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You are here: Home / Archives for common toad

common toad

Croaking Science: Amphibians in the ‘Anthropause’

October 27, 2020 by Xavier Mahele

On damp nights in the spring in temperate regions, amphibians emerge from their winter hideouts to migrate to their breeding pools. Nothing will stop their drive to reach water to spawn and so they brave a barrage of cars and artificial barriers along their route which often results in them getting squashed.

Amphibians have complex, biphasic life histories which makes their conservation challenging. Most species require high quality aquatic and terrestrial habitats which must both be connected by a transition habitat during migrations (Baldwin et al. 2006). 

As urbanisation expands around the world, many aspects of wildlife physiology, movement patterns, population genetics and overall health are affected due to anthropogenic stressors such as habitat loss and artificial light pollution. The unprecedented expansion in transport infrastructure in the past century has had massive impacts on amphibian populations around the world (Beebee 2013, Glista et al. 2008). Roads fragment habitats and cause high mortality as well as being a significant source of chemical contaminants (Petrovan and Schmidt 2016, White et al. 2017, Bird et al. 2019). 

Roads which bisect migratory routes severely restrict the dispersal of amphibians between their breeding areas and terrestrial habitat. This can have catastrophic impacts on gene flow and metapopulation dynamics potentially leading to population declines, genetic isolation and even extinction (Fahrig and Rytwinski 2009, Marsh and Trenham 2001). Therefore, mitigating road-kill and habitat fragmentation is a conservation priority (Puky 2005, Beebee 2013, Cushman 2005). Genetic bottlenecks as a result of fragmentation reduce the viability of populations and can leave amphibians more vulnerable to other synergistic environmental stressors such as climate change, pollution and emerging wildlife diseases (Cushman 2005, Laurence and Useche 2009). Urban fragmentation is known to decrease species diversity and abundance and coupled with wider habitat degradation such as edge effects and loss of breeding habitats, can make cities particularly challenging for amphibians (Bickford et al. 2011, Scheffers and Paszkowski 2012). At some field sites, mass mortality on roads can cause complete extirpation of anurans and salamanders within years (Cooke 2011, Hels and Buchwald 2000). With more and more cars on the roads, it is increasingly difficult for amphibians to avoid them. 

Common toads

Temperate amphibians such as the common toad have experienced significant and continuous declines. In the UK it is estimated that 20 tonnes of common toads (Bufo bufo) are killed annually as they migrate across roads to reach their breeding ponds, with up to 13,000 annual mortalities being recorded even at manned amphibian crossings. This has contributed to a 68% decline in their population size in the past 50 years at a rate of 2.26% per year. The severity of the population reduction means that these toads are no longer ‘common’ toads and could soon qualify as vulnerable on the IUCN Red List (Petrovan and Schmidt 2016).

The COVID-19 pandemic has caused immense human tragedy as it has spread around the world straining healthcare services and paralysing economic systems. Quarantine restrictions imposed by governments in order to slow the spread of the virus, have caused extraordinary disruption to our globalised society but have created rare opportunities for some wildlife species (Zellmer et al. 2020). As bustling metropolises slowed down they were occupied by usually elusive fauna; wild boars were seen roaming Barcelona’s quiet neighbourhoods, flamingos flocked to New Delhi’s lakes, river otters and puma stalked silent streets in Chile and sea turtles thrived on empty Brazilian beaches. A recent paper by Rutz et al. (2020) coined the term ‘anthropause’ for this rapid and unprecedented “global slowing down of modern human activities, notably travel.” It has resulted in profound short term environmental benefits such as improved air and water quality as well as reduced wildlife disturbance. 

Research conducted during the Anthropause has highlighted both known and less known impacts that we are having on the natural world and is providing a unique opportunity to study wildlife populations during a time of reduced human presence all around the world (Forti et al. 2020, Zellmer et al. 2020, Bates et al. 2020). Monitoring the ways wildlife has responded to covid lockdowns in urban areas allows researchers to quantify the impacts human mobility is having on wildlife in the Anthropocene (the term given to our geological age, dominated by human activities) and potentially find strategies to mitigate biodiversity loss (Rutz et al. 2020, Stokstad 2020). This research provides invaluable insight into the mechanisms of human-wildlife interactions that will inform conservation for decades to come. 

Lockdowns in spring and summer of 2020 meant fewer vehicles on the road which has significantly decreased road mortality for many species including amphibians. A “roadkill reprieve” this year may have made amphibian migratory journeys much safer according to Goldfarb (2020).  A study by Grilo et al. (2020) calculated that 194 million birds and 29 million mammals are killed on European roads each year under normal circumstances while in Brazil, road mortality has superseded hunting to become the “leading cause of direct human caused mortality in terrestrial vertebrates” (Carvalho et al. 2014). This year they may not suffer the same fate. Simply driving less could have been “the biggest conservation action” taken by humanity over the past 50 years according to Fraser Shilling of the Road Ecology Centre at UC Davis and could have potentially saved the lives of 500 million vertebrates (Nguyen et al. 2020). 

In March and April as traffic flows dipped by 73% across the US, many creatures received temporary respite from road collisions, with Californian mountain lion fatalities down 58% and a 48% decrease in roadkill deaths in Maine. Although much of the data focuses on large mammals, the same is true for smaller, less mobile animals such as amphibians, snakes and turtles (Katz 2020). 

At amphibian crossings this spring in Maine, wood frogs, salamanders and newts were twice as likely to survive than in previous years, which is great news for these sensitive creatures that are very vulnerable to habitat fragmentation.  Four amphibians successfully crossed the road for every one squashed this year, half as many as in previous years (Goldfarb 2020, Keim 2020).

Wood frog (Photo Credit: Brian Gratwicke)

A study by Manenti et al. (2020) examined the effects of the COVID-19 lockdown and reduced human disturbance on wildlife in Italy and describes both positive and negative effects on biodiversity conservation. As well as allowing wildlife to explore new habitats and extend their activity periods, species richness and reproductive success increased while roadkill diminished in temporarily quieter areas. Some negative ecological effects included reduced enforcement of regulations, and postponed conservation action such as invasive species management. 

A decrease in road traffic led to significantly improved survival of migrating amphibians on Italian roads this spring at eight toad crossings. Data suggests that there was an 80-90% decrease in nocturnal road traffic at these study sites during the anthropause. Four hundred and eight common toads (Bufo bufo) and 16 agile frogs (Rana dalmatina) were recorded as roadkill in 2019, and this dropped to only 38 toads and zero agile frog mortalities in 2020. The median mortality of road killed amphibians at each site decreased from 53 individuals to only one in 2020 (with some sites recording no mortalities) indicating that an increased number of adults made it to their breeding pools this spring giving populations a much needed boost. Manenti et al. (2020) also surveyed transects in Liguria, Northern Italy to quantify the effects of reduced traffic on common wall lizards (Podarcis muralis) and Western green lizards (Lacerta bilineata) and found a similar 10-fold decrease in road mortality. 

Many of the conservation benefits the Anthropause created are ephemeral, as traffic returned to baseline levels once economic activity restarted. Although breeding booms this spring may bring some respite to struggling populations, alone, they will not be able to counteract the extreme loss of genetic diversity as a result of population bottlenecks in the past. 

The information collected over the Anthropause highlights the need to improve the landscape to make it safer for all wildlife and particularly amphibians (Merrow 2007). If we can alter our transport networks to counter the effects of large-scale urban development and increased transport infrastructure we could go some way to mitigating the catastrophic impact of habitat fragmentation. The observed benefits that limiting road traffic can provide for migrating amphibians could inform more decisions about temporary, focused road closures around the world in the future to replicate this effect and to better conserve endangered amphibian and reptile species (Manteni et al. 2020).

Building fauna tunnels and bridges across dangerous roads to link habitat fragments allows animals to cross safely (Dodd et al. 2004, Gonzalez-Gallina 2018, Vartan 2017). Road mortality decreases by up to 85%-95% with animals responding surprisingly quickly to the change as ecosystems are reconnected (Vartan 2019). Wildlife tunnel projects can mitigate the effects of fragmentation and have been shown to allow amphibians to move successfully between sites bisected by roads. Tunnels and drift fences reduce road mortality, promote habitat connectivity, and allow amphibians to colonise new ponds leading to population increases and expansion into reconnected habitat (Jarvis et al. 2019). These movement corridors also allow roads to be permeable to a host of other wildlife species like reptiles and small mammals (Purky 2005, Jarvis et al. 2019). 

The incredible work done by volunteers at amphibian crossings who help migrating amphibians make it across roads (Petrovan and Schmidt 2016) could also contribute to sustaining population increases this spring from quieter road traffic. 

COVID-19 has also highlighted how explicitly intertwined human and wildlife health are and the catastrophic impacts of the overexploitation of nature. Emerging wildlife diseases such as chytrid fungi and ranaviruses threaten amphibians around the world and their spread has been catalysed by anthropogenic trade in our globalised world (O’Hanlon et al. 2019). A slowdown in global trade and human flows as a result of COVID-19 could also have gone a way to mitigating the spread of the pathogens that imperil amphibians (Forti et al. 2020). Although this benefit may only be short-lived as economies restart, there is hope that better regulation of the wildlife trade, in order to decrease the chances that future novel zoonotic diseases spill over from wildlife reservoirs in the future, could benefit amphibians too. Since the wildlife trade is responsible for the translocation of many amphibian pathogens (Kolby et al. 2014, O’Hanlon et al. 2018) better regulation and enforcement of the trade in live animals could help stem the spread of emerging amphibian diseases and invasive species (Forti et al. 2020). 

The Anthropause provides us with an excellent opportunity to reimagine our relationship with nature and our socio-economic systems so that biodiversity can flourish and acts as a reminder that biodiversity is essential for maintaining human health and wellbeing too.

The disruption to the economic status quo that the pandemic has created gives us a pivotal opportunity to consider a greener, more sustainable future where people and wildlife can thrive. In order to effectively stem biodiversity loss in the Anthropocene, we must use this pivotal moment to plan a green recovery which incorporates wildlife conservation into all economic rebound projects. In the UK this means not viewing the protection of  great crested newts as a delay to construction (Howard 2020) but valuing them as integral parts of a plan to balance our economic and environmental ambitions. It is also a perfect opportunity to invest in road mitigation measures such as wildlife tunnels and fauna bridges to reduce the detrimental impact they can have on wildlife populations (Merrow 2007), with the added benefit of being excellent economic multipliers.

November 2020 Croaking Science article by Xavier Mahele 

Bibliography

Baldwin RF, Calhoun AJK and Maynadier PG (2006) Conservation planning for amphibian species with complex habitat requirements: A case study using movements and habitat selection of the wood frog Rana sylvatica Journal of Herpetology 40 (4).

Bates AE, Primack RB, Moraga P and Duarte CM (2020). COVID-19 pandemic and associated lockdown as a “Global Human Confinement Experiment” to investigate biodiversity conservation Biological Conservation 248, 108665.

Beebee TJC (2013). Effects of road mortality and mitigation measures on amphibian populations. Conservation Biology 27(4).

Bickford D, Ng TH, Qie L, Kudavidanage EP and Bradshaw CJA (2010). Forest fragment and breeding habitat characteristics explain frog diversity and abundance in Singapore. Biotropica 42, 119-125.

Bird RJ, Paterson E, Downie JR and Mable BK (2018). Linking water quality with amphibian breeding and development: A case study comparing natural ponds and Sustainable Drainage Systems (SuDS) in East Kilbride, Scotland.The Glasgow Naturalist 27.

Carvalho NC de, Bordignon MO and Shapiro JT (2014). Fast and furious: a look at the death of animals on the highway MS-080, Southwestern Brazil Iheringia. Série Zoologia 104 (1).

Cooke A (2011). The role of road traffic in the near extinction of Common Toads (Bufo bufo) in Ramsey and Bury. Nature in Cambridgeshire 53, 45-50.

Cushman SA (2006). Effects of habitat loss and fragmentation on amphibians: A review and prospectus. Biological Conservation 128, 231-240.

Dodd C, Barichivich WJ and Smith LL (2004). Effectiveness of a barrier wall and culverts in reducing wildlife mortality on a heavily travelled highway in Florida. Biological Conservation 118, 619-631.

Fahrig L and Rytwinski T (2009). Effects of roads on animal abundance: an empirical review and synthesis. Ecology and Society 14(1): 21.

Forti LR, Japyassú HF, Bosch J and Szabo JK (2020). Ecological inheritance for a post COVID-19 world. Biodiversity and Conservation 29, 3491-3494.

Goldfarb B (2020). Lockdowns Could Be the ‘Biggest Conservation Action’ in a Century. The Atlantic.

González-Gallina A, Hidalgo-Mihart MG and Castelazo-Calva V (2018). Conservation implications for jaguars and other neotropical mammals using highway underpasses. PLOS ONE 13(11).

Hels T and Buchwald E (2001). The effect of road kills on amphibian populations. Biological Conservation 99, 331-340.

Howard J (2020). Boris ‘the Builder’ Johnson has found a new scapegoat: the humble newt. The Guardian 2/7/20.

Jarvis LE, Hartup M and Petrovan SO (2019). Road mitigation using tunnels and fences promotes site connectivity and population expansion for a protected amphibian. European Journal of Wildlife Research 65, 27.

Katz C (2020). Roadkill rates fall dramatically as lockdown keeps drivers at home. National Geographic 26/6/20.

Keim B (2020). With the World on Pause, Salamanders Own the Road: Traffic is down thanks to the pandemic. That’s good news for amphibians looking to migrate safely The New York Times

Kolby JE, Smith KM, Berger L, Karesh WB, Preston A, et al. (2014). First Evidence of Amphibian Chytrid Fungus (Batrachochytrium dendrobatidis) and Ranavirus in Hong Kong Amphibian Trade. PLOS ONE 9(3).

Laurence WF and Useche DC (2009). Environmental Synergisms and Extinctions of Tropical Species. Conservation Biology 23,1427-1437.

Manenti R, Mori E, Canio VD, Mercurio S, Picone M, Caffi M, Brambilla M, Ficetola GF, Rubolini D (2020). The good, the bad and the ugly of COVID-19 lockdown effects on wildlife conservation: Insights from the first European locked down country. Biological Conservation 249, 108728.

Marsh DM and Trenham PC (2001). Metapopulation dynamics and amphibian conservation. Conservation Biology 15(1), 40-49.

Merrow J (2007). Effectiveness of amphibian mitigation measures along a new highway. UC Davis: Road Ecology Centre.

O’Hanlon SJ, Rieux A, Farrer RA, Rosa GM, Waldman B, Bataille A, Kosch TA, Murray KA, Brankovics B, Fumagalli M, Martin MD, Wales N, Alvarado-Rybak M, Bates KA, Berger L, Böll S, Brookes L, Clare F, Courtois EA, Cunningham AA, Doherty-Bone TM, Ghosh P, Gower DJ, Hintz WE, Höglund J, Jenkinson TS, Lin C-F, Laurila A, Loyau A, Martel A, Meurling S, Miaud C, Minting P, Pasmans F, Schmeller DS, Schmidt BR, Shelton JMG, Skerratt LF, Smith F, Soto-Azat C, Spagnoletti M, Tessa G, Toledo LF, Valenzuela-Sánchez A, Verster R, Vörös J, Webb RJ, Wierzbicki C, Wombwell E, Zamudio KR, Aanensen DM, James TY, Gilbert MTP, Weldon C, Bosch J, Balloux F, Garner TWJ, Fisher MC (2018). Recent Asian origin of chytrid fungi causing global amphibian declines. Science 360, 621-627.

Nguyen T, Saleh M, Kyaw M, Trujillo G, Bejarano M, Tapia K, Waetjen D Shilling F (2020). Road Special Report 4: Impact of COVID-19 Mitigation on Wildlife-Vehicle Conflict. Ecology Centre UC Davis. 

Puky M (2005). Amphibian road kills: a global perspective. UC Davis: Road Ecology Centre UC Davis.

Rutz C, Loretto M, Bates AE et al. (2020). COVID-19 lockdown allows researchers to quantify the effects of human activity on wildlife. Nature Ecology and Evolution 4, 1156-1159.

Scheffers BR and Paszkowski CA (2012). The effects of urbanization on North American amphibian species: Identifying new directions for urban conservation. Urban Ecosystems 15(1).  

Stokstad E (2020). Pandemic lockdown stirs up ecological research. Science 369, 893.

Vartan S (2019). How wildlife bridges over highways make animals—and people—safer. National Geographic 18/4/20.

White KL, Mayes WM and Petrovan SO (2017). Identifying pathways of exposure to highway pollutants in great crested newt (Triturus cristatus) road mitigation tunnels. Water and Environment Journal 31, 310-316.  

Zellmer AJ, Wood EM, Surasinghe T, Putman BJ, Pauly GB, Magle SB, Lewis Js, Kay CAM, Fidino M (2020). What can we learn from wildlife sightings during the COVID-19 global shutdown? Ecosphere. 6:11(8), e03215.

Filed Under: Croaking Science Tagged With: anthropause, common toad, Croaking Science, Croaks, lockdown, urbanisation

What our animals are doing this month… July 2020

June 29, 2020 by admin

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!

Filed Under: What our animals are doing this month Tagged With: 2020, common toad, Croaks, july, toadlets, what our animals are doing this month

Habitat restoration in Bexley ensures vulnerable toads don’t croak

September 16, 2019 by admin

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.”

Filed Under: Uncategorized Tagged With: Amphibians, common toad, Conservation, Enovert, London T.O.A.D project

Croaking Science: The toad fly Lucilia bufonivora in common toads

August 29, 2018 by admin

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.

 

Filed Under: Uncategorized Tagged With: common toad, Croaking Science, ectoparasites, saprophages, toad fly, toads

Croaking Science: Kin Recognition

May 31, 2018 by admin

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.

Filed Under: Uncategorized Tagged With: common toad, Croaking Science, Croaks, frogs, kin recognition, tropical frogs

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

October 6, 2016 by admin

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.”

Filed Under: Uncategorized Tagged With: amphibian conservation, common toad, Froglife, PLOSONE, toad. toad decline, Toads on Roads

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