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

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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.

Royal Mail release new ‘Reintroduced Species’ stamps

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Royal Mail release new ‘Reintroduced Species’ stamps

Royal Mail have just released their ‘Reintroduced Species’ stamps to celebrate some of the biggest success stories about restoring various flora and fauna to the UK. Froglife are very pleased to see the sand lizard featured on one of these stamps as it is sometimes a neglected species like most reptiles and amphibians.

Here at Froglife, we love the humble little sand lizard and aim to protect them as well as their habitats. Here are some interesting facts about them:

  • One of the UK’s rarest reptiles
  • Populations found in coastal areas in the South and West of the UK
  • Reintroduced to sites in North Wales, Devon, Cornwall and West Sussex.
  • The UK’s only native egg-laying lizard
  • Males develop bright green flanks during the breeding season
  • Like the common lizard, sand lizards will drop their tails if they feel threatened
  • Sand lizards have full legal protection under UK law 

For more facts about sand lizards, visit the advice section of our website: www.froglife.org/info-advice/amphibians-and-reptiles/sand-lizard/

To see more of the Royal Mail’s ‘Reintroduced Species’ stamps, click here.

Amphibians and winterkill – a worse than average year?

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Amphibians and winterkill – a worse than average year?

Several species of UK amphibians overwinter in ponds, including common frogs and smooth newts. These animals tend to spend the winter in the silt and decaying leaves at the bottom of ponds. Normally this does not harm the animals and they resume breeding as usual the following spring. The advantage to spending the winter in the pond is the individuals are ready to breed as soon as the weather becomes warm enough. However, these individuals rely on absorbing oxygen through their skin, especially during periods of cold weather. This can be a problem as sometimes during the winter months oxygen levels within the pond can fall and toxic chemicals build-up. This occurs more frequently when the surface of the pond freezes over for extended periods. Unfortunately this can result in the death of some amphibians and is commonly known as winterkill. This process is natural and every year a number of amphibians, mainly common frogs, die as a result of winterkill and this has no negative impact on populations.

During January and February 2018 we experienced relatively mild winter conditions across the UK, with only light overnight frosts. This encouraged the early emergence of common frogs and other amphibians, especially within the south of the UK. Froglife had sightings of great crested newts on 25 December 2017 and the first frogspawn was reported on 17th January. The relatively mild conditions continued until late February, which triggered the movements of many common frogs towards breeding ponds. At the end of February, the UK experienced unusually cold and prolonged winter weather with hard frosts and snow. This sudden cold period of weather came quickly, when a large proportion of breeding frogs were already at ponds. Although these individuals may have tried to avoid the cold conditions, the combination of low temperatures, already low oxygen levels in ponds, along with an extended period of ice covering ponds caused mortality in many frogs across the country. The Froglife enquiry service received a sudden and high level of reports of large numbers of mainly common frogs being found dead in ponds. Between 5th and 16th March Froglife received 26 enquiries relating to frozen frogs in ponds. In several cases frogs appeared to have frozen within the ice. The worst case was from a school pond where over 120 common frogs were removed dead from the water. This number of enquiries was higher than average as in most years Froglife only receives a handful of cases of winterkill across the whole winter and spring seasons.

In addition to an increase in number of dead adult common frogs, frogspawn appears to have been affected. Spawn laid early in the season is at risk of damage due to later frosts. The cold period of weather in early March and then again on the weekend of 17-18th March occurred after the majority of frog spawn had been laid. Although spawn in the frost-free zone of the pond (usually underwater) will survive, any eggs near to the surface usually die. These often contract a white fungal infection which can later spread to all the spawn. The combination of frost and fungal infection may have resulted in a higher than average mortality of frog spawn in 2018.

It is too early to determine the impact of winterkill on common frog and other amphibian populations. Amphibians are relatively long-lived so the loss of spawn from one breeding season is unlikely to have significant impacts on populations. However, the loss of a large number of breeding adults may have an impact, especially where populations are small and are already under stress from other factors such as loss of breeding and terrestrial habitats, habitat fragmentation, introduced disease and pollutants. Climate change may impact amphibians in several ways and an increase in extreme weather events may have long-term implications on amphibian populations across the country. Long-term population monitoring is required on amphibian populations to determine whether they are negatively affected by repeated extreme weather events at key times during their breeding cycle.

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