amphibian

Croaking Science: Miniaturisation in amphibians

March 26, 2018 by editor

Miniaturisation in amphibians – evolutionary specialisation

Amphibians exhibit vast ranges in body size ranging from just 7 mm long in the smallest known species (Paedophryne amanuensis) to 33 cm in the largest frog (Conraua goliath), which represents a 250 fold increase in size. Different body sizes come with distinct advantages and disadvantages. Large amphibians have fewer predators, a lower metabolic rate, and they can more easily maintain their temperature and hydration than small amphibians. Smaller amphibians, although being more prone to predation, are better equipped to hide more easily, exploit alternative food sources, use physically smaller niches, and attain reproductive ability at an earlier age (Leavy & Heald, 2015). By being very small, individuals are able to fully utilise habitat patches and consume the smallest prey, which are also the most numerous. However, living at such small sizes puts constraints on biological processes and as a result, miniature amphibians have evolved unique features to enable them to function effectively. Many miniaturised frogs have a reduced number of skull elements, fewer digits on their limbs, fewer vertebrae and a reduction in webbing on the feet. Many miniature frogs resemble juveniles and retain of their features. Indeed, the frog genus Paedophryne, discovered in 2010 from Papua New Guinea, means ‘juvenile form’ and contains some of the world’s smallest frogs measuring just 10.1–11.3 mm (Kraus, 2010). Most miniature frogs from a range of families are usually found in wet tropical forests and live on the forest floor under leaf litter feeding on minute termites, small ants and similar species (Almeida-Santos et al., 2011).

Miniaturisation within the amphibians has evolved independently several times and in many species adults only grow to 20 mm in length. For example, miniaturisation has evolved 8 times in the puddle frogs (genus Phrynobatrachus) of Sub-Saharan Africa (Zimkus et al., 2012). The unusual reproductive mode of many tropical amphibian species has promoted the evolution of small body size. Miniature amphibian species are usually fully terrestrial with individuals laying a small number of relatively large eggs within the leaf litter which hatch into fully metamorphosed juveniles. For example, the Strabomantid frogs of the Peruvian Andes are fully terrestrial and do not require water to breed. This means that individuals do not need to undergo breeding migrations to water bodies. This promotes the evolution of small body size since individuals are able to occupy very small home ranges (Lehr & Catenazzi, 2009). In addition, the unique physiology of amphibians has allowed the evolution of small body sizes even at high altitudes, especially in the tropics. In many groups of vertebrates there is a relationship between body size and temperature (Bergmann’s Rule) where individuals at higher altitudes or latitudes attain larger body sizes, often as a protection from colder temperatures. However, due to their physiology which allows them to alter their metabolism for activity at lower temperatures, small amphibian species are able to occupy high altitudes. This removes the constraint of temperature on the evolution of body size and allows species to occupy a greater range of ecological niches even at high altitudes.

*Figure 1. The pumpkin toadlet (Brachycephalus ephippium) from the Atlantic Forest of southern Brazil is one of the smallest known frog species.*

In recent years our knowledge and understanding of miniature amphibians has increased due to discoveries of new species and research into their unique ecology. Frogs within the genus Brachycephalus are all endemic to the Atlantic Forest in Brazil (Figure 1). There are currently 35 known species (Frost, 2018) and 19 of these have been discovered in the past six years. Also known as flea-frogs, these poorly understood species inhabit the moist tropical forest floor within this biodiverse hotspot. Growing to less than 20 mm in length, Brachycephalus didactylus, occurs only in Rio de Janeiro state where it is threatened by encroaching human developments and habitat fragmentation. During the breeding season, females lay just two eggs, probably laying each on a different day (Almeida-Santos et al., 2011). Each egg is laid amongst the leaf litter where it undergoes complete development into a fully metamorphosed juvenile frog with no free-swimming larval stage. The eggs of this species are also relatively large, allowing newly metamorphosed juveniles to emerge at a larger size which offers greater protection from predators.

*Figure 2. The miniature Malabar night frog, Nyctibatrachus major, from the Western Ghats, India.*

Night frogs, genus Nyctibatrachus, live in close association with mountain streams or marshes in forests of the Western Ghats, India. Species within this genus are extremely small ranging 10 – 77 mm. In 2017 Garg et al. (2017) discovered seven new miniaturised night frog species, four of which are among the smallest frogs in India measuring just 12.2 to 15.4 mm in length. All members of the new species were found under leaf litter or in wet grass near to streams or waterfalls. One male was found clasping a clutch of 10 eggs (Garg et al., 2017). The authors believe that more surveys will discover further new species which will also aid our understanding about the evolutionary advantages of miniaturisation and adaptation to terrestrial life within these and other miniature frogs

References

Almeida-Santos, M., Siqueira, C.C., Van Sluys, M. & Rocha, C.F.D. (2011) Ecology of the Brazilian flea frog Brachycephalus didactylus (Terrarana: Brachycephalidae). Journal of Herpetology, 45 (2): 251-255.

Frost, D.R. (2018) Amphibian Species of the World: an Online Reference. Version 6.0 (09 March 2018). Electronic Database accessible at http://research.amnh.org/herpetology/amphibia/index.html. American Museum of Natural History, New York, USA.

Garg, S., Suyesh, R., Sukesan, S. & Biju, S.D. (2017) Seven new species of night frogs (Anura,

Nyctibatrachidae) from the Western Ghats biodiversity hotspot of India, with remarkably high diversity of diminutive forms. PeerJ, 5:e3007; DOI 10.7717/peerj.3007.

Kraus, F. (2010) New genus of diminutive microhylid frogs from Papua New Guinea. ZooKeys 48: 39-59.

Leavy, D.L. & Heald, R. (2015) Biological Scaling Problems and Solutions in Amphibians. In: Additional Perspectives on Size Control in Biology: From Organelles to Organisms. Eds R. Heald, I.K. Hariharan and D.B. Wake. Cold Spring Harbor Laboratory Press, doi: 10.1101/cshperspect.a019166.

Lehr, E. & Catenazzi, A. (2009) A new species of minute Noblella (Anura: Strabomantidae) from Southern Peru: the smallest frog of the Andes. Copeia, 2009 (1): 148–156.

Zimkus, B.M., Lawson, L., Loader, S.P. & Hanken, J. (2012) Terrestrialization, miniaturization and rates of diversification in African puddle frogs (Anura: Phrynobatrachidae). PLoS ONE, 7 (4): e35118. doi:10.1371/journal.pone.0035118.

Amphibian and reptile declines – UK perspective

March 23, 2018 by editor

Amphibian and reptile declines – UK perspective

The UK supports a range of iconic mammal species including hedgehogs, water voles, badgers and several bat species. However, in recent years, research by various conservation bodies has found startling declines in many of these species. Research led by the Wildlife Trusts indicates there has been a 30% decline in water vole populations since 2006, which represents an approximately 3% loss in populations per year¹. Of more concern, is the dramatic decline in the hedgehog which is estimated to have declined by 66% over the past 13 years (5% decline per year)². Increased agricultural intensification, use of pesticides, habitat loss and fragmentation have all attributed to the decline which has been reported by the British Trust for Ornithology². In addition, several of the UK’s iconic bat species are in decline, as reported by Bat Conservation, including the brown long-eared bat which has declined by 31.3% since 1999 (2.2% decline per year)³.

*Figure 1: Breeding common toads (Photo Credit- Silviu Petrovan)*

Amphibians and reptiles are generally less understood by the public who often perceive these species differently to iconic mammals. However, many populations of our once common amphibian species are in decline. Common frog, common toad and natterjack toad populations have been reported as being in decline since the 1970s^4,5. Recent research in 2016 by Froglife and the University of Zurich has shown that common toad populations have declined across the UK by 68% over the past 30 years, which approximates to a 2.26 % decline per year. This value is comparable to the declines in many of our iconic mammal species and highlights that significant declines may be widespread across our native fauna. The reasons for the decline in the common toad are similar to those affecting hedgehogs including habitat loss and fragmentation, pollution and climate change. The adder, being the only native venomous snake in the UK, often has a poor perception from the public. However research by Natural England and Froglife in 2002 has indicated significant population declines in the adder, especially from the Midlands⁶. In this study one third of adder populations were estimated to consist of less than 10 individuals which puts them at high risk of extinction. These declines are likely to be attributable to poor habitat management including agricultural intensification as well as public pressure (recreation) and persecution⁶. At Froglife we aim to raise awareness of the declines in our native amphibian and reptile species, especially those which were once common. We wish to highlight that widespread amphibian and reptile species, such as the common toad, are suffering declines equivalent to iconic mammals such as the water vole and hedgehog. At Froglife we carry out extensive practical habitat creation and restoration each year, both locally and nationally, with the aim of improving environmental conditions for our native amphibians and reptiles and aiding to conserve populations of our valuable herpetofauna.

References

¹Wildlife Trusts (2018). http://www.wildlifetrusts.org/news/2018/02/26/new-report-points-30-decline-water-vole-distribution. Accessed on 13^th March 2018.

²BTO (2018) https://www.bto.org/science/monitoring/hedgehogs. Accessed on 13^th March 2018.

³Bat Conservation (2018) http://www.bats.org.uk/pages/species_population_trends.html. Accessed on 13^th March 2018.

⁴Beebee, T.J.C. (1973) Observations concerning the decline of the British Amphibia. Biological Conservation, 5 (1): 20-24.

⁵Beebee, T.J.C. (1977) Environmental change as a cause of natterjack toad (Bufo calamita) declines in Britain. Biological Conservation, 11: 87-102.

⁶Baker, J.R., Suckling, J. & Carey, R. (2004) Status of the adder Vipera berus and slow-worm Anguis fragilis in England. English Nature Research Report 546, English Nature, Peterborough, UK.

Croaking Science: Amphibians that change colour

January 17, 2018 by editor

Amphibians that change colour – dichromatism in frogs and salamanders

Size dimorphism, where one sex is larger than the other, is common in amphibians and occurs in approximately 90% of frog and toad families. However, sexual dichromatism, where one sex is a different colour to the other has only been documented in approximately 122 (17%) of frog and toad species. There are two types of dichromatism: dynamic dichromatism, where males undergo a rapid colour change prior to the breeding season; and ontogenetic dichromatism where one sex remains a different colour the entire of its life once it has matured (Bell & Zamudio, 2012). Dynamic dichromatism occurs in 31 frog species but is probably under-recorded due to its ephemeral nature of only occurring for short periods around breeding. Ontogenetic dichromatism appears more common, being documented from 91 anuran species. However, our understanding of the mechanisms behind colour change in frogs is still limiting.

The Wood Frog (Rana sylvatica) exhibits ontogenetic dichromatism with males being tan or dark brown whereas females tend to be redder in colour (Figure 1). Previous experiments have shown that males are attracted to red females but are ambivalent towards darker coloured females. Being able to readily distinguish the sexes is likely to be important for Wood Frog males, as the breeding season may last only 1–3 days in early spring (March and April) and high male-male competition often results in only a small percentage of males succeeding in mating. Research by Lambert et al. (2017) has shown that sexual dichromatism in Wood Frogs is absent immediately after metamorphosis but develops and persists through the second spring and summer. Unlike some frog species, where the body colour change is almost instantaneous and lasts only a few days, the colouration alteration in Wood Frogs takes weeks to develop and lasts for several weeks after the breeding season. Currently, it is unclear which environmental conditions (e.g., light, temperature, food, etc.) influence the colour change after hibernation. It is also unclear why the frogs remain with colour dichromatism for extended periods when breeding only lasts a few days. It seems likely that the colour change has evolved as a result of both sexual and natural selection. Females which are redder in colouration are more easily identifiable by males during the short breeding season. In addition, the colour changes may provide the different sexes protection from predation. Redder females are more camouflaged on the forest floor during terrestrial migration and may benefit from reduced predation. In contrast, the dark tan or brown males have greater camouflage whilst aggregating around ponds when they are at greatest risk from predators. Therefore the differences in colour between males and females in Wood Frogs may offer benefits for reproduction and survival.

*Figure 1. Female (left) and male (right) Wood Frogs demonstrating colour dichromatism. (Photo Credit: Lindsey Swierk)*

Sexual dichromatism is much rarer in newts and salamanders and has only been reported from a few species. The development of graphic software has enabled researchers to examine in more detail the dorsal patterning in relation to colour quality patterns such as hue, saturation, brightness, or quantity of each spot on the dorsal and ventral sides. Using such techniques in salamanders have revealed sexual dichromatism which was previously unnoticed to the naked eye. For example, in adult Red-spotted Newts (Notophthalamus viridescens) image analysis software was used to demonstrate that males have more intensely red dorsal spots compared to females. Recent work by Balagova and Uhrin (2015) on the Fire Salamander (Salamandra salamandra) has shown that males have a greater amount of yellow dorsal patterns compared to females (Figure 2). Since the reproductive strategy involves female choice, the authors hypothesise that females may be able to select males based on their dorsal patterns. In this species the dorsal patterns indicate toxicity to predators so a brighter individual with a greater amount of patterning may be more effective at deterring predators. The authors suggest that females may select males with brighter and a greater amount of patterning since they offer greater protection from predators and their offspring will inherit this characteristic. In addition, females may have a greater proportion of black colour to absorb more heat which would result in faster egg development.

*Figure 2. Male Fire Salamanders (Salamandra salamandra) have a greater proportion of yellow markings compared to females. (Photo Credit: Adobe stock)*

Overall, recent research suggests that we are gaining in understanding of the distribution of sexual dichromatism among amphibian species, but that we still know very little about its function. In addition, dichromatism in amphibians offers benefits for investigating the relative roles of natural selection and sexual selection in the evolution and origins of sexual dichromatism and its significance for a range of amphibian species.

References

Bell, R.C. & Zamudio, K.R. (2012) Sexual dichromatism in frogs: natural selection, sexual selection and unexpected diversity. Proc. R. Soc. B. 279 (4): 4687-4693.

Lambert, M.R., Carlson, B.E., Smylie, M.S. & Swierk, L. (2017) Ontogeny of sexual dichromatism in the explosively breeding wood frog. Herpetological Conservation and Biology 12 (2):447-456.

Balogová, M. & Uhrin, M. (2015) Sex-biased dorsal spotted patterns in the fire salamander (Salamandra salamandra). Salamandra 51 (1): 12-18.

Croaking Science: The Problem of Data Deficiency in Amphibian Conservation

October 26, 2017 by editor

The problem of Data Deficiency in amphibian conservation

There are currently 7737 recognised species of amphibian and new species are being added to the list each month. This is either due to new species discoveries or as a result of taxonomic revisions where a taxonomic split of one previously recognised species results in several new species. Each species is given an extinction risk by the International Union for the Conservation of Nature (IUCN) which ranges from Extinct through four threatened categories (Extinct in the Wild, Critically Endangered, Endangered and Vulnerable) to Near Threatened, Data Deficient and Not Evaluated (NE). Species with insufficient information available are classed as Data Deficient (DD). High profile vertebrate groups such as mammals and birds have near complete IUCN coverage with few DD species. However, within the amphibians there are many poorly understood species which has resulted in a relatively high proportion of species being classed as DD. The prevalence of DD and NE species is likely to remain high as further taxonomic revisions and species discoveries in remote parts of the globe continues. This is of concern since the IUCN Red List is used in a wide range of conservation decisions, policy making, conservation management decisions and research agendas (Howard & Bickford, 2014). There is pressing need to estimate the level of extinction of DD species for a greater understanding of a group’s overall extinction risk.

Over one third of amphibian species are classified with a threatened status while a quarter of all amphibian species are unable to be assessed by the IUCN and remain DD or NE. Attempts to directly address the problem of DD species are rare since there is not the time or resources to explore the remote parts of the globe where DD species often occur. However, Morias et al. (2013) examined geographical range with time since discovery in an attempt to predict the level of risk posed to DD species in Brazil. Morias et al. (2013) concluded that recently described DD species with a small geographical range have a higher extinction risk. This has proved a useful tool in local policy development for amphibians in Brazil. However, there is still a need to fully assess the level of extinction risk to DD amphibians globally.

In 2014 Howard and Bickford (2014) attempted to address the problem of DD amphibian species at a global scale. They took data for species that had been assigned an extinction category (other than DD) to fit a model relating extinction risk to life history traits (e.g. reproductive mode), environmental variables and habitat loss. They then used this model to predict the extinction risk to DD amphibians and determine whether DD species can be considered more or less at risk compared to fully assessed species. Howard and Bickford (2014) found that DD amphibians are, on average, likely to be more threatened by extinction than fully assessed species. Their model predicted that 63% of amphibians globally are likely to be threatened, compared to the current 32%. Amphibians are already acknowledged to be the most threatened vertebrate group and the findings from this research suggest that the overall level of extinction risk is higher than previously thought. Areas with most at-risk species are likely to be South America, Central Africa and Asia. In particular, amphibian species in Indo-Burma are poorly understood. This region contains many species with DD status, high level of threats to habitat (e.g. habitat loss and pollution) and high rates of species discovery. The annual rates of deforestation are the highest among all tropical regions and less than 10% of these forests have any form of conservation protection (Sodhi et al., 2010).

*Figure 1. Anomaloglossus wothujav, a Data Deficient species from Venezuela, which is only known from one locality. (Photo © 2006 Patty Vela)*

Overcoming the problems in species identification is a key issue in relation to identifying DD species. In tropical regions cryptic species complexes (i.e. those which look nearly identical) are relatively common making identification, taxonomy and subsequent assessment of level of extinction highly challenging. The genus of frogs belonging to Anomaloglossus are a highly cryptic species group with difficulties in identifying species (Figure 1). There are currently 26 known species, mainly endemic to the Guiana Shield region in South America. Many of these species appear to be restricted to just one or two mountain tops in the Pantepui region (Figure 2). However, others within the genus appear to have more broad distributions. Therefore identifying exact species range, and thus level of extinction risk is a conservation priority. In an attempt to gain a greater understanding of species distribution within the Anomaloglossus, Vacher et al. (2017) tested species boundaries using molecular, morphometric and bioacoustic data. Results from this study highlighted that previous research has greatly underestimated the number of species with the genus. For example, six formally recognised species were found to in fact be 18 species and further species remain to be discovered. Therefore developing effective methods for identifying species and their geographical distributions remains a challenge.

*Figure 2. The high mountain peaks of the Pantepui in Surinam support a range of cryptic amphibian species.*

Understanding Data Deficiency is of key importance in effective amphibian conservation. Where time and resources are limiting and field studies to determine species distributions are not possible, the use of modelling may be important in estimating the extinction risk facing species. Developing robust and effective conservation strategies is a high priority in protection of many of the world’s threatened amphibians.

References

Howard, S.D. & Bickford, D.P. (2014) Amphibians over the edge: silent extinction risk of Data Deficient species. Diversity and Distributions, 2014: 1-10.

Morias, A.R., Siquera, M.N., Lemes, P., Macial, N.M, De Marco, P., Jr & Brito, D. (2013) Unravelling the conservation status of Data Deficient species. Biological Conservation, 166: 98-102.

Sodhi, N.S., Posa, M.R.C., Lee, T.M., Bickford, D., Koh, L.P. & Brokk, B.W. (2010) The state and conservation of Southeast Asian biodiversity. Biodiversity and Conservation, 19: 317-328.

Vacher, J-P., Kok, P.J.R., Rodrigues, M.T., Lima, J.D., Lorenzini, A., Martinez, Q., Fallet, M., Courtois, E.A., Blanc, M., Gaucher, P., Dewynter, M., Jairam, R., Ouboter, P., Thébaud, C. & Fouquet, A. (2017) Cryptic diversity in Amazonian frogs: integrative taxonomy of the genus Anomaloglossus (Amphibia: Anura: Amromobatidae) reveals a unique case of diversification within the Guiana Shield. Molecular Phylogenetics and Evolution, 112: 158-173.

Croaking Science: Biparental care and the evolution of monogamy in amphibians

August 23, 2017 by editor

Biparental care and the evolution of monogamy in amphibians

Monogamy, the mating system of only having one partner at a time, is generally rare within the animal kingdom and largely restricted to birds. Social monogamy is applied to pairs that remain together throughout their lives, but do not necessarily mate exclusively with one partner. Approximately 90% of birds are described as socially monogamous for although these pairs will remain with the same partner for life, many will seek to mate with other partners. Genetic monogamy, which refers to exclusive mating between two pairs, is rare within vertebrates. For example, only 25% of socially monogamous bird species are actually genetically monogamous. The evolution of genetic monogamy has been of interest to biologists for many decades and it is thought that biparental care, where both parents look after the offspring, has been an important factor in driving the evolution of monogamy. In species where biparental care is crucial for the offspring survival, working together results in greater survival of the young and greater reproductive output.

Parental care is generally rare within the amphibians and paternal care is considered to be the first form of parental care to have evolved. This is in contrast to birds and mammals, where maternal care appears to have evolved first. Within the amphibians parental care is often associated with tropical terrestrial species, particularly poison dart frogs belonging to the genus Ranitomeya. After females have laid their small clutches of eggs the males often carry the eggs to phytotelmata (pools of water in the axils of tree-dwelling plants) and exhibit egg-guarding. Biparental care has subsequently evolved where by females may lay non-fertile (or trophic) eggs in these small bodies of water to feed developing larvae. Known as trophic feeding, this form of maternal care has been reported from a range of terrestrial breeding tropical frog species and within the Ranitomeya, is associated with larvae developing in very nutrient poor, small bodies of water.

**Figure 1.** Mimic poison frog (Ranitomeya imitator). Both males and females exhibit parental care, which has driven the evolution of monogamy in this species.

Recent research has shown that where biparental care has evolved in amphibian species, this has also resulted in the evolution of genetic monogamy. Prior to 2010, social and genetic monogamy had not been recorded in any species of amphibian. However, research by Brown et al. (2010) documented that social and genetic monogamy occurs in the mimic poison frog (Ranitomeya imitator) (Figure 1). This species occurs in north-central Amazonian Peru, in the regions of Loreto and San Martín and occurs in rainforest habitats between 200 and 1,200 m (Figure 2). Following courtship, the female mimic poison frog lays arboreal clutches of 1–3 eggs on understorey vegetation. The male guards the egg clutches and transports individual tadpoles on their backs to small phytotelmata. The female then lays trophic eggs into the water to provide food for the developing larvae. In an experimental study, Brown et al. (2010) found that 11 out of 12 pairs investigated showed genetic as well as social monogamy by the use of molecular markers. However, the closely related R. variabilis shows no monogamy and is highly promiscuous. In this species the male provides parental care but the female does not provide trophic eggs. Pairs preferred larger pools for tadpole deposition which contain higher levels of nutrients so additional trophic feeding by the female is less required (Brown et al., 2008). It appears that small pool size with low nutrient levels is crucial in driving the evolution of biparentral care and monogamy in species of poison dart frogs. Brown et al. (2010) experimentally confirmed the importance of trophic feeding by showing that tadpoles denied trophic eggs had lower growth rates than controls. Further experiments by Tumulty et al. (2016) demonstrated a significant reduction in reproductive success when males were removed after tadpole deposition, establishing the importance of male care for tadpole growth and survival throughout development. Therefore, because R. imitator breeds in small, low-nutrient waterbodies, both males and females are required to provide parental care. This requirement for active parental care from both the male and female appears to have driven the evolution of genetic monogamy and stable pair bonds in this species.

**Figure 2.** Populations of the mimic poison frog (Ranitomeya imitator) occur within the Regional Conservation Area of Cordillera Escalera, Peru.

Many studies have shown that there are many advantages to biparental care but the high occurrence of extra pair matings, particularly in birds, indicates that there are many genetic advantages to having more than one mate. Therefore, why is the poison mimic frog so exclusively monogamous? The answer seems to lie in the importance of both male and female parental care in the pair bond. Experimental work on species where both partners are crucial for the survival of the young show that monogamy is strong, whereas in species where one partner is not obligatory, the level of monogamy is often weaker. This correlation suggests that genetic monogamy may be favoured when both male and female care is required for offspring survival. Results by Tumulty et al. (2016) indicate this to be the case in R. imitator, which has low rates (8.3%) of extra pair matings.

Overall, the biparental care hypothesis for promoting evolution of monogamy is gaining support from a variety of taxonomic groups and results from recent studies indicate that R. imitator shows a highly stable and cooperative long-term association between male and female and both care mutually for their offspring. The selection for long-term biparental care, as required by the demands of small, low nutrient pool size has driven the evolution of social and genetic monogamy in R. imitator.

References

Tumulty, J., Morales, V. & Summers, K. (2014) The biparental care hypothesis for the evolution of monogamy: experimental evidence in an amphibian. Behavioral Ecology, 25 (2): 262–270.

Brown, J.L., Morales, V. & Summers, K. (2008) Divergence in parental care, habitat selection and larval life history between two species of Peruvian poison frogs: an experimental analysis. Journal of Evolutionary Biology, 21: 1534–1543.

Brown, J.L., Morales, V. & Summers, K. (2010) A key ecological trait drove the evolution of biparental care and monogamy in an amphibian. The American Naturalist, 175 (4): 436-446.

IUCN SSC Amphibian Specialist Group (2014) Ranitomeya imitator. The IUCN Red List of Threatened Species 2014: e.T56378936A43715994. http://dx.doi.org/10.2305/IUCN.UK.2014-1.RLTS.T56378936A43715994.en. Downloaded on 11 August 2017.

Olms: Europe’s only cave dwelling vertebrate with a sixth sense

September 10, 2014 by admin

Croaking science is a new way for student volunteers and scientist to explore what’s occurring in the world of Science. Croaking Science looks at science facts, new research or old debates which are inspired by or affect amphibians and reptiles, and then communicates this in layman’s language to a wider audience. The aim of the feature is to provide a platform for those starting their foray into the world of science communications as well as established scientists. We welcome any submissions from students and scientists. Please note that the views expressed in the articles are not those of the Froglife Trust.

This week our Croaking Science reporter, Rhiannon Laubach, introduces us to the Olm one Europe’s most unusual amphibians.

Olm

The only cave dwelling vertebrate in Europe is an amphibian – a salamander known as an Olm (Proteus anguinus and it is various sub species). It is a neontenic salamander which means they do not metamorphose fully and retain some larval characteristics such as external gills and a tail fin. This rarity has a restricted range as it is completely aquatic and only found in areas of karst aquatic cave systems in limestone or dolomite rocks. They are found in the Dinaric Alps that stretch along the Adriatic Sea, from north-eastern Italy to Bosnia and Herzegovina.
The olm looks like an elongated salamander with thin legs, a long head, rounded snout and a flat tail. They are between 23 and 25cm in length with males being smaller then females. Their skin is whitish and translucent in colour, with a pink tinge due to the blood vessels being so close to the surface.

This species lives in total darkness so their eyes are very poorly developed and have regressed back into their heads. In one sub species they are completely covered over by skin. Interestingly, larvae’s eyes develop normally until they are about 4 months old when the development stops and the eyes start to atrophy. The olm’s have an area of light sensitive specialised cells called ‘melanophores’ on top of their head

To compensate for the lack of sight, the olm has other more acute senses that allow them to hunt in the dark. They have one on the best senses of smell of any amphibian. They can use their sense of smell and taste to locate very low levels of organic compounds in the water. They also have very specialised ears that can sense both vibrations from the ground and sound waves through the water. Unusually, olms have a lateral line which is common in many fish species. This is a pressure sensitivity system that can sense tiny water displacements. Olms also have sixth sense which is centred in a special sensor in their heads known as an ‘ampullary organ’ that enables them to detect weak electrical fields.

Olms feed on detritus washed into the caves as well as other endemic cave species such as crabs, snails and other insects. They swallow their prey whole. Olms can consume large amounts of food and store it as deposits of glycogen in their liver. When they can’t find food, they can use these deposits. Experiments have shown that Olms can survive up to 10 years without food.

Olms are a long lived species they have been recorded as having a life span of 58 years. There is anecdotal evidence they can live up to 100 years. They become sexually mature between the ages of 7 and 12. Females can lay up to 70 eggs hiding them under stones which she guards the eggs until they hatch.

Olms are difficult to study in the wild so most observations of their life history come from a sub-terraine CNRS laboratory in the French Pyrenees, where the olm has been studied since 1955.

It occupies an area of less than 2,000 square km and its habitat has become increasingly threatened. The Olm is threatened by over-collection in the wild, invasive species, pollution and improvements in agriculture causing an increased amount of chemical run off.

Reference

Baker N., Curnick D., Jelic, D.,. (). 19. Olm (Proteus anguinus).Available: http://www.edgeofexistence.org/amphibians/species_info.php?id=563. Last accessed 05/09/14.

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