Seychelles frog
(Sooglossus sechellensis)
The Seychelles frog measures 20 mm in length and inhabits leaf litter on the forest floor. They guard their eggs in terrestrial nests and care for their young. The female deposits 6-15 eggs in a hidden, damp nest, where they are guarded by one of the parents. The tiny tadpoles crawl onto the back of the guarding parent immediately after hatching, and become glued on by mucus. They subsequently metamorphose into miniscule froglets and remain on their parent’s back until they are ready to live independently. It is a locally common species in parts of its tiny range, but is now declining because of habitat loss in its limited distribution.
Urgent Conservation Actions
Long-term monitoring of this species; sustainable development of ecologically friendly tourism should be encouraged.
The islands of Mahé and Silhouette in the Seychelles.
The scientific name of the Seychelles frog, S. sechellensis, refers to the group of islands where this species is found, and is derived from the French spelling.
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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 Gondwana, 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.

This is a small frog, with females averaging a total length of about 20 mm, with males being smaller at around 15 mm. The upper surfaces and sides of the body are golden brown in colour, with black bands and spots patterning the back, sides and upper surfaces of the legs. Dark bands do not appear on the sides of the head and body, as is the case in this species' close relative Gardiner's Seychelles frog. A large, triangular shaped marking may often be seen on the top of the head just behind the eyes. The stomach and other lower surfaces of the body are white, but the chin and the chest also have light-brown spots. This frog is most similar in colouration to the young of another close relative in the Seychelles called Thomasetts frog, differing only in the presence of a thin white line along the centre of the back of this other species.
Seychelles frog are known to guard their eggs in terrestrial nests and exhibit parental care of the newly hatched young, which are transported on the back of the mother of father until they develop sufficiently to feed and become free-living. There is some confusion as to whether the male or female guards and carries the eggs because it is very difficult to distinguish between the sexes of this species. During the mating embrace (amplexus), the female deposits 6-15 small white eggs in a hidden, damp nest site, where they are then guarded by one of the parents. The tiny tadpoles crawl onto the back the guarding parent immediately after hatching, where they become glued on by mucus. They subsequently metamorphose into miniscule froglets and are carried on their parent’s back until they have used up all of their yolk reserves and their legs are fully developed.

The Seychelles frog feeds on small insects, mites, and other invertebrates that live in forest litter and rotten logs. This species calls more frequently during the day from hidden sites on the forest floor, but also at night. It calls commonly during wet weather. The vocalisations of the Seychelles frog have been described as being composed of a croak followed by four "tocking" sounds: "rraackkk-toc-toc-toc-toc". This call is produced isolation and the dominant frequency of the primary note is approximately 2,660 Hz.
The Seychelles frog inhabits leaf litter on the forest floor in both relatively pristine and disturbed rainforest, and is often found at the edges of forest areas. Its total range (across which this species is patchily distributed) is just 42 km sq. – less than three-quarters the size of Manhattan Island.
This species occurs on the islands of Mahé and Silhouette in the Seychelles. The area of occupancy may be less than 20 km sq..
Population Estimate
It is a locally common species, living at densities of 667-2,000 animals per hectare.
Population Trend
The current population trend of the Seychelles frog is specified as unknown by the IUCN Red List of Threatened Species.
The Seychelles frog is listed as Vulnerable in the IUCN Red List of Threatened Species because its area of occupancy is probably less than 20 km sq..
The main threat to this species is habitat degradation, mainly due to fire and invasive species, but it is not thought to be seriously threatened since it is somewhat adaptable to secondary habitats. It might be inherently at risk because of its small range, which can make the Seychelles frog vulnerable to threats such as ecological disasters and climate change.
Conservation Underway
The Seychelles frog occurs within the 30.5 km2 Morne Seychellois National Park in Mahé, 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. However, the forests are not legally protected. 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.
Conservation Proposed
The long-term monitoring of the 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 the 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.

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