Thursday, September 21, 2017

[Herpetology • 2017] Buergeria otai • Acoustic Differentiation and Behavioral Response reveals Cryptic Species within Buergeria Treefrogs (Anura, Rhacophoridae) from Taiwan


Buergeria otai 
Wang, Hsiao, Lee, Tseng, Lin, Komaki & Lin, 2017


Abstract

Buergeria japonica is a widely distributed treefrog occurring from Ryukyu Archipelago to Taiwan. Across this wide distributional range, we combined molecular, acoustic, morphological, and behavioral characters to clarify the taxonomic status among these insular populations. Genetic differentiation in mitochondrial sequences indicated an over 16% divergence among two deeply divergent clades: Japanese clade distributes in Ryukyu Archipelago and northwestern drainages of Taiwan, while Taiwanese clade distributes in the remaining drainages on Taiwan. The Taiwanese clade can be distinguished from the nominative species not only by molecular and morphological differences, but also distinguishable by considerable acoustic differentiation, which is extraordinarily noticeable for an additional type of long call that never recorded from Japanese clade. The two clades form a parapatric distribution pattern with narrow contact zones both in western and eastern Taiwan. Playback experiments indicated that male frogs show significantly stronger defensiveness against conspecific calls rather than heterospecific calls, indicating that these signals play a crucial role in species recognition. Here we describe the Taiwanese clade as a new species; the behavioral response and the magnitude of gene flow across their contact zones are especially worth for detailed studies.



Species description

Family Rhacophoridae Günther, 1859
Genus Buergeria Tschudi, 1838

Buergeria otai sp. nov.
Synonymy: 
Ixalus japonicus—Hallowell, 1861 "1860", Proc. Acad. Nat. Sci. Philadelphia, 12: 501. 
Polypedates japonicus—Stejneger, 1907, Bull. U.S. Natl. Mus., 58: 155. 
Rhacophorus (Rhacophorusjaponicus—Ahl, 1931 in Das Tierreich, 55: 111. 
Rhacophorus (Rhacophorusbuergeri japonicus—Wolf, 1936, Bull. Raffles Mus., 12: 166. 
Buergeria japonica—Liem, 1970, Fieldiana, Zool., 57: 90.

Etymology:  The specific epithet of the new species “otai” is a latinized patronymic noun in genitive case, dedicated to Prof. Hidetoshi Ota for his great contribution to herpetology and biogeography in East Asia, including Taiwan and adjacent regions. During 1980s to 1990s, Ota published four reptile species in Taiwan, carefully reviewed the herptile fauna across the East Asian Arc, and provided great assistance and encouragement to new-generation herpetologists in this region. We suggest the following common name “Ota’s stream tree frog” in English.

Diagnosis: Buergeria otai sp. nov. is characterized by a combination of the following characters: (1) a small-sized rhacophorid, body moderately slender; (2) SVL in adult males 23.1–29.3 mm (N = 133; mean ± SD = 26.57 ± 1.21 mm); females 29.7–37.5 mm (N = 3; 32.44 ± 4.42 mm); (3) dorsum slightly tubercular, with a pair of parallel tubercles on scapula; (4) head triangular, snout rounded and somewhat acute; (5) tips of fingers and toes dilated, forming expanded disks (over twice the width of phalanges); (6) tibiotarsal articulation on adpressed limb reaching beyond snout tip; (7) forelimb webbing absent; (8) hindlimb webbing partial, webbing formula (the number of phalanges free of web): I 1–1 II 1–2 III 1–1 IV 2–1 V; (9) vertebral stripe absent; (10) dark dorsal marking in the shape of inverted triangle between the eyes; (11) dark dorsal marking in a form of letter X or H extending from scapula to the middle of the back; (12) chin gray-white, with small irregular mottling; belly gray-white; (13) arms and thighs with sparse brownish bands; (14) regular tiny white spots on the ventral side of the thighs; usually concentrated at the base of the thighs.

Fig 6. Buergeria japonica (A, C) and Buergeria otai sp. nov. (B, D, E, F) in live. The irregular patches of B. japonica on the thighs could be compared to the regular tiny spots of Buergeria otai sp. nov., regardless the intraspecific variation from very few (E) to many (F).
Photographed by YJ Liang (A, C), CM Tsao (B), and HN Nguyen (D, E, F).

Natural history notes.
Although belonging to the Old-world treefrog family Rhacophoridae, Buergeria otai sp. nov. is specialized to live in the streams like all its congeners. They prefer to gather in small ditches or shallow waters near by the streams, but seldom entering into the major river course. Breeding season usually lasts from February to October, with a major peak from April to July (personal observation in this study), but may appear all year round in some habitats. Males gather to form chorus beside the streams after sunset, and the chorus reach its climax near midnight. Eggs 1.2–1.4 mm in diameter, attached on vegetation or spread on the substrates in shallow water, hatched after 24–36 hr. Tadpoles herbivorous or detritivorous, live benthically in shallow waters, with a larval stage period 15–30 days, depending on the water temperature.

Both Buergeria otai sp. nov. and B. japonica are well known for their special tolerance in geothermal hot springs, which seems to be an extraordinary adaptation from all anuran species in the world. The tadpoles of the frogs often show thermal affinity by approaching hot waters with temperature higher than 30°C, and their critical thermal maxima could reach more than 41°C. This adaptation was deduced to extend the breeding season, decrease the hatching rate, and increase the tadpole size. Furthermore, B. japonica was also well addressed for their special to salt tolerance. Although Buergeria otai sp. nov. is suspected to share the same tolerance, there was not yet an experiment designed to test this ability in this clade.


Ying-Han Wang, Yu-Wei Hsiao, Ko-Huan Lee, Hui-Yun Tseng, Yen-Po Lin, Shohei Komaki and Si-Min Lin. 2017. Acoustic Differentiation and Behavioral Response reveals Cryptic Species within Buergeria Treefrogs (Anura, Rhacophoridae) from Taiwan. PLoS ONE. 12(9); e0184005.  DOI:  10.1371/journal.pone.0184005



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