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What’s in a name? Rules and conventions for naming species

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Written by Roger Downie, Froglife and University of Glasgow

Vences and colleagues in October 2024 published a paper describing seven new species of treefrogs in the Madagascan genus Boophis: kirki, picardi, siskoi,  janewayae, archeri, pikei and burnhamae. These are all named after the captains of starships in the TV and film series Star Trek, and chosen because the frogs’ shrill advertisement calls reminded the authors of technical equipment sounds made in the series. Another case of a topical name that may require explaining to future generations (assuming climate change doesn’t destroy human civilisation) is the Panamanian cloud forest frog Pristimantis gretathunbergae (Mebert et al., 2022), named after the courageous Swedish climate campaigner because the authors felt that this frog’s habitat was a key example of a place at serious risk from climate change. These examples raise the question: how are animal names decided? Are there any rules? We’ll look first at scientific names, then in a later article at common names.

The new species in the genus ‘Boophis’ were all named after captains from the TV show, Star Trek, including ‘Boophis picardi’.

The use of Latin binomials for animal scientific names (first, a generic name with a capital initial, followed by a lower case specific, both conventionally in italics or underlined) was set out by Linnaeus in 1758, but took time to establish. The first International Zoological Congress (Paris, 1889) agreed that binomials should be used by all scientists and set about constructing what became the rules of international zoological nomenclature from 1905. After many revisions, these were re-written as the International Code for Zoological Nomenclature (first edition, 1961; the 4th edition of 2000 is currently in force,  superseding all previous versions). Different, although similar, codes apply to algae, fungi and plants.

The Code has many technical details (beyond the scope of this article, but consult the Wikipedia account if you want to know more), but essentially, the aim is to ensure that the names are universal and show continuity e.g. the principle of ‘priority’ states that the correct name for an animal species is the oldest available that has been applied to it.

A relevant example comes from the revision of the species complex long known as Bufo bufo, the common and widespread Eurasian toad. Molecular and morphological analysis by Rucuero and colleagues in 2012 recognised four distinct species: bufo (most of Europe, including north and eastern France), spinosus (North Africa, Iberia, much of France), eichwaldii (Azerbaijan and Iran) and verruccissimus (= the most warty, Caucasus and Turkey). Eichwaldii  is a relatively new name, but the others are valid names used in the past for relevant Bufo populations (spinosus given by Daudin, 1803). In France, the line dividing the bufo and spinosus populations divides the country in half, bufo east and north; spinosus west and south. Arntzen et al. (2014) confirmed that the toad population on Jersey is spinosus, adding a species to the British herpetofaunal list, as a result of the historical accidents that make Jersey British rather than French.

Because the Code uses Latin names, Latin gender and other grammatical rules apply, with the specific names usually acting as adjectives describing an aspect of the generic name (Latin scholars can come into your own here!). However, this can cause confusion when the names used do not have obvious Latin grammatical characteristics.

So, does the scientist naming a newly-discovered species (as opposed to species resulting from the unravelling of a complex previously regarded as one species) have unlimited choice? No: there are some rules: names cannot be rude and insulting (following some 19th century examples where names were used to get back at opponents); and you cannot name a species after yourself, though you can honour a colleague, who may honour you back..Usually, names are intended to describe some quality of the new species: appearance, behaviour, habitat or geographical location. Humour is allowed: for example, a set of small, round fungus beetles are in the genus Gelae, as G. baen, fish and rol.

When I began researching the habits of frogs and marine turtles in Trinidad and Tobago, I noticed that several species had been originally named by Schneider (1799), so I was intrigued when asked to review an edition of Schneider’s Historiae Amphibiorum where these names originated (Downie, 2022). The book, originally in Latin, has been translated and interpreted into modern English by Bauer and Lavilla, a task of immense scholarship, including copious notes and contemporary illustrations. Schneider was a German scholar and natural historian, post-Linnaeus but pre-Darwin, who based his account on specimens in European museum collections that had been accumulated from around the World. In 1799, the animals we now consider as reptiles and amphibians were still all classed as Amphibia, and Schneider’s book aimed to describe all the then known species (apart from the geckos and chelonians that he had covered in previous works): this came to 70 amphibians and 100 reptiles as we would now class them, a small proportion of the 8000+ and 12000+ we know now. Of the Trinidad species first named by Schneider, Leptodactylus fuscus was originally Rana fusca and has been known under 19 different scientific names so far (Frost, 2025); and the microhylid Elachistocleis ovalis (Rana ovalis in Schneider) is a species whose distribution, naming and relationships are still in dispute (Jowers et al., 2021).

The Linnaean binomial system remains an indispensable tool for research into the vast diversity of living species, but the use of long, sometimes cumbersome, Latin names, especially when altered after taxonomic revisions, does not help in  communication to non-scientists: hence the continuing value of common names.

Acknowledgement

The Wikipedia article on the International Code for Zoological Nomenclature was a key source of the historical information in this article.

References…

Arntzen et al. (2014). A new vertebrate species native to the British isles: Bufo spinosus Daudin, 1803. Herpetological Journal 24, 209-216.

Downie (2022). Review of  Bauer and Lavilla (2022). J.G.Schneider’s Historiae Amphibiorum at the dawn of the 19th Century. Contributions to Herpetology volume 32. Herpetological Bulletin 161, 47-48.

Frost (2025). Amphibian Species of the World, on-line database, accessed February 2025.

Jowers et al. (2021). Unravelling unique island colonization events in Elachistocleis frogs: phylogeography, cryptic divergence, and taxonomic  implications. Organisms, Diversity and Evolution 2, 189-206.

Mebert et al. (2022). A new rainforest frog of the genus Pristimantis from central and eastern Panama. Zookeys 1081, 1-34.

Vences et al. (2024). Communicator whistles ; a Trek through the taxonomy of the Boophis marojezenis complex reveals seven new morphologically cryptic treefrogs from Madagascar. Vertebrate Zoology 74, 643-681.

Mouth and Stomach Brooders: can they be saved from extinction?

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Written by Roger Downie, Froglife and University of Glasgow

On 3rd February 2025, many media outlets reported news of the ‘birth’ of 33 juvenile Darwin’s frogs at London Zoo. Why was this event so newsworthy? In this article, we look into two unusual modes of parental care in frogs and the plight of the species involved.

Among the more than 70 reproductive modes so far described from amphibians (see Croaking Science December 2021 and April 2019), perhaps the strangest are where the eggs are incubated either in the mouth or the stomach of a parent.

Since mouth-brooding is known from nine families of fish, most commonly in the cichlids, it is perhaps not so surprising that it has also evolved in frogs. However, biologists were astonished in the 1970s to learn of a genus of Australian frogs (only two species) where eggs are incubated in the stomach of the mother.

After fertilisation of the large (about 5mm diameter) eggs, they are swallowed by the mother and pass to her stomach. A prostaglandin E signal in the mucus coating of each egg (and later released from tadpole gills) inhibits secretion of stomach acid and enzymes. Tadpoles develop and metamorphose in the stomach, entirely fuelled by egg yolk, and froglets are born by regurgitation at about six weeks.

The two gastric-brooding frogs Rheobatrachus silus (southern species) and R. vitellinus (northern, known as the Eungella gastric-brooding frog, from the national park where it was found) lived in rainforest creeks in restricted areas of eastern Queensland. Sadly, both species became extinct soon after their discovery. R. silus has not been seen, despite repeated surveys, since the late 1970s, R. vitellinus since the mid-1980s. A well-planned expedition in 2021 checked previous locations in Eungella and found plenty of suitable habitat, and also populations of two endangered endemic frogs, the Eungella tinker frog and the tusked frog, but no R. vitellinus. Habitat destruction and chytrid infection are both thought to have contributed to steep population declines and eventual extinction.

R. silus has not been seen, despite repeated surveys, since the late 1970s

All may not be lost. Australian scientists have access to frozen Rheobatrachus specimens, and have had some limited success so far in attempting to regenerate embryos by cloning methods, where Rheobatrachus DNA is injected into host nuclei. Whether this work will result in viable reproductively-capable adults has yet to be seen.

The conservation position is a little better for the mouth-brooders. Again, only two species are known, Darwin’s frog (Rhinoderma darwinii ) and the closely related R. rufum. These frogs became known to science from specimens collected by Darwin during the voyage of The Beagle in 1834: the first species was described and named by Dumeril in 1841; the second species was described in 1902. Both species are endemic to the temperate rainforests of central and southern Chile, extending a little into neighbouring Argentina, with R. rufum having a more northern distribution than R. darwinii; there is a small area of overlap where both have been found. In Rhinoderma, after fertilisation of eggs, deposited on to land, the male takes them into his vocal sac and incubates them there: in R. darwinii, they develop through metamorphosis and are ‘born’ as froglets; in R. rufum, they emerge as tadpoles and complete development in water.

The original forested areas inhabited by the two Rhinoderma species have been much altered by anthropogenic development: urbanisation, commercial forestry and agriculture. Sadly, R. rufum has not been seen since 1981 despite repeated surveys, and is now classed by IUCN as ‘possibly extinct’. The effort to save this unusual kind of frog now concentrates on R. darwinii.

R. rufum has not been seen since 1981 despite repeated surveys, and is now classed by IUCN as ‘possibly extinct’

After several decades where steep declines in R. darwinii populations were recorded, the Chilean section of the IUCN’s Amphibian Specialist Group convened a meeting in 2017 aimed at developing a comprehensive conservation strategy. Thirty experts, including the UK’s Andrew Cunningham, contributed to the resulting plan, launched in 2018 ( Azat et al. 2021). The species was estimated to occupy 65 extant populations in Chile and 10 in Argentina with an overall area of occupancy of only 224 km2. Threats to its continued existence include a) habitat loss: little of its original habitat (coastal deciduous forest ) remains, having been replaced by exotic pine and eucalyptus plantations or agriculture; b) chytrid infection has been in Chile since the 1970s, according to analysis of museum specimens, and surveys have shown it can be lethal for R. darwinii ; c) modelling of climate change suggests that current areas where the species persists will be unsuitable in the future; while new areas may be suitable, the frog’s low dispersal ability will limit any benefit from that. Chile and Argentina combined have 30 protected areas where R. darwinii occurs; there are also three private parks where in situ conservation projects are in progress, and also two separate ex situ projects in Chile: Bourke (2010) reported on the establishment of both indoor and outdoor terraria at Concepcion University, with successful breeding occurring; Fenolio (2012) described a separate facility at the National Zoo of Chile, also with breeding success. The agreed conservation strategy includes 39 prioritised actions and aims to fill information gaps, reduce the main threats and achieve legal and financial support  by 2028.

However, a survey in 2024 of one of the largest R. darwinii populations found a 90% decline compared with the previous year. In response, a London Zoo EDGE (Evolutionarily Distinct Globally Endangered Species) team visited the main island of the Chile Archipelago and over five weeks collected 55 frogs from Parque Tantauco, a 1180 km2 private nature reserve. They kept the frogs in quarantine long enough to detect any chytrid infections (52 were chytrid-free), then, using specially-designed climate-controlled boxes, transported the frogs 7000 miles (by boat, road and plane) to London, arriving on 9th December 2024. Eleven of the males were brooding embryos during the trip, and 33 froglets were born soon after arrival in London. The plan is to breed this population in disease-free conditions as a way of rescuing a species whose future in its normal environment looks extremely gloomy. As with all ex situ conservation projects, the question is: what then?  Will it be possible to re-introduce specimens to the wild and then regenerate native populations, and if not, what is the long-term fate of the captive population?

References

Azat et al. (2021). A flagship for austral temperate forest conservation: an action plan for Darwin’s fogs brings key stakeholders together. Oryx 55, 356-363.

Bourke (2010). Darwin’s frog captive rearing facility in Chile. Froglog 94, 2-6.

Fenolio (2012). The Darwin’s frog conservation initiative. Amphibian Ark Newsletter 18, 22-23.

Climbing salamanders: perspectives from great heights

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Written by Laurence Jarvis (external contributor)

Climbing salamanders within the genus Aneides are a fascinating group with varied behaviour and ecology. There are currently 10 recognised species, found predominantly across North America and Canada, notably California and British Columbia. The genus belongs to the Plethodontidae, which is the largest salamander family, comprising approximately 518 species. Most plethodontid salamanders are endemic to North America and, unlike many European salamanders, lack lungs and instead completely rely on gaseous exchange through their skin. They have evolved to live in a large range of habitats including streams, trees, on land and underground. Most are direct developers, laying eggs on land which hatch into live juveniles which resemble miniature adults.

The arboreal salamander (Aneides lugubris) is the largest of the genus, growing up to 100 mm with a rounded, robust body. As its name suggests, it is excellent at climbing and may ascend trees up to 18 metres, using specially adapted toes with expanded tips1. Uniquely amongst salamanders, the tail is prehensile enabling it to cling to the branches of trees. Arboreal salamanders are highly aggressive, possessing rows of sharp teeth. Both males and females have been reported with scars on their bodies as a result of aggressive combat1. Despite these tendencies, arboreal salamanders perform parental care and either the male or female will guard their clutch of around 5-26 eggs whilst they develop. Like other members of the genus, the eggs are laid in damp areas of rotting wood such as under tree bark. After hatching the small juveniles remain with their parents in family groups. 

Figure 1. The Arboreal salamander (Aneides lugubris) is a highly mobile species living within Californian forests.

Wandering salamanders (A. vagrans) are as equally mobile and arboreal as A. lugubris and will climb trees very readily. They have been reported to ascent up to 87 metres in Douglas fir forests of British Colombia2. If disturbed individuals exhibit an unusual behaviour of jumping from the tree canopy and performing an aerial skydive to land safely. Unlike other species which may jump and glide from a height, such as flying squirrels or frogs, wandering salamanders do not possess obvious adaptations such as flaps of skin to slow their fall. Therefore, this behaviour seems unexpected. Recent research by Brown et al. (2022)3 examined the morphology and aerodynamics of individuals as they fell under experimental conditions in a wind tunnel. They found that, compared to other species within the genus, wandering salamanders have more flattened bodies and slightly wider toes, which they spread during their fall. In addition, individuals stretch out their limbs in a skydive posture and undulate their bodies. The researchers showed that these combined behaviours slowed their fall and prevented damage on impact with the ground.

Climbing salamanders are unusual amongst amphibians since the adults of several species are monomorphic, that is, both males and females are of equal size. The vast majority of amphibians (over 90%) show a degree of sexual dimorphism, with females often being larger than males. However, in plethodontid salamanders, males are often larger than females. It is thought this is because they are highly territorial and use their size to defend territories. Many other frog and toad species possess other dimorphic traits which may include differences in skin colour or development of secondary sex characters such as nuptial pads. The Sacramento Mountains Salamander (A. hardii) is one of the Aneides salamanders that is sexually dimorphic with males being larger and possessing wider heads than females. Other members of the Aneides genus are monomorphic, with females also having large bodies and wider heads like males.

Since many other plethodontid salamanders are sexually dimorphic it is thought that increased male size over females is the ancestral state4. Research by Staub (2021)4 examining the evolution of plethodontid salamanders suggests that the monomorphism observed in species of the Aneides genus has evolved later. These monomorphic species are therefore described as having ‘derived monomorphism’, since they have evolved from sexually dimorphic ancestors4. The exact reason for the similar size in both males and females is uncertain but Staub et al. (2024)5 postulated that higher levels of androgen hormone in females may explain their equal size to males. However, their experimental work did not confirm this. Therefore, further research is required to determine whether there are differences in steroid sensitivity or signalling within females, rather than different levels of hormone5.

Figure 2. The wandering salamander (Aneides vagrans) may jump from treetops and perform a skydive to land safely.

Climbing salamanders are a unique group and whilst several species are common and widespread, six species within the genus are listed as either Near Threatened or Vulnerable. Habitat loss is a continual problem with unsustainable logging causing the declines in several species. The Shasta Black Salamander (A. iecanus) is now classed as Vulnerable, and has suffered rapid declines due to the construction of the Shasta Reservoir in California. Like other plethodontids, climbing salamanders are also vulnerable to climate change and several species have suffered due to longer and drier summers across their range. Conserving these threatened species is a challenge and combined conservation efforts are required to protect these fascinating species.

Click for References

1AmphibiaWeb (2024). <https://amphibiaweb.org> Aneides lugubris. University of California, Berkeley, CA, USA. Accessed 12 Dec 2024.

2AmphibiaWeb (2024). <https://amphibiaweb.org> Aneides vagrans. University of California, Berkeley, CA, USA. Accessed 12 Dec 2024.

3Brown C.E., Sathe E.A., Dudley R. and Deban S.M. (2022). Gliding and parachuting by arboreal salamanders. Current Biology, 32 (10): R453-R454.

4Staub N.L. (2021). The evolution of derived monomorphism from sexual dimorphism: a case study on salamanders. Integrative Organismal Biology, 3 (1): p.obaa044.

5Staub N.L., Hayes S.G. and Mendonca M.T. (2024). Levels of Sex Steroids in Plethodontid Salamanders: A Comparative Study Within the Genus Aneides. Ecology and Evolution, 14 (11): p.e70550.

Croaking Science: Alternative strategies for amphibians – neoteny and overwintering

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Written by Dr Andrew Smart, Head of Science and Research at Froglife

People often wonder why they occasionally find tadpoles in their ponds over the winter.  This is an example of delayed metamorphosis, which can be advantageous to some individuals, particularly in northern latitudes. In newts we find overwintering larvae and also examples of neoteny when the larval form is retained and, in some cases, mature and reproduce.

The classic case of neoteny in amphibians is the axolotl, which retain their feathery gills into adulthood, becoming enlarged larvae that develop reproductive organs and can produce large numbers of fertile eggs. Axolotls evolved to live in two lakes in Mexico where the water levels were stable and food levels high, enabling animals, lacking the thyroid hormone that triggers metamorphosis, to survive and evolve a life-strategy that was more effective than having a terrestrial stage.

The classic case of neoteny in amphibians is the axolotl, which retain their feathery gills into adulthood.

In frogs and toads, there are a range of reasons why tadpoles might be found in a pond in the winter months. The first to rule out is the risk of the invasive species Lithobates catesbeianus, the American bullfrog, which has a larval stage than can be anything from 1 to 4 years.  Overwintering of this large, predatory species has been found to have a neutral or negative impact on other amphibians in introduced populations in the USA[1]. Thankfully, the bullfrog appears to have been eradicated from the UK since 2015[2].

If you have other ‘normal sized’ tadpoles in your pond, the chances are that a number of things may have happened: in some northern latitudes, frog and toad tadpoles have been shown to adopt different strategies[3], with some animals metamorphosing early while others delay metamorphosis, remaining in the pond to be able to exploit resources early in the spring , outcompeting a new cohort of smaller tadpoles[4].  As well as food availability and temperature, other unknown factors lead to this strategy[5]. This enables them to produce larger metamorphosed froglets or toadlets which have a better chance of survival through the winter. 

So why don’t all anurans follow this strategy?  It can be high risk; extreme temperatures could kill animals during hibernation or ponds could dry out before the end of the late summer period and kill all the ‘delaying’ tadpoles.  Most Anurans have developmental cues that trigger metamorphosis, linked to the proximity of other tadpoles and to reduction in water level; [6] in the case of ‘drying ponds’ reducing water depth[7],[8] leads to faster metamorphosis and smaller froglets.

Anurans that develop into ‘large’ tadpoles do have the capacity to develop gonads but in the case of Xenopus (the African clawed toad) ‘giant tadpoles’ that occur develop gonads but struggle to release eggs and sperm[9] and in any case, a ‘giant tadpole’ would be an unlikely animal to participate in amplexus. A similar situation occurs in Pseudis paradoxa, the paradoxical frog, which has evolved a ‘giant tadpole’ that metamorphoses into an adult rather than a froglet.[10] The tadpoles have developed gonads that are close to maturity but the authors point out that life stages in Anurans are very different and that the opportunity for full neoteny is unlikely because of the need for behavioural changes to enable successful reproduction.

African Clawed Frog - Xenopus laevis
In the case of Xenopus (the African clawed toad) ‘giant tadpoles’ that occur develop gonads but struggle to release eggs and sperm.

What about Caudata? There is evidence that some individuals, usually young adults, may move into ponds in the autumn and overwinter[11].  Examples of palmate newts overwintering in ponds in Scotland are well recorded[12],[13], again a strategy to enable a more robust metamorph emerging in the summer to face colder winters. 

There are now several well recorded cases of neoteny in smooth newts – in a Norfolk swimming pool, numbers of neotenous newts were found, resembling female smooth newts but with feathery gills[14].  Two of these animals were  removed for examination and very quickly metamorphosed to adult newts.  The authors of the study suggested a number of possible outcomes suggesting that a change in water quality (increase in iodine) or change in water depth could have triggered the change.

Examples of delayed metamorphosis and also total neoteny have also been recorded at a site in Cambridgeshire, where newt larvae have been seen in large numbers in autumn and early spring, after presumably hibernating in the pond. One of the newts was taken to captivity and laid fertile eggs[15]. This animal did rise to the surface for air,  a behaviour not normally linked with neotenous newts, which have fully functioning gills. As in many cases of neoteny, the records were incidental and unable to be investigated in detail.

So overwintering tadpoles and newt larvae may be a way of amphibians having two different life strategies within a population, some animals taking the risk in the pond, some taking the risk overwintering as a smaller sized individual. Neotenous individuals may be taking advantage of a stable environment with significant food sources and low levels of competition as an alternative strategy, but to really investigate this further we need more information on the habitats where these animals are found.  If you know of a site with neotenous animals, please let us know by emailing: info@froglife.org

References

[1] Boone, M.D., Little, E.E. and Semlitsch, R.D., 2004. Overwintered bullfrog tadpoles negatively affect salamanders and anurans in native amphibian communities. Copeia, 2004(3), pp.683-690

[2] New strategy launched to protect biodiversity and economy from non-native species – GOV.UK (www.gov.uk)

[3] Tattersall, G.J. and Ultsch, G.R., 2008. Physiological ecology of aquatic overwintering in ranid frogs. Biological Reviews, 83(2), pp.119-140.

[4] McNeill, D.C. and Downie, J.R., 2017. Overwintering of smooth and palmate newt larvae in the Gartcosh Nature Reserve, Scotland. The Glasgow Naturalist, 26.

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

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

[7] Merilä, J., Laurila, A., Pahkala, M., Räsänen, K. and Timenes Laugen, A., 2000. Adaptive phenotypic plasticity in timing of metamorphosis in the common frog Rana temporaria. Ecoscience, 7(1), pp.18-24.

[8] Laurila, A. and Kujasalo, J., 1999. Habitat duration, predation risk and phenotypic plasticity in common frog (Rana temporaria) tadpoles. Journal of Animal Ecology, 68(6), pp.1123-1132.

[9] Rot-Nikcevic, I. and Wassersug, R.J., 2004. Arrested development in Xenopus laevis tadpoles: how size constrains metamorphosis. Journal of Experimental Biology, 207(12), pp.2133-2145.

[10] Downie, J.R., Sams, K. and Walsh, P.T., 2009. The paradoxical frog Pseudis paradoxa: larval anatomical characteristics, including gonadal maturation. The Herpetological Journal, 19(1), pp.1-10.

[11] Beebee, T. & Griffiths, R. , 2000, Amphibians and Reptiles: A Natural History of the British Herpetofauna: Book 87 (Collins New Naturalist Library), Harper Collins, London

[12] McNeill, D.C. and Downie, J.R., 2017. Overwintering of smooth and palmate newt larvae in the Gartcosh Nature Reserve, Scotland. The Glasgow Naturalist, 26.

[13] Walker, G., Fairclough, B. and Paterson, E., 2019. Winter presence of adult male palmate newts (Lissotriton helveticus) in a pond in Scotland. Herpetological Bulletin, 149, pp.24-27.

[14] Allain, S.J. and Phillips, N., 2023. Observations of a neotenous population of Smooth NewtsLissotriton vulgaris from Norfolk. Trans. Norfolk Norwich Nat. Soc, 56(1).

[15] Leeke, C. 1990, An occurrence of neotenous sooth newts (Triturus vulgaris) in Cambridgeshire. Bulletin of the British Herpetological Society 31,

Croaking Science – a ‘new’ species of leech predating amphibians

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Written by Andrew Smart, Head of Science & Research

Lawson, B. et al , 2024. Predation of anurans in southern England by Batracobdella algira, a leech previously unknown in the UK. Herpetological Journal. 34 221-227

Leeches are often identified as potential predators of the various life stages of amphibians and in the case of frogs and toads, four native species of leech have been identified as feeding on blood and one leech, Haempois sanguisuga, (the horse leech) are know to be predatory on froglets and toadlets.

Reports of leech infestation on a common toad in 2020 led the authors of this recently published paper to explore the occurrence of leech predation on anurans more widely.  A call for Citizen Scientists to report sightings led to 41 new records between 2020 and 2023.  The authors undertook a detailed review of the species involved, either through morphological or genetic identification, and found that in 2 of the 9 cases identified, the species was Placobdella costata, while in the remaining 7 of the 9 records where leeches were identified to species, the species was Batracobdella algira, a species previously unrecorded in the UK.

Dorsal and ventral view of Placobdella costata

The genotype of the animals collected corresponds with that of individuals from Tunisia and, along with a localised distribution in the south and south west, this suggests the possibility that it is a non-native invasive species. The authors suggest that possible routes of ‘invasion’ include release through animal or plant trade or natural long distance dispersal by birds.

Two other publications from 2016[1] and 2018[2] highlight the link between this leech species and cave salamanders in Sardinia, which suggest that the leech could parasitise newt species. The leech has been recorded on painted frog (Discoglossus pictus) and marsh frog ( Pelopphylax ridibundus) [3] in Morocco and has also be found to parasitize Bufo spiniosus in Tunisia[4] and Algeria[5], a possible pre-adaptation for parasitism of Bufo bufo in the UK.

There is no evidence of the leech being a problem for amphibians within its natural range but it will certainly be worth toad patrols and amphibian surveyors looking out for any new records of leech predation this coming breeding season and notifying the Garden Wildlife Health Project at ZSL of any new records.

References

Click to read more...

[1] Manenti, R., Lunghi, E., Canedoli, C., Bonaccorsi, M. and Ficetola, G., 2016. Parasitism of the leech, Batracobdella algira (Moquin-Tandon, 1846), on Sardinian cave salamanders (genus Hydromantes)(Caudata: plethodontidae). Herpetozoa, 29(1-2), pp.27-35.

[2] Lunghi, E., Ficetola, G.F., Mulargia, M., Cogoni, R., Veith, M., Corti, C. and Manenti, R., 2018. Batracobdella leeches, environmental features and Hydromantes salamanders. International Journal for Parasitology: Parasites and Wildlife, 7(1), pp.48-53.

[3] Mabrouki, Y., Ahmed, R.B., Taybi, A.F. and Rueda, J., 2019. An annotated checklist of the leech (Annelida: Hirudinida) species of the Moulouya River basin, Morocco, with several new distribution records and a historical overview. African Zoology, 54(4), pp.199-214.

[4] Hassine, J.B. and Escoriza, D.., 2014. Bufo spinosus in Tunisia: new data on occurrence, parasitism and tadpole morphology. Herpetol. Bull, 127, p.22.

[5] Merabet, K.. and Karar, M., 2021. First cases of predation of Bufo spinosus by two leech species in Algeria. The Herpetological Bulletin, 156(156), pp.38-39.

Toe tapping frogs: is it a lure?

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Written by Dr. Laurence Jarvis (external contributor) 

Anurans (frogs and toads) are well known for their vocal abilities, particularly during the breeding season. However, visual cues are less studied and understood. Toe tapping is an unusual and interesting behaviour exhibited by a range of amphibian species. Also known as toe twitching, wiggling or trembling amphibians will typically raise or wave one or more legs or feet in the air. This may be slow or very fast. The behaviour appears to be performed by a range of amphibian species as a recent study found reports of toe tapping from 42 amphibian species from 12 families1. There is currently no consensus on the exact reason for toe tapping that can be applied to all amphibian species. The behaviour often appears to occur in response to the presence of prey and may be linked to prey capture. It has also been noted to occur in relation to mate attraction and courtship, such as in the Southern Hispaniola Crested Toad (Peltophryne guentheri), as well as aggression. However, toe tapping may vary widely within a species with individuals sometimes performing the behaviour and not at other times2. When the movements are slow with a raised limb, this is referred to as pedal luring and this is thought to attract prey through mimicking vibrations produced by the prey, as observed in the South American horned frogs (Ceratophrys spp.). However, Sloggett & Zeilstra (2008) proposed that instead, toe-tapping may cause additional vibrations that keeps the prey moving in order to allow detection by the frog3. In support of this hypothesis, a recent study of poison dart frogs (Dendrobatidae) found that individual frogs increased their toe tapping behaviour when prey were inactive which resulted in increased prey movements and more effective detection2.

Figure 1. Dyeing poison frogs (Dendrobates tinctorius) may tap their toes to enable prey capture.

Dyeing poison frogs (Dendrobates tinctorius) of South America have often been observed to tap their posterior toes4. This tapping can be incredibly rapid with reports of up to 500 taps per minute, which is near the limit of vertebrate muscular vibration4. Adults of this species feed on a range of small and fast-moving prey such as flies and other arthropods so effective prey capture is essential. Research carried out by Parrish and Fischer (2024), found that frogs performed toe tapping more whilst feeding and when on a surface that would carry the vibrations, such as smooth leaves4. The frogs performed toe tapping much less when sitting on soil which transmit vibrations more slowly. The researchers also found that individuals increased their toe-tapping whilst in the presence of a breeding partner. The reasons for this are unclear but shows that this species may adapt its tapping behaviour depending on the presence of other individuals, particularly breeding partners. Overall, this study supports the work of Sloggett and Zeilstra (2008) and suggests that toe tapping may agitate small arthropods by substrate vibrations and thereby help the individuals to detect their prey4.

Figure 2. The Yellow-striped Poison Frog (D. truncates) exhibits accelerated toe tapping.

The Yellow-striped Poison Frog (D. truncatus) is a poison dart frog native to Colombia. In an attempt to further understand the function of toe tapping in this species Vergara-Herrera et al. (2023) designed an experiment to examine the vibrations produced during toe tapping5. The results confirmed that toe tapping was performed in relation to prey capture. In addition, the researchers found that tapping rate accelerated during their sequence of attacks on prey during foraging5. This is analogous to the foraging behaviour of species including bats, dolphins and sperm whales, all of which increase call rate as they approach their prey. In these species it is thought that the increase in call rate immediately prior to capturing their prey helps to confirm its location, speed and movement and thus aid in capture. It is not known whether this is the reason for increasing tapping rate in the Yellow-striped Poison Frog but the acceleration is likely to aid in final prey capture. If the toe tapping serves to further agitate the prey, as proposed by Sloggett & Zeilstra (2008), then more rapid toe tapping would make the prey more detectable, and thus easier to capture by the frogs.

Figure 3. The Southern Corroboree Frog (Pseudophryne corroboree) is a critically endangered species native to Australia.

Toe tapping is an under recorded behaviour but is being noted in an increasing number of species worldwide. The genus Pseudophryne consists of 14 endemic Australian species, all of which are small, cryptic ground-dwelling species. Toe tapping has only previously been recorded in one other species within the genus6. The Southern Corroboree Frog (Pseudophryne corroboree) is a critically endangered species, restricted to areas above 1300 m elevation in New South Wales, Australia. Recently it was not thought to exhibit toe tapping behaviour. However, during captive breeding, McFadden et al. (2008) observed rapid toe tapping prior to being fed crickets6. In this species, for the vast majority of individuals, the tapping foot was raised off the substrate and waved as in the South American horned frogs. This is in contrast to poison frogs, which usually tap their feet whilst in contact with the substrate. The behaviour of the Southern Corroboree Frog would suggest that the moving foot is used to attract prey, rather than trigger movement. Alternatively, as stated by the researchers of the study, it is possible that the tapping could be simply an excited response to the presence of prey.

Overall, toe tapping is an interesting behaviour which has been observed in a wide range of amphibian species. Increased observations and studies on a wider range of species are demonstrating that the behaviour is more widespread than previously thought. Although the exact functional significance is not always fully understood, and may vary between species, it demonstrates the capacity for varied visual cues to be utilised by frog and toad species.

 

References

 

1Erdmann J.A. (2017). The function of toe movement in feeding by the gulf coast toad (Incilius nebulifer). Masters thesis, Southeastern Louisiana University.

 

2Claessens L.S.A., Ganchev N.O., Kukk M.M., Schutte C.J., and Sloggett J.J. (2020). An investigation of toe-tapping behaviour in anurans by analysis of online video resources. Journal of Zoology, 312 (3): 158–162. https://doi.org/10.1111/jzo.12815.

 

3Sloggett J.J. and Zeilstra I. (2008). Waving or tapping? Vibrational stimuli and the general function of toe twitching in frogs and toads (Amphibia: Anura). Animal Behaviour, 5: e1–e4.

 

4Parrish T.Q. and Fischer E.K. (2024). Tap dancing frogs: Posterior toe tapping and feeding in Dendrobates tinctorius. Ethology, p.e13465.

 

5Vergara-Herrera N., Cocroft R. and Rueda-Solano L.A. (2023). Eating to the beat of the drum: vibrational parameters of toe tapping behavior in Dendrobates truncatus (Anura: Dendrobatidae). Evolutionary Ecology, 1-17. https://doi.org/10.1007/s10682-023-10277-x

 

6McFadden M., Harlow P.S, Kozlowski S. and Purcell D. (2010). Toe-twitching during feeding in the Australian myobatrachid frog, Pseudophryne corroboree. Herpetological Review, 41(2): 153-154.