tadpoles

Watch Out: There’s toads about!

May 22, 2020 by admin

An article by Patrick Beaumont

A few years ago I created a small pond, 12ft x 6ft x 2.5ft deep and populated it with goldfish, etc. Sometime later whilst walking my dog we noticed something writhing in the road: it was a newt with a mangled front leg. I took it home and using scissors snipped off the leg, dabbed a bit of antibiotic on the stump and put the newt on a lily leaf. It lived for another five years and even grew a new leg, albeit a bit smaller than the original.

The pond was quickly colonised by toads, who as tadpoles gorged themselves on the food meant for the fish. The front lawn became a “No Mow” zone because of all the toadlets hopping about. The local corvid population loved this so I had to net the lawn, much to my partner’s annoyance. On warm Spring days it is lovely to sit out and listen to the amorous calls of dozens of romantic toads. However, last year was a disaster; it was carnage on warm moist evenings as the toads tried to cross the road. I rescued 100s but many died after I went to bed. I need my sleep.

The serious casualties were the gravid, slow-moving females and the few females that made it to the pond were pounced on by the males in great heaps and promptly drowned. I then discovered Froglife – check it out folks, it’s fascinating. They sent me a pdf file to create warning posters to put by the roadside and, bless them, the passing motorists took notice. This year I am delighted to report that only one toad croaked (couldn’t resist the pun) and we have a pond full of toads and spawn.

Croaking Science: Overwintering in Frog Tadpoles

July 27, 2018 by editor

Overwintering in frog tadpoles

During June and July in the UK the majority of Common Frog (Rana temporaria) tadpoles metamorphose into juveniles which leave ponds for terrestrial habitats. They will spend the rest of the summer and autumn foraging and feeding on small invertebrates in preparation for the winter. However, a number of common frog tadpoles each year will remain in ponds and spend the winter in the water, metamorphosing into juveniles the following spring (Figure 1). What causes some tadpoles to metamorphose and others to remain in the water over the winter? Often, ponds drying out or freezing over can limit the capacity for frog tadpoles to overwinter. However, there are many ponds in the UK where this does not occur, which allows for overwintering of tadpoles. Our understanding of the exact factors which trigger overwintering in tadpoles are not fully understood, but research by Walsh et al. (2016) found that temperature and food availability were key factors. In addition, the decision on whether to over‐winter as a tadpole appears to be made relatively early in the season (Walsh et al., 2008). Under laboratory conditions, lower temperatures and reduced food availability during the summer resulted in a higher proportion of individuals remaining as tadpoles during the winter (Walsh et al., 2016). These findings suggest that cold weather conditions in the early autumn may affect tadpole development, perhaps by affecting endocrine function. However, temperature alone does not appear to be enough to trigger overwintering in tadpoles; food availability also appears to be important. Although these two factors play an important role in triggering overwintering in common frog tadpoles, there are other factors, not fully understood, that appear to be involved.

***Figure 1.*** *Common Frog Rana temporaria tadpoles may spend the winter in their natal ponds under certain environmental conditions. (Photo credit: John Roston)*

Living in areas with variations in altitude provides challenges for the development of common frog tadpoles. Higher altitude ponds experience lower temperatures and food availability and these may promote a higher incidence of overwintering in tadpoles. However, Muir at al. (2014) found that in tadpoles living at high altitude in Scotland, individuals had a lower resting metabolic rate which allowed for more energy to be allocated to growth. This is likely to allow individuals to grow faster under cooler environmental conditions and allow tadpoles to metamorphose earlier than expected and prevent the necessity to overwinter. However, if tadpoles developing at high altitudes do need to overwinter, they are able to better tolerate the colder winter temperatures. Muir et al. (2014) found that the tadpoles of Common Frogs at high altitude were able to tolerate freezing for short periods of time. This adaptation provides common frog tadpoles with the ability to withstand the cooler pond conditions at high altitude over the winter and therefore lead to greater survival.

Across Central Europe the incidence of overwintering tadpoles varies by species and is more typical in later breeding species with large tadpoles such as the Midwife Toad Alytes obstetricans, Spadefoot Toad Pelobates fuscus, and water frogs (Pelophylax species) (Gilbert & Harmsel, 2016). The incidence of overwintering in Common Frogs Rana temporaria is rare and was reported for the first time in the Netherlands in 2013 (Gilbert, 2016). This was likely to be due to the unusual weather conditions of 2013/14 along with the sheltered site where this was observed. Overwintering in the Edible Frog (Pelophylax esculentus complex) is a relatively rare phenomenon across Central Europe (Figure 2). Research by Péntek et al. (2018) found that overwintering by tadpoles only seems to occur in unusual weather conditions. In one particular incidence cold temperatures over the winter resulted in late breeding by adults which led to tadpoles getting a late start to their growth and development. Cool conditions early in the autumn (October) appeared to trigger halting of development and the subsequent mild winter promoted successful overwintering by tadpoles of this species (Péntek et al., 2018). Although still relatively rare, overwintering may become more common across Central Europe with changing environmental conditions causing increased variability in seasonal temperatures.

**Figure 2.** Overwintering by the tadpoles of the Edible Frog is relatively rare across Central Europe.

In the United States, 15 species of Ranid frogs occur but only five of these species are known to overwinter as larvae (North American Bullfrog Rana catesbeiana, Pig Frog R. grylio, River Frog R. heckscheri, Red-legged Frog R. aurora, and Southern Mountain Yellow-legged Frog R. muscosa). It appears that pond desiccation is one of the main factors limiting Ranid frog species in North America from overwintering as tadpoles. The Southern Leopard Frog Rana sphenocephala is a common frog inhabiting freshwater ponds across the Northern United States (Figure 3). Tadpoles of this species will remain in the larval stage until reaching a critical metamorphic size and if this is not reached by the end of the autumn, then the tadpoles will overwinter (Pintar & Resetarits, 2018). If winter conditions are suitable, tadpoles will remain in the pond for several years until the critical size for metamorphosis has been reached. This is different to Common Frogs in the UK which do not need a critical size to metamorphose but do require specific environmental conditions. These results highlight the variations that occur across Ranid species in their requirements for metamorphosis.

**Figure 3.** Tadpoles of the Southern Leopard Frog from the United States have to attain a critical body size before they can metamorphose. This can result in the tadpoles spending several years in one pond.

References

Gilbert, M.J. & Harmsel, R. (2016) Hibernating larvae of the common frog (Rana temporaria) in the Netherlands. Herpetology Notes, 9: 27-30.

Muir, A.P., Biek, R., & Mabel, B.K. (2014) Behavioural and physiological adaptations to low-temperature environments in the common frog, Rana temporaria. BMC Evolutionary Biology, 14: 110.

Péntek, A.L., Sárospataki, M., & Zsuga, K. (2018) Larval overwintering of the Pelophylax esculentus complex in a sodic bomb crater pond near Apaj, Hungary. North-western Journal of Zoology, 2018: e1775023/9.

Pintar, M.R. & Resetarits Jr., W.J. (2018) Variation in pond hydroperiod affects larval growth in Southern Leopard Frogs, Lithobates sphenocephalus. Copeia, 106 (1): 70–76.

Walsh, P.T., Downie, J.R. & Monaghan, P. (2016) Factors affecting the overwintering of tadpoles in a temperate amphibian. Journal of Zoology, 298 (3): 183-190.

Walsh, P.T., Downie, J.R. & Monaghan, P. (2008) Larval over‐wintering: plasticity in the timing of life‐history events in the common frog. Journal of Zoology, 276 (4): 394-401.

Croaking Science: Mutualism- novel interactions between amphibians and other species

April 26, 2018 by editor

Mutualism: novel interactions between amphibians and other species

Mutualism is widespread within the animal kingdom and involves the close association between two organisms of different species in which both benefit. Within the Amphibia, there are a number of interesting and novel mutualistic interactions. These range from symbiosis with algae to interactions with predatory spiders and living with water buffalo. Our understanding of the range and extent of mutualistic interactions within amphibians remains relatively poorly understood and here we review some recent discoveries.

The mutualistic symbiosis between algae and embryos of the Spotted Salamander (Ambystoma maculatum) from North America was first reported more than 120 years ago (Figure 1). In this relationship, algae live inside the developing embryos and appear to provide many benefits to the salamanders including: earlier hatching, decreased mortality and reaching a larger size at hatching (Kerney et al., 2011). The algae are thought to gain through feeding on the nitrogenous wastes released by the embryos. Research by Kerney et al. (2011) found that this relationship is closer than originally thought. Through imaging and genetic experimentation, the researchers found that the algae actually invade the salamander tissues during embryo development and live inside the cells of the salamanders for a period of several weeks. At the end of larval development algal cell death occurrs in the majority of salamander cells. However, the researchers found genetic material of the algae in the reproductive tracts of adults, suggesting that the algae remains present and is transferred from one generation to another through the reproductive tract of the adults. This research raises the possibility of transfer of DNA between species and provides evidence of highly close relationships between two very different organisms.

*Figure 1. Spotted Salamanders from North America have a mutualistic interaction with an algae during embryonic development.*

Mutualism between larval amphibians and algae has been reported from other species. The tadpoles of the Dwarf American Toad (Bufo americanus charlesmithi) live in warm, shallow and temporary ponds which receive extended periods of sunlight (Figure 2). It has previously been observed that the tadpoles develop a bright green colouration during their development in these conditions. Tumlison & Trauth (2006) conducted a series of experiments and found that the green glow was the result of a symbiotic algae (Chlorogonium) living on the skin of the tadpoles. The tadpoles benefit through receiving oxygen from the algae who photosynthesise in the sunlight. Shallow, temporary ponds experience severe oxygen depletion during periods of high sunlight and warmth so as a result of obtaining oxygen from the algae, the tadpoles are able to survive longer in the ponds and reach a larger size before metamorphosis. In return, the algae received carbon dioxide from the tadpoles during respiration which aids in their growth.

*Figure 2. Dwarf American Toad tadpoles live in sunny and shallow ponds to increase their developmental rate, which is aided by the presence of mutualistic algae.*

The family of microhylid frogs from Sri Lanka comprises four genera and 10 species. Several of these species have restricted distributions and occur only in the Kanneliya Forest Reserve. The ecology of many of these microhylid frogs is poorly understood but adults appear to breed in tree holes. Karunarathna & Amarasinghe (2009) found a novel mutualistic interaction between the microhylid frog Uperodon nagaoi and two species of tarantula spider (Poecilotheria species). Both amphibian and tarantula species have been observed to share tree holes and it appears that both species protect each other’s eggs. The eggs of both the amphibian and tarantula are attacked by species of ants, mantids and other spider species. On several occasions Karunarathna & Amarasinghe (2009) recorded the tarantula attacking mantids that were feeding on U. nagaoi eggs. Similarly, individual U. nagaoi were observed predating ants that were feeding on the eggs of the tarantula. In addition, the tadpoles of U. nagaoi appeared to benefit from the remains of predated insects falling into water where they were developing.

Many species of herbivorous vertebrate harbour large populations of nematode worms in their guts. Herbivorous tadpoles are no exception with several thousand species of nematode being recorded from larvae. Several researchers have proposed that some species of nematodes may be mutualistic and provide benefits to their host. This appears to be the case with American Bullfrog (Lithobates catesbeiana) tadpoles which harbours the nematode (Gyrinicola batrachiensis) during its larval stage. Research by Pryor & Bjorndal (2005) found that America Bullfrog tadpoles infected with this nematode increased their rate of development by approximately 16 days, allowing the tadpoles to metamorphose earlier than tadpoles without the nematodes. This has many benefits as this promotes higher survival and subsequent reproductive success of the newly metamorphosed froglets. There could be two main reasons to explain this increase in development. First, the increase in gut size to allow the nematode to live may result in increased food intake and absorption by the tadpole. Second, the nematode increases rate of food fermentation in the gut, which allows the tadpole to absorb more food. The results of this study highlights that some gastrointestinal nematodes inhabiting the gut regions of other herbivores may have a beneficial effect on digestion and nutrition in those hosts.

*Figure 3. Anatonian Water Buffalo have a novel mutualistic interaction with Marsh Frogs in Turkey.*

A final form of novel mutualism has been observed between Marsh Frogs (Pelophylax ridibundus) and the Anatolian Water Buffaloes (Bubalus bubalis) in Turkey (Figure 3). Zduniak et al. (2017) reported a unique behaviour in the frogs where individuals climbed up the fur and onto the backs and heads of the buffaloes where they appeared to be predating flies. Up to 31 frogs were observed feeding on a single buffalo at any one time (Zduniak et al., 2017). It appears that both species benefit from this interaction since the frogs gain food and the buffalo has flies removed which may cause irritation. This appears to be the first record of such interaction between these two species and highlights that novel mutualistic interactions may occur more widely between amphibians and other species.

References

Tumlison, R. & Trauth, S.E. (2006) A novel facultative mutualistic relationship between bufonid tadpoles and flagellated green algae. Herpetological Conservation and Biology, 1 (1): 51-55.

Karunarathna, D.M.S.S. & Amarasinghe, A.A.T. (2009) Mutualism in Ramanella nagaoi Manamendra-Arachchi & Pethiyagoda, 2001 (Amphibia: Microhylidae) and Poecilotheriam species (Arachnida: Thereposidae) from Sri Lanka. Taprobanica, 1 (1): 16-19.

Kerney, R., Kim, E., Hangarter, R.P., Heiss, A.A., Bishop, C.D. & Hall, B.K. (2011) Intracellular invasion of green algae in a salamander host. PNAS, 108 (16): 6497-6502.

Pryor, G.S. & Bjorndal, K.A. (2005) Effects of the nematode Gyrinicola batrachiensis on development, gut morphology, and fermentation in bullfrog tadpoles (Rana catesbeiana): a novel mutualism. Journal of Experimental Biology, 303A: 704–712.

Zduniak, P., Erciyas-Yavuz, K. & Tryjanowski, P. (2017) A possible mutualistic interaction between vertebrates: frogs use water buffaloes as a foraging place. Acta Herpetologica, 12 (1): 113-11.

Thanks to our wonderful volunteers!

June 20, 2016 by editor

This month we’d like to highlight the time, passion and creativity that our volunteers bring to our projects.

All over the UK, the Froglife teams create & restore habitats and hold events to help educate the public on the importance of conserving amphibians and reptiles and saving the habitats they depend on. At all of these events, across the countryside and cities we have a strong team of volunteers who are always there to help spread the conservation message and get mucky to help our little frogs, toads, newts, snakes and lizards! vol KW2016

These volunteers not only give us their time, they also share their talents with us by regularly taking photos and creating fantastic videos after we’ve completed projects at sites.

So here’s a few bits that they’ve shared with us:

This amazing underwater video of tadpoles in Olive Branch Community Gardens, was shared to Rebecca Neal, Conservation Youth Worker, for Peterborough Green Pathways by one of her volunteers. Froglife put the ponds in 5 or 6 years ago through the Wildlife Ambassadors project, and this video clearly shows us that the frogs like the ponds we made!

This selection of videos come from Katie Garrett, one of the London Dragon Finder volunteers. Katie often comes along to our events and work days, gets muddy and still manages to take amazing photos and videos! Check her out on twitter, @katieggarrett, as she often posts more images and short videos of the amphibians and reptiles she sees when she’s out and about. When she’s not volunteering with us, she also volunteers with Honduras Amphibian Rescue and Conservation Centre, making films for their conservation efforts. She’s a Herp Hero!

So again, a MASSIVE thanks to all our volunteers from everyone here at Froglife!

This is how SMILEY you make us! — You make us all **SMILE!**

Flexibility of life history events in the Common Frog

May 29, 2014 by admin

5. Getting bigger (Rob Williams, 2011)

Croaking science is a new way for student volunteers and scientist to explore what’s occurring in the world of Science. Croaking Science looks at science facts, new research or old debates which are inspired by or affect amphibians and reptiles, and then communicates this in layman’s language to a wider audience. The aim of the feature is to provide a platform for those starting their foray into the world of science communications as well as established scientists. We welcome any submissions from students and scientists. Please note that the views expressed in the articles are not those of the Froglife Trust.

Croaking Sceince reporter Rhiannon Laubach looks at the history of Chytridiomycosis and it’s impacts on the Fire Salamanders in Europe

– See more at: http://www.froglife.org/2014/05/14/lethal-chytridiomycosis-salamandars/#sthash.ugsmA3E1.dpuf

Croaking Sceince reporter Rhiannon Laubach looks at the history of Chytridiomycosis and it’s impacts on the Fire Salamanders in Europe

– See more at: http://www.froglife.org/2014/05/14/lethal-chytridiomycosis-salamandars/#sthash.ugsmA3E1.dpuf

Croaking science is a blog for student volunteers and scientists to explore what’s occurring in the world of Science. Croaking Science looks at science facts, new research or old debates which are inspired by or affect amphibians and reptiles, and then communicates this in layman’s language to a wider audience. The aim of the feature is to provide a platform for those starting their foray into the world of science communications as well as established scientists. We welcome any submissions from students and scientists. Please note that the views expressed in the articles are not those of the Froglife Trust.

Croaking Science reporter Rhiannon Laubach looks at the flexibility of life history events and its significance for Common Frogs

Not all members of the same species undergo metamorphosis at the same rate. Metamorphosis can be described as a life history event, the transformation from the larva (tadpole) to the juvenile adult (froglet). The size of an animal, or the development stage it is at, can affect the chances of an individual surviving the winter, in temperate climates.

Most tadpoles metamorphose into froglets in the same year. However, some common frog tadpoles can over-winter in this larval stage and then transform into frogs the next spring. This phenomenon has been recorded with a greater frequency in recent years, being reported by both the media and scientific literature. There has not been much investigation into what causes this and it is not known at which point in its development an individual will determine if it will over-winter as a tadpole or not.

A recent report studied the growth and development of a population of common frogs (Rana temporaria) tadpoles throughout one year in order to see if the rate of development of tadpoles would influence in what form they over-winter. Laboratory studies were carried out to complement field work.

8. Long legs (Rob Williams, 2011) The methods of the study were as follows: between May and January of the following year, tadpole development at the field site was monitored by randomly collecting tadpoles and taking them back to the laboratory to be measured and their stage of development was noted. If an individual had not started metamorphosis by November it was considered to be over-wintering as a larva. Water temperature was continuously logged for the duration of the study. This data was used to calculate the mean fortnightly temperature. For the laboratory study, the tanks where kept at mean fortnightly temperatures and they had either a high or low food availability scenario. The tadpole’s development and condition were also recorded.

9. Front legs growing under skin (Rob Williams, 2011) The study confirmed that tadpoles do over-winter at the study site. At the site, shortly after hatching the larvae began to form two distinct development groups. One group consisted of waves of individuals that grew on and then metamorphosed. The second, smaller, group continued to grow but did not metamorphose and this decision to over-winter as tadpoles was carried out very early in their development.

It is unclear what causes this, it could be genetic or “local environmental cues triggering a particular developmental pathway in a genetic subset of the population” (Walsh& al 2008). Tadpoles that over-winter have an advantage, as they don’t have to invest so much energy into development and can use more energy for growth. Larger tadpoles will metamorphose into larger frogs. Larger frogs have an advantage. In the laboratory there was no over-wintering. The tanks where kept at a mean fortnightly temperature, which does not reflect the temperature fluctuations at the study site. Food availability was not shown to have an affect on over-wintering.

This study shows that the possibility of a tadpole over-wintering is determined very early in its development. Over-wintering of larvae might be the tadpoles’ response to local environmental conditions but temperature does not seem to be the main variable for determining this (Walsh& al 2008).

17. Freedom... (Rob Williams, 2011)

Reference
Walsh, P.,T., Downiel, J., R., Monaghan, P.. (2008). Larval over-wintering: plasticity in the timing of life history events in the Common Frog. Journal of Zoology. 276 , 394-401.

Photos: Rob Williams

Croaking Science: Gastric-brooding frogs – a uniqueness lost forever?

November 27, 2013 by admin

Croaking science is a new way for student volunteers and scientist to explore what’s occurring in the world of Science – science facts, new research or old debates which are inspired by or affect amphibians and reptiles, and then communicate this to a wider audience in their own words. The aim of the feature is to provide a platform for those starting their foray into the world of science communications as well as established scientists. We welcome any submissions from students and scientists. Please note that the views expressed in the articles are not those of the Froglife Trust.

This is the time of year where you may be getting together with friends and family for meals all over the world. When you do, think about what this frog went without, to look after it’s young. From one of our new Croaking Science Volunteers Hannah Graves.

Gastric-brooding frogs were discovered in Australia in the 1970’s ⁽¹⁾. There are two known species, the Northern (Rheobatrachus vitellinus) and the Southern (R.silus) ⁽²⁾, neither of which has been seen in the wild since the 1980’s ⁽³⁾. It isn’t known exactly what caused the demise of the two species, it is believed that logging and disturbances to the water quality in their habitats may have had an effect on the Southern species ⁽⁴⁾ and wide spread forest fires and habitat destruction could be implicated in the loss of the Northern species ⁽⁵⁾. As with all amphibian populations globally, the fungal disease Chytridiomycosis can’t be ruled out⁽¹⁾.

As the common names suggest, this genus of frog had a very unusual way of caring for their young. After the female had mated, she swallowed her eggs! This meant that the tadpoles could develop in her stomach safe from predators ⁽⁶⁾. After six to seven weeks the tadpoles metamorphosed into young frogs and crawled back out of the female’s mouth ⁽⁴⁾. During this brooding period the female switched off the production of hydrochloric acid to prevent digesting her young ⁽⁷⁾. This meant that she couldn’t eat whilst carrying her young. Just four days after her young emerged, the female’s digestive system returned to normal and she resumed eating ⁽⁴⁾. Unfortunately, as the two species are now classified as extinct ^{(1) (8)}, it is unlikely we will ever learn the secrets of how they managed to shut down their digestive systems and then start them up again.

Sadly, this story of discovering a new species only to lose them a few years later is all too common ⁽⁹⁾, and with them we lose their untold stories.

What you can do

Support initiatives to inspire the next generation of herpetologists (scientists that specialise in amphibian and reptiles) including our conservation and education work .

Even our “common” species are declining in some areas. If nothing is done now, they may not be there in the future. Use our Dragon Finder app to report any of your amphibian and reptile sightings (applicable to species found in the UK). So that the location of your local populations are recorded.

References

(1) Meyer, E.; Newell, D.; Hines, H.; May, S.; Hero, J.; Clarke, J.; Lemckert, F. (2004). Rheobatrachus silus. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.1. Downloaded on 01 October 2013.

(2) IUCN (2013). IUCN Red List of Threatened Species. Version 2013.1. www.iucnredlist.org Downloaded on 01 October 2013.

(3) Hines, H. (2002) Recovery plan for Stream Frogs of South-east Queensland 2001-2005. Environmental Protection Agency, Queensland, Australia. Downloaded on 01 October 2013.

(4) Tyler, M.J. and Davies, M. 1983. The gastric brooding frog. M.J. Tyler, eds., Croom Helm, London.

(5) Hero, J. and Morrison, C. (2004). Frog declines in Australia: global implications. Herpetological Journal 14:175-186.

(6) Tyler, M.J. and Carter, D.B. (1982). Oral birth of the young of the gastric-brooding frog Rheobatrachus silus. Animal Behaviour 29:280-282.

(7) Tyler, M.J.; Shearman, D.J.C.; Franco, R.; O’Brien, P.; Seamark, R.F.; Kelly, R. (1983). Inhabitaion of gastric acid secretion in the Gastric Brooding Frog, Rheobatrachus silus. Science 220:609-610.

(8) Hero, J.; McDonald, K.; Alford, R.; Cunningham, M.; Retallick, R. (2004). Rheobatrachus vitellinus. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.1. Downloaded on 01 October 2013.

(9) Wake, D.B. and Vredenburg, V.T. (2008). Are we in the midst of the sixth mass extinction? A view from the world of amphibians. Proceedings from the National Academy of Science 105:11466-11473.

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