Gardiner's Seychelles Frog

Sechellophryne gardineri is a small frog species with a snout-vent length of 10.1 ± 0.8 mm in males and 11.5 ± 1.0 mm in females. The head is flat and wide with a head width to head length ratio of 0.82 ± 0.08. The eyes are large and the snout is pointy, extending beyond the lower jawbone. The nostrils are closer to the snout tip than to the orbit, and the frog lacks dermal folds between the eyes. The forearm is thin. The fingers have webbing that doesn’t cover the tips completely, reaching to around one third of total finger length. Relative finger lengths are 1 < 3 < 4 < 2. The tibia is thin and short. Both the tibia and the thighs are muscular and approximately the same length. The thighs and underside are both smooth. The tips of the toes are expanded and pointed but have no webbing. Relative toe lengths are 1 < 2 < 3 < 5 < 4. There are two equally-sized metacarpal tubercles and two vertical rows of shinbone tubercles observable on live specimens. The inner row has four tubercles and the outer row consists of three equally-sized tubercles. However, the species appears to have no foot tubercles. The cloaca is directed to the rear. In life, the backs of the specimen consist of seven rows of tubercles. The first row has four tubercles, of which two are located between the eyes and one on each eyelid, and rows two to seven have two tubercles each, evenly spaced along the back. When preserved, the specimens have a smooth back and show no signs of tubercles (Gerlach and Willi 2002).When first described, S. gardineri was assigned to the genus Sooglossus, which had a total of three species in 2002. Sechellophryne gardineri has since been split from Sooglossus (Nussbaum and Wu 2007; see comments for more information). Of the three original members of the Sooglossus genus, Sechellophryne gardineri is the most widespread and is able to adapt to secondary habitats. Sooglossus sechellensis is restricted to primary high forest and Sooglossus thomasseti to the highest altitudes, especially moss forest. Sooglossus sechellensis and S. thomasseti are much larger S. gardineri, with the first up to 25 mm, and the second up to 55 mm in snout to vent length. These two species often have a black triangular spot on top of head just behind eyes, which is lacking in S. gardineri. Additionally, S. gardineri has dark lateral bands that are not present in the two Sooglossus species (Gerlach and Willi 2002, Nussbaum and Wu 2007).In life, S. gardineri has a smooth back with an upside-down V-shape back composed of numerous black spots. Live specimens’ have tubercles that are often white and surrounded by dark brown coloration. The thighs are brown with black blotches. The back is brown with bronze flecks and 88% of the Mahé specimens have a dark band on the side while 13% have a white line running down the middle of the back. The belly is black with grey spots near the bottom. Its hands and feet are black. The iris of the eye is gold. When preserved, the specimen retains the upside-down V-shape back, numerous black spots, and a thin white stripe running from the snout, passing over the eye and to the outside edge of the back limb. The back is a grey color and its inner thighs are grey-brown with the ventral side of the thighs brown with white blotches and a brown belly. The color of sides between the white stripe and the forelimbs is fading vertically. The forelimbs are brown with grey spots and the hands. The hands and feet of the specimen are brown and the finger and toe pads of all Mahé are black (Gerlach et al. 2002).Apart from the minor differences in coloration between the Mahé and Silhouette Island populations, no other differences could be found between the specimens (preserved or live; Gerlach et al. 2002).The species authority is: Gerlach J, Willi J. 2002. A new species of frog, genus Sooglossus (Anura, Sooglossidae) from Silhouette Island, Seychelles. Amphibia-Reptilia 23: 445-458.The reassessment of Sooglossus sechellensis, Sooglossus thomasseti (formerly Nesomantis thomasseti) Sechellophryne gardineri, and Sechellophryne pipilodryas has suggested that Sooglossus sechellensis is more similar to Sooglossus thomasseti than to S. gardineri. Based on an extensive analysis of morphological characters, Nesomantis and S. sechellensis were reformed into a monophyletic group to the exclusion of S. gardineri and S. pipilodryas. Thus, a new genus, Sechellophryne, was formed to accommodate the latter two species, leading to the name change from Sooglossus gardineri to Sechellophryne gardineri (Nussbaum and Wu 2007).Sechellophryne gardineri is notable due to its lack of a middle ear, as described in Boistel et al. (2013). The middle ear is important to most species because it resonates and amplifies sounds that typically would be reflected off the body wall. In frogs, it is particularly important for intra-species communication. Thus, another organ must be exapted by S. gardineri to perform these duties. Upon the analysis of a number of candidate tissues, including bones and the lung cavity, it was determined that

Sechellophryne gardineri are distributed throughout a range of forest habitats in the country of Seychelles primarily the Mahé and Silhouette islands. In Mahé, they are in Cascade, Mt. Sebert, La Reserve, La Misere, Morne Seychellois, Casse Dent, Morne Blanc, Mare aux Cochons, Foret Niore, Trois Freres, Copolia, Montagne Planeau, and Congo Rouge. In Silhouette, they are in Pisonia sechellarum forest, Jardin Marron, Mon Plaisir, Chemin Montagne Posse shrine, Gratte Fesse, Mt. Corgat, and Mt. Dauban (Gerlach et al. 2002).

Sechellophryne gardineri calls are usually from leaf-litter and consists of a high-pitched, single note squeak or whistle, very similar to that of a cricket. It has no repetitions or secondary notes and last for the duration of 0.09 – 0.2 seconds. The species produces a dominant frequency of between 4,225 and 6,767 Hz, corresponding to the first and second harmonics, with an average frequency of 5,710 ± 420 Hz (n = 52), and an advertisement call of around 5,710 Hz to which it responds to noticeably when played back (Gerlach et al. 2002, Boistel et al. 2013).The species lays its eggs, ranging from 8 – 16 at a time, on the ground. Larvae have direct development and hatch from eggs as froglets (Gerlach et al. 2002, Boistel et al. 2013, IUCN 2013).

The two major threats to this species are climate change and habitat deterioration due to more frequent fires and invasive species. Furthermore, climate change during a 10-year range has led to a 10% population decline in the area of occupation despite the fact that this species has been identified as being tolerant to dry conditions. This species is, however, is quite adaptable to secondary habitats (IUCN 2013).

This species is terrestrial and nocturnal, and feeds on small invertebrates (6). Unlike most frogs, which lay their eggs in water, this species lays its eggs in small clumps on moist ground. The young do not hatch as tadpoles, but as fully formed small adult frogs. In other Sooglossidae species, tadpoles are carried on the female's or male's back until they metamorphose (7).

The Seychelles Islands are considered as some of the most beautiful places on Earth and are extremely rich in terms of biodiversity. 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 (3) (4). These efforts are important in the protection of the islands' wildlife, though many species, including the Gardiner's tree frog, still remain threatened (7) (8). Much of the range on Mahé fall within the Morne Seychellois National Park and conservation of Silhouette island is managed by the Nature Protection Trust of Seychelles (9).

The Gardiner's tree frog is one of the smallest frogs in the world, growing to only 11 mm in length (2). This species is endemic to the Seychelles, as its other common name (Seychelles frog) suggests (3). In colour, it is green to brown, and has a distinctive dark band extending from the mouth and below the eye to the hind legs. The fore-limbs are small, while the hind-limbs are long and muscular (3).

Most members of the Sooglossidae family are restricted to high altitudes, but the Gardiner's tree frog is more adaptable and occurs in a wide variety of high and mid-altitude sites, favouring moist and deep littered rocky areas (2) (5).

This family of frogs is endemic to the Seychelles, a large group of islands in the Indian Ocean (4).

Classified as Vulnerable (VU) on the IUCN Red List (1).

Land clearance for agriculture, human settlement, timber and tourism are the main threats on the Seychelle Islands. The majority of the lowland forests have been disturbed or destroyed, and coconut, vanilla and cinnamon plantations now occupy most of the coastal plateaus (6). This habitat loss has contributed to the decline in numbers of this species in recent years. This species is now classified as Vulnerable by the IUCN (1).

Gardiner's Seychelles frog (Sechellophryne gardineri) is a small frog of the family Sooglossidae and endemic to the Seychelles. It is named after John Stanley Gardiner, English zoologist and oceanographer.