The frog with the colour of the moss (theloderma corticale) displays an extremely emotional camouflage. A physical
embodiment of its surrounding environment, a replication so intimate and empathetic to its environment that it amounts to an evolutionary love affair.
This habitat specific strategy for camouflage constitutes an environmental-phenotype adaptation. Instances of background matching can be ineffective in complex habitats where matching to one background leads to increased visibility on other backgrounds. Nature has also evolved disruptive colouration patterns, which aim to mask body shape rather than match body to background, such as the shore crab, Carcinus maenas1. Shore crabs in visually complex habitats such as rock pools favour disruptive colouration, where as background matching was more dominant in uniform mudflat habitats. Theloderma corticale has evolved background matching in a complex habitat with wild success. It displays a highly habitat specific environmental association, and the relation to environment which it shares with its visual kin only enhances the effectiveness of the adaptation across its complex cloud forest habitat. The amphibian’s skin colouration is light green with dark green markings which change their line weight over the body of the frog like an aerodynamic simulation. Over this, evolution has applied a dramatic skin texturization, an extremely bumpy and uneven surface with pits and rises creating a significant physical edge disruption. This adaptation matches near-perfectly with the moss texture which grows in and around its feeding and nesting habitats. The effectiveness of this adaptation exists in the way the moss relates with its environment. Moss forms as a non-vascular plant with no root system, it spores in small clusters, anchoring itself to the sides of trees and rocks in cool, moist and dark spaces. The crossover of favourable conditions for moss and the mossy frog are unilaterally aligned. This allows Theloderma corticale to camouflage directly in a clump of its evolutionary soulmate, or create an environmental relation on a tree or rock where it can appear as a discrete and independent anchorage of new moss growth.
The relationship between the frog with the colour of the moss and moss itself is visually anchored in the frog’s camouflage survival adaptation. They also share other more conceptual evolutionary-temporal parallels. Moss was one of the earliest plants to colonize land, acting as a link between unicellular green algae and vascular plants some 1000-700 million years ago2. The evolution of plants from aquatic to terrestrial habitation fundamentally changed the carbon cycle and elevated oxygen levels in earth’s atmosphere, enabling the water-to-land transition of animals3. In this way, it was moss, fungi and lichens which first began to garnish the primordial soup from which the first Acanthostega, and other early tetrapods with salamander-like appearances began to emerge during the Cambrian Explosion approximately 540 million years ago. As Robin Wall Kimmerer notes, ‘In order to survive on land, mosses evolved a whole new architecture that surpassed the simpler algae. The floating ribbons of algae were replaced by stems that can hold themselves upright.’4
These evolutionary-temporal scales are poetically accelerated and replicated in the complex 46 stage life cycle of Theloderma corticale. Their tadpoles evolve over a rapid lifecycle and after approximately 19 days of development from egg they have already grown, used, and evolved-on-from an external gill set5. Between days 60-80 limbs grow and toes begin to separate – millions of years of aquatic-terrestrial evolutionary transition replicated in a microcosm.
In 16th Century Japan Raku wear was developed by potters to replicate events on completely detached temporal and geological scales. Forms and ‘imperfections’ in the firing process replicated the cosmic dust in the galaxies above them. These distorted scales and the deep connections they evoked were also evident in the way moss was cultivated on the rocks and path cracks leading to Tea Houses, representing the sublime nature of vast ecosystems.
Sinking into the rocks,
A cicada’s cry
Matsuo Basho (1644-1694)
In an evolving and displaced future, the biological attunement of a mossy frog which lives in cloud forests could rapidly adapt to urbanization. It may begin to camouflage to the concrete water tanks it now finds refuge in, as its deep habitat gives way to disrupted and fragmented urban forest fringes. This species, and many more, demand a research methodology of thoughtfulness and observation to combat habitat loss, disease and the exotic pet trade.
DEEP journeyed to Northern Vietnam to better understand this mystic species and its current ecological situation by visiting Me Linh Station for Biodiversity (MLSB) to view their captive breeding program, then to Tam Dao National Park on a night expedition in an attempt to locate the Mossy Frog in its natural habitat. Driving North out of Hanoi, buildings and infrastructure reduce, the world quietens, and the landscape begins to ripple. Agriculture turns to waterways, turns to forest, turns to jungle. Vines transition their grips from one tree trunk to the next as birds monitor the undergrowth from the skies. MLSB is the field research, animal rescue and education outreach arm for the Institute of Ecology and Biological Resources (IEBR), Hanoi. The Station started as field research arm and then evolved into a rescue for animals injured by logging or whose habitats have been destroyed. From this foundation grew a primary and secondary school environmental education program and a centre for captive breeding and research program for Theloderma corticale. DEEP spoke with Dung Pham, Research Chief at MLSB, to unpack their work.
DEEP: Why was Theloderma corticale identified by MLSB as a species which required a breeding program?
Dung Pham: First, this kind of frog is one of the rarest frogs to find in its natural habitat in the world, it is one of the 15 rarest frog species in the world. Recently is has become very hot in the international black-market pet trade. So because of its small range, global pet trade and habitat destruction, MLSB decided to nurture and protect this frog.
This frog has a narrow distribution in nature, only surviving at certain elevations and with suitable moisture. We try to breed them here, and once we reach a certain population, we will release them back to the natural environment. We do research into the growth and development process of this species to understand the lifecycle and characteristic of this species to assist their protection in the natural environment.
This research assists to understand the frog and lifecycle better, in order to elevate our understanding of this species in the wild and to direct conservation strategy for habitat protection and UN Red Book Endangered Species listing. Additionally, should the numbers continue to decline in the wild, you have an assurance colony here which could be used to slowly repopulate numbers in the wild.
Have you ever reintroduced captive bred Theloderma corticale into the wild?
Not yet. There are significant challenges to releasing captive bred Theloderma corticale back into the wild. While in egg, larval and tadpole stage, the frogs are extremely vulnerable to predation, so their survival rate through this part of their lifecycle is significantly higher in captivity. If the frogs are bred and raised to juvenile frog stage before being released, then they have become used to very controlled conditions and their release poses issues for a common fungus which the frog suffers disease from.
What does the lifecycle of Theloderma corticale look like?
The main stages are egg, tadpole, juvenile and adult. Through the tadpole stage there are 46 steps before it becomes a juvenile.
Is this a long lifecycle for frogs?
Yes, it’s longer than many other frogs.
Does this frog’s particularly long egg and tadpole lifecycle increase its vulnerability?
It’s vulnerable because it is easy to become food for predators. Even adult frogs will eat the tadpole. Tadpoles in the wild can be so easily eaten.
What does it actually take to care for these animals and to ensure they survive and thrive in a captive breeding environment? I look around the laboratory here and see over 20 tanks, with aquatic and terrestrial environments, live plants, light systems, water filters. There is an intimacy and exchange between you and these non-human entities.
In the early days of the breeding program there were many lessons on environment which we developed in collaboration with Cologne Zoo. The environments we had were too clean. We learnt that we needed to allow more natural processes of decay to take place in the soil and water. We learnt that allowing some leaf material to decompose in the water allowed more frogs to reach maturity. We added more varied soil to the terrestrial component of the tank. These were learning processes which led to greater success for our care of these animals and enabled us to better observe their full lifecycle and habitat needs.
It is very detailed work and very time consuming, We breed them, check the water and control its levels, the plants need replacing, the soil needs to be checked. The most important thing is to observe the behaviour and characteristic of the frogs. If they start to have disease they must be quarantined and treated. We measure their size and development in great detail day by day. It is a very time-consuming job which requires a lot of patience and observation.
As we sit in a room surrounded by 20 thriving micro-ecosystems, the work and level of care really shows.
I would like to locate this species in its natural habitat. Their range in very specific to the cloud forests of Northern Vietnam. They prefer a cooler climate in this range and as such are usually only found above 1000m. Could you tell us a little more about the habits and habitat of the species on the wild?
This frog lives in cold weather. Tam Dao is at a high elevation, and there for a colder climate. Normally, in the forest they live in fallen down tree trunks, where water accumulates. The lay their eggs on the trunk above the water. When the egg breaks, it falls into the water and the tadpoles can continue their lifecycle. Until now they have just been found in Tam Dao, and North- East of Vietnam in the high mountain, but it’s a very limited range.
Could you tell us about wild observation, and how it informs your breeding program?
Yes, we always observe them in nature and try to replicate that here. We gain a lot of insight from the locals of Tam Do who have incredible knowledge of the plants and animals in the National Park. The locals have told us about the frogs always being found under fallen wood and in the hollows of trees, and that there is always a relationship between the eggs and a body of water. This helped us design our research environments. We have to know the natural habitat well.
How does the frog inhabit its range, what is its natural character?
They mostly hunt insects for food. They have a unique sound from other frogs, and they are very noisy in the breeding season. The call to each other for matching. Normally we just find one, or a pair of them in one place, so they don’t live in a community. Often, they will only meet for breeding before separating again. Once the eggs are laid the adults leave, they don’t nest or care for the eggs through their development.
What are the amphibious characteristics of the species?
Normally they stay hidden in a tree trunk, during the day. They come out at night to hunt. They will go to water for feeding and also to quickly avoid predators.
Ok, and then there is the amphibious nature of their lifecycle, where they develop gills while in the egg, then they burst through the egg to inhabit a small still water body. The egg’s relationship to this water body is by design, to facilitate their tadpole stages, which occurs exclusively in water. From here their gills turn into lungs as their tail turns to limbs and they emerge from water while retaining the ability to breathe through their skin membrane in water for life. As adults they use water for hunting and hiding, while always preferencing moist terrestrial environments. When it comes time for breeding, they make the same considerations for water proximity as their parents did for them.
Are they a territorial species?
As they are rare and have a scattered distribution, it is uncommon to find more than one or two individuals in a location. In this way they are not often in territorial conflict, and when they are, they don’t express territorial behaviour.
What are the biggest threats to this species I the wild?
Trading, environmental change, and fungal disease are the main threats to this species survival in the wild.
How do the captive frogs compare to the wild frogs?
What do you mean?
The captive frogs here have been bred for several generations in captivity. They have evolved in isolation, in a different environment to their natural habitat. It is a species which exhibits a phenomenal phenotype-environment plasticity. I wonder if they are beginning to show camouflage divergence in any way from the wild frogs...
Not yet? How many generations until they begin to look like the glass from their enclosures?
Yes, maybe a long time! The colour can change, some individuals are greener while some are more dark and brown. This occurs in the wild and captivity.
Could we talk about the unique camouflage of this frog, which speaks to such a strong emergent evolutionally relationship with moss. This beauty is a blessing and a curse. It has assisted its survival in the wild, but also makes it incredibly compelling to the global trade. How do you talk about this camouflage?
We don’t have so much experience in how this evolved. The colour of this species mainly comes from the wild environment. The Vietnamese name is like ‘’the frog with the colour of the moss’. They mainly stay in the trunk, and on the trunk is the moss, and they have the same colour as the moss.
Is there a specific type of moss which grows in the range of the frog that this evolution has evolved from?
They are staying in the rainforest. On the fallen trunks there are many types of moss. This species matches with a certain moss species which grows on specific trees. Actually, the colour of different individuals is different. It depends on the environment. Maybe the wood is darker, so the frog develops darker.
Are you suggesting that each individual frog’s camouflage adapts over the course of their lifetime to the specific colourations in their home range? So, when a tadpole becomes a frog, it is imprinted with some base level aspects of its camouflage, but over the course of its life the camouflage continues to adept to its specific environment?
Yes, when they are born from the egg, they are similar. When they separate to different territories they adapt to their new home and the colour also adapts.
Have you ever seen any extraordinary mutations to this camouflage?
Normally it is more or less similar, sometimes more or less transparent and more or less light and dark. Not so different. The skin texture is also quite similar. Always like moss.
How is the frog adapting to habitat change?
It’s hard for them to adapt to a new environment. Water surface is limited; trees are being removed, so it affects the growing environment for the egg and tadpole. Construction effects the environment. It is happening too quickly, and the species is becoming rarer and rarer and some years they can’t be found in the wild at all.
We find ourselves at a point where human induced environment evolution is occurring far more rapidly than biological evolution.
What do you see for this species over the next 10 years, 50 years, 100 years?
In Vietnam there is currently no regulation for preventing the trading of this species, so illegal hunting is still a big problem for them in the near future. The second thing is that there is not so much research on the breeding and protection of this species. In my opinion it is still very critical to protect this species in the wild habitat or it could become extinct. It really needs to have some research to protect them in wild habitats and also needs to have some policy advocacy strategy to raise awareness of this species, while specific regulation must be deployed to stop the illegal hunting of this species.
You are clearly very involved in the research and breeding side of this protection strategy, are you also involved in the policy side of conservation?
Our institute is involved in policy making. We are a scientific partner of CITES (the Convention on International
Trade in Endangered Species of Wild Fauna and Flora). If we put a species in the appendix of this convention, then this species is banned from international trade. Our institute is working step by step to provide a scientific position to the government, to put this species into the CITES appendix of this convention. In the near future we hope this species will be considered for the appendix.
So, you have to prove the case for vulnerability through scientific research to have a species included and ‘banned’ from trade?
Yes, you must prove it is rare and the population is decreasing. We have to carry out a lot of research to achieve this protection. The research is hard and requires a lot of care and patience and is extremely underfunded.
What are the most critical research insights on the horizon?
The government needs to have more research on the species in its wild habitat to greater understand the co-evolution between the species and the habitat. For breeding, a lot of things are needed. In addition to funds we need suitable human resources. The care takes a lot of work, that comes first, then the research. For breeding a bigger colony, we need more people. To create the enclosures is not simple, the habitat control requires a lot of external support from Cologne Zoo. At the same time, I am trying to learn a lot about ecological interaction and further my understanding of this incredible species.
Perhaps, then, we can end on the notion of care and curiosity put forth by Donna Haraway, that “caring means becoming subject to the unsettling obligation of curiosity, which requires knowing more at the end of the day than at the beginning.”
1 Price, N., Green, S., Troscianko, J. et al. Background matching and disruptive coloration as habitat-specific strategies for camouflage. Sci Rep 9, 7840 (2019). https://doi.org/10.1038/s41598-019-44349-
2 Heckman, Daniel & Geiser, David & Eidell, Brooke & Stauffer, Rebecca & Kardos, Natalie & Hedges, S.. (2001). Molecular Evidence for the Early Colonization of Land by Fungi and Plants. Science (New York, N.Y.). 293. 1129-33. 10.1126/science.1061457.
3 Reski, R., Enabling the water-to-land transition. Nature Plants. 4. 67-68. 10.1038/s41477-018-0101-5. (2018). https://www.researchgate.net/publication/322766388_Enabling_the_water-to-land_transition
4 Kimmerer, R. W. (2003). Gathering moss: A natural and cultural history of mosses.
5 Rauhaus, Anna & Gawor, Anna & Perl, R. & Scheld, Sarah & Straeten, Karin & Karbe, Detlef & Pham, Cuong & Nguyen, Truong & Ziegler, Thomas. (2012). Larval development, stages and an international comparison of husbandry parameters of the Vietnamese Mossy Frog Theloderma corticale (Boulenger, 1903) (Anura: Rhacophoridae). Asian Journal of Conservation Biology. 1. 51-66.
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