Froglife

Leaping forward for reptiles and amphibians

You are here: Home / Archives for Croaking Science

Croaking Science

Research finds the Canadian western toad shows evidence of genetic separation.

by

Written by Andy Smart, Head of Science & Research

Research finds the Canadian western toad shows evidence of genetic separation – a reminder of the need to think about the conservation of every component of biodiversity.

A recent paper published this summer by scientists at the University of Ottawa[i] has found that the western toad, Anaxyrus boreas,  a species widespread across north America, shows distinct genetic and behavioural separation linked to the presence of the Canadian Rocky Mountains. Their study into the habitat preferences and genetics of two groups of toads identified that the toads on the west of the Rocky Mountains, which have a vocal sac and make advertisement calls, are a genetic group, distinct from those animals on the east and to the south of the Canadian Rocky Mountains (which have no vocal sac and are non-calling).  Their study also produced evidence of a third distinct group to the south and possibly other distinct groups to the north which may make different advertisement calls.  This paper highlights the need to consider the genetic variation within populations of even the most widespread species when we think about their conservation. Different genetic populations may have adaptations to particular climatic or habitat conditions  and so its is important to ensure we are protecting as much genetic variation as we can. People often forget that the conservation of biodiversity isn’t just about species but that biodiversity comprises three components: genetic diversity (the variation within species), species diversity (the number and abundance of species), and ecosystem diversity (habitats and ecological processes).

Western toad (Anaxyrus boreas) By Walter Siegmund (talk) – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=9903967

The study of variation within a species can often lead to remarkable outcomes where single species are actually found to be several ‘cryptic’ species. This has been helped considerably by the development of genetic research but morphological differences and behavioural differences are important in establishing different species.  Last year, work by various natural history museums and research institutes, led by the University of Copenhagen[ii], investigated specimens of a species of Nectophrynoides, bufonid toads that are arboreal and viviparous (live bearing). Nectophrynoides viviparus was believed to be found across the  Tanzanian Eastern Arc Mountains, a region known to be of high biodiversity.  The research group investigated hundreds of museum specimens and looked at the variation in their morphology and how that related to their origin within the mountain range. Further genetic studies and audio analysis of recordings of calls from different locations found that what was believed to be one species was in fact four, distributed across different mountain peaks with the Eastern Arc mountains. The species involved, Nectophrynoides viviparus was previously identified as being of ‘least concern’ status by the IUCN but now that four species have been recognised, two are ‘critically endangered, one endangered and one vulnerable.[iii]

This speciation of Nectophrynoides and the genetic separation of Anaxyrus are examples of allopatric speciation, an evolutionary process that leads to a species becoming two or more distinct species following geographic isolation that prevents the movement of genetic material between populations. This isolation may be because of separation by, for example, mountain ranges or rivers, or it may be because of the separation of a new colonising group often isolated on ‘islands’ (and ‘islands’ in this case may be islands of habitat rather than islands in a lake or sea).

There are lots of new species of amphibians being found as more habitats are surveyed and explored but it is rare to find a new genus. In 2023, a completely new genus of toad was found from a single specimen collected in a pitfall trap on the slopes of Mouth Kenya[iv]. This small toad appears to be terrestrial but nothing is known of its habitat or behaviour other than this single specimen. Another new species identified last year was a new ‘orange toad’, found in the Atlantic rainforest of Brazil[v], this spectacularly coloured but tiny species (14mm adult) of what is actually a frog not a toad, Bracycephalus lulai, is one of 42 species within this diurnal leaf litter inhabiting genus, 35 of which have been discovered since 2000.

Brachycephalus lulai. By Luiz F. Ribeiro in M. Bornschein et al. – “A new species of Brachycephalus (Anura: Brachycephalidae) from Serra do Quiriri, northeastern Santa Catarina state, southern Brazil, with a review of the diagnosis among species of the B. pernix group and proposed conservation measures”, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=179761023

Microhylids are another group of tiny frogs that live on the floor of rainforests across Asia and  new species are regularly identified as more forests are being surveyed. A recent paper from work in Papua New Guinea[vi]  identified six new species of the genus Xenorhina, separated by different advertisement calls and by morphological differences. This type of speciation may be sympatric; evolution of species within the same area through ecological, behavioural or genetic differences.  A population may be able to exploit different resources or microhabitats within the same  area, or may behave differently, spawning at different times or using different advertising calls. Small terrestrial frogs and toads are widespread in tropical habitats and generally not well studied because of the difficulty in surveying them and exploring their natural behaviour. I spent many nights looking at the variation in dorsal patterns of two species of Microhyla in Sabah in Borneo, Microhyla bornieensis and Microhyla perparva, and wondering how many different  species they might be[vii]. These enigmatic little frogs are the size of a fingernail when adult and live in amongst the leaves on the rainforest floor, only appearing on vegetation at heights of about 20- 40cm early in the night after rainfall.

Larger amphibian species are also being discovered, two years ago a paper was published by a group of Russian and Vietnamese scientists[viii] who had found a new population of Bufonid toads within the Bufo gargarizans species complex (a group of species that are so similar its difficult to confirm them as separate  species). These animals, which have the catchy scientific name of Bufo rubroventromaculatus, are toads with a snout-vent length of around 120mm, similar in size to the common toad, Bufo bufo, and are characterised by red blotches on their belly. Having been identified as a new species in Viet-Nam, animals collected previously in China have since been re-examined and confirmed to be the same species[ix].

Just to highlight that this expansion of amphibian species isn’t limited to Anura, in September last year a new species of mountain salamander was reported found in south-east China, during a survey of a national park[x]. There are a number of different species of Pachytriton and it appears that the isolation of different mountain ranges and mountain stream habitat has led to geographic isolation and speciation and also speciation with altitude, with different species inhabiting streams found at different altitude bands. This particular species Pachytriton cheni is found between 850m and 1350m. Also in China, in Hunan province, a species of newt, Tylotriton gaowangjienensis (another great name), was found living in the Gaowangjie National Nature Reserve[xi], breeding in ponds within coniferous and mixed forest on the mountain slopes.

Lest we get carried away and start to think that all these new species are a positive indication that things are getting better for amphibians, a paper published in 2025[xii] confirmed that while 35 species improved their conservation status between 1980 and 2004 and 86 species between 2004 and 2022, during the same time periods 482 and 306 species declined in conservation status and that overall 41% of amphibians species remain ‘globally threatened’. A recent study investigating the nature of published work on amphibians over the last four decades[xiii] found a shift from research identifying ‘declines’ to research identifying the ‘reasons behind declines’ and mitigation practice, but that there remains a lack of published work on conservation and management ‘reflecting a broader gap between research and practical implementation’. The authors highlighted ‘baseline data on species’ ecology, distributions, and abundance is crucial’ in establishing declines and that ‘researchers must remain open to unexpected drivers of species decline’. The impacts of climate change, disease, invasive species and habitat loss and fragmentation must not be underestimated and we should remember that even ‘common’ species such as the UK’s common toad (Bufo bufo) can suffer significant declines[xiv].

 

Click here for references

[i] Bergman, J.C., Enciso‐Romero, J., Pauly, G.B., Gamlen‐Greene, R., Todd, M. and Lee‐Yaw, J.A., 2026. Pronounced genetic structure associated with differences in a reproductive trait and climatic barriers in Canadian populations of the western toad (Anaxyrus boreas). Diversity and Distributions, 32(5), p.e70219.

[ii] Thrane, C., Lyakurwa, J.V., Liedtke, H.C., Menegon, M., Petzold, A., Loader, S.P. and Scherz, M.D., 2025. Museomics and integrative taxonomy reveal three new species of glandular viviparous tree toads (Nectophrynoides) in Tanzania’s Eastern Arc Mountains (Anura: Bufonidae). Vertebrate Zoology 75: 459-485 [online]

[iii] IUCN Red List of Threatened Species

[iv] Liedtke, H.C., Malonza, P.K., Wasonga, D.V., Müller, H. and Loader, S.P., 2024. A new genus and species of toad from Mount Kenya illuminates East African montane biogeography. Zoological Journal of the Linnean Society, 202(1), p.zlad160.

[v] Bornschein, M.R., Pie, M.R., Nadaline, J., Confetti, A.E., Blackburn, D.C., Stanley, E.L., Mari, R.D.B., Alves, G.S., Sandretti-Silva, G., Lima, F.F.D.A. and Ribeiro, L.F., 2025. A new species of Brachycephalus (Anura: Brachycephalidae) from Serra do Quiriri, northeastern Santa Catarina state, southern Brazil, with a review of the diagnosis among species of the B. pernix group and proposed conservation measures. Plos one, 20(12), p.e0334746.

[vi] Günther, R. and Richards, S., 2021. Description of six new species of Xenorhina Peters, 1863 from southern Papua New Guinea (Amphibia, Anura, Microhylidae). Zoosystematics and Evolution, 97(2), pp.355-382.

[vii] Zainudin, R. and Alaudin, N.A., 2018. Phylogenetic Relationships of the Sarawak Microhyla (AMPHIBIAN: ANURA: MICROHYLIDAE). Malaysian Applied Biology, 47(1).

[viii] Orlov, N.L., Ananjeva, N.B., Ermakov, O.A., Lukonina, S.A., Ninh, H.T. and Nguyen, T.T., 2024. A new record of Bufo gargarizans complex (Bufonidae, Anura) from Truong Son Mounts, Ha Tinh and Ha Giang Provinces, Vietnam based on molecular evidence with a description of a new species. Diversity, 16(7), p.361

[ix] Liu, S., Hou, M., Mo, M. and Rao, D., 2024. First confirmed record of Bufo rubroventromaculatus Orlov, Ananjeva, Ermakov, Lukonina, Ninh & Nguyen, 2024 (Anura, Bufonidae) from China, with supplementary description of this species. Biodiversity Data Journal, 12, p.e134392.

[x] He, Z., Wu, S., Wang, S., Ma, L., Zhao, N., Wu, X. and Wang, S., 2025. A New Species of Pachytriton (Amphibia: Caudata: Salamandridae) from Anhui, China. Animals, 15(20), p.3018.

[xi] Huang, J., Xiang, Y., Wu, T., Zhang, Y.X., Zhang, Z.L., Wang, B.Z., Lan, X.Y., Huang, Y.P., Jiang, H.J. and Jiang, W.S., 2024. Description of a new species of the Asian newt genus Tylototriton (Amphibia, Urodela, Salamandridae) from Hunan Province, China. Herpetozoa, 37, pp.327-338.

[xii] Borzée, A., Prasad, V.K., Neam, K., Tarrant, J., Kosch, T.A., Barata, I.M., Rais, M., Bickford, D., da Fonte, L.F.M., Wilcken, J. and Ghosh, D., 2025. Conservation priorities for global amphibian biodiversity. Nature Reviews Biodiversity, pp.1-18.

[xiii] Crawford‐Ash, J., Evans, M.J., Carvalho, T., Rowley, J.J., Garner, T.W., Muths, E. and Scheele, B.C., 2026. Evolution of research on global amphibian declines. Conservation Biology, 40(1), p.e70146.

[xiv] Petrovan, S.O., Moor, H. and Schmidt, B.R., 2025. Increasingly uncommon common toads: multidecadal, ongoing abundance decline of a widespread amphibian despite volunteer conservation action. Biodiversity and Conservation, 34(12), pp.4235-4249.

[/faq-toggle

 

 

Long-term pond condition research underway

by

By Emily Seccombe, PhD student at the University of Reading, in partnership with Froglife

Evidence-based pond conservation

Within conservation practice, there is an increasing movement towards ensuring decision-making is evidence-based, to make best use of limited resources (Christie et al., 2021; Habel et al., 2013). Froglife is one of Conservation Evidence’s ‘Evidence Champions’, meaning that it is committed to using scientific evidence in its work, to test and publish research on conservation interventions used, and to generate evidence-based guidance.

Ponds are considered a “straight-forward” intervention for amphibian conservation (Moor et al., 2024) but how well do we understand how ponds created for amphibian conservation provide benefits in the long-term? For how long will created ponds provide amphibian breeding habitat, in different scenarios? What proportion of ponds are likely to fail to hold water or be filled in?

Historically, ponds have had less research effort than other freshwater ecosystems (Biggs et al., 2005), though this has been improving. A number of studies in the academic and grey literature provide assessment of pond creation for amphibian conservation, which can provide some insights for conservation interventions…

What do we know about how created ponds benefit amphibians?

Evidence shows that new ponds can support amphibian populations in the first few years after their creation. For example, Barry et al. (2008), monitored 22 constructed ponds in the USA, finding amphibians breeding in 11 ponds after one year and 14 ponds after two years. A study in Estonia by Rannap et al. (2009) looked at 208 created ponds and 22 restored ponds within 3 years of the works, and found the number of amphibian species was higher in these ponds than in local comparison ponds. Ruhí et al. (2012) found that over half of the local amphibian species used two newly created Mediterranean temporary ponds for breeding within the first hydroperiod (3 of 5 species and 6 of 11 species, at the two ponds respectively), which further increased by the second hydroperiod (to 4 of 5 species and 8 of 11 species).  

Image 1. Pond creation in progress, during Froglife’s Sheffield Living Waters project, at Woodhouse Washlands, now managed by Sheffield and Rotherham Wildlife Trust, (photo credit: Froglife). New ponds can provide habitat for amphibians within the first few years of creation.

Beyond the amphibian conservation focus, ponds have received increasing research attention in recent decades regarding their roles in providing ecosystem services (Cuenca-Cambronero et al., 2023; Hill et al., 2018). Ponds that may not support large amphibian populations may still be contributing to ecosystem health (Hill et al., 2018), climate resilience (Bartrons et al., 2024) and human well-being and health (Arnberger et al., 2017; Benejam et al., 2026).

But what do we know about how and where to create these ponds to provide the most benefit to amphibians? Much of the evidence (e.g. Baker & Halliday, 1999; Hazell et al., 2004) used to inform pond creation decisions is based on research on other pond types (such as historic natural ponds, agricultural ponds or sustainable urban drainage ponds) rather than from ponds created as part of conservation efforts. Such research shows us that the presence of fish is in conflict with amphibian breeding success (as demonstrated by numerous studies including Denoël & Ficetola, 2008, Hamer & Parris, 2011 and Skei et al., 2006) and that proximity to other ponds are a key predictor of a new pond hosting amphibians (Baker & Halliday, 1999). However, this inference from ponds created for different purposes may not always be helpful for conservation: they may be created in different places, under different management plans, and with different surrounding habitat than purpose-built conservation ponds.
Image 2: Male palmate newt in pond shallows (left) and an emergent froglet (right). Predictors of amphibian presence in new ponds include absence of fish and proximity to other ponds. Both photos taken at ponds created through Froglife’s Sheffield Living Waters project, copyright Emily Seccombe.

 

Short-term vs long-term pond research

The examples of studies on the amphibian benefits of pond creation given earlier share a short temporal scale: monitoring amphibians in ponds over 2 years since creation, 3 years since creation and 2 years since creation respectively (Barry et al., 2008; Rannap et al., 2009; Ruhí et al., 2012). The short-term bias of much of the literature may obscure the larger picture. Ponds which are quickly colonised by amphibians may not support long-term breeding success, or they may suffer from issues, such as pollution or invasive plant species, in later years. One of the few published studies that did undertake long-term monitoring of ponds in the UK found that new ponds had limited success: ponds had a high turnover, and were often lost or in poor condition by end of the monitoring period (Beebee, 1997). For how long do created ponds continue to benefit amphibians, and under what conditions? Improving our understanding of this could help to inform pond creation in the future.

Of the 30 studies listed in the Conservation Evidence database as providing evidence on pond creation as an amphibian conservation intervention, 9 studies look at ponds 10 or more years since creation, compared to 12 studies that look at ponds created less than 5 years prior (the remaining 9 looked at ponds of intermediate ages, don’t specify the ages of the ponds studied, or present a mix of evidence). Of the 9 studies that look at pond creation in the long-term, only one uses data from the last 20 years (Berroneau et al., 2010).

Challenges to pond creation in the 21st century

The key study by Beebee (1997) noted above, and several of other informative longer-term studies (such as (Banks et al., 1993; Petranka et al., 2003; L. R. Williams, 2005), are over 20 years old. Whilst many factors of pond ecology remain relevant over this time frame, these studies may not explore the climate-related challenges faced when creating ponds today, such as the increased frequency of hot, dry summers, as seen in the UK (Dunford & Berry, 2012). Increased temperatures due to climate change reduce saturated oxygen levels in ponds (Ali et al., 2016). Furthermore, increased summer temperatures cause common toads to emerge in poorer condition, which may reduce their winter survival chances (Reading & Jofré, 2023). In recent research, pond creation and restoration practitioners were reported as perceiving climate change as the highest threat to their pond projects’ success (de Necker et al., 2025). In light of these climatic threats, new research to understand whether created ponds hold sufficient depths of water throughout the breeding season is needed.
Image 3: Two examples of ponds with water levels that drop drastically during the amphibian breeding season, leaving limited space for larvae to develop. Both photos taken at ponds created through Froglife’s Sheffield Living Waters project, copyright Emily Seccombe.

 

Froglife and University of Reading research on conservation impacts

To tackle this research gap, Froglife are supporting a University of Reading PhD project exploring the temporal and spatial impacts of conservation actions on British reptiles and amphibians, funded by a CROCUS NERC Doctoral Landscape Award (Training Grant Reference: UKRI1349). A key part of this research is to look at ponds created by Froglife over the last 15 years and assess their current amphibian breeding potential.

In the first year of the study, 56 ponds in Sheffield were surveyed in four repeated visits in Spring 2026. These ponds were created by Froglife’s Sheffield Living Waters projects, which ran between 2013 and 2019.

Data was collected to understand what proportion currently provide suitable amphibian breeding habitat and what factors affect this, such as water quality, invertebrate diversity, site management and vegetation levels. Surveys were carried out following standardised protocols used by the Countryside Survey (Williams et al., 2010), the PondNet pond habitat survey (Freshwater Habitats Trust, 2015) and the National Amphibian Survey (Amphibian and Reptile Conservation Trust, 2021). Amphibian surveys between March and June were used to assess breeding success. At each pond, water levels and temperature are recorded, with the aim of better understanding whether high water temperatures and reduced hydroperiods are a concern in these created ponds.

Additionally, desk-based research will be used to gather existing amphibian records at these sites, and to assess geographical data, such as urban density, around each of the study’s ponds. Findings of this research will be shared by Froglife following further analysis. By investigating how these ponds have fared in the long-term, including identifying key challenges to pond condition, we hope to be able to better inform pond creation efforts going forward.
Image 4: Assessment of a pond that has filled with vegetation (left) and pond dipping at a created pond (right). The current research by the University of Reading and Froglife hopes this fieldwork will provide insight into how purpose-built amphibian conservation ponds fare in the long-term. Both photos taken at ponds created through Froglife’s Sheffield Living Waters project, copyright Emily Seccombe.

Contact Emily Seccombe: e.r.seccombe@pgr.reading.ac.uk

Click here for references

Ali, S., Mishra, P. K., Islam, A., & Alam, N. M. (2016). Simulation of Water Temperature in a Small Pond Using Parametric Statistical Models: Implications of Climate Warming. Journal of Environmental Engineering, 142(3). https://doi.org/10.1061/(asce)ee.1943-7870.0001050

Amphibian and Reptile Conservation Trust. (2021). National Amphibian Survey Protocol: V2021.1.

Arnberger, A., Allex, B., Eder, R., Ebenberger, M., Wanka, A., Kolland, F., Wallner, P., & Hutter, H. P. (2017). Elderly resident’s uses of and preferences for urban green spaces during heat periods. Urban Forestry and Urban Greening, 21, 102–115. https://doi.org/10.1016/j.ufug.2016.11.012

Baker, J. M. R., & Halliday, T. (1999). AMPHIBIAN COLONIZATION OF NEW PONDS IN AN AGRICULTURAL LANDSCAPE. HERPETOLOGICAL JOURNAL, 9, 55–63.

Banks, B., Beebee, T. J. C., & Denton, J. S. (1993). Long-term management of a natterjack toad (Bufo calamita) population in southern Britain. Amphibia-Reptilia, 14, 155–168.

Barry, D. S., Pauley, T. K., & Maerz, J. C. (2008). Amphibian use of man-made pools on clear-cuts in the Allegheny Mountains of West Virginia, USA. Applied Herpetology, (5), 121–128. www.brill.nl/ah

Bartrons, M., Trochine, C., Blicharska, M., Oertli, B., Lago, M., & Brucet, S. (2024). Unlocking the potential of ponds and pondscapes as nature-based solutions for climate resilience and beyond: Hundred evidences. Journal of Environmental Management, 359. https://doi.org/10.1016/j.jenvman.2024.120992

Beebee, T. J. C. (1997). CHANGES IN DEWPOND NUMBERS AND AMPHIBIAN DIVERSITY OVER 20 YEARS ON CHALK DOWNLAND IN SUSSEX, ENGLAND. Biological Conservation, 81, 215–219.

Benejam, L., Perrin, J.-A., Blicharska, M., Brucet, S., Başoğlu, D., Beklioglu, M., Boissezon, A., Boix, D., Colina, M., Davidson, T. A., Lemmens, P., Sancha, A. L., Martin, B., Meerhoff, M., Mehner, T., Nicolet, P., Oertli, B., Passadore-Romero, C., Patil, S. D., … Robin, J. (2026). The role of pondscapes in supporting identities. Hydrobiologia. https://doi.org/10.1007/s10750-025-06105-8

Berroneau, M., Miaud, C., & Bernaud, J.-P. (2010). Creusement de mares en milieu dunaire de Gironde : intérêt pour les amphibiens et nouvelles données de répartition – Digging ponds on grey dune in Gironde: importance for amphibians and new distribution data. Bulletin de La Société Herpétologique de France, (133), 5–16. http://www.societeherpetologiquedefrance.asso.fr

Christie, A. P., Amano, T., Martin, P. A., Petrovan, S. O., Shackelford, G. E., Simmons, B. I., Smith, R. K., Williams, D. R., Wordley, C. F. R., & Sutherland, W. J. (2021). The challenge of biased evidence in conservation. Conservation Biology, 35(1), 249–262. https://doi.org/10.1111/cobi.13577

Cuenca-Cambronero, M., Blicharska, M., Perrin, J. A., Davidson, T. A., Oertli, B., Lago, M., Beklioglu, M., Meerhoff, M., Arim, M., Teixeira, J., De Meester, L., Biggs, J., Robin, J., Martin, B., Greaves, H. M., Sayer, C. D., Lemmens, P., Boix, D., Mehner, T., … Brucet, S. (2023). Challenges and opportunities in the use of ponds and pondscapes as Nature-based Solutions. Hydrobiologia, 850, 3257–3271. https://doi.org/10.1007/s10750-023-05149-y

de Necker, L., Brendonck, L., Vanschoenwinkel, B., Florencio, M., Rhazi, L., & Gołdyn, B. (2025). Lessons from pond creation and restoration projects in Europe. Restoration Ecology, 33(3), e14342. https://doi.org/10.1111/rec.14342

Denoël, M., & Ficetola, G. F. (2008). Conservation of newt guilds in an agricultural landscape of Belgium: The importance of aquatic and terrestrial habitats. Aquatic Conservation: Marine and Freshwater Ecosystems, 18, 714–728. https://doi.org/10.1002/aqc.853

Dunford, R. W., & Berry, P. M. (2012). Climate change modelling of English amphibians and reptiles: Report to Amphibian and Reptile Conservation Trust (ARC-Trust).

Freshwater Habitats Trust. (2015). Pond habitat survey method booklet. www.freshwaterhabitats.org.uk/projects/waternet

Habel, J. C., Gossner, M. M., Meyer, S. T., Eggermont, H., Lens, L., Dengler, J., & Weisser, W. W. (2013). Mind the gaps when using science to address conservation concerns. Biodiversity and Conservation, 22(10), 2413–2427. https://doi.org/10.1007/s10531-013-0536-y

Hamer, A. J., & Parris, K. M. (2011). Local and landscape determinants of amphibian communities in urban ponds. Ecological Applications, 21(2), 378–390. https://doi.org/10.1890/10-0390.1

Hazell, D., Hero, J. M., Lindenmayer, D., & Cunningham, R. (2004). A comparison of constructed and natural habitat for frog conservation in an Australian agricultural landscape. Biological Conservation, 119, 61–71. https://doi.org/10.1016/j.biocon.2003.10.022

Hill, M. J., Hassall, C., Oertli, B., Fahrig, L., Robson, B. J., Biggs, J., Samways, M. J., Usio, N., Takamura, N., Krishnaswamy, J., & Wood, P. J. (2018). New policy directions for global pond conservation. Conservation Letters, 11, e12447. https://doi.org/10.1111/conl.12447

Moor, H., Bergamini, A., Vorburger, C., Holderegger, R., Bühler, C., Bircher, N., & Schmidt, B. R. (2024). Building pondscapes for amphibian metapopulations. Conservation Biology, 38, e14165. https://doi.org/10.1111/cobi.14281

Petranka, J. W., Kennedy, C. A., & Murray, S. S. (2003). RESPONSE OF AMPHIBIANS TO RESTORATION OF A SOUTHERN APPALACHIAN WETLAND: A LONG-TERM ANALYSIS OF COMMUNITY DYNAMICS. In WETLANDS (Vol. 23, Number 4).

Rannap, R., Lõhmus, A., & Briggs, L. (2009). Restoring ponds for amphibians: A success story. Hydrobiologia, 634(1), 87–95. https://doi.org/10.1007/s10750-009-9884-8

Reading, C., & Jofré, G. (2023). The relationship between temperature, growth rate and body condition of Bufo bufo toadlets prior to their first hibernation. Amphibia Reptilia, 162(6), 1–12. https://doi.org/10.1163/15685381-bja10142

Ruhí, A., Sebastian, O. S., Feo, C., Franch, M., Gascón, S., Richter-Boix, À., Boix, D., & Llorente, G. (2012). Man-made Mediterranean temporary ponds as a tool for amphibian conservation. Annales de Limnologie – International Journal of Limnology, 48, 81–93. https://doi.org/10.1051/limn/2011059

Skei, J. K., Dolmen, D., Rønning, L., & Ringsby, T. H. (2006). Habitat use during the aquatic phase of the newts Triturus vulgaris (L.) and T. cristatus (Laurenti) in central Norway: proposition for a conservation and monitoring area. Amphibia-Reptilia, 27, 309–324. www.brill.nl

Williams, L. R. (2005). Restoration of ponds in a landscape and changes in Common frog (Rana temporaria) populations, 1983–2005. Herpetological Bulletin, 94, 22–29.

Williams, P., Biggs, J., Crowe, A., Murphy, J., Nicolet, P., Weatherby, A., & Dunbar, M. (2010). Countryside Survey: Ponds Report from 2007. CS Technical Report No. 7/07.

 

Alien snakes are bad news for island endemics

by

Roger Downie, University of Glasgow and Froglife Patron

It is common for animals that first colonise isolated islands in the absence of predators to lose the defences that protected them on the mainland: a well-known example is the dodo, a species of pigeon that lost the ability to fly after many generations living predator-free on the island of Mauritius. For his reason, we need to be vigilant in avoiding the accidental introduction of predators on to islands with vulnerable endemic species. Unfortunately, we have not been careful in the past, and accidental introductions continue to occur. In this article, I discuss some examples involving snakes.

The Brown Tree Snake (Boiga irregularis) is a colubrid, native of Australia, New Guinea and the Solomon islands. It arrived by accident on the isolated Pacific island of Guam soon after World War 2. Its population remained low and localised for some years, but during the 1960s, its numbers increased rapidly and it migrated to populate the whole island. It preyed principally on birds, but also on lizards and bats. Many of the bird species had lost their defences to predators such as snakes and by the 1970s, 15 species had been lost to the island, including three endemic species and two sub-species (Wiles et al., 2003).

Brown tree snake (Boiga irregularis), By Pavel Kirillov from St.Petersburg, Russia – CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=46853510

An example recently in the news (Jones, 2026) is the Horseshoe Whip Snake (Hemorrhois hippocrepis), another colubrid, native to north-west Africa, Portugal and Spain, but not to the Balearic Islands (Ibiza, Mallorca and Menorca). In the early 2000s, this snake arrived on Ibiza, probably as eggs buried in soil attached to olive trees being shipped to the island from Spain. Since arriving, its numbers have grown very rapidly , and this population explosion has had devastating effects on the endemic Ibiza Wall Lizard (Podarcis pityusensis), formerly very abundant, but, since 2024, classed as Endangered by IUCN. The lizards are estimated to comprise about half of the snakes’ diet. Efforts are being made to cull the snake population: over 12,000 have been captured and removed since 2016.

Alarmingly, it turns out that these snakes can disperse by swimming in the sea (presumably, they did not reach Ibiza by this route earlier because the distance is too long, almost 150 km). Casbas et al.(2026) have filmed snakes swimming vigorously from Ibiza to the offshore islet of Santa Eularia, a distance of only 430 metres, and they have also collected confirmatory reports of swimming snakes observed by members of the general public. Santa Eularia is only 4.7 hectares in area, but snake traps set out there captured 58 individuals over the period September 2023 to May 2025. Surveys of the islet for wall lizards found them to be abundant as recently as 2022, but all gone by 2025. An interesting question is what motivates the snakes to set off in the sea, presumably quite a hazardous journey for a snake not normally living in an aquatic environment, and how do they detect their destination? Possibly migration is driven by competition once numbers get too high in one place, but Casbas and colleagues say that no answers are yet known to these questions.

Genetic and morphological studies of the Ibiza Wall Lizard across Ibiza, Formentera and their islets have shown there to be 30 ‘evolutionarily significant units’: this diversity is at high risk of being lost because of the snake invasion. Also lost will be the unique ecology of the islands where the lizards have major roles in pollination, seed dispersal and arthropod control.

Are there any alien snake populations in the UK? The best known is the Aesculapian Snake (Zamenis longissimus) which occurs at three British localities: near Colwyn Bay in north Wales; beside Regent’s canal in north London; and at Bridgend in south Wales. The common name of this large (140-160 cm) colubrid is derived from Asclepius, the Greek god of healing: the snakes were encouraged to live round his temples and a snake coiled around a staff became a symbol of the medical professions. The species occurs in Europe from France east to Iran, but has not been native to the UK for millennia.

Aesculapian Snake (Zamenis longissimus) © Matt Wilson

The Regent’s Canal population has been much studied (Langton et al., 2011; Atkins, 2020). The initial population was accidentally (or deliberately) released from a research facility near the canal in the 1980s. The snakes have bred successfully, reaching a peak population of around 40 in 2013, possibly declining a little since then.

The Colwyn Bay population derives from an escape in the 1970s from the Welsh Mountain Zoo. Successful breeding has again occurred, with an estimated population of 70 adults by 2022, all still in the Colwyn Bay area. Major et al. (2025) have reported on an extensive study of the snakes’ movements and habitat preferences. They captured 13 males and 8 females, surgically inserted radio transmitters then released the snakes at the point of capture (capture was not easy, as the snakes are hard to find: the authors estimate an average hunt of 8 hours per snake). Daily movements were on average 52 metres for males; males showed some preference for buildings as habitat, while females preferred woodland. Snakes fed on small mammals and birds, but were in turn predated by larger mammals and in one case, a buzzard. Mortality during the study was quite high, including on roads.

Unlike the Brown Tree Snake on Guam and the Horseshoe Whip Snake on Ibiza, there is no evidence that the Aesculapian Snake poses any danger to the long term survival of our native wild species, but the UK is not a small island relatively free of predators.

Click to see references

References

Atkins, W. (2020). Observations on a feral population of Aesculapian snakes. The London Naturalist 99, 77-112.

Casbas, G. et al.(2026). Swimming snakes wipe out endemic lizards from Mediterranean islets. Ecology 107, e70373.

Langton, T. et al. (2011). On the distribution, ecology and management of non-native reptiles and amphibians in the London area: 1- Distribution and predator/prey impacts. The London Naturalist 90, 83-155.

Major, T. et al. (2025). A reliance on human habitats is key to the success of an introduced predatory reptile. PLoS ONE 20 (2), e0310352.

Wiles et al. (2003). Impacts of the Brown Tree Snake: patterns of decline and species persistence in Guam’s avifauna. Conservation Biology 17, 1350-1360.

Polyandry in frogs and toads: evidence of mixed paternity?

by

Written by Dr Laurence Jarvis (external contributor)

Polyandry, where a female mates with multiple males, is widespread across the animal kingdom. It has been documented from several taxa, particularly fish, insects and birds.

Polyandry has been observed in many species of amphibians (Roberts & Bryne, 2011) and may be more common than previously thought (Halliday, 1998). There are two main types of polyandry in frogs and toads: simultaneous and sequential (Roberts and Bryne, 2011). Simultaneous polyandry typically occurs where the sperm from several males reaches a female’s eggs at the same time. This is most likely in explosively breeding species such as the European Common Frog (Rana temporaria) or Common Toad (Bufo bufo) where several males may be present around one female.

Each male may attempt to fertilise a female’s eggs as she releases them into the water. In these instances, a female may be forced to obtain sperm from several males due to continued harassment. In sequential polyandry, a female may seek out additional males. This occurs more frequently in species where males defend territories and there are opportunities for the female to mate multiple times, perhaps over hours or days.

This may confer significant benefits for the female such as enhanced protection or parental care of young, as well as obtaining mixed genes for her offspring (Roberts and Bryne, 2011). However, despite the fact that polyandry may be relatively common in frogs and toads, actually proving mixed paternity can be difficult (Wang et al., 2017). Genetic studies using molecular markers from DNA sequences are required to fully understand the paternal origins of a given female’s clutch. Over recent decades several studies have examined the potential for polyandry in a range of frog and toad species.

Figure 1. Farmland green treefrog (Zhangixalus arvalis) from Taiwan, a similar species to the Omei treefrog. Photo credit: Catalogue of Life in Taiwan, CC BY 2.5 <https://creativecommons.org/licenses/by/2.5>, via Wikimedia Commons.

The Omei treefrog (Zhangixalus omeimontis) lives in subtropical and mountainous forests of China. It is an arboreal species, laying its eggs on leaves overhanging water (IUCN SSC Amphibian Specialist Group, 2020). Wang et al. (2017) provide a useful summary of the breeding behaviour this species. During the breeding season males will congregate in standing water, forming leks, each calling to attract a female.

On arrival, a female will be grabbed by a male and she will ascend a tree to find a suitable leaf on which she will lay her eggs. Several additional males will follow and attempt to fertilise her eggs as she releases them. In some cases, up to eight males may attempt to form amplexus with a female (Wang et al., 2017). The male provides no parental care and once a female has laid her eggs she will produce mucus to envelope them within a foam. Once hatched, the tadpoles will fall into the water below and continue their development (Wang et al., 2017).

Wang et al. (2017) examined the degree of multiple paternity in the Omei treefrog using genetic markers. Perhaps unsurprisingly, in nearly all cases, females had genes from multiple males. Out of the 30 females studied, only one had genetic material from a single male. The rest had genes from between two and four fathers. Interestingly, the greater the number of males present around a given female, the less the chances of obtaining paternity. For example, when only one or two males were present, each male had 100% chance of paternity. However, with seven or eight males, for a given male, there was only a 45% chance of passing on his genes. Therefore, in this species, it is more advantageous for a male to join a mating crowd with fewer competitors (Wang et al., 2017). Although it appears that a female is at the mercy of advancing males, there may be benefits for her. By receiving sperm from several males, she is more likely to receive multiple genes, some of which may be ‘good genes’ or those with compatible genotypes (Wang et al., 2017).

It is perhaps not surprising that simultaneous polyandry occurs in frog species with large breeding aggregations, since many males are present at one time and there are many opportunities for males to release their sperm onto the eggs of different females. However, does this occurrence actually provide genetic benefits?

The quaking frog (Crinia georgiana) has been a model species for behavioural studies for many decades. It is a common and widespread frog across the coastal plains of southwestern Australia. Males congregate in large numbers at water bodies during the spring. Females are attracted to aggregations of males and upon arrival are immediately engaged in amplexus by a male.

Previous research has demonstrated that approximately 50% of matings result in polyandry (Roberts et al., 1999). However, it is uncertain whether there are any genetic benefits for this occurrence. For example, do egg clutches fertilized from more than one male experience greater viability, especially in an unpredictable breeding environment? Bryne and Roberts (2000) tested this hypothesis by carrying out laboratory experiments on the quaking frog. Interestingly, clutches fertilised by more than one male did not experience any increase in survival or growth (Bryne and Roberts, 2000). This suggests that multiple paternity in this species does not provide increased genetic benefits such as more robust larvae in an unpredictable environment.

This was unexpected, since studies on other taxa (e.g. bumblebees and field crickets) have demonstrated distinct advantages of multiple paternity such as improved hatching success or lower parasite load. Therefore, multiple paternity may not necessarily result in genetic benefits to the offspring and may have evolved due to other selective pressures.

The quaking frog (Crinia georgiana) is well known for its breeding aggregations at ponds in Australia. Photo credit: Jean-Marc Hero, CC BY-SA 2.5 <https://creativecommons.org/licenses/by-sa/2.5>, via Wikimedia Commons.

There is increasing evidence to demonstrate the existence of sequential polyandry in amphibians. This is more subtle and involves deliberate attempts by a female to seek additional males with which to mate.

Pickersgill’s Banana Frog (Afrixalus delicatus) is a widespread species inhabiting grasslands of south and east Africa. In this species, the male and female pair and the female lays a clutch of eggs on a leaf just above, or on top of, the surface of water (AmphibaWeb, 2026). She carefully folds this over and leaves them to develop. However, she may obtain another male with which to mate and repeats the process several times. Therefore, the female fertilises portions of her whole clutch from different males.

This sequential laying of different portions of the clutch may occur in other species. The green and golden bell frog (Litoria aurea) from Australia has been documented to partake in simultaneous polyandry (Beranek et al., 2021). Males congregate in large aggregations at breeding ponds during the spring and there are opportunities for many males to congregate around one female. However, there is unconfirmed evidence that a female may withhold releasing her whole clutch at once (Christy, 2001 in Beranek et al., 2021). This provides the female with the opportunity to move to another area of the pond to allow the rest of her clutch to be fertilised by a different male.

Figure 3. Male and female Pickersgill’s Banana Frog (Afrixalus delicatus) in amplexus. Photo credit: John Lyakurwa, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons.

Terrestrial toadlets of the genus Pseudophryne inhabit grasslands and forests of Australia. The brown toadlet (P. bibronii) has an unusual breeding strategy. The male constructs a terrestrial nest, usually out of dead leaves or soil. Here he will call to attract a female. Mating occurs within the nest and the male will carry out all parental care duties, attending the eggs until they are flooded by rainwater and hatch (O’Brien et al., 2018). Females will move to the territories of several males and potentially mate multiple times. In this species Bryne and Keogh (2009) found that females mated with up to eight different males, laying clutches in the nests of each.

Similar sequential polyandry has been observed in other Pseudophryne frogs. However, this behavioural trait is not necessarily consistent across similar species. More recently, O’Brien et al. (2018) found that in the red-backed toadlet (P. coriacea) 92.6% of females mated just once with only 3.7% taking part in sequential polyandry. The reasons for these stark differences between species are not clear, but may be linked to the evolutionary status of different species (O’Brien et al., 2018).

Overall, polyandry is widespread amongst many frog and toad families. Several studies have demonstrated that females may mate with multiple males, either incidentally, or actively seeking additional matings. Genetic studies have been crucial in demonstrating the degree of multiple paternity in different species. The evidence for the genetic benefits of polyandry appears inconclusive and experimental studies are required to determine the relative costs and benefits of polyandry in frogs and toads.

Click here for references...

AmphibiaWeb. (2026). <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 18 May 2026.

Backwell P.R.Y. and Passmore N.I. (1990). Polyandry in the leaf-folding frog Afrixalus delicatus. Herpetologica. 46: 7–10.

Beranek C.T., Clulow J. and Mahony M. (2021). Genetic evidence for polyandry in the threatened green and golden bell frog. Genetica, 149 (5): 327-333.

Byrne P.G. and Roberts J.D. (2000). Does multiple paternity improve fitness of the frog Crinia georgiana? Evolution, 54 (3): 968-973.

Byrne P.G. and Keogh J.S. (2009). Extreme sequential polyandry insures against nest failure in a frog. Proceedings of the Royal Society B: Biological Sciences, 276 (1654): 115-120.

IUCN SSC Amphibian Specialist Group. (2020). Zhangixalus omeimontis. The IUCN Red List of Threatened Species 2020: e.T58961A63884080. https://dx.doi.org/10.2305/IUCN.UK.2020-1.RLTS.T58961A63884080.en. Accessed on 15 May 2026.

Halliday T. (1998). Sperm competition in amphibians. In: Sperm Competition and Sexual Selection, pp 466-493. Eds. T.R. Birkhead and A.P. Møller. Academic Press, London.

O’Brien D.M., Keogh J.S., Silla A.J. and Byrne P.G. (2018). The unexpected genetic mating system of the red‐backed toadlet (Pseudophryne coriacea): A species with prolonged terrestrial breeding and cryptic reproductive behaviour. Molecular Ecology, 27 (14): 3001-3015.

Roberts J.D. and Byrne P.G. (2011). Polyandry, sperm competition, and the evolution of anuran amphibians. Adv Stud Behav, 43: 1–53.

Roberts J.D., Standish R.J., Byrne P.G. and Doughty P. (1999). Synchronous polyandry and multiple paternity in the frog Crinia georgiana (Anura: Myobatrachidae). Animal Behaviour, 57: 721–726.

Wang H., Luo Z., Chen J., Zhao M. and Wu H. (2017). Social polyandry and multiple paternity in the Omei Treefrog in the Southwest China. Asian Herpetological Research, 8 (1): 48-54.

The Alpine Newt: what should it be called, and where does it belong?

by

Roger Downie, Froglife and University of Glasgow

The Alpine Newt was first scientifically described by Laurenti in 1768 from the Austrian Alps and named Triton alpestris. However, although it can occur up to 2370m in altitude, it is not a high-altitude specialist (unlike the Alpine Salamander, Salamandra atra found at heights above 700m), and occurs across much of continental Europe at low and higher levels. It has a continuous distribution but also some isolated populations, such as that in northern Spain, and four sub-species have been described, with some researchers suggesting that these should be designated as separate species, though Frost (2026) argues that more evidence is needed before such a change could be justified.

What about its scientific name? For some time, the Alpine Newt has been in a single-species genus as Ichthyosaura alpestris. However, Mutz and Bohme (2025) contended that this had long been an error, based on a misidentification of Laurenti’s larval drawing, and that the generic name Mesotriton is the correct one. This contention has been rapidly rebutted by Gollmann and Gollmann (2026). For connoisseurs of arcane academic arguments, these two papers are a delight, and I wish the International Commission on Zoological Nomenclature the best of luck in sorting it out. At present, Wikipedia uses Mesotriton  and Frost retains Ichthyosaura.

The distribution map for the Alpine Newt shows it lined up across the English Channel from the UK, suggesting that it is one of the many species with limited dispersal abilities that failed to recolonise the British Isles after the last Ice Age (or was it ever here in the first place?). Its absence as a member of our native fauna is certainly not because conditions here are unfavourable. The most recent survey of its occurrence in the UK by Allain and Lynn (2021) shows that it is the most widely distributed of the non-native amphibians inhabiting the UK. They combined existing records with information from social media posts to identify eleven new populations, many throughout England and a few in both Wales and Scotland. Use of social media in this way had to be done with caution and care: for many members of the general public, the differences between Great Crested and Alpine Newts are not obvious (Alpine adults are a bit bigger than Smooth or Palmates and darker in colour, like Great Cresteds, so confusion is understandable for people not familiar with the different species).

Since, Allain and Lynn, Cathrine (2024) has provided a focussed account of the Alpine Newt in Scotland. He reports four distinct populations: Edinburgh, Dollar, Glenboig and Helensburgh, each at considerable distance from the others. Even in Edinburgh, Cathrine reports three separate populations at Duddingston, Mortonhall Golf Course and Ratho. Ball et al (2024) have shown that the Ratho population is genetically distinct from the other two Edinburgh populations and Cathrine claims that the Ratho newts were deliberately released in an attempt to halt a local development (the objectors thinking that they were releasing protected Great Crested Newts!). Deliberate release of non-native species into the wild is illegal: it is thought that most Alpine Newt populations in the UK are the result of accidental escapes from private collections, although the Edinburgh population apparently came from a University whose colony had grown too large (released before this was illegal). Cathrine claims that the Scottish populations are spreading, especially the one close to the Union canal that is acting as a dispersal corridor.

Three substantial scientific papers have recently investigated the introduced populations of Alpine Newt, aiming to assess their threats to native species. Robbemont et al (2023) sampled 456 individuals across 234 localities throughout Europe, including the British Isles (12 from England; 5 from Scotland; 16 from Wales; 7 from Northern Ireland and 12 from Ireland). One aim of the study was to investigate the effectiveness of trained citizen scientists using the methods of skin and buccal swabbing to recover usable mitochondrial DNA samples. Nearly all recovered samples contained mtDNA and skin swabbing was as effective as buccal, an important result since buccal swabbing needs careful training and is stressful for the newts, whereas skin swabbing is much easier.  The mtDNA confirmed the seven clades identified by previous work (Eastern/Western Europe plus Spain; Italy; Northern Balkans plus Romania; Central Balkans; Montenegro; Vlasina; Southern Balkans. The results were used to ascertain the sources of introduced populations in the Netherlands and the British Isles.

Ball et al (2023) used a variety of approaches to determine the origins of the UK’s Alpine newt populations. Their report is highly technical, but the Discussion section provides a very accessible  account of their findings. The UK population is mostly urban, related to its origins as escapes or deliberate releases from captive collections. Dispersal has been generally low, possibly related to origins in urban habitats with few possible routes for dispersal (an exception being the Edinburgh population noted earlier). They noted that Harper et al’s (2018) eDNA survey of 532 suspected Great Crested newt ponds in three English counties (Cheshire, Kent and Lincolnshire)  had not detected any ponds containing Alpine Newts, despite some of these counties containing  recorded populations. Suggested dangers  from Alpine Newts discussed are: a) hybridisation with native newts: but this is unlikely given that in continental Europe Alpine Newts co-occur with all three native UK newt species with no evidence of hybridisation; b) spread of diseases such as Ranavirus and chytrid: Alpine Newts can carry these diseases, but this threat is most likely only important from specimens imported from the continent, rather than those bred in the UK; c) predation by Alpine Newts on native amphibians, especially eggs and juveniles.

Most recently, North et al (2025) carried out a modelling study on the Alpine Newt’s potential to be an invasive species in Britain. They noted that the first records are from the 1920s, and that there are now over 100 geographically independent sightings. Their assessment is that UK habitats are highly favourable for Alpine Newts, especially the central European clade, and especially central and eastern England, and central and northern Scotland.

Conclusion

It is clear that the Alpine Newt is well suited to inhabiting the UK and already occurs in a large number of small isolated populations across the British Isles. Because most of these are in urban  settings with limited potential for dispersal, rather few of them appear to be  spreading in their range. Many of them derive from the release or escape of captive-bred individuals, so are unlikely to be carrying diseases. However, it remains an offence to release further individuals into the wild. There is currently no plan  to carry out a (no doubt costly) attempt to eradicate these non-native amphibians. If eradication is considered, the example of New Zealand is worth checking out. Alpine newts were first recorded there in 2013, but had likely been released (illegally) a decade before. An eradication programme is in progress, having with some difficulty detected and removed over 2000 newts in the first year (Bell, 2016). The best contribution that interested naturalists can make is to help extend our knowledge of Alpine Newt distribution in the UK, since it is very likely that unrecorded populations remain to be discovered. Please send any records to Froglife who will forward them to the NBN database.

Click here for references

Allain and Lynn (2021). Distribution of the alpine newt Ichthyosaura alpestris in Great Britain updated using social media. Herpetological Bulletin 158, 28-31.

Ball et al (2023). Multiple introductions and human-aided dispersal of the UK’s most widespread non-native amphibian. Frontiers in Amphibian and Reptile Science 1, 1215723.

Bell, B.D. (2016). A review of potential Alpine newt impacts on native frogs in New Zealand. Journal of the Royal Society of New Zealand 46, 214-231.

Cathrine (2024). Distribution of non-native terrestrial and freshwater amphibians and reptiles in Scotland. The Glasgow Naturalist 28 (2), 72-78.

Frost (2026). Amphibian Species of the World. On-line database. Accessed 10/3/2026.

Gollmann and Gollmann (2026). The identity of Proteus tritonius Laurenti, 1768: comments on a really doubtful case of literary interpretation. Herpetozoa 39, 17-21.

Harper et al (2018). Needle in a haystack? A comparison of eDNA barcoding and targeted qPCR for detection of the great crested newt. Ecology and Evolution 8, 6330-6341.

Mutz and Bohme (2025). Ichthyosaura as a generic nomen for the Alpine Newt (Caudata: Salamandridae): a doubtful case of literarian archaeology. Salamandra 61, 41-52.

North et al (2025). Predicting the invasiveness of alpine newt in the UK. Biological Invasions 27, 99.

Robbemont et al (2023). An extended mtDNA phylogeny for the alpine newt illuminates the provenance of introduced populations. Amphibia Reptilia 44, 347-361.

Endotrophic tadpoles: a widespread occurrence?

by

Written by Dr. Laurence Jarvis (external contributor)

The larval form of frogs and toads, the tadpole, is a well-recognised developmental stage. Globally, tadpoles appear in a range of forms, or ecomorphotypes. According to McDiarmid and Altig (1999), there are 21 tadpole ecomorphotypes. However, there are still many anuran species where the ecomorphotype is still unknown. In a recent review of the then 7,665 known anuran species, Nori et al. (2025) found that an astonishing 4,502 anuran species (approx. 59%) still have their larval form yet to be described. This highlights the shortfall in our basic understanding of the larval ecology of many amphibian species worldwide.

Perhaps the most familiar ecomorphotype is the exotrophic tadpole which are generally free-swimming and feed on a range of prey from macroinvertebrates to microscopic algae. These may occur in a vast range of water bodies including freshwater ponds, rivers, fast-flowing streams and phytotelm-dwelling (living in small pockets of water formed within the cupped leaves of terrestrial plants). They may also occur in terrestrial habitats such as damp moss, soil and even sand. Not surprisingly, free-living, aquatic tadpoles are the most common, occurring in approximately 6,550 of anuran species (Nori et al., 2025). However, this is not the only type of anuran tadpole ecomorphotype. Less common are the endotrophic tadpoles. These are essentially non-feeding, instead relying on the yolk derived from the egg or their parents. Free-living forms typically lack the keratinised mouth parts of their feeding counterparts and possess a relatively large volume of yolk in their intestines. They use this to fuel their growth and their metamorphosis into the adult form.

Figure 1. Endotrophic tadpoles (Blythophryne beryet) showing yolk in their intestines.
Figure 2. Mouthparts of an endotrophic tadpole (Blythophryne beryet) showing lack of teeth and keratinised mouthparts.

Photo credit for Figures 1 and 2: Chandramouli SR, Vasudevan K, Harikrishnan S, Dutta SK, Janani SJ, Sharma R, Das I, Aggarwal RK, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons

There are five main groups, or guilds, of endotrophic tadpole (McDiarmid and Altig, 1999). Nidicolous endotrophic tadpoles are generally free-living but often remain in a nest created by the parent. Three guilds involve the froglet either birthing from the mother’s oviducts or from other parts of the body (e.g. stomach or skin surface). Lastly, there are the direct developers, which develop within the egg and hatch as tiny juveniles (Nori et al., 2025). The larvae belonging to the latter four groups are often referred to as embryos, rather than tadpoles, as they lack a free-living form. Free-living endotrophic tadpoles are rare, with just 226 species of anuran known to have this ecomorphotype (Miñarro et al., 2024). However, scientists suspect that in reality up to 30% of anuran tadpoles may live in this form, but have yet to be described (Vera Candioti et al., 2023). In addition, among the 68 genera with unknown tadpoles, around 60% are likely to be endotrophic (Vera Candioti et al., 2023). Currently, most anurans with free-living, endotrophic larvae are concentrated in South and Central America, Madagascar, Southwest India, Borneo and New Guinea (Vera Candioti et al., 2023). It is likely that there are a greater number of anurans with this tadpole ecomorphotype within these, and surrounding, regions. These distributional patterns of endotrophic tadpoles are perhaps not unsurprising but highlight where future research needs to be focussed for greater understanding of tadpole ecomorphology across a range of anuran taxa.

The Philippine flat-headed frog (Barbourula busuangensis) is an enigmatic species belonging to an ancient lineage of amphibian. Until recently virtually nothing was known of its tadpoles, behaviour or ecology. However, thanks to tireless work by field researcher Marta Miñarro and colleagues, we now understand more of this species’ fascinating ecology. The Philippine flat-headed frog is nocturnal, living within rocky, fast-flowing streams within rainforests and is consequently very difficult to observe (Miñarro et al., 2024). Since 1954 this frog was suspected to have direct development since it lays a small number of large eggs under stones, and no tadpoles had ever been observed. However, in 2023, tadpoles were discovered for the first time, clinging to rocks close to the eggs (Miñarro et al., 2024). These tadpoles had a typical form for an endotrophic tadpole, lacking specialised mouthparts and having an abundance of yolk in their intestines (Miñarro et al., 2024). It appears, contrary to expectation, that the female lays her small clutch of around 100 eggs in a nest attached to an underwater boulder. These eggs are guarded either by the male or female until they hatch into specialised non-feeding endotrophic tadpoles. These tadpoles possess an effective oral sucker enabling them to cling to the rocks in the fast-flowing waters. Of particular interest, and perhaps unique to this species, is that these tadpoles lack a row of keratinised teeth around its oral sucker (Miñarro et al., 2024). Most other tadpoles living in fast-flowing waters have these teeth for feeding and to help secure them to the rocks. Since the Philippine flat-headed frog does not feed, it lacks these teeth and the oral sucker has a unique and modified design. Miñarro et al. (2024) suspect that suction alone, without the aid of gripping teeth, enables these tadpoles to cling to the rock surface.

Figure 3. Adult Barbourula busuangensis

Photo credit: Pierre Fidenci, CC BY-SA 2.5 <https://creativecommons.org/licenses/by-sa/2.5>, via Wikimedia Commons

The South American genus of frog Adenomera, often referred to as thin-toed frogs, currently comprises 32 species, but this number changes due to new discoveries and taxonomic revisions (AmphibiaWeb, 2026). Frogs within this genus have an interesting mode of reproduction, laying their eggs in a terrestrial underground chamber. Males create a small depression in the ground using their snouts, in which the females lay their eggs. Kokubum and Giaretta (2005) studied an unknown species of Adenomera, describing its tadpole form and function. The number of eggs laid was around 20, which is similar to other species within the genus. Once hatched, the relatively large endotrophic tadpoles created a foam nest by blowing bubbles through their mouths and writhing around. These tadpoles lived within the foam, not feeding, until metamorphosis. There has been much discussion as to the exact function of the foam nest but it may serve multiple discussions. Hypotheses include: protection from predators (Menin and Giaretta, 2003); absorbing and maintaining moisture; aiding in respiration and gas exchange (Downie and Smith, 2003); and avoiding compaction of the tadpoles at the bottom of the basin (Kokubum and Giaretta, 2005 quoting Silva et al., in prep). Whichever of these is the most critical for this species of Adenomera is not known but a combination is likely to ensure effective survival to metamorphosis.

Figure 4. Adult Adenomera saci, a newly described species in 2013, endemic to northwest Brazil.

Photo credit: Reuber Brandão, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons

These case examples demonstrate the fascinating ecology of species with endotrophic tadpoles. Unfortunately, many of the species lacking formal tadpole description live in remote and difficult to study locations and often face multiple threats such as habitat loss, fragmentation and disease. Given the suspected number of anuran species with this ecomorphotype, further research is vital to address this lack of knowledge and to enable effective conservation strategies for these species.

Click here for references

AmphibiaWeb (2026) <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 17 Mar 2026.

Downie J.R. and Smith J. (2003) Survival of larval Leptodactylus fuscus (Anura: Leptodactylidae) out of water: developmental differences and interspecific comparisons. Journal of Herpetology, 17: 107-115.

Kokubum M.N.D.C. and Giaretta A.A. (2005). Reproductive ecology and behaviour of a species of Adenomera (Anura, Leptodactylinae) with endotrophic tadpoles: systematic implications. Journal of Natural History, 39 (20): 1745-1758.

McDiarmid R.W. and Altig R. (1999) Research: materials and techniques. In: McDiarmid R.W., Altig R., editors. Tadpoles: the biology of anuran larvae. Chicago: The University of Chicago Press. p 7-23.

Menin M. and Giaretta A.A. (2003) Predation on foam nests of Leptodactyline frogs (Anura, Leptodactylidae) by larvae of Beckeriella niger (Diptera, Ephydridae). Journal of Zoology (London) 26: 1-5.

Miñarro M., Burrowes P.A., Lansac C., Afuang L. and De La Riva I. (2024). Mystery solved: unravelling the life history of the enigmatic and ancient Philippine frog Barbourula busuangensis (Anura: Bombinatoridae). Salamandra, 60 (4).

Nori J., Baldo D., Pereyra M., Grosjean S., dos Santos Dias P.H., Müller H., Cordier M., Huais P.Y., Tomba A. and Vera Candioti F. (2025) Global key areas for anuran tadpole discovery. Biological Journal of the Linnean Society, 145 (1), p.blaf017.

Vera Candioti F., Baldo D., Grosjean S., Pereyra M.O. and Nori J. (2023). Global shortfalls of knowledge on anuran tadpoles. Biodiversity, 2 (1): 22.