70.
Gardiner's Seychelles frog
(Sooglossus gardineri)
VU
Overview
Perhaps the smallest frog in the world, Gardiner’s Seychelles frog grows to a maximum of just 11 mm. This species is ground-dwelling and forages at night for small invertebrates, such as mites. It breeds on land, where this species lays small clumps of eggs on moist ground. Breeding is known to occur throughout the year and the young do not hatch as tadpoles, but as fully metamorphosed froglets. This species is common at many sites, but populations are declining across their tiny range because of habitat degradation, mainly due to fire and invasive species, agriculture, human settlement, timber, and the tourism industry, particularly on the larger and more populated island of Mahé.
Urgent Conservation Actions
Long-term monitoring of this species; sustainable development of ecologically friendly tourism should be encouraged.
Distribution
The islands of Mahé and Silhouette in the Seychelles.
Fact
Gardiner’s Seychelles frog is one of the smallest frogs in the world, reaching a maximum length of 11 mm. Newly emerged froglets measure just 3 mm in length, and adult males are only 8 mm long.

This species was named in honour of British zoologist and oceanographer John Stanley Gardiner (Professor of Zoology and Comparative Anatomy at Cambridge 1909-1937) when it was formally described in 1911.
Media from ARKive
ARKive video - Gardiner’s tree frog - overview
ARKive image - Gardiner's tree frog
ARKive image - Gardiner's tree frog on moss
ARKive image - Gardiner’s tree frog on moss
ARKive image - Gardiner's tree frog sitting on human finger nail - to show size
ARKive image - Gardiner's tree frog next to coin
ARKive image - Gardniner's tree frog walking across ground
Evolutionary Distinctiveness
Order: Anura
Family: Sooglossidae
Oceanic islands are typically lacking in native amphibians, because very few species have any tolerance to salt water as a result of their sensitive skin, which is often used as a respiratory surface. The Seychelles is the only island group with an endemic family of frogs, i.e. one where all of the member species occur in the same island group and nowhere else on earth. This family is called the Sooglossidae (or sooglossids), and is commonly referred to as the “Seychelles frogs”. Although it is thought that amphibians may occasionally make the perilous journey across seas and oceans via rafting on mats of vegetation, being carried by strong air currents, or human introductions, the Seychelles frogs were transported to their current location by continental drift over millions of years. Around 200 million years ago at the beginning of the Jurassic period, the Seychelles islands were joined to the eastern part of the ancient southern supercontinent Gonwana, which went on to split apart into Australia, Antarctica, India, Madagascar and the Seychelles over millenia of movement of the earth’s plates. The sooglossids survived the geological breakup of India and the Seychelles around 65 million years ago, which is around the same time as the dinosaurs became extinct, and the closest known relatives of the Seychelles frogs are today found in India.

The sooglossids include some of the world’s smallest frogs, with adult Gardiner’s Seychelles frogs measuring just 10-11 mm in total length. Their closest living relative is the purple frog (EDGE rank 4) in the Western Ghats, India, which was only formally discovered in 2003 because it spends most of the year buried up to 4 metres underground. These lineages of amphibians may have been more diverse on Indo-Madagascar in the Cretaceous period, but now they are reduced to two miniscule ancient families that are consequently highly evolutionarily distinct. It is thought that the two lineages diverged around 131 million years ago in the Early Cretaceous period, which is over 30 million years before humans and elephants shared a common ancestor. The slow migration and fragmentation of the Indo-Madagascan fragment of Gondwana subsequently brought each landmass to its current position, separating the Seychelles frogs and the purple frog by about 2,500 km of Indian Ocean.

The Seychelles comprise eight main granitic islands and over 80 tiny islands and coral atolls. The group of islands is 1,000 km across at its widest point and the total land area is around 455 km sq., with the highest point being Morne Seychellois on the granitic island of Mahé, which 914 metres above sea level. The distribution of amphibian species across the Seychelles has probably been impacted by changing sea levels over the millennia. The central granite Seychelles islands were once a continuous landmass of around 130,000 km sq. called the Seychelles Bank, which has been reduced over time by erosion and rising sea levels. It was reduced to its present condition of scattered islands about 10,000 years ago. As a result, there is little endemism between islands since they were all connected relatively recently.

Today, the Seychelles frogs are only present on the larger granitic islands of Mahé and Silhouette. In total, the Seychelles contains 13 species of amphibians – 6 caecilians and 7 frogs, all of which are endemic apart from the Mascarene grassland frog (Ptychadena mascareniensis), which is widespread across sub-Saharan Africa, the Mascarene Islands and Madagascar. All the amphibian species are confined to the granitic islands of the Seychelles, with the larger islands having more species than the smaller islands. They are all ground dwelling, reproducing independently of water. They exhibit a high degree of parental care, with egg guarding occurring in all four species, and parents carrying tadpoles on their back until metamorphosis in one species, the Seychelles frog. Despite being very similar in external appearance, the Seychelles frogs may be identified by their advertisement calls, which are all highly distinctive.
Description
Gardiner's Seychelles frog is one of the smallest frogs in the world. Adults reach a total length of just 10-11 mm. They have a pointed snout and relatively large protruding eyes. The fore-limbs are small, and the hind-limbs are long and muscular .The colouration of the back is highly variable – individuals are generally reddish brown to light tan, with additional patterning of either a white stripe running down the centre of the back or dark/light blotches. The sides of the head and body are always darker than the upper and lower surfaces of the body, as a distinctive dark band extends from the mouth and below the eye to the hind legs.
Ecology
This species is ground dwelling, but is also found in low level vegetation, particularly hiding within the leaf axils. It is night-active and feeds on small invertebrates, comprising mites, sciarid fly larvae, ants and amphipods.

Gardiner’s Seychelles frog breeds on land, where this species lays its relatively large, yolky eggs in small clumps (of around 10) on moist ground (e.g. in leaf litter, under stones, in hollow stems of fallen tree fern branches). The young do not hatch as tadpoles, but as fully metamorphosed miniature adult frogs – a strategy of breeding termed “direct development”. The tadpole phase occurs entirely within the gelatinous capsule of the egg, and the female guards the eggs until they hatch and is usually found sitting on top of them. In other sooglossids, tadpoles are carried on the back of the female or male back until they metamorphose into independently living froglets, but there is no tadpole carrying in Gardiner’s Seychelles frog.

Breeding is known to occur throughout the year, since clutches of eggs have been collected in every month. The vocalisations of Gardiner's Seychelles frogs have been described as a high-pitched "peep" or whistle lasting a fraction of a second, similar to that of a cricket. Calls occur in isolation, almost always during the day.
Habitat
Gardiner’s Seychelles frog occurs in a wide variety of high and mid-altitude sites, favouring moist and deep littered rocky areas. This species lives both on the ground in forest litter and on low vegetation in leaf axils. It is unusual among the Seychelles frogs in inhabiting lower altitudes, since most are restricted to higher latitudes that have a stable climate due to constant mist. Gardiner’s Seychelles frog therefore has the widest elevational range of any sooglossids, since it has been reported from 200 metres above sea level to the top of Morne Seychellois at 914 metres above sea level. This species may be found both in disturbed and undisturbed rainforest, and also occurs in areas dominated by introduced trees such as cinnamon.
Distribution
Gardiner’s Seychelles frog occurs on the islands of Mahé and Silhouette in the Seychelles. Its total are of occupancy is probably greater than 20 km sq. across these two islands.
Population Estimate
This species is common at many sites in both disturbed and relatively undisturbed rainforest, occurring at densities of up to 2,000 animals per hectare in the best habitat.
Population Trend
The current population trend of Gardiner’s Seychelles frog is specified as unknown by the IUCN Red List of Threatened Species.
Status
Gardiner’s Seychelles frog is listed as Vulnerable in the IUCN Red List of Threatened Species because it is known from fewer than five locations.
Threats
The main threat to this species is habitat degradation, mainly due to fire and invasive species, as well as for agriculture, human settlement, timber, and the tourism industry, especially on the larger and more populated island of Mahé. The majority of the lowland forests have been disturbed or destroyed, and coconut, vanilla and cinnamon plantations now occupy most of the coastal plateaus in the Seychelles. However, Gardiner’s Seychelles frog is not thought to be seriously threatened because it is somewhat adaptable to secondary habitats. It might be inherently at risk to ecological disasters and climate change because of its small range.
Conservation Underway
Much of the range of this species on Mahé occurs within the 30.5 km2 Morne Seychellois National Park, whilst its Silhouette distribution falls partly in the site of a conservation project that has been established on the island by the Nature Protection Trust of the Seychelles (an NGO with coordinates conservation work on Silhouette) via their Islands Development Company Silhouette Conservation Project. In addition, many small reserves on the islands have been set up by the Seychelles Government and independent agencies to protect specific species and general habitat areas.

The challenges facing conservation projects are very different on the islands of Mahé and Silhouette, the former being a much larger island (148 km2) with a population of 70,000 and number land use conflicts, and the latter being small (just 20 km2) with a population of only 150 people. Silhouette appears to support healthy populations of all four species of Seychelles frog with no immediate threats. However, future hotel and infrastructure development might be a potential threat to these species. In contrast, significant tracts of potentially suitable habitat in Mahé’s central and southern mountains lack any protection against encroaching development, and the distribution and status of Seychelles frogs in these areas is completely unknown.

Nature Seychelles (another local conservation NGO in the Seychelles) recently initiated a project to investigate the status of these frogs on Mahé, supported by the Royal Society for Protection of Birds (RSPB) and the Herpetological Conservation Trust in the U.K. This project tested methods for monitoring Seychelles frog populations and made recommendations regarding the most practical system for determining distribution and numbers of frogs in the field. It also outlined a long-term monitoring programme for regular assessment of the status and abundance of the Seychelles frogs, and identified priority research needs. Following this work, Nature Seychelles is implementing a programme to look at the long-term status of these frogs. This will enable the population trend of this species to be determined, which is essential for appropriate conservation actions to be made.
Projects
Conservation Proposed
The long-term monitoring of Gardiner’s Seychelles frog is a vital priority to ensure its conservation in the wild, allowing for any population declines to be quickly detected and investigated. Further research should be conducted into the threat processes impacting this species in Mahé’s central and southern mountains, and a Conservation Action Plan should be developed to address the conservation of Gardiner’s Seychelles frog in this region. The development of Mahé and Silhouette for the tourism industry and local population increase is a significant threat to the Seychelles’ biodiversity, including the Seychelles frogs. Wherever possible, sustainable development of ecologically friendly tourism should be encouraged. The Seychelles is marketed as a tourist destination on the basis of its natural beauty, so strategic development of eco-tourism could be immensely beneficial to the conservation of the Seychelles’ endemic amphibians.
Associated EDGE Community members

Justin is the Scientific Co-ordinator of Nature Protection Trust of Seychelles

James is an EDGE Fellow working on sooglossid frogs in the Seychelles.

Links
References
AmphibiaWeb: Information on amphibian biology and conservation [web application]. 2006. Berkeley, California: AmphibiaWeb. Available: Global Amphibian Assessment. Accessed: 08 December 2006.

Behler, J.L. and Behler, D.A. 2005. Frogs: A Chorus of Colors. Sterling Publishing, NY, U.S.A. Biju, S.D. and Bossuyt, F. 2003. New frog family from India reveals an ancient biogeographical link with the Seychelles. Nature 425: 711-714.

Frost, D. R., T. Grant, J. Faivovich, R. H. Bain, A. Haas, C. F. B. Haddad, R. O. De Sá, A. Channing, M. Wilkinson, S. C. Donnellan, C. J. Raxworthy, J. A. Campbell, B. L. Blotto, P. Moler, R. C. Drewes, R. A. Nussbaum, J. D. Lynch, D. M. Green, and W. C. Wheeler. 2006. The Amphibian Tree of Life. Bulletin of the American Museum of Natural History 297: 1-370.

Frost, Darrel R. 2006. Amphibian Species of the World: an Online Reference. Version 4 (17 August 2006). Electronic Database accessible at: . American Museum of Natural History, New York, USA.

Gerlach, J. and Willi, J. 2002. A new species of frog, genus Sooglossus (Anura, Sooglossidae) from Silhouette Island, Seychelles. Amphibia-Reptilia 23: 445-458.

Green, D.M., Nussbaum, R.A. and Datong, Y. 1988. Genetic divergence and heterozygosity among frogs of the family Sooglossidae. Herpetologica 44: 113-119.

Groombridge, B. (ed.) 1994. 1994 IUCN Red List of Threatened Animals. IUCN, Gland, Switzerland.

Halliday, T. and Adler, C. (eds.). 2002. The new encyclopedia of reptiles and amphibians. Oxford University Press, Oxford.

IUCN Conservation Monitoring Centre. 1986. 1986 IUCN Red List of Threatened Animals. IUCN, Gland, Switzerland and Cambridge, UK.

IUCN Conservation Monitoring Centre. 1988. 1988 IUCN Red List of Threatened Animals. IUCN, Gland, Switzerland and Cambridge, UK.

IUCN, Conservation International and NatureServe. 2006. Global Amphibian Assessment. Global Amphibian AssessmentAccessed on 08 December 2006.

IUCN. 1990. 1990 IUCN Red List of Threatened Animals. IUCN, Gland, Switzerland and Cambridge, UK.

Mitchell, S.L. and Altig, R. 1983. The feeding ecology of Sooglossus gardineri. Journal of Herpetology 17(3): 283-285.

Nussbaum, R. & Gerlach, J. 2004. Sooglossus gardineri. In: IUCN 2006. 2006 IUCN Red List of Threatened Species. . Downloaded on 31 July 2007.

Nussbaum, R.A. 1984. Amphibians of the Seychelles. In: D.R. Stoddart (ed.), Biogeography and Ecology in the Seychelles Islands, pp. 379-415. Dr. W. Junk Publishers, The Hague.

Nussbaum, R.A., Jaslow, A. and Watson, J. 1982. Vocalization in frogs of the family Sooglossidae. Journal of Herpetology 16: 198-204.

Obst, F.J., Richter, K. and Jacob, U. 1984. The Completely Illustrated Atlas of Reptiles and Amphibians for the Terrarium. T.F.H. Publication Inc., N.J., U.S.A.

Roelants, K., Gower, D. J., Wilkinson, M., Loader, S. P., Biju, S. D., Guillaume, K., Moiau, L. and Bossuyt, F. 2007. Global patterns of diversification in the history of modern amphibians. Proceedings of the National Academy of Sciences 104: 887-892.

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