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A brief introduction to Marsh Frogs
Froglife volunteer, Victoria L, has taken the time to look into Marsh Frogs, one of the non-native frog species that you could come across in ponds and ditches across the UK, Most commonly spotted in South-eastern areas of England.
What are Marsh Frogs and where do they come from?
Marsh frogs (Pelophylax ridibundus) are a species of frog which are native to continental Europe and Western Asia. They are not a native species in the UK and were introduced in the 1930’s from eastern Europe. They are Europe’s largest native frog species, growing up to 15cm in length. In the UK, they are most frequently found in the Southeast of England, particularly in marshland areas.
Where do Marsh Frogs like to live?
Marsh Frogs are most prominent in the South-east of England due to having been imported from Hungary in 1935 and introduced to the Walland Marsh in Kent, already making it the main location of the species in the UK. Marsh Frogs prefer to spend most of their time either at the edge of or inside a body of water. They have an affinity towards wet, humid habitats such as lakes, ponds, and rivers. When they are not in the depths of these water bodies, they bathe in the sun.
This aquatic preference makes Marsh Frogs differ from other species, like the common frog, which travel around the landscape without much need to be in a constantly wet environment.
What makes Marsh Frogs unique?
Marsh Frogs may seem like any ‘typical’ frog, yet they have some unique features in plain sight. Marsh Frogs are bigger than the usual frog, usually being 13cm long but have the potential to reach 15cm. This contrasts with other frog species which are usually smaller, around 8cm. Another special identification detail about Marsh Frogs is that males have two grey vocal sacs on either side of their head which produce their call. Marsh Frogs have an interesting call which sounds like a cackle or a laugh, which can be produced by both females and males. Their calls travels far and can be used to attract mates.
Marsh Frogs have the ability to have hybrid offspring with other frog species, the green frog group. They can also easily adapt, for example them being able to survive in salt marshes.
Although Marsh Frogs are not native to the UK, their close relative, the pool frog, is. They belong to a group called ‘Green Frogs’ along with their hybrid, the edible frog.
What do Marsh Frogs look like?
They have large heads, males having the two grey vocal sacs on either side. Marsh Frogs also have textured skin along with folds on either side of their body. They come in a variety of colours, be it green, brown or grey.
What is the diet of Marsh Frogs?
Like any other frog, Marsh Frogs consume insects such as worms and spiders. Yet, they may also consume other frogs and even mice, contributing to the threat of native species in the UK.
What impact do Marsh Frogs have in the UK?
With Kent having a rise in the invasive, non-native, Marsh Frog population there has been a simultaneous decline in the populations of common frogs and native newts. Studies have shown that this is likely due to the Marsh Frog species preying on the common frogs and native newts while also bringing them diseases such as chytridiomycosis which they carry and is a threat to native species.
Other studies have shown a decrease in common frogs occurring in habitats which do not contain Marsh Frogs. This is likely due to the changes in habitats caused by pollution and climate change. This has led researchers to believe that the cause of this decline in common frogs is caused by both factors, which also affects other native species as well.
The affect of climate change on Marsh Frogs and other Herpetofauna:
Climate change also plays an important role on the future of Marsh Frogs and UK native frog species. Reptiles and amphibians are sensitive to the changes in precipitation of their environment, being two animal groups which are highly affected by climate change. As climate change and other severe events increase, research and monitoring of vulnerable species become even more important to drive effective conservation efforts.
Warmer temperatures have an unforeseen affect on herpetofauna, impacting their behaviour, reproduction and distribution traits. With climate change and global warming, this is currently affecting them.
Halloween, Folklore and Myths
“Fillet of a fenny snake, In the cauldron boil and bake; Eye of newt and toe of frog, Wool of bat and tongue of dog, Adder’s fork and blind-worm’s sting, Lizard’s leg and owlet’s wing, For a charm of powerful trouble, Like a hell-broth boil and bubble.”
For many, the above passage will be familiar as a scene from Shakespeare’s Macbeth. For those who are not familiar, most will at least know that it is in reference to a witch’s brew. Amphibians and reptiles have long been associated with the occult, having deep rooted ties to ancient folklore and mythology. Though these links are not as strong in the present, the negative stigma surrounding these species has pervaded. What better time than Halloween to delve into these stories and perform some much-needed myth busting?
Did witches really go around carving out newt eyes, leaving blind newts to stumble around lost? The answer is no. In Shakespeare’s Elizabethan England, jobs such as midwives, herbalists and healers were easily misunderstood, and deemed witchcraft as a result. In an age predating modern medicine, people had to be more connected with nature to create medicines. They had to understand what was usable and what was not, which combinations worked for which illnesses etcetera. This makes complete sense, as we today still rely on nature for the base ingredients of many of our own medicines. These tradespeople relied on knowledge passed down through generations to create herbal remedies. To protect their livelihoods, their ingredients had to be shrouded in secrecy. This is no different to giant companies today like Coca Cola hiding the ingredients to their “magical brews”.
In order to keep their ingredients secret, they renamed a lot of what they used. This would also deter others from taking up the same practices; as animal body parts hardly sounds appealing and there’s no business in having everyone trained as a healer! If we look at Shakespeare’s cauldron, what was really being used was mustard seeds (eye of newt), buttercup (toe of frog), holly leaves (wool of bat) and houndstongue (tongue of dog). The use of body parts to refer to parts of plants was common within these circles. Eyes would refer to seeds, tongues to petals, guts to roots, tail to stem and so forth. Admittedly, adder’s fork did refer to an adder’s tongue and a blind worm’s sting referred to a slow worm’s tail. That aside, selling potions with mysterious names would prevent customers from simply going off and making their own potions. The witchy aura of it all also may have legitimised the healer and had consumers convinced that they were taking magical cures – not too different to the placebo effect we know of today.
Still, this does not answer the question of why there is such a gravitation towards reptiles and amphibians. Why do they inspire such revulsion? From medieval times, it was believed that all toads and frogs were poisonous. This is the case for some species, but certainly not within the UK. The fear stemmed from the fact that some amphibians can cause sickness or fatality if ingested – in particular, toads, as they release bufotoxin to deter predators when frightened. Furthermore, during breeding season, it is known that these animals can swarm in large numbers. In times past, animals swarming was not seen as a marvel of nature, but instead a precursor of evil. Think of a swarm of locusts for example. They can be found in such quantities that people feared that they were spontaneously multiplying. Their choice of habitat invoked further fear as swamps and stagnant pools of water were the antithesis of consecrated holy water. The list goes on.
However, it did not always use to be that way. Frogs used to symbolise fortune, rebirth, rain, fertility and heightened spirituality. The Egyptian goddess Heqet, occasionally depicted with a frog’s head, was the goddess of fertility and childbirth. Rain was a giver of life, allowing crops to grow and rivers to flow and consequently frogs became predictors of rain as they would gather in large numbers as the heavens showered. This was a trait that was also shared with other amphibians such as our toads and newts. Snakes symbolised immortality with their skin shedding, lizards represented regeneration due to their ability to regrow tails. As we celebrate Halloween, it is perhaps a time to reflect and rediscover the awe of the Ancient Egyptians and Mesopotamians. Rather than perceive the brilliant nature of metamorphosis as these species morph from egg to adult as something to fear, it is time to shift back to the perspective that it is a magic to be revered and protected at all costs.
Emily Robinson, London T.O.A.D Project Trainee
Croaking Science: See-through frogs are worth a look
Glass frogs comprise a family (Centrolenidae) of 158 species found in the forests of the neotropics: Central America and northern South America. They get their name from the transparency of their belly skin, which allows the internal organs to be easily seen. They are adapted to life in the trees, possessing pads on the tips of their digits that allow them to adhere to leaves. These structures appear to have evolved independently in several lineages of frogs, since molecular phylogenetic results show that the main families where these pads occur (Hylidae, Rhacophoridae, Centrolenidae) are not closely related.
One of the special features of glass frogs is their mode of reproduction. Clutches of eggs, as flat round sheets, each egg encased in jelly, are laid on the surfaces of leaves overhanging streams. Once the eggs have developed into larvae, they hatch and fall into the stream below, often from a considerable height. Glass frogs are divided into two main sub-families: the Centroleninae (121 species) which lay on the upper sides of leaves and then leave the eggs to develop on their own; and the Hyalinobatrachinae (35 species) which lay their eggs on the lower sides of leaves; in these species, the father cares for the eggs, sometimes up till the point of hatching.
We studied the glass frog Hyalinobatrachium orientale which has distinct populations in northern Venezuela and northeast Tobago: this distribution is a bit of a puzzle. Northeast Tobago is quite distant from Venezuela and between these two locations is the large island of Trinidad, which has abundant forests, but no glass frogs. Walking along the forest streams of Tobago at night, once the rainy season (June to December) has started, you soon hear the high-pitched peeping of male glass frogs, located on the huge leaves of Heliconia bihai that overhang the water. With the aid of a good torch, you can locate the calling frogs; often, near them, you can spot the little patches of eggs. If you are lucky, you may locate a mating pair. We observed the behaviour of a mating pair. It took them about four hours to complete their clutch of around 30 eggs, laid as a spiral pattern, starting at the centre, with the pair turning as they proceeded. Once egg-laying was complete, the female departed, but the male stayed close to the clutch. Often, when searching for egg clutches, we found the father sitting on top of his eggs. We also found that some fathers, presumably good quality males, were looking after more than one egg clutch at a time. These are at different stages of development, so clearly produced on different nights. It is not entirely clear what functions male egg attendance performs, particularly given that it is not constant. However, observers have seen males driving away egg predators such as wasps and ants; it is also likely that males keep the eggs hydrated by reducing evaporation, simply by sitting on them, or by emptying their bladders over the eggs (this is established in some cases of frog parental care). But this raises another mystery. If paternal care is helpful to incubation success in the Hyalinobatrachinae, why does it not occur in other glass frogs, especially when they lay their eggs on leaf upper surfaces, where you would guess that desiccation and predation would be higher risks.
In the Tobago glass frog, hatching occurs around nine days after laying, although the actual time is variable, allowing tadpoles to be earlier or later stages of development when entering the water. Such variability may be quite common in frog development and represents a trade-off. Early hatchers are less well developed and more vulnerable when they enter the water; but it may be better to risk this than to be predated while still in the nest. It therefore pays the developing larvae to monitor conditions: if the father has deserted his clutch, or hot sun and no rain are risking desiccation, better to hatch early and hope for a stream with few predators.
The streams where glass frog tadpoles are found are fast-flowing when it rains, and are heavily populated with predatory fish and crustaceans. They are also shaded, making plant productivity low. As a consequence, glass frog tadpoles spend much of their time hidden under rocks, reducing the risks of predation and of being swept away by currents (unlike the tadpoles of some species that inhabit fast streams, glass frog tadpoles lack the kind of suctorial mouthparts that can help cling on to rocks). The tadpoles have long muscular tails, indicating an ability to move rapidly, and are relatively unpigmented, associated with a concealed lifestyle. Their behaviour limits foraging opportunities, so growth is slow. Glass frog tadpoles can take a year to reach metamorphosis, very slow by tropical frog standards, where many species reach that stage in a few weeks. We have been able to locate metamorphosing glass frogs near the edges of streams. They climb up on to the upper surfaces of leaves close to the ground, and take about four days to complete the process, reducing their tail to a stump. To our surprise, we found that they do not remain in one place through this process, but occasionally move around, possibly to confuse potential predators.
The transparency of glass frogs has long puzzled biologists. Recently, a research team from Bristol, Canada and Ecuador has tested an explanation. Their evidence suggests that it is not so much transparency that matters, but translucence. When a glass frog is at rest with its limbs tucked in, the translucence of the limbs blurs the edges of the body, and makes detection by predators more difficult.
Barnett et al. Imperfect transparency and camouflage in glass frogs. PNAS (2020).
Byrne et al. The behaviour of recently hatched Tobago glass frog tadpoles. Herpetological Bulletin 144, 1-4 (2018).
Byrne et al. Observations of metamorphosing tadpoles of the Tobago glass frog. Phyllomedusa (in press) (2020).
Delia et al. Glass frog embryos hatch early after parental desertion. Proceedings of the Royal Society B 281, 2013-2037 (2014).
Downie et al. The tadpole of the glass frog Hyalinobatrachium orientale from Tobago. Herpetological Bulletin 131, 19-21 (2015).
Nokhbatolfoghahai et al. Oviposition and development in the glass frog Hyalinobatrachium orientale. Phyllomedusa 14, 3-17 (2015).
Contributing authors : Roger Downie, Isabel Byrne, Chris Pollock.
Help Froglife secure funds to improve Cowdenbeath Grasslands (Fife, Scotland)
Froglife is fundraising to restore and create standing water habitats (ponds) at Cowdenbeath Grasslands. Cowdenbeath Grassland is a large, predominantly grassland site with numerous over-grown ponds and pools, these will be restored to provide vital, open water for amphibians, reptiles, aquatic invertebrates, wading birds, aquatic plants and small mammals such as water voles, bats and hedgehogs.
Our ambition is to restore four non-functioning ponds and two scrapes and to create thirty new ponds and sixteen scrapes. Additionally, we will create basking banks, plant a range of native scrub/tree species and hawthorn planting to improve connectivity and provide sheltering habitat.
This project forms part of Froglife’s Living Water programme that operates across the UK creating and restoring amphibian and reptile habitats. In order to secure the grant we need to show that we have support for our Living Water programme. Please support us through our social media feeds or by emailing Info@froglife.org.
Croaking Science: Miniaturisation in amphibians
Amphibians exhibit vast ranges in body size ranging from just 7 mm long in the smallest known species (Paedophryne amanuensis) to 33 cm in the largest frog (Conraua goliath), which represents a 250 fold increase in size. Different body sizes come with distinct advantages and disadvantages. Large amphibians have fewer predators, a lower metabolic rate, and they can more easily maintain their temperature and hydration than small amphibians. Smaller amphibians, although being more prone to predation, are better equipped to hide more easily, exploit alternative food sources, use physically smaller niches, and attain reproductive ability at an earlier age (Leavy & Heald, 2015). By being very small, individuals are able to fully utilise habitat patches and consume the smallest prey, which are also the most numerous. However, living at such small sizes puts constraints on biological processes and as a result, miniature amphibians have evolved unique features to enable them to function effectively. Many miniaturised frogs have a reduced number of skull elements, fewer digits on their limbs, fewer vertebrae and a reduction in webbing on the feet. Many miniature frogs resemble juveniles and retain of their features. Indeed, the frog genus Paedophryne, discovered in 2010 from Papua New Guinea, means ‘juvenile form’ and contains some of the world’s smallest frogs measuring just 10.1–11.3 mm (Kraus, 2010). Most miniature frogs from a range of families are usually found in wet tropical forests and live on the forest floor under leaf litter feeding on minute termites, small ants and similar species (Almeida-Santos et al., 2011).
Miniaturisation within the amphibians has evolved independently several times and in many species adults only grow to 20 mm in length. For example, miniaturisation has evolved 8 times in the puddle frogs (genus Phrynobatrachus) of Sub-Saharan Africa (Zimkus et al., 2012). The unusual reproductive mode of many tropical amphibian species has promoted the evolution of small body size. Miniature amphibian species are usually fully terrestrial with individuals laying a small number of relatively large eggs within the leaf litter which hatch into fully metamorphosed juveniles. For example, the Strabomantid frogs of the Peruvian Andes are fully terrestrial and do not require water to breed. This means that individuals do not need to undergo breeding migrations to water bodies. This promotes the evolution of small body size since individuals are able to occupy very small home ranges (Lehr & Catenazzi, 2009). In addition, the unique physiology of amphibians has allowed the evolution of small body sizes even at high altitudes, especially in the tropics. In many groups of vertebrates there is a relationship between body size and temperature (Bergmann’s Rule) where individuals at higher altitudes or latitudes attain larger body sizes, often as a protection from colder temperatures. However, due to their physiology which allows them to alter their metabolism for activity at lower temperatures, small amphibian species are able to occupy high altitudes. This removes the constraint of temperature on the evolution of body size and allows species to occupy a greater range of ecological niches even at high altitudes.
In recent years our knowledge and understanding of miniature amphibians has increased due to discoveries of new species and research into their unique ecology. Frogs within the genus Brachycephalus are all endemic to the Atlantic Forest in Brazil (Figure 1). There are currently 35 known species (Frost, 2018) and 19 of these have been discovered in the past six years. Also known as flea-frogs, these poorly understood species inhabit the moist tropical forest floor within this biodiverse hotspot. Growing to less than 20 mm in length, Brachycephalus didactylus, occurs only in Rio de Janeiro state where it is threatened by encroaching human developments and habitat fragmentation. During the breeding season, females lay just two eggs, probably laying each on a different day (Almeida-Santos et al., 2011). Each egg is laid amongst the leaf litter where it undergoes complete development into a fully metamorphosed juvenile frog with no free-swimming larval stage. The eggs of this species are also relatively large, allowing newly metamorphosed juveniles to emerge at a larger size which offers greater protection from predators.
Night frogs, genus Nyctibatrachus, live in close association with mountain streams or marshes in forests of the Western Ghats, India. Species within this genus are extremely small ranging 10 – 77 mm. In 2017 Garg et al. (2017) discovered seven new miniaturised night frog species, four of which are among the smallest frogs in India measuring just 12.2 to 15.4 mm in length. All members of the new species were found under leaf litter or in wet grass near to streams or waterfalls. One male was found clasping a clutch of 10 eggs (Garg et al., 2017). The authors believe that more surveys will discover further new species which will also aid our understanding about the evolutionary advantages of miniaturisation and adaptation to terrestrial life within these and other miniature frogs
Almeida-Santos, M., Siqueira, C.C., Van Sluys, M. & Rocha, C.F.D. (2011) Ecology of the Brazilian flea frog Brachycephalus didactylus (Terrarana: Brachycephalidae). Journal of Herpetology, 45 (2): 251-255.
Frost, D.R. (2018) Amphibian Species of the World: an Online Reference. Version 6.0 (09 March 2018). Electronic Database accessible at http://research.amnh.org/herpetology/amphibia/index.html. American Museum of Natural History, New York, USA.
Garg, S., Suyesh, R., Sukesan, S. & Biju, S.D. (2017) Seven new species of night frogs (Anura,
Nyctibatrachidae) from the Western Ghats biodiversity hotspot of India, with remarkably high diversity of diminutive forms. PeerJ, 5:e3007; DOI 10.7717/peerj.3007.
Kraus, F. (2010) New genus of diminutive microhylid frogs from Papua New Guinea. ZooKeys 48: 39-59.
Leavy, D.L. & Heald, R. (2015) Biological Scaling Problems and Solutions in Amphibians. In: Additional Perspectives on Size Control in Biology: From Organelles to Organisms. Eds R. Heald, I.K. Hariharan and D.B. Wake. Cold Spring Harbor Laboratory Press, doi: 10.1101/cshperspect.a019166.
Lehr, E. & Catenazzi, A. (2009) A new species of minute Noblella (Anura: Strabomantidae) from Southern Peru: the smallest frog of the Andes. Copeia, 2009 (1): 148–156.
Zimkus, B.M., Lawson, L., Loader, S.P. & Hanken, J. (2012) Terrestrialization, miniaturization and rates of diversification in African puddle frogs (Anura: Phrynobatrachidae). PLoS ONE, 7 (4): e35118. doi:10.1371/journal.pone.0035118.