Conservation efforts undertaken for the moor frog are most effective when executed in small scale phases. These small scale phases are more easily managed and receive more attention.

References

*Some parts of this article were translated from the article Grenouille des champs on the French language Wikipedia.

External links

The Animal Files
{{DEFAULTSORT:frog, moor moor frog Arctic land animals Amphibians of Russia Amphibians of Europe Amphibians of Asia Amphibians described in 1842 Taxa named by Sven Nilsson