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Research Article
Taxonomic clarifications on the floating frogs (Anura: Dicroglossidae: Occidozyga sensu lato) in southeastern China
expand article infoZhi-Tong Lyu, Jian Wang, Zhao-Chi Zeng, Lin Luo§, Yan-Wu Zhang§, Chun-Peng Guo|, Jin-Long Ren|, Shuo Qi, Yun-Ming Mo, Ying-Yong Wang
‡ Sun Yat-sen University, Guangzhou, China
§ Shenzhen Administrative Bureau for Wildlife and Forest Plants Protection, Shenzhen, China
| Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu, China
¶ Natural History Museum of Guangxi, Nanning, China
Open Access

Abstract

The recognition for the floating frogs’ genus Occidozyga is in controversy for decades, and the species diversity of these frogs has recently been considered to be underestimated. In southeastern China, two floating frog species are currently recorded, namely Occidozyga lima and Occidozyga martensii. However, their current taxonomic statuses are unresolved after a series of recent taxonomic revisions. In this work, we perform morphological examinations and phylogenetic analyses on these two recorded floating frogs from southeastern China, to clarify their current taxonomic placements. The population previously recorded as Occidozyga lima should be re-assigned to the nomenclature Occidozyga obscura comb. nov., and the population previously recorded as Occidozyga martensii should be an undescribed species which is erected as Occidozyga lingnanica sp. nov. in this work.

Keywords

Diversity, Generic recognition, Occidozyga lingnanica sp. nov., Occidozyga obscura comb. nov., Phrynoglossus

Introduction

The floating frog subfamily Occidozyginae Fei, Ye & Huang, 1990 was originally established as a subfamily under the family Ranidae Batsch, 1796 (Fei et al. 1990), and was subsequently transferred to the family Dicroglossidae Anderson, 1871 (Frost et al. 2006). Currently, Occidozyginae is comprised of 19 recognized species distributed in northeastern India, Bangladesh, southern China, and mainland and islands of Southeast Asia (Frost 2022). These frogs usually inhabit wetlands such as paddy fields, natural or artificial ponds, ditches, and even small temporary puddles, thus most of the species are also known as “ floating frogs” or “puddle frogs”. Due to their morphological similarities, the taxonomy of these frogs was in prolonged controversy, especially for the membership of its type genus Occidozyga Kuhl & Van Hasselt, 1822 (Stoliczka 1872; Boulenger 1882; Smith 1931; Dubois 1981, 1987; Inger 1996; Frost et al. 2006; Fei et al. 2010; Pyron & Wiens 2011; Dubois et al. 2021; Flury et al. 2021; Köhler et al. 2021; Trageser et al. 2021; Frost 2022; summarized in Table 1 in this study).

Table 1.

Different generic affiliations for the congeners of Occidozyga sensu lato in several important revisions, and the subclade assignment in this study. NA: species was not involved in the relative revision.

Species original nomen Authorship Frost et al. 2006 Köhler et al. 2021 Dubois et al. 2021 Subclade in this study References for morphological characters
Rana lima Gravenhorst, 1829 Occidozyga Occidozyga Occidozyga I: Occidozyga sensu stricto Gravenhorst 1829; Iskandar 1998; Iskandar et al. 2011; Köhler et al. 2021; Trageser et al. 2021
Houlema obscura Gray, 1831 NA NA NA I: Occidozyga sensu stricto Gray 1831; Müller 1878; Stejneger 1925; Wu 1929; Pope 1931; Smith 1931; Liu & Hu 1961; Fei et al. 1990, 2009, 2010, 2012; this study
Rana rhacoda Inger, Boeadi & Taufik, 1996 NA NA NA II Inger et al. 1996; Flury et al. 2021
Occidozyga berbeza Matsui, Nishikawa, Eto, Hamidy, Hossman & Fukuyama, 2021 NA NA NA II Matsui et al. 2021; Trageser et al. 2021
Occidozyga shiwandashanensis Chen, Peng, Liu, Huang, Liao & Mo, 2022 NA NA NA III This study
Oreobatrachus baluensis Boulenger, 1896 Occidozyga Phrynoglossus Oreobatrachus IV: Oreobatrachus Boulenger 1896; Smith 1931; Inger 1966; Iskandar et al. 2011; Trageser et al. 2021
Micrixalus diminutiva Taylor, 1922 Occidozyga Phrynoglossus Frethia IV: Oreobatrachus Taylor 1922; Inger 1954; Iskandar et al. 2011; Trageser et al. 2021
Microdiscopus sumatranus Peters, 1877 Occidozyga Phrynoglossus Phrynoglossus V: Microdiscopus Peters 1877; Iskandar 1998; Iskandar et al. 2011; Eto & Matsui 2012 Matsui et al. 2021; Köhler et al. 2021; Trageser et al. 2021
Oxyglossus laevis Günther, 1858 Occidozyga Phrynoglossus Frethia VI: Frethia Günther 1858; Inger 1954; Iskandar 1998; Iskandar et al. 2011; Trageser et al. 2021
Micrixalus magnapustulosus Taylor & Elbel, 1958 Occidozyga Phrynoglossus Phrynoglossus VIII: Phrynoglossus Taylor & Elbel 1958; Iskandar et al. 2011; Köhler et al. 2021; Trageser et al. 2021
Phrynoglossus myanhessei Köhler, Vargas, Than & Thammachoti, 2021 NA Phrynoglossus NA VIII: Phrynoglossus Köhler et al. 2021; Trageser et al. 2021
Phrynoglossus swanbornorum Trageser, Al-Razi, Maria, Nobel, Asaduzzaman & Rahman, 2021 NA NA NA VIII: Phrynoglossus Trageser et al. 2021
Occidozyga lingnanica Lyu & Wang sp. nov. NA NA NA VIII: Phrynoglossus This study
Phrynoglossus martensii Peters, 1867 Occidozyga Phrynoglossus Phrynoglossus VIII: Phrynoglossus Peters 1867; Taylor 1962; Inger 1966; Iskandar et al. 2011; Poyarkov 2020; Köhler et al. 2021; Trageser et al. 2021
Ooeidozyga celebensis Smith, 1927 Occidozyga Phrynoglossus Frethia NA Smith 1927, 1931; Iskandar et al. 2011; Trageser et al. 2021
Oxydozyga floresiana Mertens, 1927 Occidozyga Phrynoglossus Frethia NA Mertens 1927; Smith 1931; Iskandar et al. 2011; Trageser et al. 2021
Ooeidozyga semipalmata Smith, 1927 Occidozyga Phrynoglossus Frethia NA Smith 1927, 1931; Inger 1954; Iskandar et al. 2011; Trageser et al. 2021
Occidozyga tompotika Iskandar, Arifin & Rachmanasah, 2011 NA Phrynoglossus Frethia NA Iskandar et al. 2011; Trageser et al. 2021

As the earliest introduced genus and also the type genus of Occidozyginae, Occidozyga was erected with its type species Rana lima (Kuhl & Van Hasselt 1822; Stejneger 1925). Subsequently, several genera were respectively proposed for some other floating frogs, such as Houlema Gray, 1831 (type species H. obscura), Phrynoglossus Peters, 1867 (type species P. martensii), Microdiscopus Peters, 1877 (type species M. sumatranus), Oreobatrachus Boulenger, 1896 (type species Oreobatrachus baluensis), Osteosternum Wu, 1929 (type species Osteosternum amoyense Wu, 1929), and Frethia Dubois, Ohler & Pyron, 2021 (type species Oxyglossus laevis). Nonetheless, the validations for all of these generic nomenclatures are in controversy (Table 1; Frost 2022). A recent work based on morphology, bioacoustics, molecules, and behaviors, has suggested Occidozyga is monotypic with O. lima and resurrected Phrynoglossus as a full genus for all other congeners (Köhler et al. 2021). Published on the same day, Dubois et al. (2021) resurrected genera Phrynoglossus and Oreobatrachus, and further proposed a new genus Frethia. Nevertheless, due to the inadequate sampling in these studies for settling the phylogeny for all of the floating frogs species, Frost (2022) considered to retain the sole genus Occidozyga sensu lato tentatively.

Despite the continuous controversy on the generic recognitions, taxonomic studies on species level of Occidozyga floating frogs are relatively stagnant, until recent years. Chan (2013) suggested the cryptic diversity within O. lima based on phylogeny but did not carry out corresponding taxonomic revision. O. martensii is revealed to be a species complex, and two populations from Myanmar and Bangladesh have been described as new species respectively (Köhler et al. 2021; Trageser et al. 2021). Matsui et al. (2021) described a new species O. berbeza which is suggested phylogenetically close to O. martensii and O. lima, while this species is confused with another congener O. rhacoda (Frost 2022). Several phylogenetic analyses also discovered a number of candidate species of floating frogs from Southeast Asia recently (Zug et al. 2018; Chan et al. 2020; Flury et al. 2021), but related taxonomic descriptions were not presented either.

In southeastern China where includes the subdivisions of Guangdong, Hong Kong, Macao, Fujian, and Hainan, two Occidozyga floating frog species are currently recorded, i.e. O. lima and O. martensii (Fei et al. 2009, 2012). Nevertheless, these records were majorly based on early morphological identifications. Their current taxonomic statuses are unresolved after the dramatic taxonomic changes mentioned above, especially for their phylogenetic relationships as samples from this region were seldom included in such recent publications (Zug et al. 2018; Chan et al. 2020; Flury et al. 2021; Köhler et al. 2021; Trageser et al. 2021). In this work, we perform morphological examinations and phylogenetic analyses on these two recorded floating frogs from southeastern China, to clarify their current taxonomic placements.

Material and methods

Phylogenetic sampling and analyses

Thirty-two newly collected samples of Occidozyga floating frogs were used in this study, encompassing 9 samples previously recorded as O. lima, and 23 samples previously recorded as O. martensii. Additional three samples of species of Dicroglossinae are used as outgroups (Table 2). All samples were attained after euthanasia of specimens, and then preserved in 95% ethanol and stored at –40 °C. Genomic DNA was extracted from muscle tissue, using a DNA extraction kit from Tiangen Biotech (Beijing) Co., Ltd. Segments of mitochondrial genes for 16S ribosomal RNA (16S) and cytochrome C oxidase subunit I (CO1) were amplified using the primers and conditions employed by Lyu et al. (2019). PCR products were purified with spin columns and then sequenced with both forward and reverse primers using BigDye Terminator Cycle Sequencing Kit following the guidelines, on an ABI Prism 3730 automated DNA sequencer by Wuhan Tianyi Huiyuan Bioscience & Technology Inc.

Table 2.

Localities, vouchers, and GenBank accession numbers for all samples used in this study.

ID Species Voucher Locality 16s CO1
1 Occidozyga lima Alive individual Indonesia: Java AB530619 /
2 O. cf. lima JBS 5405 Myanmar: Mandalay: Na Htoe Gyi MG935923 MG935629
3 O. cf. lima USNM 520376 Myanmar: Sagaing: Chatthin MG935924 MG935630
4 O. cf. lima SMF 103817 Myanmar: Naypyidaw: near Yamethin MW217494 /
5 O. cf. lima CAS 213254 Myanmar: Yangon: Hlaw Ga Park DQ283224 /
6 O. cf. lima SMF 103815 Myanmar: Yangon: near Taw Hlan village MW217492 /
7 O. cf. lima USNM 586924 Myanmar: Tanintharyi: Yeybu village MG935925 MG935631
8 O. cf. lima MNHN 0086Y Thailand: Prachuap Khiri Khan: Huay Yang NP KR827958 /
9 O. cf. lima SMF GK7721 Thailand: Rayong: near Rayong MW217498 /
10 O. cf. lima MNHN 2003.0327 Cambodia: Pouthisat: Pneum Kravanh KR827959 KR087831
11 O. cf. lima MNHN T2814 Laos: Louangphrabang: Luang Prabang KR827960 KR087832
12 O. obscura comb. nov. SYS a008397 China: Guangdong: Mt Danxia ON615073 ON615613
13 O. obscura comb. nov. SYS a008118 China: Guangdong: Yingde ON615066 ON615606
14 O. obscura comb. nov. SYS a008119 China: Guangdong: Yingde ON615067 ON615607
15 O. obscura comb. nov. SYS a008120 China: Guangdong: Yingde ON615068 ON615608
16 O. obscura comb. nov. SYS a008121 China: Guangdong: Yingde ON615069 ON615609
17 O. obscura comb. nov. SYS a008122 China: Guangdong: Yingde ON615070 ON615610
18 O. obscura comb. nov. SYS a008123 China: Guangdong: Yingde ON615071 ON615611
19 O. obscura comb. nov. SYS a008124 China: Guangdong: Yingde ON615072 ON615612
20 O. obscura comb. nov. SYS a008195 China: Guangxi: Guiping ON615074 ON615614
21 O. lingnanica sp. nov. SYS a005585 China: Guangdong: Shenzhen ON615075 ON615615
22 O. lingnanica sp. nov. SYS a005586 China: Guangdong: Shenzhen ON615076 ON615616
23 O. lingnanica sp. nov. SYS a005587 China: Guangdong: Shenzhen ON615077 ON615617
24 O. lingnanica sp. nov. SYS a005588 China: Guangdong: Shenzhen ON615078 ON615618
25 O. lingnanica sp. nov. SYS a005589 China: Guangdong: Shenzhen ON615079 ON615619
26 O. lingnanica sp. nov. SYS a005590 China: Guangdong: Shenzhen ON615080 ON615620
27 O. lingnanica sp. nov. SYS a004650 China: Guangdong: Xinyi ON615081 ON615621
28 O. lingnanica sp. nov. SYS a007657 China: Guangdong: Xinyi ON615082 ON615622
29 O. lingnanica sp. nov. SYS a007658 China: Guangdong: Xinyi ON615083 ON615623
30 O. lingnanica sp. nov. SYS a005540 China: Guangdong: Zhanjiang ON615084 ON615624
31 O. lingnanica sp. nov. SYS a005541 China: Guangdong: Zhanjiang ON615085 ON615625
32 O. lingnanica sp. nov. SYS a007645 China: Guangdong: Zhuhai ON615086 ON615626
33 O. lingnanica sp. nov. SYS a007646 China: Guangdong: Zhuhai ON615087 ON615627
34 O. lingnanica sp. nov. SYS a005441 China: Hainan: Changjiang ON615096 ON615636
35 O. lingnanica sp. nov. SYS a005442 China: Hainan: Changjiang ON615097 ON615637
36 O. lingnanica sp. nov. SYS a005267 China: Hainan: Mt Diaoluo ON615095 ON615635
37 O. martensii sensu stricto Not given Malaysia: Kuala Lumpur AB488903 /
38 O. martensii sensu stricto USNM 586941 Myanmar: Tanintharyi, Yeybu village MG935929 MG935635
39 O. martensii sensu stricto USNM 586942 Myanmar: Tanintharyi, Yeybu village MG935941 MG935647
40 O. martensii sensu stricto CUMZ PT2634 Thailand: Bangkok: Bangkok MW217475 /
41 O. martensii sensu stricto KUHE 19790 Thailand: Chachoengso KP318725 /
42 O. martensii sensu stricto SMF GK7349 Thailand: Chonburi: Ya Teng Homestay MW217491 /
43 O. martensii sensu stricto MNHN P324 Thailand: Phangnga: Sa Nang Manora KR827986 KR087857
44 O. martensii sensu stricto Alive idividual Thailand: Ranong AB530610 /
45 O. martensii sensu stricto FMNH 266020 Thailand: Sa Kaeo MW007312 /
46 O. martensii sensu stricto CUMZ PT2754 Thailand: Songkhla: Wang Pha MW217483 /
47 O. martensii sensu stricto CUMZ PT2755 Thailand: Songkhla: Wang Pha MW217482 /
48 O. martensii sensu stricto FMNH 268335 Thailand: Surat Thani MW007314 /
49 O. martensii sensu stricto FMNH 268805 Thailand: Krabi MW007315 /
50 O. martensii sensu stricto SMF GK7713 Thailand: Trat: Ko Kut Resort MW217505 /
51 O. martensii sensu stricto SMF GK7695 Thailand: Trat: Trat MW217504 /
52 O. martensii L1 SYS a002967 China: Yunnan: Jinghong ON615088 ON615628
53 O. martensii L1 SYS a003935 China: Yunnan: Jinghong ON615089 ON615629
54 O. martensii L1 SYS a003029 China: Yunnan: Mengla ON615090 ON615630
55 O. martensii L1 SYS a008259 China: Yunnan: Mengla ON615091 ON615631
56 O. martensii L1 SYS a008260 China: Yunnan: Mengla ON615092 ON615632
57 O. martensii L1 SYS a007810 China: Yunnan: Menglian ON615093 ON615633
58 O. martensii L1 SYS a007811 China: Yunnan: Menglian ON615094 ON615634
59 O. martensii L1 SCUM H020 China DQ458254 /
60 O. martensii L1 MNHN 2004.0357 Laos: Phongsali: Buon Tai KR827983 KR087854
61 O. martensii L1 CUMZ PT0167 Thailand: Chaiyaphume: Ban Na Si Nuan MW217484 /
62 O. martensii L1 CUMZ PT1543 Thailand: Chiang Mai: Huai Hong Khrai MW217477 /
63 O. martensii L1 CUMZ PT1544 Thailand: Chiang Mai: Huai Hong Khrai MW217476 /
64 O. martensii L1 MNHN 0119Y Thailand: Phetchabun: Thung Salaeng Luang KR827985 KR087856
65 O. martensii L1 MNHN 0026Y Thailand: Uttaradit: Nam Pad district KR827984 KR087855
66 O. martensii L2 JBS 19932 Myanmar: Yangon: Mingalardon MG935921 MG935627
67 O. martensii L2 USNM 587386 Myanmar: Yangon: Mingalardon MG935914 MG935620
68 O. martensii L2 USNM 587389 Myanmar: Yangon: Mingalardon MG935919 MG935625
69 O. swanbornorum JnUZool-A0719 Bangladesh: Chattogram MN705433 /
70 O. swanbornorum JnUZool-A0819 Bangladesh: Chattogram MN705434 /
71 O. swanbornorum JnUZool-A0919 Bangladesh: Chattogram MN705435 /
72 O. swanbornorum JnUZool-A1019 Bangladesh: Chattogram MN705436 /
73 O. swanbornorum JnUZool-A1117 Bangladesh: Chattogram MN705437 /
74 O. magnapustulosus MNHN 712D Laos: Vientiane: Viangchan KR827981 KR087852
75 O. magnapustulosus FMNH 255134 Laos: Champasak: Mounlapamok MW007295 /
76 O. magnapustulosus NKMA 2196-15 Thailand: Kalasin MW007297 /
77 O. magnapustulosus SMF GK7855 Thailand: Nakhon Phanom: Ban Kan Luang MW217490 /
78 O. magnapustulosus SMF GK7396 Thailand: Roi Et: near Ban Sa At Na Di MW217487 /
79 O. magnapustulosus SMF GK7532 Thailand: Sakon Nakhon: Ban Phaeng Yai MW217486 /
80 O. magnapustulosus SMF GK7533 Thailand: Sakon Nakhon: Ban Phaeng Yai MW217485 /
81 O. magnapustulosus FMNH 261789 Cambodia: Koh Kong MW007298 /
82 O. myanhessei USNM 587105 Myanmar: Bago: Dawei MG935916 MG935622
83 O. myanhessei USNM 587107 Myanmar: Bago: Dawei MG935920 MG935626
84 O. myanhessei SMF 103800 Myanmar: Magwe: near Taungdwingyi MW217503 /
85 O. myanhessei SMF 103840 Myanmar: Yangon: East Yangon University MW217499 /
86 O. myanhessei SMF 103841 Myanmar: Yangon: East Yangon University MW217500 /
87 O. myanhessei USNM 587402 Myanmar: Yangon: Mingalardon MG935917 MG935623
88 O. shiwandashanensis NNU 202103284 China: Guangxi: Mt Shiwandashan MZ747455 /
89 O. shiwandashanensis NNU 202103285 China: Guangxi: Mt Shiwandashan MZ747456 /
90 O. shiwandashanensis NNU 202103320 China: Guangxi: Mt Shiwandashan MZ747457 /
91 O. shiwandashanensis NNU 202103321 China: Guangxi: Mt Shiwandashan MZ747458 /
92 O. berbeza KUHE 17327 Malaysia: Sarawak: Matang LC593607 /
93 O. berbeza KUHE 17327 Malaysia: Sarawak: Matang LC593609 /
94 O. berbeza KUHE 17327 Malaysia: Sarawak: Matang LC593610 /
95 O. rhacoda complex NMBE 1064176 Malaysia: Sarawak: Kubah NP MW007293 /
96 O. rhacoda complex NMBE 1065363 Malaysia: Sarawak: Gunung Penrissen MW007173 /
97 O. rhacoda complex NMBE 1061694 Malaysia: Sarawak: Gunung Murud MW007275 /
98 O. rhacoda complex NMBE 1066057 Malaysia: Sarawak: Payeh Maga MW007281 /
99 O. rhacoda complex NMBE 1069835 Malaysia: Sarawak: Usun Apau MW007274 /
100 O. rhacoda complex NMBE 1074010 Malaysia: Sarawak: Batang Ai MW007290 /
101 O. laevis complex NMBE 1072307 Malaysia: Sabah: Danum Valley Conservation Area MW007227 /
102 O. laevis complex FMNH 234895 Malaysia: Sabah: Sipitang MW007219 /
103 O. laevis complex NMBE1072456 Malaysia: Sabah: Tawau Hills NP MW007254 /
104 O. laevis complex NMBE 1056418 Malaysia: Sarawak: Gunung Mulu NP MW007217 /
105 O. laevis complex KU 310493 Philippinen: Eastern Samar: Taft MW007237 /
106 O. laevis complex FMNH 259486 Philippinen: Kalinga: Balbalasang MW007236 /
107 O. laevis complex KU 306652 Philippinen: Negros Oriental: Valencia MW007235 /
108 O. laevis complex PNM 7446 Philippinen: Quezon: Lao AY313684 /
109 O. laevis complex KU 302276 Philippinen: Romblon: Magdiwang MW007234 /
110 O. laevis complex EMD 424 Philippines: Agusan Del Norte MT820178 /
111 O. laevis complex PNM ACD2011 Philippines: Isabela MT820166 /
112 O. laevis complex KU 302322 Philippines: Oriental Mindoro MT820171 /
113 O. laevis complex KU 308966 Philippines: Palawan: Irawan MW007231 /
114 O. laevis complex PNM ACD5414 Philippines: South Cotobato MT820170 /
115 O. laevis complex KU 306301 Philippines: Western Samar MT820173 /
116 O. laevis complex KU 314471 Philippines: Zamboanga: Pasonanca MT820168 /
117 Occidozyga sp. USNM 586929 Myanmar: Tanintharyi: Yeybu village MG935915 MG935621
118 Occidozyga sp. USNM 586928 Myanmar: Tanintharyi: Yeybu village MG935922 MG935628
119 O. sumatrana complex MZB Amph 16392 Indonesia: Java LC593611 /
120 O. sumatrana complex MZB RMB2134 Indonesia: Java MT820186 /
121 O. sumatrana complex Not given Indonesia: Sumatra: Bukit Barisan Selatan NP MW007270 /
122 O. sumatrana complex Not given Indonesia: Sumatra: Hutan Harapan MW007273 /
123 O. sumatrana complex Not given Indonesia: Sumatra: Hutan Harapan MW007269 /
124 O. sumatrana complex FRIM 1136 Malaysia: Pahang: Bukit Rengit MT820183 /
125 O. sumatrana complex FMNH 267890 Malaysia: Sarawak: Bintulu MW007260 /
126 O. sumatrana complex FMNH 269753 Malaysia: Sarawak: Binyo-Penyilam MW007268 /
127 O. sumatrana complex FRIM 1132 Malaysia: Selangor: Kepong MT820181 /
128 O. baluensis complex NMBE 1072541 Malaysia: Sabah: Danum Valley Conservation Area MW007193 /
129 O. baluensis complex FMNH 235605 Malaysia: Sabah: Kota Marudu MW007178 /
130 O. baluensis complex FMNH 242747 Malaysia: Sabah: Sipitang DQ283143 /
131 O. baluensis complex FMNH273695 Malaysia: Sarawak: Bintulu MW007215 /
132 O. baluensis complex NMBE 1064771 Malaysia: Sarawak: Gunung Mulu NP MW007177 /
133 O. baluensis complex NMBE 1073926 Malaysia: Sarawak: Payeh Maga MW007211 /
134 O. baluensis complex Not given Malaysia: Sarawak: Pelagus NP MW007175 /
135 O. baluensis complex Not given Malaysia: Sarawak: Pelagus NP MW007216 /
136 O. diminutiva KU 321225 Philippines: Mindanao: Zamboanga: Pasonanca MT820199 /
137 O. diminutiva KU 321226 Philippines: Mindanao: Zamboanga: Pasonanca MT820200 /
138 O. diminutiva KU 321227 Philippines: Mindanao: Zamboanga: Pasonanca MT820201 /
139 Ingerana tenasserimensis USNM 587302 Myanmar: Mon: Kyaikhtiyo Wildlife Sanctuary MG935840 MG935546
140 Ingerana tenasserimensis USNM 586921 Myanmar: Tanintharyi: Yeybu village MG935837 MG935543
141 Hoplobatrachus rugulosus SYS a006157 China: Guangdong: Mt Danxia ON615100 ON615640
142 Nanorana parkeri SYS a006617 China: Tibet: Jiacha ON615099 ON615639
143 Quasipaa shini SYS a006594 China: Guangxi: Mt Dayao ON615098 ON615638

For phylogenetic analyses, 108 additional sequences of floating frogs species were obtained from GenBank and incorporated into our dataset (Table 2). DNA sequences were aligned by the Clustal W algorithm with default parameters (Thompson et al. 1997). The final alignment includes 1,069 base pairs (bp) of 16S and 666 bp of CO1. PartitionFinder2 was used to test the best partitioning scheme and jModelTest v2.1.2 was used to test the best fitting nucleotide substitution models, resulting in the partition by gene and for CO1 further partitioned by codon position, and the best fit models for all partitions as GTR+I+G. Sequenced data were analyzed using Bayesian inference (BI) in MrBayes 3.2.4 (Ronquist et al. 2012), and maximum likelihood (ML) in RaxmlGUI 1.3 (Silvestro & Michalak 2012). Two independent runs were conducted in a BI analysis, each of which was performed for 100,000,000 generations and sampled every 1000 generations with the first 25% samples discarded as burn-in, resulting in a potential scale reduction factor (PSRF) of < 0.005. Convergence of the Markov Chain Monte Carlo simulations was assessed using Tracer v1.5 (Rambaut & Drummond 2009), verifying that all ESS values exceeded 200. In the ML analysis, the bootstrap consensus tree inferred from 1000 replicates was used to represent the evolutionary history of the taxa analyzed. Genetic distances based on 16S gene among samples were calculated in MEGA 6 using the uncorrected p-distance model.

Specimens and morphological examination

Thirty-one newly collected samples of Occidozyga floating frogs were used in this study, encompassing 10 specimens previously recorded as O. lima, and 21 samples previously recorded as O. martensii. Detailed collection data for these specimens are given in the Taxonomic accounts. Abbreviations for museums are SYS (the Museum of Biology, Sun Yat-sen University, Guangzhou, China), CIB (Herpetological Museum, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu, China), and BMNH (British Museum Natural History, now Natural History Museum, London, UK).

External measurements were made on the examined specimens, using digital calipers (Neiko 01407A Stainless Steel 6-Inch Digital Caliper) to the nearest 0.1 mm, including snout–vent length (SVL) from the tip of snout to posterior margin of the vent, head length (HDL) from the tip of snout to the articulation of the jaw, head width (HDW) at the commissure of the jaws, snout length (SNT) from the tip of snout to the anterior corner of the eye, internasal distance (IND), the shortest interorbital distance between the upper eyelids (IOD), eye diameter (ED) from the anterior corner of the eye to posterior corner of the eye, hand length (HND) from the proximal border of the outer palmar tubercle to the tip of digit III, radioulna length (RAD) from the flexed elbow to the proximal border of the outer palmar tubercle, foot length (FTL) from the distal end of the shank to the tip of digit IV, and tibial length (TIB) from the outer surface of the flexed knee to the heel.

Results

The BI and ML analyses resulted in identical topologies (Fig. 1). The p-distances based on the 16S gene among all samples used in this study are presented in Supplementary Table S1.

As illustrated in the phylogenetics, all samples of genus Occidozyga sensu lato gather together in a clade with Bayesian posterior probabilities (BPP) = 1.00 and ML bootstrap supports (BS) = 100, forming the sister taxon to the other genus Ingerana Dubois, 1987 within the subfamily. The clade of Occidozyga sensu lato can be further divided into eight subclades, however, the phylogenetic relationships among these eight subclades remain unresolved due to the weak supports.

All samples previously recorded as O. lima formed the subclade I, which represents the concept of “Occidozyga sensu stricto” (BPP=1.00, BS=100). This subclade was composed of three lineages. The single sample from the type locality of O. lima in Java, Indonesia (ID 1 in Figs 1, 2) formed an independent lineage I-2. The samples from Indochina Peninsula (ID 2–11) formed a complicated lineage I-3 (BPP=1.00, BS=86) with distinct inner divergences (p-distance 0.0–4.4% in 16S), which was provisionally designated as O. cf. lima here. The samples from southeastern China (ID 12–20) formed the remaining lineage I-1 (BPP=1.00, BS=100) without divergence (p-distance 0), which was the basal lineage of the subclade I and distinctly separated from the other two lineages. The relationships among these lineages remain unresolved due to the weak supports.

Figure 1. 

Phylogenetic trees of the genus Occidozyga sensu lato based on mitochondrial genes 16S and CO1. Bayesian posterior probabilities (BPP) and bootstrap supports (BS) are labeled above and below the nodes respectively. Numbers at the terminal of the lineages correspond to the IDs in Table 1.

Figure 2. 

Map showing the floating frogs Occidozyga obscura comb. nov., Occidozyga lingnanica sp. nov., and their closest congeners. Numbers correspond to the IDs in Table 1.

All samples previously recorded as O. martensii were seated in the subclade VIII (BPP=1.00, BS=100) which represents the concept of “Phrynoglossus”. This subclade was composed of seven lineages. Three lineages VIII-1, VIII-3, and VIII-4 were corresponding to three recognized species O. myanhessei comb. nov. (BPP=1.00, BS=98), O. swanbornorum comb. nov. (BPP=1.00, BS=100), and O. magnapustulosa (Taylor & Elbel, 1958) (BPP=1.00, BS=99), respectively. Samples in the remaining four lineages were all previously recorded as O. martensii (actually O. myanhessei comb. nov. and O. swanbornorum comb. nov. were also recorded as O. martensii for decades and just recognized recently), however, they were paraphyletic. The sample from the type locality of O. martensii in Bangkok, Thailand (ID 40 in Figs 1, 2) was clustered with the samples from southern and peninsular Thailand, peninsular Myanmar, and peninsular Malaysia (ID 37–51), which represented the lineage VIII-5 of the O. martensii sensu stricto (BPP=1.00, BS=99). Samples from Yangon, Myanmar (ID 66–68) formed an independent lineage VIII-2 (BPP=1.00, BS=100), and were provisionally designated as O. martensii L2 here. The lineage VIII-6 (BPP=1.00, BS=87) contained samples from Yunnan, southwestern China (ID 52–59) and northern Indochina Peninsula (ID 60–65), which was provisionally designated as O. martensii L1. Samples from southeastern China (ID 21–36) formed the last lineage VIII-7 (BPP=1.00, BS=100). The relationships among these lineages remain unresolved either, due to the weak supports.

The inner relationships for the other subclades of Occidozyga sensu lato were also complicated. Subclade II (BPP=1.00, BS=90) included samples of O. berbeza (ID 92–94) and O. rhacoda (ID 95–100), while the samples identified as O. rhacoda were paraphyletic and separated into three distinct lineages. Furthermore, a sample of O. rhacoda (ID 95) was indeed conspecific with samples of O. berbeza. The most recently described species O. shiwandashanensis (ID 88–91) formed a monotypic subclade III (BPP=1.00, BS=100). Subclade IV (BPP=1.00, BS=100) included samples of O. baluensis (ID 128–135) and O. diminutiva (ID 136–138), while the samples identified as O. baluensis were paraphyletic and separated into three distinct lineages too, indicating that this species should be a species complex. Samples identified as O. sumatrana (ID 119–127) and O. laevis (ID 101–116) formed the subclade V (BPP=0.99, BS=89) and subclade VI (BPP=1.00, BS=100) respectively, however, distinct deep divergences were presented in these two subclades. The remaining subclade VII (BPP=1.00, BS=100) was consist of two unknown samples from peninsular Myanmar.

Discussion

Generic recognition for Occidozyga sensu lato

In this work, it is the first time to integrate the molecular data of floating frogs published in recent years (e.g. Chan et al. 2020; Flury et al. 2021; Köhler et al. 2021; Matsui et al. 2021) to reconstruct the phylogeny of Occidozyga sensu lato. As indicated by the phylogenetic result, the genus Occidozyga sensu lato can be divided into eight subclades, while the relationships among these eight subclades were not clearly revealed. It seems that these subclades are partly corresponding to the different generic nomenclatures proposed in the taxonomic history, i.e., subclade I for “Occidozyga sensu stricto” (type species R. lima), subclade IV for “Oreobatrachus” (type species Oreobatrachus baluensis), subclade V for “Microdiscopus” (type species M. sumatranus), subclade VI for “Frethia” (type species Oxyglossus laevis), and subclade VIII for “Phrynoglossus” (type species P. martensii). However, because of the inadequate species sampling (four congeners O. celebensis, O. floresiana, O. semipalmata, and O. tompotika were not included) and the inadequate genetic segments employed (most of the samples lack comparable nuDNA segments which are unable to perform the phylogeny of nuDNA), we consider to cautiously retaining all these species within a sole genus Occidozyga sensu lato. Thus, two new combinations of nomenclatures appeared due to this suggestion, namely O. myanhessei comb. nov. and O. swanbornorum comb. nov. as they were originally described under the generic name Phrynoglossus (Köhler et al. 2021; Trageser et al. 2021).

Particularly, since there are distinct morphological differences among some of these subclades (especially between the “Phrynoglossus” and “Occidozyga sensu stricto” subclades), we speculate that Occidozyga sensu lato would be partitioned into multiple genera after comprehensive phylogenetic analyses and detailed morphological re-examination in the future.

Species diversity of floating frogs

The species diversity of floating frogs is dramatically underestimated as indicated in our analysis. Deep divergences are presented among the samples currently identified as O. rhacoda, and similar situations are also revealed in those of O. baluensis, O. sumatrana, and O. laevis. Therefore, these four species are all tentatively designated as species complex in this work, and further clarifications with morphological study are required. Particularly, the relationship between O. rhacoda and O. berbeza are still unclear, and the data from the topotype of O. rhacoda are required to settle this puzzle.

Within subclade I (“Occidozyga sensu stricto” subclade), similar to the result by Chan (2013), O. lima is revealed to include three lineages for the populations from type locality Java, Indonesia (ID 1), Indochina Peninsula (ID 2–11), and southeastern China (ID 12–20). The relationships among these three lineages are unresolved due to the weak support values. Morphological examination on the specimens from lineage I-1 substantiates their differences from the populations in Indonesia and Indochina (see below in Taxonomic accounts). Therefore, we resurrect the former nomenclature Houlema obscura to accommodate the lineage of the southeastern China population as Occidozyga obscura comb. nov., with providing a re-description for this species based on the newly collected fresh specimens. The lineage I-3 for the Indochina Peninsula population is tentatively designated as O. cf. lima due to the unstable supported values (BS=86) and complicated inner relationship, calling for detailed morphological examinations on the related specimens.

Within subclade VIII (“Phrynoglossus” subclade), the samples previously recorded as O. martensii are paraphyletic into four different lineages, among which the relationships are also unresolved, due to the weak support values. The lineage VIII-5 of O. martensii sensu stricto involves populations throughout southern and peninsular Thailand, peninsular Myanmar, and peninsular Malaysia (ID 37–51). The lineage VIII-7 for the population from Guangdong and Hainan, southeastern China (ID 21–36) is considered to be an undescribed species of the genus Occidozyga, based on the phylogenetic results and the morphological differences (see below in Taxonomic accounts). Because of the unstable supported values (BS=87) and inadequate specimens, the taxonomic status for the lineage VIII-6 of O. martensii L1 is not defined in this work. This lineage might be close to the nomen Oxyglossus laevis var. vittata Andersson, 1942 and further study is in preparation. The lineage VIII-2 of O. martensii L2 seems to represent another cryptic species, calling for detailed morphological examinations on the related specimens.

Taxonomic accounts

Occidozyga obscura (Gray, 1831), comb. nov.

Houlema obscura Gray 1831

Oxyglossa lima var. chinens Müller 1878

Oxydozyga limaStejneger 1925

Osteosternum amoyense Wu 1929

Ooeidozyga limaPope 1931; Smith 1931; Liu & Hu 1961

Occidozyga limaDubois 1981; Fei et al. 1990, 2009, 2010, 2012; Zhao & Adler 1993; Li et al. 2011; Mo et al. 2014.

Type materials

Holotype. BMNH 1932.5.1.2, adult female, collected from China (discussion for the exact locality see Remarks below).

Specimens examined

Seven adult males and three adult females. Males CIB 44475–44476, from Guangzhou, Guangdong Province, China; male SYS a000534, from Mt Danxia (25.0347 N, 113.7407 E), Renhua County, Guangdong; males SYS a008120–8121, 8123, 8125, and females SYS a008122, 8124, from Shimentai Nature Reserve (24.3818 N, 113.3927 E), Yingde City, Guangdong; female SYS a000488, from Mt Luoyang, Lingshan County, Guangxi Zhuang Autonomous Region, China.

Etymology

The specific name obscura means ‘obscure’ in Latin.

Common name

“Chinese floating frog” in English / “中国浮蛙 (zhōng guó fú wā)” in Chinese.

Diagnosis

(1) Body stocky, size small, SVL 24.2–27.5 mm in adult males (n=7) and 31.5–32.2 mm in adult females (n=3); (2) snout short triangular shaped; (3) nostrils located dorsally; (4) eye orientation vertically; (5) loreal region oblique, not concave or convex; (6) interorbital space narrower than internarial distance; (7) tongue narrow and slender, unnotched, pointed distally, lingual papilla absent; (8) vomerine ridge and vomerine teeth absent; (9) supratympanic fold distinct, raised, and granulated, curved on the temporal region; (10) tympanum hidden, edge invisible; (11) fingers with rudimentary webs, toes with full webs; (12) heels not meeting, tibio-tarsal articulation reaching between the posterior and anterior of the eye.

Comparisons

Occidozyga obscura comb. nov. was previously synonymized with O. lima. These two species are most similar to each other. However, Occidozyga obscura comb. nov. can be distinguished by the combination of the following characteristics: loreal region oblique, not concave or convex (vs. slightly concave in O. lima), interorbital space narrower than internarial distance (vs. subequal), supratympanic fold distinct, raised, and granulated (vs. indistinct), inner metatarsal tubercle large and raised (vs. weakly projecting), and tibio-tarsal articulation reaching between the posterior and anterior of the eye (vs. reaching tip of nostril).

Occidozyga obscura comb. nov. furthers differs from O. berbeza by the supratympanic fold curved on the temporal region (vs. straight), fingers with rudimentary webs (vs. unwebbed), and outer metatarsal tubercle present (vs. absent). O. obscura comb. nov. distinctly differs from O. rhacoda by the dorsolateral fold absent (vs. present), and fingers with rudimentary webs (vs. unwebbed).

Occidozyga obscura comb. nov. can be easily distinguished from the remaining 13 congeners O. baluensis, O. celebensis, O. diminutiva, O. floresiana, O. laevis, O. magnapustulosa, O. martensii, O. myanhessei comb. nov., O. semipalmata, O. sumatrana, O. shiwandashanensis, O. swanbornorum comb. nov., and O. tompotika, by the tongue narrow and slender (vs. wide and swollen in all of these 13 species).

Re-description

Based on the examined specimens (n=10). All specimens were similar in morphology. The measurements are given in Table 3.

Body stocky, small-sized, SVL 24.2–27.5 mm (n=7) in males and 31.5–32.2 mm (n=3) in females. Head flat above, almost as wide as long (HDW/HDL 0.97–1.09, n=10); pineal ocellus absent; snout short triangular shaped, distinctly protruding beyond lower jaw, tip of snout rounded in dorsal view and profile; canthus rostralis absent, loreal region oblique, not concave or convex; nostril rounded, located dorsally, distinctly raised, closer to the tip of snout than to the eye; eye orientation vertically, pupil diamond shaped; interorbital space narrower than internarial distance; tympanum hidden, edge invisible; vomerine ridge and teeth absent; tongue narrow and slender, unnotched, pointed distally, lingual papilla absent.

Table 3.

Measurements (in mm) of the examined specimens of Occidozyga obscura comb. nov.

Specimen CIB 44475 CIB 44476 SYS a000534 SYS a008120 SYS a008121 SYS a008123 SYS a008125 SYS a008122 SYS a008124 SYS a000488
Sex Male Male Male Male Male Male Male Female Female Female
SVL 24.2 24.7 27.5 24.3 26.2 27.0 24.8 32.2 32.0 31.5
HDL 9.1 9.4 8.9 8.8 9.4 9.4 8.8 10.4 10.4 10.1
HDW 8.8 9.6 9.7 8.6 9.4 9.3 8.6 11.0 11.4 10.0
SNT 2.7 3.1 3.3 2.8 3.3 3.1 3.2 4.2 4.0 3.7
IND 1.5 1.3 1.6 1.4 1.4 1.5 1.2 1.6 1.5 1.6
IOD 1.5 1.2 1.5 1.3 1.4 1.4 1.1 1.5 1.4 1.4
ED 3.2 2.8 2.7 2.7 2.8 2.9 2.6 3.1 3.0 3.2
HND 7.7 7.5 7.8 7.1 7.3 7.4 6.6 8.2 8.8 8.5
RAD 4.0 4.5 3.6 4.1 4.4 4.0 3.9 4.9 5.1 4.9
FTL 19.3 18.4 18.4 18.0 18.8 18.8 17.5 21.3 21.5 21.6
TIB 11.3 11.4 11.2 11.1 11.7 11.5 10.9 13.4 13.6 12.8

Forelimbs short, lower arm 13–18% (n=10) of SVL and hand 26–32% (n=10) of SVL; fingers distinctly thin and long, relative finger lengths I<II<IV<III; tips of fingers pointed, not dilated, and without disks; distinct lateral fringes on inner and outer sides of each finger, fingers with rudimentary webs, more distinct between fingers I and II; subarticular tubercles present at the bases of each finger, prominent and rounded; supernumerary tubercles absent; inner and outer palmar tubercles prominent and rounded.

Hind limbs robust, tibia 41–47% (n=8) of SVL and foot 66–80% (n=8) of SVL; heels not meeting when hind limbs flexed at right angles to the axis of the body; tibio-tarsal articulation reaching between the posterior and anterior of the eye when hind limb is stretched along the side of the body; toes distinctly long and thin, relative lengths I<II<III<V<IV; tips of toes pointed, dilated into pear-shaped disks; toes with full webs, metatarsal web present, distinct lateral fringes on lateral edges of toes I and V; subarticular tubercles rounded, prominent; inner metatarsal tubercle large and long-elliptic, slightly raised, length twice the width; outer metatarsal tubercle relatively smaller than the inner metatarsal tubercle, distinctly raised and pointed, length slightly larger than width; inner tarsal fold relatively flat, in contact with the inner metatarsal tubercle; tarsal tubercle large and distinctly raised, close to the tibio-tarsal articulation.

Dorsal surface relatively rough, transverse wrinkles and dense tubercles on the dorsum, head, flanks, and limbs; small granules on the dorsal rears of hands and tarsi; not bearing spinules on the dorsal skin; supratympanic fold distinct, raised and granulated, extending from the posterior corner of the eye, curved on the temporal region, to the previous shoulder; dorsolateral fold absent. Ventral surface with large flattened tubercles, denser on the throat and thighs; dense granules on the ventral feet and tarsi.

Coloration

In life (Fig. 3), dorsal surfaces vary from olive brown to dark brown; dorsum and flanks interspersed with irregular black speckles; mid-dorsal stripe grass-green with distinct border; lateral line system grayish brown to yellowish brown. Pupil bordered with yellow, iris beige to brown. Supratympanic fold olive-brown to dark brown. Skin of throat, chest, and belly uniform creamy white; gular with a pair of distinct or indistinct longitudinal dark stripes; skin of limbs dark gray, tubercles on ventral thighs and tibias creamy white.

In preservative (Fig. 4A, B), dorsum light gray; black speckles on dorsal surface light brown; mid-dorsal stripe fainted and the border indistinct; ventral skin grayish white; tubercles on ventral surface more distinct.

Figure 3. 

Morphological features of Occidozyga obscura comb. nov. in life. AD dorsolateral view, ventral view, left hand, and right foot of SYS a008122 E dorsolateral view of SYS a008123 F dorsolateral view of an uncaptured individual in situ from Shimentai Nature Reserve.

Figure 4. 

Morphological features of Occidozyga obscura comb. nov. and Occidozyga lingnanica sp. nov. in preservative. Occidozyga obscura comb. nov.: A adult male SYS a008121 B adult female SYS a008122; Occidozyga lingnanica sp. nov.: C adult male paratype SYS a007373 D adult female paratype SYS a007375. 1 dorsal view 2 ventral view.

Male secondary sexual characteristics

Male with a single subgular vocal sac; in breeding season, a single, light grey nuptial pad on the dorsal surface of finger I, nuptial spinules invisible. Males (SVL 24.2–27.5 mm) distinctly smaller than females (SVL 31.5–32.2 mm) (Fig. 4A, B).

Ecology

This frog inhabits natural or artificial ponds and paddy fields in plain areas. They quickly dive underwater after being disturbed during the daytime, while become relatively insensitive at night. Males call in the water surface or waterside grass from dusk to dawn, more active during the rain. The breeding season is from April to August (this study; Fei et al. 2009).

Distribution

Occidozyga obscura comb. nov. can be recognized from several localities of Guangdong and Guangxi, southeastern China (Figs 1, 2), based on the analyzed vouchers in this work. The previous records of O. lima from Guangdong, Guangxi, Hong Kong, Macao, and Fujian, southeastern China are reassigned to O. obscura currently (see Remarks below). The records of O. lima from Yunnan require further clarifications with molecular and morphological vouchers (which might be close to the lineage of O. cf. lima based on the biogeographical similarity).

Conservation status

This species was previously reported as common and widespread species in southeastern China under the nomen O. lima, but its population quantity is found rapidly declining due to the influence of human activities such as pesticide abuse and urban construction. The populations in Hong Kong, Macao, Shenzhen, Guangzhou, and Xiamen might disappear, as no more reports and vouchers in nearly 20 years (this study; Chan 2013). We recommend Occidozyga obscura comb. nov. to be listed as Endangered (EN) [IUCN Red List criteria A2cd].

Remarks

The type specimen of Occidozyga obscura comb. nov. was collected by John Reeves (1774–1856) but the exact type locality was not given in the original description (Gray 1831). Zhao & Adler (1993) speculated that the type specimens may be from somewhere in southeastern China, especially Macao or Canton (= Guangzhou) in Pearl River Delta, where John Reeves lived and worked in.

Moreover, there were two historic species currently regarded as synonymies of O. lima, namely Oxyglossa lima var. chinens and Osteosternum amoyense (Stejneger 1925; Smith 1931; Pope 1931). The type locality for Oxyglossa lima var. chinens is Lilong, Canton (= Lilang, Shenzhen, Guangdong), and for Osteosternum amoyense is Amoy (= Xiamen, Fujian). During our field surveys, we are unable to observe any frogs that resembled these two historic species from Shenzhen or Xiamen, possibly due to the dramatic urbanization of these two cities. Nevertheless, according to their original descriptions and distributions, we propose to transfer these two taxa to be the synonymy of Occidozyga obscura comb. nov.

Occidozyga lingnanica Lyu & Wang, sp. nov.

Ooeidozyga laevis martensiPope 1931; Liu & Hu 1961

Occidozyga martensiiFei et al. 1990; Zhao & Adler 1993; Li et al. 2011

Phrynoglossus martensiiFei et al. 2009, 2010, 2012

Type materials

Holotype. SYS a008846, adult male, collected on 18 July 2021 by Zhi-Tong Lyu from Mt Wugongling (22.5914 N, 114.4927 E), Shenzhen City, Guangdong. Paratypes. Seven adult males and three adult females. Male SYS a008847 CIB 118529, collected at the same time as the holotype; males SYS a005589–90, collected on 15 November 2016 by Zhi-Tong Lyu and Jian Wang from Mt Wugongling; males SYS a007372–7373, and females SYS a07374–7375, collected on 5 September 2018 by Jian Wang and Hong-Hui Chen from Qi’ao Island (22.4140 N, 113.6446 E), Zhuhai City, Guangdong Province, China; female SYS a004650, collected on 14 April 2016 by Jian Wang from Mt Yunkai (22.2786 N, 111.1886 E), Xinyi City, Guangdong; males SYS a007657–7658, collected on 8 April 2019 by Jian Wang from Mt Yunkai.

Other examined specimens

Five adult males and five adult females. Male SYS a005543 and female SYS a005542, from Mt Jiaoyiling (21.1592 N, 110.3093 E), Zhanjiang City, Guangdong; female SYS a005267, from Mt. Diaoluo (18.6408 N, 109.9317 E), Lingshui Li Autonomous County, Hainan; males SYS a005436–5437, 5440–5441 and females SYS a005438–5439, 5442, from Mt Bawangling (19.0944 N, 109.0491 E), Changjiang Li Autonomous County, Hainan.

Etymology

The specific name lingnanica refers to the lingnan region, a geographic area covering Guangdong, Guangxi, and Hainan in southeastern China, where this new frog species occurs in. This specific name is also dedicated to the former Lingnan University (1888–1952) that was incorporated into Sun Yat-sen University after 1953.

Common name

“Lingnan floating frog” in English / “岭南浮蛙 (lǐng nán fú wā)” in Chinese.

Diagnosis

(1) Body stocky, size small, SVL 19.9–22.1 mm in males (n=8) and 26.8–28.8 mm in females (n=3); (2) snout short triangular shaped; (3) nostrils located laterally; (4) eye orientation laterally; (5) canthus rostralis visible, rounded; (6) loreal region vertical, not concave/convex; (7) tongue wide and swollen, unnotched, rounded distally, lingual papilla absent; (8) vomerine ridge and vomerine teeth absent; (9) supratympanic fold distinct and raised, slightly curved on the temporal region; (10) tympanum hidden, edge invisible; (11) relative finger lengths II=I<IV<III, relative toe lengths I<II<V<III<IV; (12) fingers without webs, toes with two third webs; (13) heels not meeting, tibio-tarsal articulation reaching at the posterior margin of supratympanic fold; (14) tarsal fold absent.

Comparisons

Occidozyga lingnanica sp. nov. has been long-term misidentified as O. martensii, however, it differs from the latter by a combination of the following morphological characters: tympanum hidden, edge invisible (vs. tympanum edge raised), relative finger lengths II=I<IV (vs. II=IV<I), relative toe lengths V<III (vs. III<V), tarsal fold absent (vs. present), tibio-tarsal articulation reaching the posterior margin of supratympanic fold (vs. reaching the region of eye).

Occidozyga lingnanica sp. nov. can be distinguished from the remaining three known congeners in Clade VIII (Fig. 1) by the canthus rostralis rounded (vs. absent in O. magnapustulosa), loreal region oblique, not concave or convex (vs. slight convex in O. magnapustulosa and O. swanbornorum comb. nov.), relative finger lengths II=I<IV (vs. II<IV<I in O. myanhessei comb. nov., IV<II<I in O. swanbornorum comb. nov.), tarsal fold absent (vs. present in O. magnapustulosa and O. myanhessei comb. nov.).

For the remaining 13 congeners, Occidozyga lingnanica sp. nov. distinctly differs from O. lima, O. obscura comb. nov., and O. berbeza by the tongue wide and swollen (vs. narrow and slender); from O. rhacoda by the dorsolateral fold absent (vs. present); from O. shiwandashanensis by the tarsal fold absent (vs. present); from O. celebensis, O. laevis, and O. sumatrana by the eye orientation laterally (vs. vertically); from O. baluensis, O. floresiana, and O. semipalmata by the canthus rostralis rounded (vs. absent); from O. diminutiva and O. tompotika by the supratympanic fold curved (vs. straight).

Description of holotype

SYS a008846, adult male (Fig. 5). Body stocky, small-sized, SVL 21.4 mm. Head longer than wide (HDW/HDL 0.97), plat above; pineal ocellus distinct; snout short triangular shaped, distinctly protruding beyond lower jaw, tip of snout rounded in dorsal view and profile; canthus rostralis rounded, loreal region oblique, not concave or convex; nostril rounded, laterally, not raised, at the middle between tip of snout and eye; eye orientation laterally, pupil diamond shaped; interorbital space distinctly narrower than internarial distance; tympanum hidden, edge invisible; vomerine ridge and teeth absent; tongue wide and swollen, unnotched, rounded distally, lingual papilla absent.

Figure 5. 

Morphological features of the adult male holotype SYS a008846 of Occidozyga lingnanica sp. nov. in life. A dorsolateral view B ventral view C left hand D right foot E dorsal view of right hand showing the nuptial pad F calling in situ showing the subgular vocal sac.

Forelimbs short, lower arm 15% of SVL and hand 25% of SVL; fingers relatively thin and long, relative finger lengths II=I<IV<III; tips of fingers rounded, not dilated and without disks; fingers without webs and fringes; subarticular tubercles present at the bases of each finger, prominent and rounded; supernumerary tubercles absent; inner and outer palmar tubercles prominent and rounded.

Hind limbs robust, tibia 44% of SVL and foot 63% of SVL; heels not meeting when hind limbs flexed at right angles to the axis of the body; tibio-tarsal articulation reaching at the posterior margin of supratympanic fold when hind limb is stretched along the side of the body; toes distinctly long and thin, relative lengths I < II < V < III < IV; tips of toes rounded, dilated into rounded disks; toes with two third webs, metatarsal web present, distinct lateral fringes on lateral edges of toes I and V; subarticular tubercles rounded, prominent; inner metatarsal tubercle large and long-elliptic, distinctly raised, length triple the width; outer metatarsal tubercle absent; tarsal fold absent.

Dorsal surface relatively rough, large tubercles scattering on skin of dorsum, flanks, and dorsal limbs, not bearing spinules on the dorsal skin; a faint fold across head between orbits; supratympanic fold distinct, raised, extending from the posterior corner of the eye, slightly curved on the temporal region, to the previous shoulder; dorsolateral fold absent. Ventral surface with large flattened tubercles; a fold across breast; dense granules on the ventral tarsi.

Coloration of holotype

In life (Fig. 5), dorsal surface grayish brown with irregular black speckles; dorsal limbs with dark brown transverse bars; mid-dorsal stripe yellowish brown but indistinct; a narrow transverse bar between orbits; supratympanic fold dark brown. Pupil bordered with yellow; iris brown with irregular dark or light speckles. Skin of throat dark with white mottling; skin of chest and belly uniform creamy white; ventral surface of limbs grayish pink with dark speckles. Nuptial pad light yellow, slightly transparent.

In preservative, dorsum light gray; black speckles on dorsum and transverse bars on limbs light brown; mid-dorsal stripe grayish white and more distinct; nuptial pad light gray, slightly transparent; ventral surface grayish white; mottling on throat gray white.

Variation

The measurements of the type series are given in Table 4. All individuals were similar in morphology. Dorsal coloration varies in life, from light brown, yellowish brown, to dark brown (Figs 5, 6); mid-dorsal stripe varies among individuals, distinct (Figs 4C, 6C), indistinct (Fig. 5), or absent (Figs 4D, 6A, B, D–F); an irregular orange marking on the occipital region in some individuals (Fig. 6F).

Figure 6. 

Color variation of Occidozyga lingnanica sp. nov. in life. A adult male paratype SYS a008847 B adult female paratype SYS a004650 C adult male paratype SYS a007373 D adult female paratype SYS a007375 E adult male SYS a005437 F adult male SYS a005440.

Table 4.

Measurements (in mm) of the examined specimens of Occidozyga lingnanica sp. nov.

Specimen SYS a007372 SYS a007373 SYS a008846 SYS a008847 SYS a005589 SYS a005590 SYS a007657 SYS a007658 SYS a007374 SYS a007375 SYS a004650
Sex Male Male Male Male Male Male Male Male Female Female Female
SVL 22.1 21.6 21.4 21.5 19.9 20.2 21.8 21.7 26.8 28.5 28.8
HDL 7.8 7.1 7.5 7.5 6.6 6.6 7.1 7.8 9.0 9.5 9.0
HDW 7.4 6.7 7.2 7.2 6.5 6.5 6.6 7.5 8.9 9.3 9.0
SNT 2.9 2.7 2.5 2.6 2.3 2.3 2.9 2.9 3.0 3.5 3.3
IND 1.9 1.8 1.6 1.6 1.5 1.6 1.7 1.8 2.1 2.2 2.3
IOD 1.5 1.4 1.1 1.2 1.0 1.1 1.3 1.3 1.7 1.8 1.9
ED 2.6 2.5 2.5 2.5 2.3 2.3 2.5 2.7 3.3 3.4 3.0
HND 5.4 5.3 5.3 5.3 4.7 4.6 5.5 5.4 5.6 6.8 6.1
RAD 3.7 3.5 3.2 3.4 3.5 3.7 3.4 3.3 4.2 4.4 4.8
FTL 14.1 14.4 13.4 14.2 12.9 13.8 14.7 14.1 17.9 19.2 19.5
TIB 9.8 9.7 9.4 9.8 8.6 9.2 9.5 9.5 11.7 11.4 11.8

Male secondary sexual characteristics

Male with a single subgular vocal sac; in breeding season, a single, light yellow, swollen, and granular nuptial pad on the dorsal surface of finger I, nuptial spinules invisible. Males (SVL 19.9–22.1 mm) distinctly smaller than females (SVL 26.8–28.8 mm) (Fig. 4C, D).

Ecology

This frog inhabits natural or artificial ponds and paddy fields in hilly regions. Males call in the water surface or waterside grass from dusk to dawn. The breeding season is from May to August (this study; Fei et al. 2009). In southeastern China, Occidozyga lingnanica sp. nov. shares a similar environment to that of Occidozyga obscura comb. nov., but prefers to hilly regions compared with the latter in plain areas.

Distribution

Occidozyga lingnanica sp. nov. can be recognized from multiple localities in Guangdong and Hainan of southeastern China based on the phylogenetic result in this work (Figs 1, 2). The records of O. martensi from Yunnan, southwestern China require further clarifications with morphological examinations (see Discussion).

Conservation status

Occidozyga lingnanica sp. nov. was previously reported as common and widespread species in southeastern China under the nomen O. martensii. Nevertheless, during our repeated surveys throughout southeastern China, the population quantity of this species is found rapidly declining due to the influence of human activities such as pesticide abuse and urban construction. We recommend Occidozyga lingnanica sp. nov. to be listed as Vulnerable (VU) [IUCN Red List criteria B1b(ii)(iii)].

Acknowledgments

We thank Guangdong Yunkaishan National Nature Reserve, Guangdong Nanling National Nature Reserve, Guangdong Shimentai National Nature Reserve, Guangdong Danxiashan National Nature Reserve, Qing Du, Wei-Liang Xie, Run-Lin Li, Hai-Long He, Yong-You Zhao, and Hong-Hui Chen, for their help in the fieldwork, lab work, and manuscript preparation. We thank Gunther Köhler for his useful comments on our manuscript. This research was supported by the DFGP Project of Fauna of Guangdong-202115, the National Animal Collection Resource Center, China, the Project of Animal Diversity Survey and Monitoring System Construction of Guangdong Shimentai National Nature Reserve, and the Project of Survey of Terrestrial Vertebrate Diversity in Guangdong Danxiashan National Nature Reserve.

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Supplementary material

Supplementary material 1 

Table S1

Lyu Z-T, Wang J, Zeng Z-C, Luo L, Zhang Y-W, Guo C-P, Ren J-L, Qi S, Mo Y-M, Wang Y-Y (2022)

Data type: .xlsx

Explanation note: Pairwise distances based on the 16S gene among all Occidozyga samples used in this study.

This dataset is made available under the Open Database License (http://opendatacommons.org/licenses/odbl/1.0). The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.
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