Tenasserim Cave Frog
Species Description: Suwannapoom C, Sumontha M, Tunprasert J, Ruangsuwan T, Pawangkhanant P, Korost DV, Poyarkov NA. (2018) A striking new genus and species of cave-dwelling frog (Amphibia: Anura: Microhylidae: Asterophryinae) from Thailand. PeerJ 6:e4422
© 2018 Nikolay A. Poyarkov (1 of 3)
Siamophryne troglodytes is a cave dwelling frog with a snout vent length that ranges from 19.1 - 24.9 mm for adult males, and 25.0 - 27.8 mm for adult females. It has a number of features indicative of its cave-dwelling lifestyle, including a slender body with long limbs. It has a short, rounded snout with rounded lateral nostrils near the tip. The canthus rostralis is gently rounded, and the loreal region is slightly concave. The eye is medium-sized and protuberant, about the same length or slightly longer than the snout, and has a horizontal, oval pupil. By the eye, the tympanum is distinct and circular, outlined by a tympanic rim with no supratympanic fold. The back of the head is flat (Suwannapoom et al. 2018).
The forelimbs are long, but less than half the length of the hindlimbs. The hand is slightly longer than the lower arm, but less than half the length of the forelimb. Siamophryne troglodytes has long, thin fingers, with relative lengths of I < II < IV < III. The fingers are flattened in the cross section and lack webbing and dermal fringes. The tips of fingers II - IV expand into broad triangular discs 1.2 - 2.5 times wider than the penultimate phalanges, with relative widths II < IV < III. The tip of finger I is rounded with the same width as the penultimate phalanges, while the terminal phalanges are T-shaped in fingers II - IV and bobbin-shaped in finger I. The subarticular tubercles on the fingers are flat, oval, indistinct and singular. There is no longitudinal furrow on the dorsal surface of fingers or nuptial pads. There are two palmar tubercles, a small, rounded inner palmar tubercle and an indistinct oval outer palmar tubercle about the same length. There are no supernumerary palmar tubercles (Suwannapoom et al. 2018).
The hindlimbs are also long and slender, with the foot being shorter than the tibia. Toes II - IV have smaller discs than the finger discs that are only slightly wider than the penultimate phalanges. The tips of toe I and V are rounded with the same width as the penultimate phalanges. The terminal phalanges are T-shaped in toes II - V, and bobbin-shaped in toe I. The subarticular tubercles are singular and pronounced on the toes. While the outer metatarsal tubercle is absent, the inner metatarsal tubercle is present but small, rounded, and flattened. The relative toe lengths are I < II < V < III < IV. The tarsus is smooth and the tarsal fold is absent (Suwannapoom et al. 2018).
The skin of the ventral surface is completely smooth, and the skin of the dorsal and lateral surfaces are smooth with occasional flat tubercles or pustules. The tubercles become larger and more prominent on the dorsal surfaces of hindlimbs, while the dorsal surface of the forelimbs are smooth with few small tubercles on the forearm. The upper eyelids and ventral sides of the trunk, head, and limbs are smooth. There are no dermal ridges or skin macroglands (Suwannapoom et al. 2018).
Based on a Gosner stage 36 tadpole, S. troglodytes tadpoles have a long guitar-shaped body with a large, bluntly rounded anterior part. The body narrows sharply behind the eyes to form notably angular edges. The mouth is located at the very front of the body towards the ventral surface and is not visible from dorsal view. The opening of the mouth is horizontal, relatively wide, and looks like a slit from the ventral view. From the side, the upper labium hangs slightly over the mouth opening with an even edge, and the lower labium is short with a U-shaped edge. Overall, the snout is blunt with a shallow notch in the middle and small narial protuberances. The eyes of S. troglodytes tadpoles are very small and dorsal, with pupils that are oriented dorsolaterally. From the side, the head and the body appear very flat. Tadpoles have a wide gular fold across the anterior half of the body, as well as a narrow, slit-like, transversal spiracle in the middle of the anterior half of the body. There is a membrane covering the spiracle with an even, free margin. The vent tube is oblique and medial. The tail is strong with well-developed muscles, and is less than two times longer than the body. The tail width at the base is about the length of the interorbital distance, and the tail tip is gently rounded. The tail fins are low with even edges and equal heights, and the dorsal fin does not extend on the trunk (Suwannapoom et al. 2018).
In general, S. troglodytes can be distinguished from all other microhylids in mainland Southeast Asia by its long limbs and large finger discs, its lack of tibiotarsal projection, its uniform brown color of ventral surfaces, by a small, subtle subarticular tubercle at the base of each finger, by the lack of a bony ridge along the posterior border of each choana, and by the presence of a distinct tympanum. As the first member of the genus Siamophryne, this species was only compared to members of other genera in its original description (Suwannapoom et al. 2018).
Members of the genera Kalophrynus, Glyphoglossus, Microhyla, and Micryletta do not have prominent finger discs. Chaperina has a bony tibiotarsal projection and a spotted yellow belly. Phrynella and Metaphrynella have enlarged subarticlar tubercles, Kaloula has a well-developed bony ridge along the posterior of each choana, and Glyphoglossus, Microhyla, Micryletta, Kaloula, Phrynella, and Metaphrynella all have hidden tympanum (Suwannapoom et al. 2018).
Siamophryne troglodytes has eleutherognathine maxillae and dentaries, unlike Asterophyrs, Callulops, Mantophryne, Oninia, and Xenorhina, other Aesterophryinae genera that only have a symphignathine state of these traits, and Barygenys, which has symphignathine dentaries. Siamophryne troglodytes has eight presacral vertebrae that lack neural crests, while Aphantophryne and Cophixalus have well-developed neural crests, and Aphantophryne only has seven prescaral vertebrae. In general, Sphenophryne has longer clavicles and broader vomeropalatines than Siamophryne, as well as a spine-like projection on the upper eyelid and an arboreal lifestyle, as opposed to S. troglodyte’s smooth eyelids and cave-dwelling customs. Genyophryne has no clavicles, a stout body, and lacks large finger discs, while S. troglodytes has tiny but present clavicles, a slender body, and very large finger discs. Liophryne has longer clavicles and smaller finger discs. Oxydactyla does not have finger discs at all. Genyophryne, Liophryne, and Oxydactyla have recently been considered to be part of Sphenophryne. Paedophryne has a much smaller body, has cartilaginous, not ossified, phalanges in the first digit, lacks clavicles and procoracoids, and has only seven presacral vertebrae. Choreophryne also lacks clavicles and procoracoids, unlike S. troglodytes, and has palatine portions of comer-palatines fused with broad sphenethmoids, which are not fused in S. troglodytes. Copiula lacks clavicles, has small discs on the fingers, has a cartilaginous, not ossified sternum, and has a conspicuous rostral dermal gland that is absent in S. troglodytes. Austrochaperina has fingers with smaller or absent discs, has expanded vomeropalatines, and has a broad cultriform process of parasphenoid, as opposed to S. troglodytes’ not expanded vomeropalatines and narrow cultriform process of parasphenoid. Siamophryne troglodytes has better developed nasals, larger discs, and smooth skin on the dorsum, while Hylophorbus has poorly developed nasals, absent or small finger discs, and shagreened to tubercular skin on the dorsum. Oreophryne has distinct toe webbing while S. troglodytes has none; Oreophryne has an arboreal or terrestrial lifestyle, and expanded comer-palatines as well (Suwannapoom et al. 2018).
Unlike its sister genus Gastrophrynoides, Siamophryne has large and wide finger discs, a larger eye, and a distinct tympanum. Siamophryne troglodytes also has a slender body and a short rounded snout rather than a robust body and a long, pointed snout (Suwannapoom et al. 2018).
In life, S. troglodytes adults have a rather uniform coloration, with the dorsal surface of the head and trunk being a chocolate brown, the dorsal surface of limbs an ochre-brown, and the ventral surface of limbs and throat a light orange-pink. On the sides of the body, S. troglodytes ranges from gray to gray-brown, while its underside is a pinkish-gray. Its fingers and toes are also gray, but with dark brown mottling. The tympanum is slightly gray as well, but with only a slight brown mottling. Tubercles on the dorsal surfaces of the body, limbs, and head are copper-brown, and the iris is a dark brown, surrounded by a bluish-gray sclera and surrounding a black pupil (Suwannapoom et al. 2018).
In preservative, the dorsal surfaces fade to a grayish-brown and the upper eyelids appear dark gray. The ventral surface of the chest, belly, and limbs fade to a yellowish-gray, and the iris turns black (Suwannapoom et al. 2018).
In life, S. troglodytes tadpoles at Gosner stage 36 are almost translucent with dark-black colored eyes. In a lab, weak brown pigmentation can be seen on dorsal surfaces of the body and tail. Over the semi-transparent body, a strongly-pigmented dark stripe runs along the dorsal surface from between the eyes to the base of the tail. The tail fins and ventral sides are clear, but the limb buds are brown (Suwannapoom et al. 2018).
When the S. troglodytes tadpole is in preservative, any brown color fades to a brown-gray (Suwannapoom et al. 2018).
There is no significant variation in coloration, but specimens in their natural environment tend to appear darker with a dark gray-brown dorsum and gray ventral surfaces and body flanks (Suwannapoom et al. 2018).
Distribution and Habitat
Siamophryne troglodytes is found in limestone caves in the tropical forests of western Thailand. At time of description, S. troglodytes was only found in a single limestone cave system in Sai York District of Kanchanaburi Province of the northern Tenasserim Region of western Thailand. The cave is located at an elevation of 440 m (Suwannapoom et al. 2018).
Life History, Abundance, Activity, and Special Behaviors
At the time of the species description, calling behavior, diet, and predators of S. troglodytes were not identified (Suwannapoom et al. 2018).
Most species of Asterophryinae have life cycles that are still unknown, but there is sufficient evidence that all members of Asterophryinae have direct development. Thus, S. troglodytes is the only known Asterophryinae with a free-living larval stage, as well as the only known Asterophryinae with a cave-dwelling lifestyle (Suwannapoom et al. 2018).
Adults S. troglodytes were only found inside the cave, about 25 m or more away from the entrance, sitting on the cave walls or hiding inside small caverns in the limestone or under flat stones. The three S. troglodytes tadpoles discovered were found in a small water-filled cavity in the limestone cave floor, about 10 m from the entrance. The average depth was 4 - 5 cm (Suwannapoom et al. 2018).
Trends and Threats
Siamophryne troglodytes is primarily threatened by illegal bat guano mining and other human activities. It is at a high risk for habitat loss and is especially threatened due to its ecological specialization and small known range. In addition, limestone karst areas like the one S. troglodytes resides in are endangered due to intensive deforestation and cement manufacturing (Suwannapoom et al. 2018).
Possible reasons for amphibian decline
General habitat alteration and loss
The species authority is: Suwannapoom, C, Sumontha, M, Tunprasert, J, Ruangsuwan, T, Pawangkhanant, P, Korost, DV, Poyarkov, NA. (2018) “A striking new genus and species of cave-dwelling frog (Amphibia: Anura: Microhylidae: Asterophryinae) from Thailand.” PeerJ 6:e4422
Siamophryne troglodytes was assigned to Microhylidae due to its lack of maxillary teeth, its lack of paranoid glands, and distinct features of its bone structure, it differed morphologically from any other known Microhylidae genus in Thailand or Indochina (Suwannapoom et al. 2018).
Phylogenetic relationships were determined from a 12S rRNA-16S rRNA mtDNA fragment using Maximum Likelihood and Bayesian Inference. The genetic differentiation between Siamophryne and other Microhylidae genera ranges from 14.8% (genus Liophryne) to 20.6% (genus Barygenys). Morphological, osteological, and phylogenetic analyses placed the new genus into the subfamily Asterophryinae, which is primarily Australasian, as a sister genus of Gastrophrynoides, the only known subfamily member from Sundaland (Suwannapoom et al. 2018) .
The genera name, Siamophryne, is derived from “Siam” the old name of present-day Thailand, the currently known residence of Siamophryne, and “phryne” is a Greek feminine noun meaning “toad”. The species epithet, “troglodytes” is a Latin adjective that means “cave-dweller”. “Trogle” means hole or mouse-hole, and “dyein” means to go or dive in (Suwannapoom et al. 2018).
Siamophryne troglodytes is classified as part of the Microhylidae family, which includes 641 species to date with 9.4% of anuran diversity. Due to the high morphological variation in Microhylidae, the family-level taxonomy of the Microhylidae is known as a “phylogeneticist’s nightmare” and continues to be debated (Suwannapoom et al. 2018).
The limestone cave system specific to S. troglodytes is known for an exceptionally high number of squamates, discovered by previous herpetofaunal surveys. Siamophryne troglodytes notably shares its habitat with several species of bats that deposit guano on the cave floor (Suwannapoom et al. 2018).
Limestone karst areas, like the habitat of S. troglodytes, also provide unique microhabitats such as cracks and caves that form from the natural geological structure, erosion, and water drainages of limestone areas. Karst habitats are known to host a diversity of surface and cave faunas and are speculated to protect small vertebrates against periods of climate change (Suwannapoom et al. 2018).
This species was featured as News of the Week on 23 April 2018:
Many new species result from splitting existing species; novel, distinctive frogs are rare. An exception is Siamophryne troglodytes, a new genus and new species of microhylid frog endemic to a single limestone cave of Thailand (Suwannapoom et al. 2018). More unusual, few frogs are cave dwellers, and Siamophryne shares many features of troglodytes: large eyes, long limbs, with slender digits and expanded digital tips. In contrast, most microhylids are squat with short limbs and small eyes. What is equally interesting is its biogeography. Siamophryne is mostly closely related to Gastrophrynoides from the Malay Peninsula and Borneo. Gastrophrynoides in turn is the sister-group of a diverse clade of Asterophryinae, a group endemic to the Papuan region and southern Phillipines. Thus, Siamophryne and Gastrophrynoides connect the mainland to a diverse endemic archipelago lineage (Written by David Cannatella).
Suwannapoom, C., Sumontha, M., Tunprasert, J., Ruangsuwan, T., Pawangkhanant, P., Korost D.V., and Poyarkov, N.A. (2018). ''A striking new genus and species of cave-dwelling frog (Amphibia: Anura: Microhylidae: Asterophryinae) from Thailand.'' PeerJ, 6, e4422.
Written by Rina Lu (rinaq AT berkeley.edu), UC Berkeley
First submitted 2018-10-30
Edited by Ann T. Chang (2018-12-23)
Species Account Citation: AmphibiaWeb 2018 Siamophryne troglodytes: Tenasserim Cave Frog <http://amphibiaweb.org/species/8786> University of California, Berkeley, CA, USA. Accessed Oct 20, 2019.
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Citation: AmphibiaWeb. 2019. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 20 Oct 2019.
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