Giant salamanders can grow to be up to 4 and a half feet long. They tend to crawl up onto the shore in fresh-water rivers. They may look gross, but they are generally harmless and some say they’re even “cute”!

Seven new species of miniaturised frogs have been found in the Brazilian Atlantic rainforest. Among the smallest vertebrates on the planet, these colourful creatures can fit comfortably on a human thumbnail.

To understand just how tiny these frogs are, consider this: the largest living vertebrate is the blue whale, measuring around 26m, while the smallest was believed to be a fish (Paedocypris progenetica) with an adult size of 7.9-10.3mm.

Then two years ago a new species of miniature frog was described, and it was a record breaker. Paedophryne amauensis, which lives on the island of New Guinea, only grows to an average size of just 7.7mm and is now considered the world’s smallest vertebrate.

The latest discoveries in Brazil, announced in the journal PeerJ, are slightly larger, at between 9 and 13mm. But they’re still tiny compared to pretty much anything else with a backbone.

The frogs belong to the genus Brachycephalus, sometimes labelled “pumpkin toads” due to the often bright orange skin of some members. They live only in permanently-foggy patches of mountainside in Brazil’s Atlantic rainforest known as “cloud forest”.

The first Bracycephalus species was described as early as 1824 but most of the currently recognised 21 species have only been discovered in the last 15 years. The recent finding of seven new species and the difficulty of exploring the inaccessible habitat in which these animals live, suggests the actual diversity in the genus is considerably higher.

Why so small?

Most miniaturised frog species have simplified things as a consequence of their reduced size. They have fewer vertebrae than their larger relatives, and fewer skull elements. They also often have reduced numbers of digits; regular frogs generally have four fingers and five toes, whereas miniature frogs have just three and two respectively.

Miniaturised frogs share a number of ecological traits – they are found in wet tropical regions, primarily in forests, living near the ground in the moist leaf litter. This makes sense for such tiny amphibians. After all, their high surface-to-volume ratio makes them vulnerable to desiccation (drying out) and thus they are very sensitive to water loss.

Many, however, are not dependent on water for reproduction. In fact, some species entirely lack the larval tadpole stage typical of most frogs. Females in these cases instead produce a small number of large eggs that develop directly into small independent froglets.

Although this elimination of a tadpole stage may have paved the way for the exploitation of new niches and miniaturisation, the relationship between miniaturisation and terrestrial breeding is not well understood. It is believed that miniaturisation has evolved independently at least 11 times in terrestrial frogs and species measuring less that 13mm include representatives from 5 families and 9 genera.

Brazil’s frog paradise

The Atlantic cloud forests of Brazil have the sort of diverse and humid microclimates in which frogs thrive. The forests are home to more than 400 different species, around 8% of the world’s frog and toad species.

The region’s frogs are noted for the extraordinary diversity in reproductive modes, In fact, they exhibit 27 different reproductive modes in total including, of course, the typical reproductive cycle characterised by aquatic eggs (or “frog spawn”) that develop into tadpoles that in turn metamorphose into four-legged frogs.

But in many other species, including several found in the cloud forests, eggs and/or tadpoles are partially or completely removed from water. For example, some frogs lay their eggs in foam nests that float on the surface of ponds or on water accumulated on plants. The eggs hatch into tadpoles that complete development in water.

The recently found species, and most of their closest relatives, have gone a step further and completely removed their eggs from water and in the process eliminated the tadpole stage completely.

Decimation of the Brazilian Atlantic forest is one of the most alarming and desperate conservation problems in the world. In the year 1500 at the beginning of European colonisation, the area covered by the forest was approximately 1,300,000 km². Today the forest has been reduced to 7.6% of its original extent and the remaining forest is still under severe anthropogenic pressure.

Deforestation causes areas to dry out and eliminates those species, like miniature frogs and toads that depend on humid forests in order to breed successfully. Of the frog and toad species occurring in cloud forest, 81% occur nowhere else on earth.

No doubt there are many other frog species in Brazil that have not yet been discovered. Sadly, given the current rate of destruction and species extinction, it is possible they never will be.

Miranda Dyson is Senior Lecturer in Biology at The Open University.

This article was originally published on The Conversation.
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By Matthew Fisher, Imperial College London

The loss of amphibian species across the world from chytridiomycosis, an infectious disease caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), has been described as “the most spectacular loss of vertebrate biodiversity due to disease in recorded history”. So it’s of grave concern that the pathogen has been discovered in Madagascar, an incredibly biodiverse region previously thought free of the fungus.

Madagascar has the 12th highest rate of amphibian species richness in the world, with more than 400 species, 99% of which are indigenous to the region. But this biodiversity hotspot is already under severe pressure – a quarter of its species are under threat, according to the latest Global Amphibian Assessment. It’s rightly feared that the arrival of Bd, as reported in the journal Scientific Reports, could bring about mass amphibian decline – and even extinctions – as has been seen elsewhere.

Testing of the samples of the Bd fungus found in Madagascar reveals the strain is closely related to BdGPL, the hyper-virulent lineage behind all the known outbreaks of the chytrid fungus pathogen that have decimated amphibian populations. However what’s interesting is that the rate of infection is extremely low and there’s no clinical signs of chytridiomycosis: the frogs have the fungus, but they haven’t developed the disease.

What could this mean?

This discovery presents us with a number of scenarios, which need further investigation.

Perhaps the comprehensive monitoring plan put in place by A Conservation Strategy for the Amphibians of Madagascar (ACSAM) has worked as planned, in that the presence of the Bd pathogen has been detected – for the first time in 2010 – before amphibian declines have occurred.

Perhaps the strain of Bd detected in Madagascar is not a virulent kind that poses a serious threat to amphibians. This was seen with the introduction of the BdCape fungus lineage into Mallorca, where it had little effect on the population of Alytes muletensis toads there.

It’s possible that the Bd detected in Madagascar has been present on the island for a long time, but undetected. It may be an endemic, non-virulent lineage as seen in Brazil and Asia, where certain lineages endemic to the regions appear to have evolved alongside the native amphibians.

Or perhaps there is an endemic, previously undetected chytrid fungus on the island, related or not to Bd, which could be acting as a buffer for local amphibians against the invasion of BdGPL – acting, in effect, as a natural vaccine.

Alternatively, Malagasy amphibians may have developed some intrinsic resistance to Bd, for example through protective bacteria in their skin. This could explain the low infection rates and the ambiguous test results reported in the paper showing that some Bd-positive samples did not conform to any known lineage of the fungus. Although rare, resistance to BdGPL is not unprecedented – this has been seen and documented in Brazil.

A potential threat or a potential benefit

The first scenario would be a disaster – and should be a priority. If this turns out to be the case, the survival of Malagasy amphibians could depend on the conservation and scientific groups involved in ACSAM managing to restrict the spread of the disease. Tackling invasive species such as the Asian Toad that might spread the disease and ensuring tourists and researchers stick to strict hygiene protocols would be necessary. Perhaps even more drastic conservation measures, such as capturing animals from particularly vulnerable species for raising in captivity.

On the other hand, the fourth scenario presents an intriguing possibility: if it’s the case that Malagasy amphibians are resisting a fungal invasion, discovering how this works could provide crucial information to help save amphibians elsewhere from the disease.

The research on the amphibian skin microbiome, for example, and its role in the creature’s immune system is producing some exciting results. It’s also apparent that the diversity of the Chytrid fungus species as a whole, and in particular of Bd, has not been appreciated. It’s possible there are many types of chytrid fungus associated with amphibians that we’re not yet aware of which provide some protection against BdGPL.

So without a doubt, this report will sound warning bells loud and clear for conservationists, and Bd’s appearance in Madagascar could still result in a huge loss of amphibians. However, the lack of chytridiomycosis symptoms also suggest there’s something special in Madagascar that could yield a breakthrough in how the disease spreads – something that may not only benefit Malagasy amphibians, but those throughout the world.

This article was co-authored with Pria Ghosh, researcher at the Fisher Lab

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