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Roger Downie

Croaking Science: Red Alert! The alarming state of marsupial frogs

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Amphibians have evolved a fascinating variety of ways to produce and look after their young. Parental care occurs in many families, with either the mother or the father, or occasionally both, spending time and effort to give their young a better chance in life. Recent Croaking Science articles have described the glass frogs (July), where fathers guard incubating eggs on leaves above streams; Phyllomedusa tree frogs (August) where the parents enclose the eggs in folded leaves above water; Mannophryne stream frogs (September), where fathers guard their eggs on land, then transport the hatched tadpoles on their backs to safe water. This month, we look at the marsupial frogs, where mothers carry their developing eggs on their backs. As well as considering their reproductive arrangements, we look at their conservation status: overall, an alarming picture.

The Hemiphractidae are a family of New World frogs, composed of 118 species in six genera. They are distributed across Central and South America, as well as some Caribbean islands. They are very small arboreal frogs, with a primarily nocturnal lifestyle. The main distinguishing feature of the family is the storage and development of eggs on the backs of females, either externally or within a pouch (which has earned some the nickname of marsupial frogs). They also have unusually large embryonic external gills compared to other frogs.

Males of several species have been seen to actively place the eggs on the backs of females during amplexus, during which time they are assumed to contribute their half of the required gametes. They have mostly been seen to breed during wet seasons in tropical areas, as most frogs do. In northern parts of South America there are two wet seasons, a long one lasting from April until August and a shorter one lasting from November until January. Hemiphractid frogs have been seen carrying eggs during both of these, suggesting that they do not possess a strict reproductive timetable but carry out opportunistic breeding when conditions suit.

You can see a range of specialisations between hemiphractid genera, none more apparent than the egg-carrying strategy (to pouch or not to pouch). The genera that utilise enclosed dorsal pouches include Gastrotheca, Flectonotus and Fritziana. Cryptobatrachus, Stefania and Hemiphractus don’t have pouches, instead using mucosal secretions to keep the eggs in place.

Within the pouchless genera, Stefania stand out due to the development of young. In this genus there is no free-swimming tadpole stage, resulting in the hatching of froglets directly from the eggs carried on the female’s back. Female Stefania individuals have been found carrying up to 25 eggs on their back! With a gestation period of around 3 months, those kids are one heck of a burden. Within the pouched or “marsupial” species, the two belonging to the genus Flectonotus stand out due to their mysterious nature, with little research being conducted on either. It is known, however, that hatching occurs within the pouch and that individuals are then deposited into small bodies of water, such as in the ‘tanks’ enclosed by bromeliad leaves; they are at the stage of being well developed tadpoles, which soon metamorphose, without feeding. It is not clear why Flectonotus retains this requirement for a brief aquatic phase, rather than progressing to the froglet stage in the pouch.

Conservation status

Analysis of IUCN’s Red List status for the family Hemiphractidae shows 32% of species in the four threatened categories (critically endangered to near threatened), similar to the figure for amphibians as a whole. However, only 25% of species are in the least concern category, which provides a much more alarming picture. This is because 24% of species are listed as data deficient, and 20% more have yet to be assessed. This is the reality behind some of the global figures for the state of nature. In some parts of the world, especially the tropics, the state of our knowledge of many groups and individual species is very poor. Because of the continuing loss and alteration of natural habitats around the world, the expectation is that species whose status is poorly known are unlikely to be doing well. However, this is not always the case, as we show below for one species of hemiphractid frog.

The dwarf marsupial frog (Flectonotus fitgeraldi) was brought into the spotlight by a recent piece of collaborative research between researchers in Scotland, Trinidad, the USA, Portugal and Venezuela. This study aimed to clarify the conservation status of the species, by establishing an accurate picture of their distribution. Currently, IUCN lists the species as Endangered, but this status appeared to be based on no published original research. Finding these frogs is easier said than done, since they are sized between 2 and 3cm (roughly the size of a 2 pence coin). They have been reported to exist across the islands of Trinidad and Tobago, as well as northern parts of Venezuela. However, there was uncertainty as to whether these three populations fit within a single species, since there had been several cases previously when close examination of widely distributed amphibian species revealed the different populations to be divergent enough to merit description as separate species.

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Pictured: F. fitzgeraldi male perched on a leaf, caught mid-croak by Paul Hoskisson

F. fitzgeraldi are most reliably found by identification of the plant species they use as homes and tadpole deposition sites. These are commonly bromeliads, heliconias and aroids. The larval young of F. fitzgeraldi are deposited in phytotelmata, small pools of water contained within plant structures. The hatching tadpoles are at a late non-feeding stage, having been nourished by yolk content of the egg. In the days following deposition in a bromeliad tank, tadpoles develop limbs and emerge from the water as froglets. Metamorphosis is normally complete within 5 days, during which the tail is reabsorbed and froglets graduate to become fully-fledged frogs.

In order to review the Endangered classification of F. fitzgeraldi, the study made use of molecular techniques as well as surveys over the course of several years. Genomic DNA samples were compared for sequence similarity to determine whether the populations in Trinidad, Tobago and Venezuela all belonged to the same species. Surveys were initially conducted to determine the hours of peak activity in F. fitzgeraldi and found that they exclusively call between 6pm and 8pm, roughly an hour either side of sunset. Based on this information, presence/absence surveys were carried out using the call to determine presence (seeing the frogs is difficult, and moving vegetation to attempt to see them disturbs the frogs) at locations across Trinidad, Tobago and Venezuela. These took the form of transects through forested areas, either on foot or in vehicles, while listening for the raspy calls of F. fitzgeraldi, which sound like running your finger along a comb. This presence/absence data was used to build up a map of their distribution.

Pictured: F. fitzgeraldi perched on a leaf

Results from the study showed the three populations belong to the same species, with no taxonomic changes needed. It was also shown that F. fitzgeraldi was distributed more widely across Trinidad,  Tobago and Venezuela than previously thought. This, combined with the lack of evidence showing deforestation on these two islands, was sufficient to demonstrate that ‘Endangered’ is too extreme a label for the species. However, deforestation in Venezuela, mainly for cattle farming, was found to threaten the habitat quality of F. fitzgeraldi, so the study concluded that a categorisation of the species as ‘Vulnerable’ was appropriate.

Pictured: Female F. fitzgeraldi: left- showing slit on the back, entrance to the brood pouch; right- ‘pregnant’ female. Each bump is a developing embryo in the brood pouch.

Although F. fitzgeraldi is sheltered from mainland deforestation by the island refuges provided by Trinidad and Tobago, many other hemiphractid frogs do not share the same luxury. This means that habitat loss caused by deforestation poses a threat to species whose distribution is restricted to northern areas of the South American continent, such as Venezuela and Guyana. For this reason, species of the hemiphractid family must be monitored closely in these areas over the following decade.

The work on F. fitzgeraldi that we summarise here shows that detailed fieldwork can sometimes reveal that the status of a species is better than previously thought. It also shows the value of student expeditions, which can deploy significant numbers of enthusiastic young people to carry out detailed field research which would be prohibitively expensive otherwise.

Acknowledgements

We thank Paul Hoskisson and Joanna Smith for permission to use their photographs.

Further reading

Our account of the conservation status of F. fitzgeraldi is based on a research paper currently under review.

Cameron Boyle and Roger Downie
University of Glasgow

Croaking Science: More than meets the eye- cryptic frogs are more colourful than you think

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Mannophryne is a genus of 20 frog species found in the forests of Venezuela and Trinidad and Tobago. They belong to the family Aromobatidae, the sister family to the well-known Dendrobatidae, or poison dart frogs. Unlike poison dart frogs, that are brightly coloured to advertise their toxicity, aromobatids use cryptic colouration to blend into their surroundings as they do not have toxic compounds in their skins. In addition, they have a very effective escape response and can identify and reach cover quickly. This has led to one of their common names of rocket frogs, as well as being known as stream frogs, because of their normal habitat of stream margins.

In Trinidad and Tobago, we studied the endemic Mannophryne trinitatis (Trinidad) and M. olmonae (Tobago). Previous assessments of both species for IUCN indicated that they are threatened with extinction on account of habitat loss or degradation. An additional worry was the finding that both species were infected with chytrid fungus, the cause of numerous amphibian population declines across the world, although Mannophryne seemed not to suffer from the infection. We conducted population surveys of M. trinitatis in the Northern Range of Trinidad and found them to be numerous, no longer infected with chytrid, and with no sign of significant habitat loss. In Tobago, M. olmonae are very restricted in their distribution and are found at much lower numbers along streams in the northeast of the island. However, they also showed a lack of chytrid infection and no serious loss of habitat. We contributed to a review of IUCN’s frog assessments and recommend that M. trinitatis now be classed as Least Concern, and M. olmonae as Vulnerable.

Mannophryne are small mottled brown frogs, only a few centimetres in length, which are active during the day close to small mountain streams in primary and secondary forests. They feed on small  arthropods such as beetles, flies and spiders present on the abundant rotting fruit. During the rainy season (June to December), calling males can be heard morning and afternoon trying to attract a mate with their quick “weep, weep, weep” whistling calls. If you follow the calls and look carefully, they can be seen perched on rocks, roots, plants or at the mouths of small caves but will jump quickly away to safety if approached. Meanwhile, females hold a territory, which they defend from other females. When a female has chosen a mate, she follows the male into his cave and lays up to 14 eggs on the damp leaf litter. The males provide parental care, defending and cleaning the eggs until they hatch. This takes around 21 days and then each tadpole flips onto its father’s back and he begins the journey to look for a safe pool of water for his tadpoles to develop in. When a pool free from predatory fish or crustaceans and with a good supply of food is located, the father deposits some of the tadpoles and then searches for another. Tadpoles from a single clutch may be deposited in several bodies of water and will take around 2 months to develop to the stage of metamorphosis.

Figure 1: Calling male (left) and non-calling male (right) M. trinitatis.

One of the most interesting and recently studied aspects of this genus is their colouration. Sexual dichromatism is the difference in colouration between the males and females of a species. This is often used in communication as a visual signal to warn off competitors or highlight quality to potential mates. Sexual dichromatism can be split into two categories. Dynamic dichromatism only occurs in males and involves the development of temporary colouration, often as part of a courtship display, whilst ontogenetic dichromatism can occur in males or females and involves the development of a permanent colour difference as they mature.  Mannophryne are a very rare example among frogs in showing both, where males turn a jet-black colour when they call, and females develop a yellow patch on their throats as they mature.

This is noteworthy, because both forms of dichromatism are energetically expensive, stressing their importance. As male Mannophryne are active and calling during the day, their colour change seems counter- productive as it makes them more conspicuous. Additionally, it appears that open areas are a preferred calling site, and in turn attract a mate, further increasing their predation risk. Therefore, both signals (visual and audio) must be essential in attracting a mate. The role of the yellow throat in females is likely a signal of quality. We found that throat colour is individually variable in the extent of the colour patch and in its hue, ranging from pale yellow to bright orange. Larger and heavier females have more orange throats. Animals often use bright or bold colours to signal their quality to others and to avoid physical confrontation. In M. trinitatis, females can be see raising their heads to show their pulsing throat patch when confronted by another female. This signal shows that the defending female has the additional energy to dedicate to the “expensive” orange colouration and often provides enough incentive to dissuade the challenger from further conflict. Yellow and orange colours are based on carotenoid pigments, and there is evidence from many kinds of animals that carotenoids signal health and quality, as they are related to immune system functions. As a test of this idea that colour differences in the females are a sign of quality, we tested their escape responses in a semi-natural experiment: frogs with the brightest yellow throats showed more effective escape responses than the others.

Figure 2: Female (yellow throat) and male (grey throat) M. trinitatis

An extra facet to throat colour use by Mannophryne females  may be signalling their quality to males. As males take such exhaustive care of their clutch through to deposition of tadpoles, it is unlikely that they could manage more than one at a time. Therefore, it is important that they choose a high-quality female. Mate selection on both sides may be a more significant and understudied aspect to sexual selection in animals where males take all or the majority of parental care responsibilities.

Another fascinating piece of the puzzle is the timing of these colour changes. We observed the colour change on a male M. trinitatis, with the whole process taking around 20 minutes. The male was located by erratic calling and found to still be in its mottled brown colouration. As the calling became more consistent and frequent, the colouration changed to become darker until its change was complete. This is interesting because colour change in frogs is generally quite slow, mediated by hormones, and it will be interesting to discover if there is a special mechanism in Mannophryne. We found through rearing juveniles for several months after metamorphosis, that the yellow colouration develops very gradually in females, well before they reach sexual maturity.

Even though they do not have the bright colours or toxicity of their dart frog cousins, these little frogs are a lot more interesting and special than you might think at first glance.

Further Reading

Downie, J. R., Livingstone, S. R., & Cormack, J. R. (2001). Selection of tadpole deposition sites by male Trinidadian stream frogs, Mannophryne trinitatis (Dendrobatidae): an example of anti-predator behaviour. Herpetological Journal 11, 91-100.

Downie, J. R., Robinson, E., Linklater‐McLennan, R. J., Somerville, E., & Kamenos, N. (2005). Are there costs to extended larval transport in the Trinidadian stream frog, Mannophryne trinitatis (Dendrobatidae)?. Journal of Natural History 39, 2023-2034.

Greener, M. S., Hutton, E., Pollock, C. J., Wilson, A., Lam, C. Y., Nokhbatolfoghahai, M., … & Downie, J. R. (2020). Sexual dichromatism in the neotropical genus Mannophryne (Anura: Aromobatidae). PloS ONE 15(7), e0223080.

Greener, M. S., Shepherd, R., Hoskisson, P. A., Asmath, H., & Downie, J. R. (2017). How many Trinidad stream frogs (Mannophryne trinitatis) are there, and should they be regarded as vulnerable to extinction?. Herpetological Journal 27, 5-11.

Jowers, M. J., & Downie, J. R. (2005). Tadpole deposition behaviour in male stream frogs Mannophryne trinitatis (Anura: Dendrobatidae). Journal of Natural History 39, 3013-3027.

Lehtinen, R. M., Mannette, R. P., Naranjit, K. T., & Roach, A. C. (2007). Ecological observations on the critically endangered Tobago endemic frog Mannophryne olmonae. Applied Herpetology 4, 377-386.

Manzanilla, J., Jowers, M. J., La Marca, E., & García-París, M. (2007). Taxonomic reassessment of Mannophryne trinitatis (Anura: Dendrobatidae) with a description of a new species from Venezuela. Herpetological Journal 17, 31-42.

Contributing authors : Mark S. Greener and Roger Downie

Croaking Science: Egg protection is a sealed deal for Trinidad leaf frogs

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Classification and Biogeography

Figure1: Distribution of Phyllomedusa trinitatis. (IUCN)

The Trinidadian leaf frog (Phyllomedusa trinitatis) is a neotropical tree frog belonging in the Family Phyllomedusidae. The family currently includes over 60 species in eight genera, notably Agalychnis (including the poster species, the red-eyed tree frog) and Phyllomedusa (16 species). Phyllomedusa are commonly known as leaf frogs (because of their bright green colour) or monkey frogs (because of the way they perch and grasp twigs with their long fingers and toes). Members of the family are found throughout the tropical forests of Central and South America. P. trinitatis are distributed across the forests along the northern coast of Venezuela and throughout the island of Trinidad. This distribution suggests that the species has changed very little since Trinidad split from the South American mainland. Tobago, on the other hand, was created through volcanic activity, and is not home to any P. trinitatis individuals.

General Ecology

P. trinitatis are sized between 50 and 90 cm, with females larger (roughly 1.5x) than males. The species shows a mostly nocturnal activity pattern, which allows escape from unfavourable hot and dry conditions present during the dry season in tropical regions. They have been seen to feed on insects present in tropical forests, with a particular penchant for grasshoppers. However, the general ecology of the species is relatively understudied, with not much more known. We made a start by using radio-trackers and thread bobbin tracking to follow where the frogs go after leaving the breeding site. Females moved more than males, with some climbing high into the trees, and others staying at lower levels. The majority of studies on the species focus on breeding ecology. All Phyllomedusa species lay egg clutches on leaves, usually above standing water, and cover the eggs by folding the leaves around them. In contrast, the egg clutches of Agalychnis are laid on leaves, but not covered.

Figure 2: Male P. trinitatis individual gracefully moving between perches at breeding site.

Courtship and Mate Selection

During the wet season in Trinidad, typically starting with rains in early June and ending in November, individuals begin to gather around suitable bodies of still water at sunset. Higher densities of frogs are seen on nights showing higher levels of humidity, mostly due to rains from the preceding day. Sunset occurs at roughly 6.30pm in Trinidad, with little variation throughout the year due to the island’s location close to the Equator. Male individuals are the first to descend from the trees, taking up positions within the vegetation surrounding a pond.

From these perches, males begin emitting advertisement calls to entice females and demonstrate their superiority over other males present. Calls of a lower frequency have been associated with a greater body condition. The calls of P. trinitatis individuals are relatively quiet in comparison to other anuran species present in the forests of Trinidad, and can be drowned out by the raucous sounds of other species. An interesting and unexplored question is whether the calls of other species interfere with Phyllomedusa mating behaviour. Some frogs are explosive breeders, with large numbers gathering at a breeding site over a day or two, mating, then dispersing. Phyllomedusa does not show this pattern. Variable numbers of individuals appear at breeding sites over a period of weeks, even months. Some males appear to adopt a strategy of attending the breeding site frequently, others only occasionally. There may be a trade-off here: since the attendance of fertile females is unpredictable, frequent attendance increases the chance of mating opportunities. On the other hand, frequent attendance may be costly, through reduced opportunities to feed and increased chances of predation. Studying site attendance patterns requires the ability to recognise individuals. We found that Phyllomedusa have individually variable ventral patterns of ‘islands’ and spots, which allow the construction of a photo-catalogue of all the individuals in an area. Fortunately, these are quite docile frogs which are not fazed by being picked up to photograph their belly patterns!

Figure 3: Trinidadian leaf frogs are known to be placid around humans, but are not fans of paparazzi. This frog demonstrates the ventral ‘island’ marking which is variable enough to allow the identification of individuals.

Fertile females arrive after hearing males calling and select a mate from the males on display. The females are weighed down with a clutch of eggs ready to lay. They are commonly outnumbered, which can produce a high level of competition between males, resulting in conflict behaviours including scramble competition where several males crawl over each other and wrestle to achieve amplexus with a female.

Figure 4: Scramble competition events in P. trinitatis. (Left) Female sandwiched between two competing males. (Right) Amplexing pair hassled by two rival males during nest building.

Nest-building Process

Once amplexus is achieved a period of inactivity takes place, presumably for the mating pair to gain familiarity and for the female to judge the suitability of the male. After courtship is completed a mating pair will move to find an appropriate leaf on which to lay the clutch and construct a nest. The leaf selected is either overhanging still water or in close proximity to it, and broad enough to support the weight of an egg clutch (although in locations lacking broad leaves, they are able to construct nests from a number of narrower leaves, even grass stems). The pair remains in amplexus while constructing the leaf nest, using their back legs to hold the edges of the leaf together in a narrow cone shape while the female lays the egg mass which is covered in adhesive jelly to secure the nest structure. Nest construction can last anywhere between 30 and 90 minutes, after which the male departs, leaving the female to hold the leaf in place while the adhesive compounds set to cement the nest structure.

Figure 5: Breeding pair after completing nest construction. Male (rear) has left female (front) to hold the nest in place while it sets.

The egg mass within also contains eggless capsules which provide hydration for the developing eggs (since the sealed nest does not allow the entry of rainwater). Hatching tends to take place around 8 days after nest construction, with tadpoles falling out of the bottom end of nest into the water below where they develop until metamorphosis. The development time between tadpole and froglet is roughly 3 weeks in P. trinitatis, during which juveniles grow to over five times their original size. Upon exiting the pond froglets ascend into the surrounding vegetation where the adolescent tail is fully reabsorbed, metamorphosis is completed, and life as an adult frog begins.

Figure 6: P. trinitatis juvenile, reaching end of metamorphosis, climbing from pond to finish development.

Further reading

Downie, J.R. et al. (2013). Nest structure, incubation and hatching in the Trinidadian leaf-frog Phyllomedusa trinitatis. Phyllomedusa 11, 13-32.

Gourevitch, E.H.Z. and Downie, J.R. (2018). Evaluation of tree frog tracking methods using the Trinidad monkey frog Phyllomedusa trinitatis. Phyllomedusa17, 233-246.

Smith, J.M. et al. (2019). Stable individual variation in ventral spotting patterns in Phyllomedusa trinitatis and other Phyllomedusa species: a minimally invasive method for recognising individuals. Phyllomedusa 18, 13-26.

IUCN (International Union for Conservation of Nature), Conservation International & NatureServe. 2008. Phyllomedusa trinitatis. The IUCN Red List of Threatened Species. Version 2020-2  (https://www.iucnredlist.org/species/55867/11382870; accessed on 8/7/2020)

Authors Cameron Boyle and Roger Downie, University of Glasgow

Croaking Science: See-through frogs are worth a look

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Glass frogs comprise a family (Centrolenidae) of 158 species found in the forests of the neotropics: Central America and northern South America. They get their name from the transparency of their belly skin, which allows the internal organs to be easily seen. They are adapted to life in the trees, possessing pads on the tips of their digits that allow them to adhere to leaves. These structures appear to have evolved independently in several lineages of frogs, since molecular phylogenetic results show that the main families where these pads occur (Hylidae, Rhacophoridae, Centrolenidae) are not closely related.

One of the special features of glass frogs is their mode of reproduction. Clutches of eggs, as flat round sheets, each egg encased in jelly, are laid on the surfaces of leaves overhanging streams. Once the eggs have developed into larvae, they hatch and fall into the stream below, often from a considerable height. Glass frogs are divided into two main sub-families: the Centroleninae (121 species) which lay on the upper sides of leaves and then leave the eggs to develop on their own; and the Hyalinobatrachinae (35 species) which lay their eggs on the lower sides of leaves; in these species, the father cares for the eggs, sometimes up till the point of hatching.

Figure 1: Several egg clutches on a single leaf

We studied the glass frog Hyalinobatrachium orientale which has distinct populations in northern Venezuela and northeast Tobago: this distribution is a bit of a puzzle. Northeast Tobago is quite distant from Venezuela and between these two locations is the large island of Trinidad, which has abundant forests, but no glass frogs. Walking along the forest streams of Tobago at night, once the rainy season (June to December) has started, you soon hear the high-pitched peeping of male glass frogs, located on the huge leaves of Heliconia bihai that overhang the water. With the aid of a good torch, you can locate the calling frogs; often, near them, you can spot the little patches of eggs. If you are lucky, you may locate a mating pair. We observed the behaviour of a mating pair. It took them about four hours to complete their clutch of around 30 eggs, laid as a spiral pattern, starting at the centre, with the pair turning as they proceeded. Once egg-laying was complete, the female departed, but the male stayed close to the clutch. Often, when searching for egg clutches, we found the father sitting on top of his eggs. We also found that some fathers, presumably good quality males, were looking after more than one egg clutch at a time. These are at different stages of development, so clearly produced on different nights. It is not entirely clear what functions male egg attendance performs, particularly given that it is not constant. However, observers have seen males driving away egg predators such as wasps and ants; it is also likely that males keep the eggs hydrated by reducing evaporation, simply by sitting on them, or by emptying their bladders over the eggs (this is established in some cases of frog parental care). But this raises another mystery. If paternal care is helpful to incubation success in the Hyalinobatrachinae, why does it not occur in other glass frogs, especially when they lay their eggs on leaf upper surfaces, where you would guess that desiccation and predation would be higher risks.

In the Tobago glass frog, hatching occurs around nine days after laying, although the actual time is variable, allowing tadpoles to be earlier or later stages of development when entering the water. Such variability may be quite common in frog development and represents a trade-off. Early hatchers are less well developed and more vulnerable when they enter the water; but it may be better to risk this than to be predated while still in the nest. It therefore pays the developing larvae to monitor conditions: if the father has deserted his clutch, or hot sun and no rain are risking desiccation, better to hatch early and hope for a stream with few predators.

Figure 2: Metamorphosing glass frog tadpole on a leaf; with pen for scale

The streams where glass frog tadpoles are found are fast-flowing when it rains, and are heavily populated with predatory fish and crustaceans. They are also shaded, making plant productivity low. As a consequence, glass frog tadpoles spend much of their time hidden under rocks, reducing the risks of predation and of being swept away by currents (unlike the tadpoles of some species that inhabit fast streams, glass frog tadpoles lack the kind of suctorial mouthparts that can help cling on to rocks). The tadpoles have long muscular tails, indicating an ability to move rapidly, and are relatively unpigmented, associated with a concealed lifestyle. Their behaviour limits foraging opportunities, so growth is slow. Glass frog tadpoles can take a year to reach metamorphosis, very slow by tropical frog standards, where many species reach that stage in a few weeks. We have been able to locate metamorphosing glass frogs near the edges of streams. They climb up on to the upper surfaces of leaves close to the ground, and take about four days to complete the process, reducing their tail to a stump. To our surprise, we found that they do not remain in one place through this process, but occasionally move around, possibly to confuse potential predators.

The transparency of glass frogs has long puzzled biologists. Recently, a research team from Bristol, Canada and Ecuador has tested an explanation. Their evidence suggests that it is not so much transparency that matters, but translucence. When a glass frog is at rest with its limbs tucked in, the translucence of the limbs blurs the edges of the body, and makes detection by predators more difficult.

Further reading

Barnett et al. Imperfect transparency and camouflage in glass frogs. PNAS (2020).

Byrne et al. The behaviour of recently hatched Tobago glass frog tadpoles. Herpetological Bulletin 144, 1-4 (2018).

Byrne et al. Observations of metamorphosing tadpoles of the Tobago glass frog. Phyllomedusa (in press) (2020).

Delia et al. Glass frog embryos hatch early after parental desertion. Proceedings of the Royal Society B 281, 2013-2037 (2014).

Downie et al. The tadpole of the glass frog Hyalinobatrachium orientale from Tobago. Herpetological Bulletin 131, 19-21 (2015).

Nokhbatolfoghahai et al. Oviposition and development in the glass frog Hyalinobatrachium orientale. Phyllomedusa 14, 3-17 (2015).

Contributing authors : Roger Downie, Isabel Byrne, Chris Pollock.

Book Review: Wild Child

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Wild Child: coming home to nature

Patrick Barkham, Granta (2020). Hardback, £16.99. 342 pp.

This is a lovely book, and could be read for enjoyment and instruction by anyone who works with younger children, at home or elsewhere. Patrick Barkham is a nature writer, author of four previous books (on butterflies, badgers, coasts and islands) and a regular contributor to The Guardian. This is not a ‘how to’ book, although it includes many experiences of exploring nature with children. It is more a reflection on how children learn about everything, and nature in particular. The focus is Barkham’s own family (the children are non-identical twin girls and a younger boy), but he also interacts with many other children while volunteering at his local outdoor nursery, and visiting forest schools in other parts of England.

His children first discover nature in the overgrown cemetery beyond the garden of their first house in Norwich. As the children grow, the family moves to more space in a village outside the city, and the children attend a nearby, highly innovative outdoor nursery. They are fortunate with the headteacher of the local primary school who allows the children one day at the outdoor nursery even after they are school age.

Some of the book’s chapters describe the changing seasons at the nursery: spring, summer, autumn and a muddy, snowy winter (it’s the year of the ‘beast from the east’). Barkham volunteers there throughout the year, but not on the days his own children attend. Other chapters cover different aspects of nature: birds’ nests and chicks; ponds and dipping for tadpoles, beetles and newts; caterpillars and butterflies. The children learn in a matter-of-fact way about death, and bury dead birds, or take good specimens to the local taxidermist. There’s a running debate about collecting and keeping specimens, and whether wildlife can be pets.

Amongst lively and colourfully worded descriptions of what children do and say (with many verbatim quotations), Barkham discusses in a very straightforward way the many studies which demonstrate the positive impacts on child development of interacting with nature. He also discusses the negative effects of too much time indoors, interacting with screens and anxious about the outside world. For those readers who wish to look further into such studies, there is a full set of references, arranged by book chapter at the end.

Some readers may be thinking: rural Norfolk, Guardian– writer, typical middle-class elitist with no idea of the problems ‘real people’ face. But two of the forest schools Barkham visits belie that stereotype. ‘Wild things in Nottingham works with ‘English as a second language’ children, mostly refugees, many of them coping with horrific past experiences, and few of them speaking much English as yet. Being in nature provides them with experiences for which spoken communication is non-essential. ‘Wilderness schooling’ in Northumberland helps under-achieving children to regain motivation for learning, while experiencing the outdoors and wildlife, and the organiser is accumulating data to prove it works.

Barkham does not hide the fact that children are individuals and not always 100% motivated to learn from wild nature all the time. However, he does insist that ‘however imperfect our lives and our homes, we can add doses of daily nature in a way that enriches us all’. To make this happen for everyone, we need to re-think how our towns, especially our roads are organised. The book was written before the covid19 crisis, but the message fits well with much discussion of how reduced traffic is improving air quality in cities and how provision needs to be made for the resurgence in cycling. He also urges reform of the national curriculum and the emphasis on testing children: modern schools too often stifle the natural creativity and self-motivation that children show. If I have a criticism of the book, it’s the relative lack of engagement with the extensive literature on alternative ways to organise educational systems. This seems a pity given that the original ‘free -school’, A.S. Neill’s Summerhill, is not far from Norwich (in east Suffolk) and is about to celebrate its centenary.

Although I noted that this is not a ‘how to’ book, it ends with a helpful appendix: ‘sixty-one things to do and ways of being with children outdoors’ and a bibliography of helpful and relevant books. The book has no photographs, but includes some maps and delightful chapter-title line drawings. Highly recommended.

Roger Downie

Froglife Trustee; honorary lecturer, University of Glasgow.

Croaking Science: Mud-packing frogs: new approaches to protecting eggs

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The amphibian family Nyctibatrachidae forms one of the three oldest frog families and these species are found only in India and Sri-Lanka. Within the genus Nyctibatrachus there are currently 36 species, many of which have unique reproductive behaviours (see Croaking Science May 2019: https://www.froglife.org/2019/04/). Three closely related species within the genus occupy similar habitats on the forest floor, close to streams. Two of the species, Jog’s Night Frog (Nyctibatrachus jog) and the Kempholey Night Frog (N. kempholeyensis) both lay small clutches of eggs on leaves or branches overhanging slow-moving or still water bodies. The male then guards the eggs and provides water to prevent them drying out (AmphibiaWeb, 2011). However, the recently discovered Kumbara night frog (Nyctibatrachus kumbara) has a unique strategy for protecting its eggs. After laying a small clutch of between 4 and 6 eggs on a branch over-hanging water, the male collects mud and covers the eggs (Figure 1). This is thought to help protect the eggs from predators and prevent them from drying out (Gururaja et al., 2014). Covering eggs with mud in this way has not been recorded in any other species of frog and represents a unique method of protection (Gururaja et al., 2014). After covering the eggs with mud, the males will call to attract females which lay further clutches nearby. The male remains close to the egg clutches for several days until the eggs hatch. By exhibiting an alternative reproductive strategy, this species reduces competition between closely related species which occupy similar ecological niches.

Figure 1. The male Kumbara night frog (Nyctibatrachus kumbara) covers its eggs with mud. Left: a male starting to cover eggs with mud. Right: the male leaving the eggs once they have been covered with mud.  [Photo credit: Gururaja et al., 2014.]

References

AmphibiaWeb (2011) Nyctibatrachus jog: Jog’s Night Frog <http://amphibiaweb.org/species/7715> University of California, Berkeley, CA, USA. Accessed Jan 3, 2020.

Gururaja, K.V., Dinesh, K.P., Priti, H. & Ravikanth, G. (2014) Mud- packing frog: a novel breeding behaviour and parental care in a stream dwelling new species of Nyctibatrachus (Amphibia, Anura, Nyctibatrachus). Zootaxa, 3796: 33-61.