Froglife

Leaping forward for reptiles and amphibians

You are here: Home / Archives for common toad

common toad

What our animals are doing this month… July 2020

by

July can be a great month to see our common toad complete metamorphosis and become toadlets.  It usually takes around two to four weeks for tadpoles to hatch out from the egg and roughly sixteen weeks for tadpoles to reach the stage where legs have developed.  This is often affected by the water temperature in the pond as well as numbers of larvae present and food availability – as tadpoles are busy eating algae in the pond for their nutrition.  Toadlets will form legs, absorb their tails, form lungs to breathe out of the water and eventually leave their pond to head out onto land.

You may have been lucky enough to see toadlets emerge, in huge numbers, in previous years near ponds.  They won’t move too far from their breeding pond however as they will be busy foraging and developing in summer and early autumn to get ready for the overwintering period.  Emergence occurs in higher numbers after periods of rainfall at any time of day.

Keep an eye out from July onwards for emerging toadlets!

Habitat restoration in Bexley ensures vulnerable toads don’t croak

by

Vulnerable amphibian species across south east London have been given a boost thanks to a habitat restoration project in Bexley. Two sites in Bexley have been restored to provide stable and sustainable habitats for toads and other amphibians, as part of The Froglife Trust’s ‘London Tails of Amphibian Discovery’ (T.O.A.D.) project.

Enovert Community Trust provided grants totalling £80,000 towards the project which has seen sites at Foots Cray Meadow and Lesnes Abbey Woods significantly enhanced. Wetland areas have been created at both sites to provide suitable habitats to support amphibian populations, while a large toad breeding pond at Lesnes Abbey Woods that had become overgrown has been restored.

The project has also greatly improved the visual appeal of the sites to encourage the local community to visit, watch and learn about toads and other aquatic wildlife. Much of the work has been delivered by youth volunteers, while a volunteer training programme will give visitors the opportunity to learn more about toads and how to protect their habitats.

Kathy Wormald, CEO of The Froglife Trust, said: “Toad numbers have declined by 68% over the past three decades, with London and the South East experiencing the highest rates of decline. The T.O.A.D. programme aims to create habitats were toads and other amphibians can flourish, and we are extremely pleased with the results at Foots Cray Meadows and Lesnes Abbey Woods.”

Angela Haymonds, Trust Secretary of Enovert Community Trust, said: “The Trustees were delighted to support this innovative project which will make an important contribution to protecting amphibians and hopefully support some local recovery in toad numbers in Bexley. As well as the ecological benefits, the Trust was also keen to support the project as the approach demonstrated a clear commitment to involve volunteers and provide an amenity for local people to enjoy.”

Croaking Science: The toad fly Lucilia bufonivora in common toads

by

Croaking Science: The toad fly Lucilia bufonivora in common toads

Blow-flies are dipteran flies that evolved 105 million years ago and there are now over 1,000 species occurring in 150 genera in a range of countries worldwide (Figure 1) (McDonagh, 2009). Within the family Calliphoridae there are 80 species which are known to cause myiasis, which is the infestation of live human and vertebrate animals, where the fly larvae feed on the host’s dead or living tissue, liquid body substances, or ingested food (Zumpt, 1967). There are three main types of blow-fly that cause myiasis. The first are known as saprophages and simply infect animal carcasses that are already dead and decaying. These species do not initiate myiasis but rather take advantage of animals that are already decaying. The second group of blow-flies are generally ectoparasites (i.e. parasites that attach to the skin or fur of an animal) that occasionally initiate myiasis by feeding on damaged tissue of their host. These flies sometimes feed on dead decaying matter, like the saprophages. The last group of blow-flies are known as obligate parasites, only feeding on the living tissue of their host and initiating myiasis as a result (Stevens & Wall, 1997). It has been proposed that the obligate myiasis-causing blow-fly parasites have evolved from an ancestral saprophageous stage, with flies occasionally being attracted to dead or decaying tissue or wounded animals. This later involved into flies which relied more on living tissue until obligate parasites evolved (Zumpt, 1967; McDonagh, 2009).

Figure 1. Blow-flies belonging to the genus Lucilia range from feeding on flower nectar to liquefied dead vertebrate tissues.

The blow-fly genus Lucilia comprises approximately 27 species, all of which are similar in appearance. The larvae of the majority of these species are saprophageous, feeding on dead matter. However, there are several species which are occasionally ectoparasites on large mammal species and which may cause myiasis, particularly in sheep (Stevens & Wall, 1997). One species, Lucilia silvarum, sometimes feeds on dead amphibian species, but the toad fly, Lucilia bufonivora, is a highly specialised blow-fly and is an obligate parasite of live prey.  Adult L. bufonivora make their first emergence in May to July and seek out living common toads (Bufo bufo) and their lays eggs on the back and flanks of an amphibian host. The larvae then hatch and migrate to the head and nasal cavities of the toad where they continue to feed on the live host (Figure 2). Infected toads tend to change their behaviour and instead of hiding away in sheltered areas, move out into exposed locations where they are susceptible to further infestation by blow-flies. The nasal cavities and head are gradually consumed until eventually the infected toad dies. Once the toad has died, the larvae continue to feed on the flesh of the toad before dropping off to pupate in the soil. Here they undergo metamorphosis and hatch into new adult flies a few weeks later. Toad flies are capable of having three generations each year, depending on the weather and availability of toads.

Figure 2. A common toad (Bufo bufo) infected with blow-fly larvae from Lucilia bufonivora. The larvae have migrated to the nostrils where they will continue to consume the living flesh.

Toad-flies have a wide distribution across Europe, North Africa and Asia and are particularly common in the Netherlands where between 15 and 70% of common toads may be affected each year, with adults being most commonly affected (Weddeling & Kordges, 2008). Despite this high level of infection, there is no evidence of toad flies causing decline in the common toad. In the UK, toad flies are relatively uncommon and the number of reports each year is low.

L. bufonivora and another blow-fly species L. silvarum are highly similar in appearance. In Europe, L. silvarum tends to only feed on carrion with a preference for dead toads. However, in North America, the species has been recorded as infecting living toads with larvae found in the neck, legs and parotid glands (Eaton et al., 2008). Research by the University of Bristol and Exeter, in collaboration with RAVON, has looked at how closely related L. bufonivora and L. silvarum are to each other. The two species are so similar in appearance it is possible that the eggs found on toads in Europe are from one or both species. Using genetic analysis, the researchers found that the two are sister species, being genetically distinct, but are very closely related and have only recently diverged as separate species. In addition, the researchers found that L. silvarum blow-flies in North America are more closely related to toad flies L. bufonivora, than they are to their own L. silvarum species in Europe. This suggests that obligate parasitism in Lucilia blow-flies may have evolved independently several times and originally diverged from L. silvarum (Arias-Robledo et al., 2008). The obligate parasite traits of L. bufonivora may have evolved as the two species diverged. The findings from this research also show that in Europe and the UK common toads are only infected by L. bufonivora and L. silvarum has yet to become an obligate parasite in these countries (Arias-Robledo et al., 2008). Further research is required to determine the evolutionary status of other closely related blow-fly species such as L. elongata, which is relatively poorly understood.

 

References

Arias-Robledo, G., Stark, T., Wall, R.L. & Steven, J. R. (2018) The toad fly Lucilia bufonivora: its evolutionary status and molecular identification. Medical and Veterinary Entomology, doi: 10.1111/mve.12328.

Eaton, B. R., Moenting, A. R., Paszkowski, C. A. & Shpeley, D. (2008) Myiasis by Lucilia silvarum (Calliphoridae) in Amphibian Species in Boreal Alberta, Canada. Journal of Parasitology, 94 (4): 949 – 952.

McDonagh, L. M. (2009) Assessing patterns of genetic and antigenic diversity in Calliphoridae (blowflies). PhD thesis, University of Exeter.

Stevens, J. & Wall, R. (1997) The evolution of ectoparasitism in the genus Lucilia (Diptera: Calliphoridae). International Journal of Parasitology, 27 (1): 51-59.

Wellling, K. & Kordges, T. (2008) Lucilia bufonivora-Befall (Myiasis) bei Amphibien in

Nordrhein-Westfalen – Verbreitung, Wirtsarten, Ökologie und Phänologie. Zeitschrift für Feldherpetologie, 15: 183–202.

Zumpt F. & Ledger J. (1967) A malign case of mylasts caused by Hemipyrellia fernandica (Macquart) (Diptera Calliphoridae) in a cape hedgehog (Erinaceus frontalis A. Smith). Acta Zoologica et Pathologica Antverpiensia, 43: 85-91.

 

Croaking Science: Kin Recognition

by

Kin recognition – when recognising relatives is important

During the spring in temperate countries tadpoles of frogs and toads often develop in a range of water bodies from small ponds to lakes. Swimming around in the open water, tadpoles are highly vulnerable to predation so in many species such as the common toad (Bufo bufo), tadpoles swim in large groups or shoals (Figure 1). By living in groups the tadpoles gain advantages such as decreased risks of predation and increased access to food. However, there are costs to group living such as an increase in the risk of transmitting infectious disease and intraspecific competition. Research has shown that tadpoles further increase the benefits of group living by associating with relatives, or close kin. If forming shoals reduces the risk of predation, then swimming with relatives who possess similar genes will increase the chances that these genes will survive to the next generation. The exact mechanism of kin recognition in anuran tadpoles is not clear but studies suggest that frog and toad tadpoles recognise each other through chemical cues (Eluvathingal et al., 2009). The persistent dense swimming shoals of tadpoles of many amphibians from the genera Rana and Bufo (e.g. wood frog (Rana sylvatica); common toad (Bufo bufo); and boreal toad (Bufo boreas)) have been shown to consist primarily of associations of closely related kin (Blaustein & Waldman, 1982). However, in the red-legged frog (Rana aurora), Schneider’s toad (Duttaphrynus scaber) and Günther’s golden-backed frog (Indosylvirana temporalis), tadpoles only exhibit kin recognition early in their development when they form dense shoals. As they mature, tadpoles disperse and kin recognition drops (Rajput et al., 2014). During late development the risks of pond desiccation are high and individual tadpoles seek isolated patches of water. Under these conditions the risks of suffocation through desiccating water is higher than the benefits of associating with relatives. Further to this, recent research has shown that the persistence of associating with kin varies considerably even within a single species. For example, larvae of the wood frog (Rana sylvatica) from North America exhibits kin recognition and individuals often choose to swim with relatives. However, Halverston et al. (2006) have shown that the level and occurrence of swimming with relatives is not consistent but depends on a range of factors including levels of competition, predation and parasitism. Tadpoles from two adjacent ponds exhibited different levels of association with kin due to localised differences in these factors (Halverston et al., 2006). This demonstrates that associating and swimming with relatives only occurs under certain environmental conditions and groups of tadpoles may show variations in their degree of kin association.

Figure 1. Several species of Bufo tadpole form shoals which may consist of close relatives.

Many amphibians within temperate zones are herbivorous, however there are a number of tropical species of tadpole which are carnivorous. This provides the opportunity for cannibalism to evolve where larger tadpoles may predate smaller ones within the same species. In these species it may be advantageous for tadpoles to recognise kin to avoid potential predation on relatives who carry the same genes. Research has shown that cannibalism generally occurs when the nutritional benefits gained from eating relatives outweigh the disadvantages such as risks of injury, transmitting infectious diseases and losing potential members of the same species who carry similar genes. As a result, cannibalism has evolved in some carnivorous amphibian larval species, but not others, depending on the environmental conditions and the relative advantages and disadvantages of consuming close kin.

Many tropical frogs in the genus Dendrobates lay their eggs in terrestrial habitats that are then transported by males to small water-filled water bodies formed in the axils of tree leaves (phytotelmata). Females of the poison dart frog Dendrobates auratus only lays a few eggs per year, so the number of tadpoles developing within any given water body is low. In some species of Dendrobates frogs, the female lays non-fertile eggs into the water to feed the tadpoles. However, female D. auratus does not perform this behaviour so the tadpoles rely completely on external food sources e.g. fallen insects, for survival.  Starvation within such small water bodies is very high and therefore cannibalism has evolved to allow some of the tadpoles to survive.  In this species the larger tadpoles predate the smaller ones which provides additional nutrition which is crucial for survival. However, male D. auratus may bring tadpoles from a number of clutches so there is also the potential for kin recognition i.e. larger tadpoles may choose to consume non-relatives over relatives since the latter may share the same genes. However, experiments carried out by Gray et al. (2009) suggest this is not the case and that larger tadpoles indiscriminately predate kin from non-kin. The authors hypothesise that since food sources are so scarce for developing tadpoles then the benefits of individual survival outweigh the costs of losing genetic relatives.

Additional research by Poelman & Dicke (2007) has shown that in the poison dart frog Ranitomeya ventrimaculata, females exhibit a plasticity in where she lays her eggs, which depends on environmental conditions (Figure 2). In this species, like D. auratus, tadpoles are highly cannibalistic, consuming both kin and non-kin. At the beginning of the breeding season, when water-filled phytotelmata do not contain many tadpoles, the female will spread her eggs widely amongst different water bodies, avoiding those which already contain a tadpole. This reduces the chances that her eggs will get consumed by another tadpole (which may or may not be her own). However, nearer to the end of the breeding season, the female changes behaviour and actively starts laying more eggs in phytotelmata which already contain large tadpoles. Poelman & Dicke (2009) hypothesise that this is because at the end of the breeding season there are few free phytotelmata left and by provisioning those that already contain tadpoles with fertilised eggs, she is providing food to the tadpoles which may be her own. This sacrifice of eggs will indirectly improve the survival of her existing tadpoles, the eggs of which she laid early in the breeding season. This plasticity in behavioural response allows a greater number of tadpoles to survive when the risk of desiccation of water bodies is high.

Figure 2. The poison dart frog Ranitomeya ventrimaculata exhibits different egg-laying strategies depending on the environmental conditions.

The green and golden bell frog (Litoria aurea) was once a common species widely distributed in south eastern Australia (Figure 3). It has also been introduced into New Zealand and surrounding islands. However, the extreme sensitivity of these species to the infectious chytrid fungus has been the major cause of the species’ decline in its native range and the species is currently restricted to small isolated populations. The tadpoles form groups where individuals gain protection from predators, increased foraging efficiency and better growth. Associating with relatives is advantageous since individuals would be indirectly protecting those carrying similar genes. Pizzatto et al. (2016) examined the behaviour of tadpoles of the green and golden bell frog in relation to kin recognition. The authors found that in the bell frog L. aurea tadpoles did indeed distinguish kin from non-kin and thus formed shoals containing mainly relatives. The authors suggest the advantages to this species include increased growth and increased resistance to disease since related members are likely to carry the same disease resistance genes.

Figure 3. Tadpoles of the green and golden bell frog (Litoria aurea) from Australia congregate in groups containing related individuals.

References

Blaustein, A.R. & Waldman, B. (1982) Kin recognition in anuran amphibians. Animal Behaviour, 44: 207 -221.

Eluvathingal, L.M., Shanbhag, B.A. & Saidapur, S.K. (2009) Association preference and mechanism of kin recognition in tadpoles of the toad Bufo melanostictus. Journal of Bioscience, 34 (3): 435–444.

Gray, H.M., Summers, K. & Ibáñez, R.D. (2009) Kin discrimination in cannibalistic tadpoles of the Green Poison Frog, Dendrobates auratus (Anura: Dendrobatidae). Phyllomedusa, 81 (1): 41-50.

Halverson, M.A., Skelly, D.K. & Caccone, A. (2006) Kin distribution of amphibian larvae in the wild. Molecular Ecology, 15: 1139–1145.

Poelman, E.H. & Dicke, M. (2007) Offering offspring as food to cannibals: oviposition strategies of Amazonian poison frogs (Dendrobates ventrimaculatus). Evolution and Ecology, 21: 215–227.

Pizzatto, L., Stockwell, M., Clulow, S., Clulow, J. & Mahony, M. (2016) How to form a group: effects of heterospecifics, kinship and familiarity in the grouping preference of green and golden bell frog tadpoles. Journal of Herpetology, 26: 157–164.

Rajput, A.P., Saidapur, S.K. & Shanbhag, B.A. (2014) Kin discrimination in tadpoles of Hylarana

temporalis (Anura: Ranidae) and Sphaerotheca breviceps (Anura: Dicroglossidae): influence of hydroperiod and social habits. Phyllomedusa, 13 (2): 119–131.

Goodbye Mr Toad? Scientists chart a worrying drop in numbers of our most lovable amphibian.

by

A new study led by Froglife, together with experts from Switzerland has shown how the efforts of ordinary members of the public are identifying big declines in our native amphibians.

©Jules Howard

Every year thousands of volunteers in the UK, working as part of Froglife’s ‘Toads on Roads’ patrols, help save amphibians as they migrate to their breeding ponds across busy roads. Toads are particularly vulnerable and over 800,000 are carried to safety by volunteers each year in the UK and Switzerland.

Froglife’s conservation scientists teamed up with Swiss counterparts to analyse millions of records of common toads (scientific name Bufo bufo) collected by these patrols over more than three decades from the two countries. Unfortunately, despite the effort of the volunteers, the researchers show that our toads have undergone huge declines.

On average common toads have declined by 68% over the last 30 years in the UK. In some areas, such as the south east of England, declines have been even more pronounced.

The team’s results, published in the open-access journal PLOS ONE (http://dx.plos.org/10.1371/journal.pone.0161943), show that toads have declined rapidly and continuously since the 1980s in both countries. It is likely that hundreds of thousands of toads have disappeared from the countryside in the past 30 years.

In the UK, south east England suffered the worst declines while in the west (including Wales, south west and west England) populations also declined but have remained stable for the past decade. The North, including northern counties and Scotland, has also seen significant toad declines in the past 20 years.

It is not clear what has caused numbers of toads to drop so dramatically but likely causes are a combination of changes to farming practices, loss of ponds, an increase in urbanisation and more deaths on roads as traffic values have increased. Climate change could also be a factor as research has shown that milder winters are detrimental for hibernating toads.

Dr. Silviu Petrovan, Conservation Coordinator at Froglife and one of the authors of the study said:

“Toad declines at this scale over such large areas are really worrying. Toads are extremely adaptable and can live in many places ranging from farmland and woodland to suburban gardens. They are also important pest controllers eating slugs, snails and insects and are food themselves for many of our most likeable mammals such as otters and polecats. Without the efforts of the thousands of volunteers that go out and move amphibians across busy roads we would have no idea that these declines had occurred and the situation could be much worse. One thing that is clear is that we need to do more to look after our environment in order to protect the species that depend on it.”

Paul Edgar, The Senior Amphibian and Reptile Specialist from Natural England, the government’s adviser for the natural environment in England and who have funded Froglife on road mitigation research, said:

“This paper highlights a number of important issues for our native amphibians and conservation more generally in the UK. The common toad is sadly on a downward trend. This is partly because of habitat fragmentation, and so understanding and mitigating the impacts of this issue is vital. We need to continue to build good quality habitat links across the wider landscape if we are to offer opportunities for this species to recover. We’re working hard to do this through measures such as Countryside Stewardship in the rural setting, and ensuring good quality Green Infrastructure is included in new developments. This paper reinforces the vital positive role that the public play in both protecting and recording data about our wildlife. We need to build on this engagement to further help us collaboratively reverse these declines as a matter of urgency.”