Tuesday, February 27, 2018

[Herpetology • 2018] Siamophryne troglodytes | อึ่งถ้ำตะนาวศรี • A Striking New Genus and Species of Cave-dwelling Frog (Anura: Microhylidae: Asterophryinae) from Thailand


Siamophryne troglodytes
Suwannapoom, Sumontha, Tunprasert, Ruangsuwan, Pawangkhanant, Korost & Poyarkov, 2018

Tenasserim Cave Frog  • อึ่งถ้ำตะนาวศรี   |   DOI: 10.7717/peerj.4422 

Abstract

We report on a discovery of Siamophryne troglodytes Gen. et sp. nov., a new troglophilous genus and species of microhylid frog from a limestone cave in the tropical forests of western Thailand. To assess its phylogenetic relationships we studied the 12S rRNA–16S rRNA mtDNA fragment with final alignment comprising up to 2,591 bp for 56 microhylid species. Morphological characterization of the new genus is based on examination of external morphology and analysis of osteological characteristics using microCT-scanning. Phylogenetic analyses place the new genus into the mainly Australasian subfamily Asterophryinae as a sister taxon to the genus Gastrophrynoides, the only member of the subfamily known from Sundaland. The new genus markedly differs from all other Asterophryinae members by a number of diagnostic morphological characters and demonstrates significant mtDNA sequence divergence. We provide a preliminary description of a tadpole of the new genus. Thus, it represents the only asterophryine taxon with documented free-living larval stage and troglophilous life style. Our work demonstrates that S. troglodytes Gen. et sp. nov. represents an old lineage of the initial radiation of Asterophryinae which took place in the mainland Southeast Asia. Our results strongly support the “out of Indo-Eurasia” biogeographic scenario for this group of frogs. To date, the new frog is only known from a single limestone cave system in Sai Yok District of Kanchanaburi Province of Thailand; its habitat is affected by illegal bat guano mining and other human activities. As such, S. troglodytes Gen. et sp. nov. is likely to be at high risk of habitat loss. Considering high ecological specialization and a small known range of the new taxon, we propose a IUCN Red List status of endangered for it.

Keywords: Kanchanaburi Province, Siamophryne troglodytes Gen. et sp. nov., Tadpole, Troglophilous life style, Tenasserim, Sundaland, mtDNA, Biogeography, microCT-scanning


Taxonomy
Based upon the results of phylogenetic analyses of 12S rRNA–16S rRNA mtDNA fragment sequences, the Microhylidae frog from Kanchanaburi Province represents a previously unknown highly divergent mtDNA lineage, clearly distinct from all other members of Microhylidae for which comparable genetic data were available. This lineage falls into the Australasian subfamily Asterophryinae and with high values of node support is reconstructed as a sister group to the genus Gastrophrynoides that inhabits Borneo and the Peninsular Malaysia. Subsequent analyses of osteology and external morphology (see below) clearly indicate that the recently discovered population of Microhylidae Gen. sp. from Kanchanaburi Province represents a new previously undescribed genus and species which we describe herein as:

Amphibia Linnaeus, 1758
Anura Fischer von Waldheim, 1813

Microhylidae Günther, 1858
Asterophryinae Günther, 1858



Figure 5: Male paratype of Siamophryne troglodytes Gen. et sp. nov. (ZMMU A-5818) in life in dorsolateral aspect. Photo by N. A. Poyarkov.

Siamophryne Gen. nov.

Diagnosis: A medium-sized (19 mm < SVL < 30 mm) member of the Australasian subfamily Asterophryinae (family Microhylidae), with the following combination of morphological attributes: (1) both maxillae and dentaries eleutherognathine, no maxillary teeth; (2) vertebral column procoelous with eight presacral vertebrae (PSV) lacking neural crests; (3) no sagittal crest on cranium; (4) frontoparietals conjoined, connected by long suture; (5) nasals wide, calcified, but not contacting each other medially; (6) vomeropalatines small, not expanded, vomerine spikes absent; (7) cultriform process of parasphenoid comparatively narrow; (8) clavicles present as slender tiny bones, lying on the procoracoid cartilage not reaching scapula or the midline; (9) omosternum absent; (10) sternum large, anterior portion consists of calcified cartilage, xiphisternum cartilaginous; (11) weak dorsal crest present on urostyle, absent on ilium; (12) terminal phalanges large T-shaped; (13) all fingers and toe discs with terminal grooves; (14) subarticular tubercles weak, discernible only at digit basis; (15) toe webbing absent; (16) tympanum distinct; (17) two transverse smooth palatal folds; (18) pupil round; (19) snout rounded, equal to EL; (20) development with a larval stage, tadpole with peculiar dorso-ventrally compressed morphology.

Type species. Siamophryne troglodytes sp. nov.
Other included species. None are known at present.

Distribution: To date, S. troglodytes sp. nov. is only known from a small cave system in a karst region of Sai Yok District, Kanchanaburi Province, northern Tenasserim Region, western Thailand (see below the description of the species) (see Fig. 1).

Etymology: The generic nomen Siamophryne is derived from “Siam”—the old name of present-day Thailand; referring to the range of the new genus, which to date is only known from western Thailand; and the Greek noun “phryne” (φρÚνη; feminine gender), meaning “toad” in English; this root is often used in the generic names in Asterophryinae microhylid frogs. Gender of the new genus is feminine.

Figure 10: Breeding habitat of Siamophryne troglodytes Gen. et sp. nov. at the type locality—Sai Yok District, Kanchanaburi Province, northern Tenasserim Region, western Thailand.  (A) Entrance to the limestone cave where the frogs were recorded; (B) female in situ sitting on the limestone wall of the cave; (C) male in situ sitting in a water-filled crevice; (D) female in situ on the wall of the cave (photos by M. Sumontha);  

  

Figure 10: Breeding habitat of Siamophryne troglodytes Gen. et sp. nov. at the type locality—Sai Yok District, Kanchanaburi Province, northern Tenasserim Region, western Thailand.
 (A) Entrance to the limestone cave where the frogs were recorded; (B) female in situ sitting on the limestone wall of the cave; (C) male in situ sitting in a water-filled crevice; (D) female in situ on the wall of the cave (photos by M. Sumontha); (E, F) tadpole in situ in a water-filled crevice (photos by T. Ruangsuwan).


Figure 8: Tadpole of  Siamophryne troglodytes Gen. et sp. nov. in life (AUP-00509; Gosner stage 36).
 (A) In dorsal and (B) in ventral aspects. Scale bar equals to 5 mm. Photos by N. A. Poyarkov. Tadpole of Siamophryne troglodytes Gen. et sp. nov. in preservative (AUP-00509; Gosner stage 36). 

Figure 9: Tadpole of Siamophryne troglodytes Gen. et sp. nov. in preservative (AUP-00509; Gosner stage 36). (A) In lateral, (B) in dorsal, and (C) in ventral views. Scale bar equals to 5 mm. Photos by T. Ruangsuwan.

Figure 10: Breeding habitat of Siamophryne troglodytes Gen. et sp. nov. at the type locality—Sai Yok District, Kanchanaburi Province, northern Tenasserim Region, western Thailand.
 
 (C) male in situ sitting in a water-filled crevice; (D) female in situ on the wall of the cave (photos by M. Sumontha); (E, F) tadpole in situ in a water-filled crevice (photos by T. Ruangsuwan).

Siamophryne troglodytes sp. nov.

Etymology: The specific name “troglodytes” is a Latin adjective in the nominative singular meaning “cave-dweller”, derived from the Greek “τρωγλoδύτης”, with “trogle” meaning “holemouse-hole” and “dyein” meaning “go indive in”; referring to the troglophilous biology of the new species, which was recorded only in a limestone karst cave system.

Suggested common names: We recommend the following common names for the new species: “Tenasserim Cave Frog” (English); “อึ่งถ้ำตะนาวศรี - Eung Tham Tenasserim” (Thai).

Natural history notes:  
Siamophryne troglodytes Gen. et sp. nov. has a troglophilous life style and to date is only known from a small limestone cave system in western Thailand. All specimens were collected within a narrow area inside a limestone cave located on elevation 440 m a.s.l. in a polydominant tropical forest in Sai Yok District, Kanchanaburi Province, western Thailand (Fig. 10A). The cave was examined twice on the 1st of August and the 27th of October, 2016. In both cases, adult specimens of S. troglodytes Gen. et sp. nov. were only recorded inside the cave, at a distance of more than 25 m from the entrance, sitting on walls of the cave (Figs. 10B and 10D) or hiding inside small caverns in limestone (Fig. 10C) or under flat stones. Despite the thorough search, no animals were recorded near the cave entrance or in the forest close to the cave. Animals were active from 23:00 to 24:00, when the air temperature inside the cave was 28 °C in August and 26 °C in October, in both cases with 100% humidity. No calling activity was recorded during both surveys. Diet and enemies of the new frog are unknown.

Three tadpoles (one of which was collected) were observed during the survey on the 1st of August, 2016, in a small water-filled cavity in the limestone on the floor of the cave, ca. 10 m from the cave entrance (Figs. 10E and 10F). The cavity was filled with water, the average depth was 4–5 cm; mosquito larvae (Chironomidae) were also observed in the same water body. Four other tadpoles (not collected) were discovered in another similar water-filled cavity inside the cave (30 m from the cave entrance).

The cave system where S. troglodytes Gen. et sp. nov. was discovered is inhabited by several species of bats which produce significant amount of guano that accumulates on the cave floor. According to a local guide, the locals mine this guano and that affects the ecosystem of the cave.

Distribution: As for the genus. At present, S. troglodytes Gen. et sp. nov. is known from a single limestone karst cave in Sai Yok District of Kanchanaburi Province in western Thailand. To date, numerous surveys in the nearby karst massifs have not yielded discoveries of additional populations of the new species. However, further fieldwork in Kanchanaburi Province of Thailand and the adjacent parts of Tanintharyi Division of Myanmar are required.


Conclusion: 
Siamophryne troglodytes, a new genus and species of microhylid frogs from western Thailand, belongs to the subfamily Asterophryinae, which is most diverse in Australasia. Siamophryne and its sister genus Gastrophrynoides are the only two asterophryine lineages found in the areas derived from the Eurasian landmass. Our work demonstrates that S. troglodytes represents an old lineage of the initial radiation of Asterophryinae which took place in the mainland Southeast Asia. Our results strongly support the “out of Indo-Eurasia” biogeographic scenario for this group of frogs. To date, the new frog is the only known asterophryine with a free-living tadpole and troglophilous life style. Further studies might reveal new members of Asterophryinae in the mainland Southeast Asia.


 Chatmongkon Suwannapoom, Montri Sumontha, Jitthep Tunprasert, Thiti Ruangsuwan, Parinya Pawangkhanant, Dmitriy V. Korost and Nikolay A. Poyarkov. 2018. A Striking New Genus and Species of Cave-dwelling Frog (Amphibia: Anura: Microhylidae: Asterophryinae) from Thailand.  PeerJ. 6:e4422.  DOI: 10.7717/peerj.4422

           

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