Research Article
Print
Research Article
A cryptic species of the Amolops ricketti species group (Anura, Ranidae) from China–Vietnam border regions
expand article infoJian Wang§|, Jing Li, Lingyun Du, Mian Hou, Guohua Yu
‡ Guangxi Normal University, Guilin, China
§ Honghe University, Mengzi, China
| Hainan Normal University, Haikou, China
¶ Sichuan Normal University, Chengdu, China
Open Access

Abstract

It was supposed that the current records of Amolops ricketti might be a species complex composed of multiple species. In this study, on the basis of wide sampling, we found that the records of A. ricketti from Yunnan, China, and northern Vietnam actually represent a cryptic species based on morphological and molecular evidence. Amolops shihaitaoi sp. nov. can be distinguished from other members of the A. ricketti species group by its moderate body size (SVL 35.5‒37.3 mm in males and 39.2‒45.7 mm in females); white spines on the temporal region, loreal region, snout, and lips in breeding males but absent in females; overlapping heels; tibiotarsal articulation reaching tip of snout; indistinct longitudinal glandular folds on the skin of the shoulders; presence of supernumerary tubercles below the base of fingers II‒IV, distinct pineal body; presence of vomerine teeth; and absence of vocal sacs. Phylogenetic analysis supports that the new species is sister to Amolops yatseni and the populations from Jingxi, Guangxi and Lào Cai, Vietnam previously reported as A. yatesni also belong to it. Additionally, our results indicate that more cryptic species may exist within the A. ricketti species group, implying that more studies are needed to achieve a complete understanding of the species diversity of this group.

Keywords

Amolops shihaitaoi sp. nov., Amolops yatseni, new species, Northern Vietnam, Yunnan

Introduction

The cascade frog genus Amolops Cope, 1865, which occurs throughout Southeast Asia, southern China, and the southern and eastern Himalayas (Yu et al. 2019; Gan et al. 2020a; Frost 2021), currently contains 73 species (Frost 2021). In China, 42 cascade frog species have been reported (AmphibiaChina 2022), and recently they were assigned into eight species groups, including the A. monticola group, A. chayuensis group, A. mantzorum group, A. viridimaculatus group, A. marmoratus group, A. ricketti group, A. daiyunensis group, and A. hainanensis group (Jiang et al. 2021).

Generally, members of same species group within Amolops share a very similar external adult morphology (e.g. A. monticola group), and even some species are more similar in external adult morphology to species of the genus Odorrana Fei, Ye & Huang, 1990 (Stuart et al. 2010), which has heavily hampered our understanding of the species diversity in Amolops (Wu et al. 2020). During the past two decades, many efforts have been conducted to clarify species diversity within Amolops and, notably, a high number of cryptic lineages were discovered. For example, Bain et al. (2003) found six cryptic species in the Rana chloronota complex and one of them was later moved to Amolops [A. daorum (Bain, Lathrop, Murphy, Orlov & Ho, 2003)] by Stuart (2008); Dever et al. (2012) investigated diversity in the Amolops marmoratus species complex in Myanmar and identified a cryptic species; Lu et al. (2014) suggested that the A. mantzorum species group contains five putative species and the nominal species A. mantzorum (David, 1872) may in fact include two cryptic species; Fei et al. (2017) recognized the clade consisting of a high-altitude population of the A. mantzorum complex in the Yalong river basin as a new species; Jiang et al. (2021) revealed multiple cryptic lineages in the Amolops chunganensis complex within A. monticola group; and Zeng et al. (2021) found that the populations previously recorded as A. hongkongensis (Pope & Romer, 1951) or A. daiyunensis (Liu & Hu, 1975) from the coastal hills in eastern Guangdong and southern Fujian represents a cryptic lineage within the A. daiyunensis species group. Overall, efforts since 2000 have described more than half of the known species within Amolops (Wu et al. 2020), which greatly improves our understanding on the taxonomy and species diversity of this genus.

The A. ricketti group is a monophyletic species group containing six recognized species mainly known from southeast China: A. yunkaiensis Lyu, Wang, Liu, Zeng & Wang, 2018, A. albispinus Sung, Wang & Wang, 2016, A. wuyiensis (Liu & Hu, 1975), A. ricketti (Boulenger, 1899), A. sinensis Lyu, Wang & Wang, 2019, and A. yatseni Lyu, Wang & Wang, 2019 (Lyu et al. 2019; Jiang et al. 2021). Amolops ricketti was originally described based on specimens from Mount Wuyi, Fujian, China (Boulenger 1899) and had been recorded widely from southern China (i.e. Guangdong, Zhejiang, Jiangxi, Hubei, Hunan, Anhui, and Sichuan; Fei et al. 2012) and northern Vietnam (Nguyen et al. 2009). However, relatively high morphological variation had been observed among populations (Ngo et al. 2006), and recently several cryptic species have been recognized including A. albispinus, A. sinensis, and A. yatseni (Sung et al. 2016; Lyu et al. 2019), indicating that current records of A. ricketti might be composed of multiple species and further surveys and studies are required to investigate the species diversity of A. ricketti group.

In Yunnan, China, A. ricketti has been recorded from Hekou County for over two decades (Yang 1991), but samples of this population have never been included in previous systematic studies. Given that the records of A. ricketti from the central region of its geographic range (Hunan, Guizhou, Sichuan, and northeastern Guangxi) have been revised to A. sinensis (Lyu et al. 2019; Xiao et al. 2019; Zeng et al. 2021), the records of A. ricketti from west region (Yunnan and adjacent Vietnam) probably also need to be revised. Recently, Poyarkov et al. (2021) supposed that Amolops tonkinensis (Ahl, 1927 “1926”), a junior synonym of A. ricketti described from northern Vietnam, is probably valid, also implying that the taxonomic status of A. ricketti from China–Vietnam border regions needs further examination.

During our recent herpetological surveys in Hekou, Yunnan, China, we have collected several Amolops specimens previously recorded as A. ricketti. Morphological and molecular examinations indicated that these specimens were distinct from A. ricketti and other members of the A. ricketti group and herein we describe them as a new species.

Material and methods

Sampling

Field surveys were conducted in June 2020 at Hekou, Yunnan, China (Fig. 1). Nine specimens were collected, and they were photographed, euthanized, fixed, and then stored in 75% ethanol. Liver tissues were preserved in 99% ethanol. Specimens were deposited at Guangxi Normal University (GXNU), Guangxi, China.

Figure 1. 

Map showing the collection sites of samples of the Amolops ricketti species group used in this study. The red star indicates the type locality of Amolops shihaitaoi sp. nov. and numbers correspond to the locality IDs in Table 1.

Morphology

Morphometric data were taken using digital calipers to the nearest 0.1 mm. Morphological terminology follows Yu et al. (2019). Measurements included: snout–vent length (SVL, from tip of snout to vent); head length (HL, from tip of snout to rear of jaws); head width (HW, width of head at its widest point); snout length (SL, from tip of snout to anterior border of eye); internarial distance (IND, distance between nares); interorbital distance (IOD, minimum distance between upper eyelids); upper eyelid width (UEW, maximum width of upper eyelid); eye diameter (ED, diameter of exposed portion of eyeball); nostril-eye distance (DNE, distance from nostril to anterior border of eye); tympanum diameter (TD, the greater of tympanum vertical and horizontal diameters); forearm and hand length (FHL, from elbow to tip of third finger); tibia length (TL, distance from knee to heel); foot length (FL, from proximal end of inner metatarsal tubercle to tip of fourth toe); and length of foot and tarsus (TFL, from tibiotarsal joint to tip of fourth toe). Comparative morphological data of other species in the A. ricketti group were taken from their original descriptions or redescriptions (Fei et al. 2009; Sung et al. 2016; Lyu et al. 2018, 2019).

Molecular phylogenetic analyses and species delimitation

Total genomic DNA was extracted from liver tissues. Tissue samples were digested using proteinase K, and subsequently purified following a standard phenol/chloroform isolation and ethanol precipitation. Sequences encoding 16S rRNA (16S) and cytochrome oxidase subunit I (COI) genes were amplified using the primers and experimental protocols of Du et al. (2020). PCR amplifications were performed in 50 μl reactions using the following cycling conditions: an initial denaturing step at 95 °C for 4 min; 35 cycles of denaturing at 94 °C for 60 s, annealing at 46 °C (for COI) or 51 °C (for 16S), and extending at 72 °C for 60 s; and a final extension step of 72 °C for 10 min. Sequencing was conducted directly using the corresponding PCR primers. All new sequences were deposited in GenBank (accession no. OK754585OK754596 and OK788663OK788670; Table 1). Available homologous sequences of members of the A. ricketti group were obtained from GenBank (Table 1). Amolops mengdingensis Yu, Wu & Yang, 2019, A. torrentis (Smith, 1923), A. hainanensis (Boulenger, 1900), A. hongkongensis, and A. daiyunensis were selected as outgroups according to Gan et al. (2020a).

Table 1.

Samples used in phylogenetic analyses of this study.

Species Voucher number Locality (ID) 16s COI
A. ricketti SYS a4143 Mt. Wuyi, Fujian, China (1) MK263261 MG991929
SYS a4142 Mt. Wuyi, Fujian, China (1) MK263260 MG991928
SYS a4141 Mt. Wuyi, Fujian, China (1) MK263259 MG991927
SYS a4106 Shanghang, Fujian, China (2) MK263256 MK263311
SYS a3342 Shanghang, Fujian, China (2) MK263246 KX507331
SYS a2492 Mt. Emeifeng, Fujian, China (3) MK263244 KX507329
WUSTW01 Mt. Wugong, Jiangxi, China (4) KF956111 KF956111
A. yunkaiensis SYS a4683 Yunkaishan, Guangdong, China (5) MK263273 MG991912
SYS a4684 Yunkaishan, Guangdong, China (5) MK263274 MG991913
A. albispinus SYS a3452 Mt. Wutong, Guangdong, China (6) MK263247 KX507332
SYS a3453 Mt. Wutong, Guangdong, China (6) MK263248 KX507333
A. sinensis SYS a7106 Shimentai, Guangdong, China (7) MK263298 MK263330
SYS a7107 Shimentai, Guangdong, China (7) MK263299 MK263331
SYS a5710 Mt. Nankun, Guangdong, China (8) MK263287 MK263321
SYS a5089 Dupangling, Guangxi, China (9) MK263279 MK263319
SYS a7268 Yangming, Hunan, China (10) MK263302 MK263334
SYS a4257 Hengshan, Hunan, China (11) MK263265 MK263315
GZNU2018052038 Huangping, Guizhou, China (12) MN640863 MN643605
GZNU201805201 Mt. fanjingshan, Guizhou, China (13) MN640865 MN643607
GZNU201805001 Danzhai, Guizhou, China (14) MN640867 MN643609
GZNU201805002 Leishan, Guizhou, China (15) MN640868 MN643610
GZNU201806001 Majiang, Guizhou, China (16) MN640869 MN643611
GZNU20170815001 Xishui, Guizhou, China (17) MN640874 MN643616
GZNU20170815003 Shuiyang, Guizhou, China (18) MN640876 MN643618
YU000067 Mt. Dayao, Guangxi, China (19) OK754585
YU000068 Mt. Dayao, Guangxi, China (19) OK754586
YU20160156 Jishou, Hunan, China (20) OK754587
YU20160406 Xing,an, Guangxi, China (21) OK754588
Longshen, Guangxi, China (22) AY851090
061001 Hejiang, Sichuan, China (23) KU840608
SCUM040518CJ Hejiang, Sichuan, China (23) DQ359987
A. wuyiensis SYS a4140 Mt. Wuyi, Fujian, China (1) MK263258 MK263313
SYS a4139 Mt. Wuyi, Fujian, China (1) MK263257 MK263312
SYS a2723 Jingning, Zhejiang, China (24) MK263245 MK263303
A. shihaitaoi sp. nov. GXNU YU000351 Hekou, Yunnan, China (25) OK754589 OK788663
GXNU YU000352 Hekou, Yunnan, China (25) OK754590 OK788664
GXNU YU000353 Hekou, Yunnan, China (25) OK754591 OK788665
GXNU YU000354 Hekou, Yunnan, China (25) OK754592 OK788666
GXNU YU000355 Hekou, Yunnan, China (25) OK754593 OK788667
GXNU YU000482 Hekou, Yunnan, China (25) OK754594 OK788668
GXNU YU000483 Hekou, Yunnan, China (25) OK754595 OK788669
HM 081419 Hekou, Yunnan, China (25) OK754596 OK788670
YPX6306 Jingxi, Guangxi, China (26) MN953758 MN961459
2000.2938 Tam Dao, Vĩnh Phúc, Vietnam (27) KR827707 KR087622
2000.2939 Tam Dao, Vĩnh Phúc, Vietnam (27) KR827708 KR087623
ROM26365 Cao Bằng, Cao Bằng, Vietnam (28) DQ204486
ROM27276 Sa pa, Lào Cai, Vietnam (29) MN953723 MN958781
AMNH168687 Van Ban, Lào Cai, Vietnam (30) FJ417157
A. yatseni SYS a6806 Zhongshan, Guangdong, China (31) MK263289 MK263323
SYS a6807 Zhongshan, Guangdong, China (31) MK263290 MK263324
SYS a6808 Zhongshan, Guangdong, China (31) MK263291 MK263325
SYS a3633 Shangchuan, Guangdong, China (32) MK263250 MK263304
SYS a6818 Gudou, Guangdong, China (33) MK263294 MK263306
SYS a3978 Ehuangzhang, Guangdong, China (34) MK263252 MK263308
SYS a4642 Yunkaishan, Guangdong, China (5) MK263269 MK263316
SYS a7545 Mt. Darong, Guangxi (35) MZ447966 MZ448269
A. hongkongensis SYS a4577 Hongkong, China MK263266 MG991919
A. daiyunensis SYS a1739 Mt. Daiyun, Fujian, China MK263243 KX507328
A. torrentis SYS a5291 Mt. Wuzhi, Hainan, China MK263286 MG991932
A. hainanensis SYS a5283 Mt. Wuzhi, Hainan, China MK263283 MG991918
A. mengdingensis KIZ 20160317 Mengding, Yunnan, China MK501810 MK501813

Sequences were aligned using MUSCLE with the default parameters in MEGA 7 (Kumar et al. 2016). Uncorrected pairwise distances between species were calculated in MEGA 7. Because sequence of COI gene is not available for nine individuals (Table 1), two datasets were prepared for phylogenetic analysis, one including all individuals and one only including individuals for which both two genes are available. The best substitution model of the concatenated data of 16S rRNA and COI genes was selected using the Akaike Information Criterion (AIC) in MODELTEST v. 3.7 (Posada and Crandall 1998). Bayesian inferences were performed in MRBAYES v. 3.2.6 (Ronquist et al. 2012) under the selected substitution model (GTR + I + G). Two runs were performed simultaneously with four Markov chains starting from random tree. The chains were run for 3,000,000 generations and sampled every 100 generations. The first 25% of the sampled trees were discarded as burn-in after the standard deviation of split frequencies of the two runs was less than a value of 0.01, and then the remaining trees were used to create a consensus tree and to estimate Bayesian posterior probabilities (BPPs).

We used the method of Assemble Species by Automatic Partitioning (ASAP; Puillandre et al. 2021) to attempt to delimit the species boundary among the A. ricketti species group based on the combined data of 16S rRNA and COI sequences. For this analysis, the substitution model of simple distance (p-distances) was selected and the partitioning with lowest ASAP-score was selected as the best according to Puillandre et al. (2021).

Results

The obtained 16S and COI alignments were 1036 and 667 bp, respectively. The A. ricketti group was a monophyletic species group containing seven well-supported distinct clades, of which six (Clades I‒VI) correspond to the six known species of this group. The clade VII is comprised of populations previously recorded as A. ricketti from Yunnan and Vietnam and a specimen previously classified as A. yatseni from Jingxi, Guangxi, China (YPX6306), and it was the sister to A. yatseni (Fig. 2). The genetic divergences between clade VII and A. yatseni estimated from 16S and COI genes are 1.9% and 5.7%, respectively (Table 2).

Table 2.

Uncorrected pairwise distances among members of the A. ricketti species group estimated from 16S rRNA (lower triangle) and COI sequences (upper triangle).

Species 1 2 3 4 5 6 7
1 A. shihaitaoi sp. nov. 0.057 0.061 0.064 0.102 0.101 0.104
2 A. yatseni 0.019 0.066 0.072 0.105 0.100 0.103
3 A. sinensis 0.020 0.019 0.060 0.099 0.101 0.111
4 A. albispinus 0.021 0.025 0.025 0.096 0.108 0.104
5 A. yunkaiensis 0.048 0.049 0.046 0.052 0.118 0.113
6 A. wuyiensis 0.036 0.041 0.035 0.046 0.058 0.095
7 A. ricketti 0.040 0.046 0.043 0.044 0.058 0.028
Figure 2. 

Bayesian phylogram of the Amolops ricketti species group inferred from the combined data of 16S and COI genes with inclusion of all individuals (A) and inclusion of only individuals for which both the two genes are available (B).

The analysis of species delimitation based on the combined data found 10 partitions (Fig. 3a). The best partition (score = 1.00) grouped the samples into eight species with a distance threshold of c. 2% (Fig. 3b) and one of them corresponds to the clade consisting of the samples from Yunnan and northern Vietnam (Clade VII). All other clades were recognized as distinct species by the ASAP analysis with the exception of clade II, which was grouped into two different species, one containing the samples of A. ricketti from Fujian (including the type locality) and one containing the sample of A. ricketti from Mount Wugong, Jiangxi, China (WUSTW01).

Figure 3. 

ASAP species delimitation within the A. ricketti species group based on the combined data of 16S and COI sequences. The best partition with lowest score is highlighted with red frame.

Morphologically the specimens from Hekou, Yunnan, China were distinguished from all other recognized members of the A. ricketti group by a series of characters. Thus, we consider that the clade VII represents a distinct species. Ahl (1927 “1926”) once described Rhacophorus tonkinensis Ahl, 1927 “1926” based on one specimen from Tonkin (probably Mau Son, Lang Son Province, Vietnam according to Bourret [1942]; Fig. 1), but later Bourret (1942) regarded it to be a junior synonym of A. ricketti. Recently, Poyarkov et al. (2021) supposed that A. tonkinensis should be treated as a distinct species or as a senior synonym of A. yatseni. Body size of the type of A. tonkinensis (sex unknown) is 56 mm (Ahl 1927 “1926”), which is obviously larger than our specimens from Hekou, Yunnan, China in body size (35.5‒37.3 mm in males and 39.2‒45.7 mm in females). In addition, specimens from Hekou differ from A. tonkinensis by tibiotarsal articulation reaching tip of snout and upper eyelid width greater than interorbital space (vs tibiotarsal articulation reaching central of eye and upper eyelid width equal to interorbital space; Ahl 1927 “1926”). Therefore, we consider that the clade VII is not conspecific with the nomen A. tonkinensis and describe it as new.

Amolops shihaitaoi sp. nov.

Figs 4, 5, 6, 7

Chresonymy

Amolops ricketti in Yang (1991), Inger et al. (1999), Ngo et al. (2006), Yang and Rao (2008), Nguyen et al. (2009), Stuart et al. (2010), Grosjean et al. (2015); Amolops yatseni in Wu et al. (2020); Amolops tonkinensis in Poyarkov et al. (2021).

Holotype

GXNU YU000353 (Figs 4, 5), adult female, collected on 21 June 2020 by Jian Wang from Hekou, Yunnan, China (22.6287°N, 103.8776°E; 532 m a.s.l.).

Figure 4. 

Views of the holotype of Amolops shihaitaoi sp. nov. (GXNU YU000353) in life.

Figure 5. 

Holotype of Amolops shihaitaoi sp. nov. (GXNU YU000353) in preservative A dorsal view B ventral view.

Paratypes

Six adult females (GXNU YU000351, GXNU YU000352, GXNU YU000354, GXNU YU000355, GXNU YU000478, and GXNU YU000479) and two adult males (GXNU YU000482 and GXNU YU000483) with same collection information as holotype.

Etymology

Specific epithet shihaitaoi is named after Prof. Hai-Tao Shi from Hainan Normal University for his outstanding contribution to the herpetology of China. We suggest the common English name “Hekou torrent frog” and Chinese name “Hé Kǒu Tuān Wā (河口湍蛙)”.

Diagnosis

The new species is assigned to genus Amolops and further to the A. ricketti group morphologically based on the absence of dorsolateral folds, presence of circummarginal groove on disc of the first finger, disc of first finger distinctly smaller than that of second finger, absence of tarsal fold and tarsal glands, and presence of nuptial pads with conical nuptial spines on the first finger in breeding male.

Amolops shihaitaoi sp. nov. can be distinguished from other members of A. ricketti group by having a combination of the following characters: body size moderate (SVL 35.5‒37.3 mm in males and 39.2‒45.7 mm in females); white spines on temporal region, loreal region, snout, and lips present in breeding males but absent in females (Fig. 5); presence of small, dense, translucent or white spines on the dorsal skin of the body, dorsal and dorsolateral skin of limbs; heels overlapping; tibiotarsal articulation reaching tip of snout; longitudinal glandular folds on the skin of shoulders indistinct; presence of supernumerary tubercles below the base of fingers II‒IV, pineal body distinct; presence of vomerine teeth; and absence of vocal sacs.

Description of holotype

Adult female (SVL 43.8 mm; Table 3); head width (HW 15.2 mm) greater than head length (HL 13.6 mm; HW/HL = 1.12); snout short and rounded in profile, projecting beyond margin of lower jaw in ventral view; canthus rostralis distinct; loreal region sloping, concave; nostrils oval, lateral; internarial distance (IND 5.5 mm) greater than interorbital distance (IOD 3.3 mm; IND/IOD = 1.67); upper eyelid width (UEW 4.3 mm) greater than interorbital space (UEW/IOD = 1.30); pineal spot present; pupil oval, horizontal; tympanum small (TD 1.5 mm), rounded, less than half eye diameter (ED 5.9 mm; TD/ED = 0.25); supratympanic fold distinct, start from posterior edge of eye and extending to should; vomerine teeth in two oblique rows between choanae; choanae oval; tongue cordiform, deeply notched posteriorly.

Table 3.

Measurements (in mm) of Amolops shihaitaoi sp. nov. from the type locality (Holotype is marked with asterisk; M: male; F: female).

Voucher no. sex SVL HL HW SL IND IOD UEW ED TD DNE FHL TL TFL FL
GXNU YU000351 F 39.2 13.3 14.9 5.2 5.5 3.3 3.9 5.2 1.6 2.8 20.4 22.7 30.0 20.3
GXNU YU000352 F 43.2 13.4 15.3 5.2 5.5 3.6 4.1 5.5 1.6 3.0 21.6 24.5 33.4 21.8
GXNU YU000353* F 43.8 13.6 15.2 5.3 5.5 3.3 4.3 5.9 1.5 2.8 20.5 22.7 30.7 20.9
GXNU YU000354 F 39.4 12.7 14.8 5.1 5.2 3.3 4.3 5.5 1.5 2.7 20.8 23.2 30.9 20.2
GXNU YU000355 F 45.7 14.3 15.5 5.9 5.7 4 4.1 5.3 1.5 2.4 21.6 23.7 33.5 22.4
GXNU YU000478 F 45.1 13.9 16.2 5.9 5.6 3.9 4.2 5.7 1.8 2.5 22.5 25.2 32.5 22.6
GXNU YU000479 F 45.3 13.6 15.7 5.5 5.4 3.2 4.2 5.7 1.9 2.7 22.0 25.2 33.5 22.2
GXNU YU000482 M 37.3 11.7 13.4 4.8 5.3 2.7 3.7 5.0 1.8 2.2 19.3 21.8 29.6 19.7
GXNU YU000483 M 35.5 10.9 13.2 4.7 5.0 3.0 3.1 4.9 1.6 1.9 19.2 21.1 28.5 18.4

Forelimbs moderately robust; relative length of fingers I<II<IV<III; all fingertips expanded into discs with circummarginal grooves, relative width of finger disks I<II<III=IV; webbing between fingers absent; subarticular tubercles prominent and rounded, formula 1, 1, 2, 2; supernumerary tubercle present and prominent below the base of fingers II‒IV; two metacarpal tubercles.

Hindlimbs long and robust, tibiotarsal articulation reaching tip of snout when hindlimb stretched alongside of body; heels slightly overlapping when legs positioned at right angles to body; tarsal glands absent; relative length of toes I<II<III=V<IV; all toe tips expanded into discs with circummarginal grooves; toes fully webbed, webbing formula I1-1II1-1III1-1IV1-1V; lateral fringes of toes I and V developed; subarticular tubercles prominent and rounded, formula 1, 1, 2, 3, 2; inner metatarsal tubercle prominent; outer metatarsal tubercle absent.

Dorsolateral fold absent; dorsal surface rough and granular with denser small translucent or white warts on dorsal body and dorsal limbs; flanks very rough and granular, scattered with large raised white tubercles; rictal gland prominent; large white and small translucent warts present around the vent; skin of throat, chest, and venter slightly wrinkled, both sides of venter obviously granular; ventral surface of limbs smooth.

Coloration in life

Dorsal surface of olive-brown with dark brown patches on dorsal surface of head and trunk and dark brown irregular transverse bars on dorsal surface of limbs; dorsal surface of discs white-mottled with cropper on discs of fingers III and IV and all toe discs; region around cloaca olive-brown with rusty mottling on both sides; sides of head olive-brown with dark brown blotches; rictal gland light yellow; flanks olive-brown, warts on flanks dark or white; throat and chest creamy white scattered with distinct dark blotches and mottled with light yellow; belly creamy white mottled with light yellow; ventral surface of limbs semi-opaque, grey, mottled with light yellow; webbing between toes beige, mottled with black; iris black with brown mottling (Fig. 4).

Coloration in preservative

Dorsal surface dark brown, with irregular light patches; dark brown transverse bars on limbs distinct; ventral surface grayish white, with dark mottling on throat and chest (Fig. 5).

Morphological variation

The new species is sexually dimorphic. Males are smaller than females (Table 1) and possess nuptial pads with spines in the breeding season (Fig. 6). Additionally, spines on dorsal skin in males are less distinct than in females. A male specimen in breeding season (GXNU YU000483) has distinct spines on the temporal region, loreal region, snout, lips, and chin, and has conical spines on the nuptial pad, whereas a male specimen in the early stage of development (GXNU YU000482) lacks distinct spines on the temporal region, loreal region, snout, lips, and chin and its nuptial spines are papillate (Fig. 6). All types have no beige snowflake-like patches on the ventral surface of limbs with the exception of GXNU YU000482. In addition, the three types (GXNU YU000352, GXNU YU000353, GXNU YU000355, and GXNU YU000479) nearly have no light yellow coloration of on the undersides of the limbs. Compared to other types, GXNU YU000482 has less distinct dark patches on the throat and chest (Fig. 7).

Figure 6. 

Two male paratypes of Amolops shihaitaoi sp. nov. A GNXU YU000483 B GXNU YU000482.

Figure 7. 

Ventral view of paratypes of Amolops shihaitaoi sp. nov. in life.

Distribution

In addition to the type locality in Hekou, Yunnan, China, the new species also occurs in Jingxi, Guangxi, China and northern Vietnam (Vĩnh Phúc, Cao Bằng, and Lào Cai) because our molecular analyses revealed that samples from Jingxi, Vĩnh Phúc, Cao Bằng, and Lào Cai that were sequenced by previous studies also belong to the new species. In Yunnan, the new species inhabits rocky streams (Fig. 8). Much of the ecology and behavior of this species remains unknown.

Figure 8. 

Habitat of Amolops shihaitaoi sp. nov. at the type locality.

Comparisons

The absence of dorsolateral folds, presence of circummarginal groove on disc of the first finger, disc of first finger distinctly smaller than that of second finger, absence of tarsal fold and tarsal glands, and presence of nuptial pads with conical nuptial spines on the first finger in breeding males suggest that the new species belongs to the A. ricketti species group, which is supported by the molecular evidence (Fig. 2). Morphological comparisons among the members of the A. ricketti species group are summarized in Table 4. Amolops shihaitaoi sp. nov. is recovered as the sister taxon to A. yatseni, but morphologically it differs from the later by the absence of white spines on temporal region and lower lips in female (vs present; Fig. 9), supernumerary tubercles moderate developed (vs very distinct; Fig. 9), and heels overlapping (vs just meeting).

Table 4.

Morphological comparison between members of the A. ricketti species group. Characters are: ① vomerine teeth: 0 = absent, 1 = present; ② vocal sacs: 0 = absent, 1 = present; ③ spines on temporal region and lower lips in female: 0 = absent, 1 = present; ④ heels: 0 = overlapping, 1 = just meeting; ⑤ translucent or white spines on dorsal body, dorsal and dorsolateral limbs: 0 = absent, 1 = present; ⑥ spines on temporal region, loreal region, and lips in breeding male: 0 = absent, 1 = present; ⑦ tibiotarsal articulation: 0 = reaching tip of snout, 1 = reaching eye; ⑧ supernumerary tubercle below the base of fingers II: 0 = absent, 1 = present; ⑨ pineal body: 0 = distinct, 1 = indistinct; ⑩ female SVL (mm). “?” = unknown.

Species Source
A. shihaitaoi sp. nov. 1 0 0 0 1 1 0 1 0 39.2‒45.7 This study
A. yatseni 1 0 1 1 1 1 0 1 0 42.1–48.9 a
A. ricketti 1 0 0 0 0 0 1 0 0 53.5‒67.0 a, b
A. sinensis 1 0 0 0 0 1 0 0 0 47.7–52.7 a
A. albispinus 1 0 0 ? 0 1 0 0 1 43.1–50.9 a, b
A. wuyiensis 0 1 0 0 0 0 0 1 0 45.2–52.7 a, b, c
A. yunkaiensis 0 1 0 0 0 0 0 1 1 35.2–39.0 a, d
Figure 9. 

A, B Amolops shihaitaoi sp. nov. A head of female holotype GXNU YU000353 B hand of male paratype GXNU YU000483 C, D A. yatseni (reproduced from Lyu et al. 2019) C head of female paratype SYS a003981 D hand of male holotype SYS a006807.

The new species has been previously reported as A. ricketti, but it can be distinguished from the later by smaller body size (39.2‒45.7 mm vs 53.5‒67.0 mm in females), presence of dense small translucent or white spines on the dorsal skin of the body, dorsal and dorsolateral skin of limbs (vs absent), presence of spines on skin of temporal region, loreal region, and lips in breeding males (vs absent), and tibiotarsal articulation reaching tip of snout (vs reaching eyes). Amolops shihaitaoi sp. nov. differs from A. sinensis by relatively smaller body size (SVL 39.2‒45.7 mm vs 47.7‒52.7 mm in females), presence of small, dense, translucent or white spines on the dorsal skin of the body, dorsal and dorsolateral skin of limbs (vs absent), presence of supernumerary tubercles below the base of finger II (vs absent), and longitudinal glandular folds on the skin of shoulders indistinct (vs distinct); from A. albispinus by the presence of dense translucent or white spines on the dorsal skin of the body, dorsal and dorsolateral skin of the limbs (vs absent), ventral surface relatively smooth (vs with numerous small tubercles and ridges on the throat and ventral surfaces of trunk and limbs), and pineal body distinct (vs indistinct); and from A. wuyiensis and A. yunkaiensis by the presence of vomerine teeth (vs absent) and absence of vocal sacs (vs present). The new species further obviously differs A. wuyiensis by nuptial spines beige (vs black).

Discussion

Amolops ricketti was once recorded widely from southern China and Indochina (Fei et al. 2012), but recent studies based on samples mainly from east and middle parts of its distribution range showed that it actually contains multiple cryptic species (Sung et al. 2016; Lyu et al. 2019; Xiao et al. 2019), indicating that a taxonomic investigation for the records from west part of its distribution range is needed to precisely determine the species diversity and distribution of the A. ricketti species group. In this study, we found that the populations from Yunnan and Vietnam previously recorded as A. ricketti represent a distinct species based on morphological and molecular evidence, and the population from Jingxi, Guangxi, which was recently classified as A. yatseni in Wu et al. (2020), also belongs to it. This finding further improves our understanding of the taxonomy and distribution of the A. ricketti species group (Fig. 1).

The taxonomy of A. ricketti species group in northern Vietnam is complicated and needs further study. Recently, A. tonkinensis, a junior synonym of A. ricketti described from Tonkin (probably Lang Son Province of Vietnam according to Bourret [1942]), was considered probably valid or a senior synonym of A. yatseni by Poyarkov et al. (2021). We think that A. shihaitaoi sp. nov. is not conspecific with A. tonkinensis because the new species described here has smaller body size, longer hindlimbs, and upper eyelid width greater than interorbital space as we mentioned above. Additionally, Pham et al. (2020) reported that males of A. ricketti from Hai Ha forest, Quang Ninh Province, Vietnam have vocal sacs, which is questionable and needs further confirmation because A. ricketti sensu stricto, A. sinensis, A. yatseni, and A. shihaitaoi sp. nov. have no vocal sacs. It is possible that the record of A. ricketti from Quang Ninh represents a cryptic species or refers to A. tonkinensis. In addition, the taxonomic status of A. ricketti from Mount Wugong, Jiangxi also needs further investigation because the sample from this locality was not grouped into same species with A. ricketti from the type locality by the analysis of species delimitation. In summary, more cryptic species may exist within the A. ricketti species group, implying that more studies are needed to achieve a complete understanding on the species diversity of this group.

The genus Amolops is the most diverse group of ranid frogs and currently contains 74 species including A. shihaitaoi sp. nov. Of these 74 species, more than a third (30) were described in the last decade (2010‒2021), indicating that the species diversity of Amolops was highly underestimated and the taxonomy of Amolops has attracted much attention of herpetologists during the last decade (e.g. Stuart et al. 2010; Dever et al. 2012; Sun et al. 2013; Jiang et al. 2016; Fei et al. 2017; Yuan et al. 2018; Yu et al. 2019; Che et al. 2020; Gan et al. 2020a, 2020b; Zeng et al. 2021). Most of the newly named Amolops species during the last ten years are from China (especially southwestern China), reflecting high species diversity of Amolops in China and probably the shortage of amphibian surveys in adjacent countries (e.g. Myanmar; Gan et al. 2020b).

Yunnan is the region with highest amphibian species diversity in China (AmphibiaChina 2022), and in recent years a number of new species or newly recorded Amolops were discovered from Yunnan (e.g. Yuan et al. 2018; Yu et al. 2019; Gan et al. 2020a; Wu et al. 2020). Including the new species described here, up to now there are 14 Amolops species known from Yunnan, including A. afghanus (Günther, 1858), A. bellulus Liu, Yang, Ferraris & Matsui, 2000, A. daorum, A. jinjianensis Su, Yang & Li, 1986, A. loloensis (Liu, 1950), A. mantzorum, A. mengdingensis, A. mengyangensis Wu & Tian, 1995, A. shihaitaoi sp. nov., A. splendissimus Orlov & Ho, 2007, A. tuanjieensis Gan, Yu & Wu, 2020, A. tuberodepressus Liu & Yang, 2000, A. viridimaculatus (Jiang, 1983), and A. wenshanensis Yuan, Jin, Li, Stuart & Wu, 2018. Amolops chunganensis (Pope, 1929) was once recorded from Jinghong and Menglian in Yunnan (Yang and Rao 2008), but these two records should be revised to A. mengyangensis and A. tuanjieensis, respectively (Jiang et al. 2021).

Compared to Yunnan, the species diversity of Amolops in Guangxi is much lower and currently only five species are exactly known from there including A. chunganensis (Jiang et al. 2021), A. sinensis (Lyu et al. 2019; this study), A. wenshanensis (Yuan et al. 2018), A. yatseni (Zeng et al. 2021), and the new species described here.

A key to the members of Amolops ricketti species group

1 Vomerine teeth absent and vocal sac present 2
Vomerine teeth present and vocal sac absent 3
2 Nuptial spines black A. wuyiensis
Nuptial spines white A. yunkaiensiis
3 Breeding male lacks spines on temporal region, loreal region, and lips A. ricketti
Breeding male has spines on temporal region, loreal region, and lips 4
4 Pineal body barely visible A. albispinus
Pineal body very distinct 5
5 Translucent or white spines absent on dorsal body, dorsal and dorsolateral limbs and supernumerary tubercle below the base of fingers II absent A. sinensis
Translucent or white spines present on dorsal body, dorsal and dorsolateral limbs and supernumerary tubercle below the base of fingers II present 6
6 Spines present on temporal region and lower lips in female and heels just meeting A. yatseni
Spines absent on temporal region and lower lips in female and heels overlapping A. shihaitaoi sp. nov.

Acknowledgements

Thanks go to colleagues from Daweishan National Nature Reserve for their assistances during the fieldwork. This work was supported by grants from the National Natural Science Foundation of China (32060114, 31872212), Guangxi Natural Science Foundation Project (2022GXNSFAA035526), Key Laboratory of Ecology of Rare and Endangered Species and Environmental Protection (Guangxi Normal University), Ministry of Education (ERESEP2022Z04), and Guangxi Key Laboratory of Rare and Endangered Animal Ecology, Guangxi Normal University (19-A-01-06).

References

  • Ahl E (1927 “1926”) Ueber neue oder seltene Froschlurche aus dem Zoologischen Museum Berlin. Sitzungsberichte der Gesellschaft Naturforschender Freunde zu Berlin 1926: 111–117.
  • Boulenger GA (1900 “1899”) On the reptiles, batrachians, and fishes collected by the late Mr. John Whitehead in the interior of Hainan. Proceedings of the Zoological Society of London 1899: 956–962.
  • Bourret R (1942) Les Batraciens de l’Indochine. Institut Océanographique de l’Indochine, Hanoi.
  • Che J, Jiang K, Yan F, Zhang Y (2020) Amphibians and Reptiles in Tibet—Diversity and Evolution. Chinese Academy of Sciences. Science Press, Beijing.
  • Cope ED (1865) Sketch of the primary groups of Batrachia Salientia. Natural History Research 5: 97–120.
  • David A (1872 “1871”) Rapport adressé a MM. les Professeurs-Administráteurs du Museum d’histoire naturelle. Nouvelles Archives du Muséum d’Histoire Naturelle 7: 75–100.
  • Dever JA, Fuiten AM, Konu Ö, Wilkinson JA (2012) Cryptic torrent frogs of Myanmar: An examination of the Amolops marmoratus species complex with the resurrection of Amolops afghanus and the identification of a new species. Copeia 2012(1): 57–76. https://doi.org/10.1643/CH-10-180
  • Du LN, Liu S, Hou M, Yu GH (2020) First record of Theloderma pyaukkya Dever, 2017 (Anura: Rhacophoridae) in China, with range extension of Theloderma moloch (Annandale, 1912) to Yunnan. Zoological Research 41(5): 576–580. https://doi.org/10.24272/j.issn.2095-8137.2020.083
  • Fei L, Ye CY, Huang YZ (1990) Key to Chinese Amphibians. Publishing House for Scientific and Technological Literature, Chongqing.
  • Fei L, Hu SQ, Ye CY, Huang YZ (2009) Fauna Sinica. Amphibia. Volume 3. Anura Ranidae. Science Press, Beijing.
  • Fei L, Ye CY, Jiang JP (2012) Colored Atlas of Chinese amphibians and their distributions. Sichuan Publishing House of Science and Technology, Chengdu.
  • Fei L, Ye CY, Wang YF, Jiang K (2017) A new species of the genus Amolops (Anura: Ranidae) from high-altitude Sichuan, southwestern China, with a discussion on the taxonomic status of Amolops kangtingensis. Zoological Research 38: 138–145. https://doi.org/10.24272/j.issn.2095-8137.2017.022
  • Grosjean S, Ohler A, Chuaynkern Y, Cruaud C, Hassanin A (2015) Improving biodiversity assessment of anuran amphibians using DNA barcoding of tadpoles. Case studies from Southeast Asia. Comptes Rendus Biologies 338(5): 351–361. https://doi.org/10.1016/j.crvi.2015.03.015
  • Jiang YM (1983) A new species of the genus Staurois (Ranidae), Staurois viridimaculatus. Acta Herpetologica Sinica 2(3): 71.
  • Jiang K, Ren JL, Lyu ZT, Wang D, Wang Z, Lv K, Wu JW, Li JT (2021) Taxonomic revision of Amolops chunganensis (Pope, 1929) (Amphibia: Anura) and description of a new species from southwestern China, with discussion on Amolops monticola group and assignment of species groups of the genus Amolops. Zoological Research 42(5): 574–591. https://doi.org/10.24272/j.issn.2095-8137.2021.107
  • Kumar S, Stecher G, Tamura K (2016) MEGA7: Molecular evolutionary genetics analysis version 7.0 for bigger datasets. Molecular Biology and Evolution 33(7): 1870–1874. https://doi.org/10.1093/molbev/msw054
  • Liu CC, Hu SQ (1975) Report on three new species of Amphibia from Fujian Province. Dong Wu Xue Bao 21: 265–271.
  • Lu B, Bi K, Fu JZ (2014) A phylogeographic evaluation of the Amolops mantzorum species group: Cryptic species and plateau uplift. Molecular Phylogenetics and Evolution 73: 40–52. https://doi.org/10.1016/j.ympev.2014.01.008
  • Lyu ZT, Wu J, Wang J, Sung YH, Liu ZY, Zeng ZC, Wang X, Li YY, Wang YY (2018) A new species of Amolops (Anura: Ranidae) from southwestern Guangdong, China. Zootaxa 4418(6): 562–576. https://doi.org/10.11646/zootaxa.4418.6.4
  • Lyu ZT, Huang LS, Wang J, Li YQ, Chen HH, Qi S, Wang YY (2019) Description of two cryptic species of the Amolops ricketti group (Anura, Ranidae) from southeastern China. ZooKeys 812: 133–156. https://doi.org/10.3897/zookeys.812.29956
  • Ngo A, Murphy RW, Liu WZ, Lathrop A, Orlov NL (2006) The phylogenetic relationships of the Chinese and Vietnamese waterfall frogs of the genus Amolops. Amphibia-Reptilia 27(1): 81–92. https://doi.org/10.1163/156853806776052010
  • Nguyen SV, Ho CT, Nguyen TQ (2009) Herpetofauna of Vietnam. Edition Chimaira, Frankfurt am Main.
  • Orlov NL, Ho CT (2007) Two new species of cascade ranids of Amolops genus (Amphibia: Anura: Ranidae) from Lai Chau Province (Northwest Vietnam). Russian Journal of Herpetology 14: 211–229.
  • Pham CT, Do QH, Ngo HN, Tran TT, Ziegler T, Nguyen TQ (2020) First report on the anuran fauna of Hai Ha forest, Quang Ninh Province, Vietnam. Check List 16(4): 1025–1041. https://doi.org/10.15560/16.4.1025
  • Pope CH (1929) Four new frogs from Fukien Province, China. American Museum Novitates 352: 1–5.
  • Poyarkov NA, Nguyen TV, Popov ES, Geissler P, Pawangkhanant P, Neang T, Suwannapoom C, Orlov NL (2021) Recent progress in taxonomic studies, biogeographic analysis, and revised checklist of amphibians of Indochina. Russian Journal of Herpetology 28(3A): 1–110. https://doi.org/10.30906/1026-2296-2021-28-3A-1-110
  • Ronquist F, Teslenko M, van der Mark P, Ayres DL, Darling A, Höhna S, Larget B, Liu L, Suchard MA, Huelsenbeck JP (2012) MrBayes 3.2: Efficient Bayesian phylogenetic inference and model choice across a large model space. Systematic Biology 61(3): 539–542. https://doi.org/10.1093/sysbio/sys029
  • Smith MA (1923) On a collection of reptiles and batrachians from the Island of Hainan. The Journal of the Natural History Society of Siam 6: 195–212.
  • Stuart BL, Bain RH, Phimmachak S, Spence K (2010) Phylogenetic systematics of the Amolops monticola group (Amphibia: Ranidae), with description of a new species from northwestern Laos. Herpetologica 66(1): 52–66. https://doi.org/10.1655/08-073.1
  • Sun GZ, Luo WX, Sun HY, Zhang GY (2013) A new species of Cascade Frog from Tibet: China. Forestry Construction 20: 14–16.
  • Wu GF, Tian WS (1995) A new Amolops species from southern Yunnan. In: Zhao EM (Ed.) Amphibian Zoogeographic Division of China. A Symposium Issued to Celebrate the Second Asian Herpetological Meeting Held at Ashgabat, Turkmenistan 6 to 10 September 1995. Sichuan Journal of Zoology (Supplement), 51–52.
  • Wu YH, Yan F, Stuart BL, Prendini E, Suwannapoom C, Dahn HA, Zhang BL, Cai HX, Xu YB, Jiang K, Chen HM, Lemmon AR, Lemmon EM, Raxworthy CJ, Orlov NL, Murphy RW, Che J (2020) A combined approach of mitochondrial DNA and anchored nuclear phylogenomics sheds light on unrecognized diversity, phylogeny, and historical biogeography of the torrent frogs, genus Amolops (Anura: Ranidae). Molecular Phylogenetics and Evolution 148: 106789. https://doi.org/10.1016/j.ympev.2020.106789
  • Xiao N, Luo QH, Deng HQ, Zhou J, Luo T (2019) Morphology, phylogeny and taxonomy of Amolops ricketti (Amphibia, Ranidae) in Guizhou Province. Journal of Zhejiang University 45(6): 736–745. [Agriculture and Life Sciences]
  • Yang DT (1991) The Amphibia Fauna of Yunnan. China Forestry Publishing House, Beijing.
  • Yang DT, Rao DQ (2008) Amphibia and Reptilia of Yunnan. Yunnan Science and Technology Press, Kunming, China.
  • Yuan ZY, Jin JQ, Li J, Stuart BL, Wu J (2018) A new species of cascade frog (Amphibia: Ranidae) in the Amolops monticola group from China. Zootaxa 4415(3): 498–512. https://doi.org/10.11646/zootaxa.4415.3.5
  • Zeng ZC, Wang J, Lyu ZT, Wang YY (2021) A new species of Torrent frog (Anura, Ranidae, Amolops) from the coastal hills of southeastern China. Zootaxa 5004(1): 151–166. https://doi.org/10.11646/zootaxa.5004.1.6