Research Article |
Corresponding author: Zhao-Liang Guo ( zlguo@fosu.edu.cn ) Academic editor: Célio Magalhães
© 2021 Shuo Feng, Qing-Hua Chen, Zhao-Liang Guo.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Feng S, Chen Q-H, Guo Z-L (2021) Integrative taxonomy uncovers a new stygobiotic Caridina species (Decapoda, Caridea, Atyidae) from Guizhou Province, China. ZooKeys 1028: 29-47. https://doi.org/10.3897/zookeys.1028.63822
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Collecting much-needed information on the taxonomy, distribution, and ecology of cave-dwelling shrimp is vital for addressing the urgent challenges in conservation biodiversity in fragile cave ecosystems. Caridina incolor sp. nov., a new atyid shrimp from an underground stream of Yaoshui Cave, Daqikong scenic area, Libo County, Guizhou Province, southwestern China is described based on morphology and DNA analysis (mitochondrial COI). Caridina incolor sp. nov. differs from epigean congeners by its smaller eyes which range from reduced to completely blind; colorless body and appendages; long stylocerite and sixth abdominal segment; and relatively large eggs. In comparison to other cave species, Caridina incolor sp. nov. presents a long rostrum and stylocerite; slender sixth abdominal segment; and unique shape of the appendix masculina. Data on the habitat, ecology, and levels of threat are provided and suggest that it should be categorized as Critically Endangered (CR) under the current IUCN criteria.
Caridina, COI, conservation biodiversity, freshwater biodiversity, southwestern China, speleology, taxonomy
China is rich in subterranean environments, with more than 500,000 documented caves, most of which are located in the southwest karst region, such as Guangxi, Guizhou, and Yunnan Province (Chen 2006;
In China, most cave systems have not been adequately surveyed because of the difficulty in sample collection. To date, 24 described species of four genera of atyids are presently known as inhabitants of the subterranean aquatic realm, some of which are completely adapted to subterranean life, and the majority from the genus Caridina H. Milne Edwards, 1837 (
Guizhou Province is the central area of karst landforms in southwest China, with 73% of the land covered with carbonate rocks (
During our biospeleological surveys in Guizhou Province, stygobiont atyid shrimps belonging to the genus Caridina were collected from Yaoshui Cave, Daqikong scenic area, Libo County. The specimens collected could not be assigned to any known species of this genus based on a combination of morphological and molecular features (COI). Caridina incolor sp. nov. is rare and has a restricted distribution; its taxonomic uniqueness also suggests that it may be relictual. The impact of anthropogenic activities on the new species are also noted and suggests it is in need of urgent conservation intervention.
Daqikong scenic area is named after a seven span bridge on the Dagou River near Mengtang Village, Wangmeng Township. It is situated about 25 km southwest of Libo County, at the border region of Guizhou and Guangxi in southwestern China. Yaoshui Cave is near the Mengtang scenic spot of Daqikong scenic area, at 25°17'1"N, 107°45'8"E and an altitude of 520 m. The entrance is about 120 m away from the tour plank road, located halfway up a limestone hill. The opening of the cave is arched and 2 m wide and 4 m high. There is naked shale above the entrance, with some ferns, bryophytes and vines present in the surrounding areas (Fig.
During the November collection trip, the water was clear and the water parameters of the river were: temperature 21 °C, pH 7.5, and dissolved oxygen 8.8 mgl-1. Water levels of Yaoshui Cave fluctuate dramatically throughout the year. During spring and summer, heavy precipitation inundates the passage and blocks access to the entrance. Also, an outflowing stream snakes down into Dagou River (Fig.
Type locality and schematic diagram of the cave of Caridina incolor sp. nov. A Yaoshui Cave is located near Libo County and is marked by the red dot B the sampling point of shrimp C the sampling point of fish D side view of the cave E plan view of the cave F a pool in a weak light zone G river in the dark zone.
On August 3, the cave gallery was inundated due to the rain. Sample collectors managed to wade in, but only a juvenile female was collected. On November 27, the water level was lower, sample collectors successfully entered the cave. Under the light of our headlights, a school of translucent white shrimps were observed swimming or clinging to the cave wall of the river. Forty-two individuals were collected in the shallow muddy areas. Samples were collected with a hand net (mesh size 0.6 mm). The sampling scene was recorded with photographs and video-recordings. Specimens were placed in oxygenated polythene bags, anaesthetized with ice, then transported back to the hotel. The shrimps were fixed in 95% ethanol after they were photographed. The ethanol was changed after 24 h with fresh 75% ethanol. The blind fish (Oreonectes daqikongensis) was also collected. Basic hydrological and physicochemical parameters of the cave were measured by the following instruments: Bosch GLM-30 Laser rangefinder, eTrex Venture GPS locator, JWSA2-2 temperature and hygrometer, BDO820 Portable dissolved oxygen determining meter, and BPH-220 pH measuring apparatus.
Specimens were examined using a dissecting microscope (Olympus SZX7). Morphometric measurements on selected characters and illustrations were made using a digital camera (DP22) mounted on a stereomicroscope (Olympus SZX7) with Olympus CellSens Entry v1.18 software. The measuring method of morphometric characters follows that of
Genomic DNA was extracted from abdominal muscle tissue using the Universal Genomic DNA Kit (Beijing, China), following manufacturer instructions. Segments of the mitochondrial cytochrome coxidase I (COI) were amplified by using the primers LCO1490 and HCO2198 (
For the phylogenetic analyses, we included species similar in morphology to the new species and also other Caridina species that are known to occur in the neighboring areas. A total of 47 nucleotide sequences of 13 Caridina and 3 Neocaridina species and an outgroup (Table
Species used in the molecular analysis, with details on sampling locations and GenBank accession numbers (COI).
Species | Sampling locality | GenBank numbers |
---|---|---|
Caridina incolor sp. nov. | Libo, Guizhou | MW237749–MW237753 |
Caridina sinanensis | Sinan, Guizhou | MT433962–MT433964 |
Caridina zhongshanica | Zhongshan, Guangdong | MN701597–MN701598 |
Palaemon modestus | Dongting lake, Hunan | MK412768–MK412769 |
Neocaridina denticulata | Hulun lake, Inner Mongolia | MW222157–MW222159 |
Neocaridina palmata | Hong Kong, China | MW226891–MW226893 |
Caridina mariae | Nankun Mountarin, Huizhou | MN701601–MN701602 |
Caridina serrata | Dong’ao Island, Zhuhai | MN701599–MN701600 |
Caridina tetrazona | Zhuhai, Guangdong | MN701593–MN701594 |
Caridina cantonensis | Qingyuan, China | MN701589–MN701590 |
Caridina sp. 2 | Huanjiang, Guangxi | MW237763–MW237764 |
Caridina huananensis | Yingde, Qingyuan | MN701607–MN701608 |
Caridina lanceifrons | Dongfang, Hainan | MN701605–MN701606 |
Caridina zhujiangensis | Dong’ao Island, Zhuhai | MN701603–MN701604 |
Caridina carvernicola | Mashan, Guangxi | MW237867 |
Neocaridina heteropoda | Guilin, Guangxi | MW221964–MW221966 |
MW222154–MW222156 | ||
Caridina sp. 1 | Mashan, Guangxi | MW237861–MW237866 |
Pairwise genetic distance among 17 species based on COI (below diagonal) gene.
Species | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | |
1 | Caridina incolor sp. nov. | |||||||||||||||||
2 | Caridina sinanensis | 0.13 | ||||||||||||||||
3 | Caridina zhongshanica | 0.17 | 0.14 | |||||||||||||||
4 | Palaemon modestus | 0.24 | 0.20 | 0.19 | ||||||||||||||
5 | Neocaridina denticulata | 0.18 | 0.14 | 0.15 | 0.20 | |||||||||||||
6 | Neocaridina palmata | 0.18 | 0.14 | 0.16 | 0.21 | 0.05 | ||||||||||||
7 | Caridina mariae | 0.17 | 0.15 | 0.08 | 0.21 | 0.16 | 0.17 | |||||||||||
8 | Caridina serrata | 0.16 | 0.12 | 0.11 | 0.21 | 0.14 | 0.16 | 0.12 | ||||||||||
9 | Caridina tetrazona | 0.17 | 0.14 | 0.12 | 0.21 | 0.17 | 0.17 | 0.13 | 0.09 | |||||||||
10 | Caridina cantonensis | 0.16 | 0.14 | 0.01 | 0.19 | 0.15 | 0.16 | 0.08 | 0.11 | 0.12 | ||||||||
11 | Caridina sp. 2 | 0.15 | 0.11 | 0.14 | 0.21 | 0.15 | 0.15 | 0.15 | 0.13 | 0.14 | 0.15 | |||||||
12 | Caridina huananensis | 0.16 | 0.12 | 0.14 | 0.21 | 0.15 | 0.17 | 0.14 | 0.13 | 0.14 | 0.14 | 0.14 | ||||||
13 | Caridina lanceifrons | 0.19 | 0.18 | 0.18 | 0.22 | 0.20 | 0.18 | 0.19 | 0.18 | 0.18 | 0.18 | 0.19 | 0.19 | |||||
14 | Caridina zhujiangensis | 0.18 | 0.16 | 0.17 | 0.20 | 0.18 | 0.18 | 0.19 | 0.18 | 0.19 | 0.17 | 0.16 | 0.18 | 0.17 | ||||
15 | Caridina carvernicola | 0.16 | 0.12 | 0.14 | 0.21 | 0.14 | 0.15 | 0.14 | 0.13 | 0.13 | 0.14 | 0.02 | 0.13 | 0.20 | 0.15 | |||
16 | Neocaridina heteropoda | 0.18 | 0.14 | 0.16 | 0.20 | 0.13 | 0.15 | 0.16 | 0.15 | 0.15 | 0.16 | 0.16 | 0.16 | 0.18 | 0.20 | 0.15 | ||
17 | Caridina sp. 1 | 0.16 | 0.11 | 0.14 | 0.21 | 0.15 | 0.15 | 0.14 | 0.14 | 0.14 | 0.14 | 0.05 | 0.14 | 0.19 | 0.15 | 0.03 | 0.15 |
Genus Caridina H. Milne Edwards, 1837
Holotype : Adult male (FU, 2018-11-27-01), tl 21.8 mm, cl 5.1 mm, rl 3.0 mm; Yaoshui Cave, Mengtang Village, Wangmeng Township, Daqikong scenic area, Libo County, Guizhou Province, China (25°17'1"N, 107°45'8"E, alt. 520.0 m), November 27, 2018.
Paratypes : 1 male (FU, 2018-11-27-02) tl 25.9 mm, cl 6.1 mm, rl 3.1 mm; 16 males (FU, 2018-11-27-03) tl 17.4–25.9 mm, cl 4.2–6.0 mm, rl 2.4–3.4 mm; 10 females (FU, 2018-11-27-04), tl 17.8–25.2 mm, cl 4.5–6.1 mm, rl 2.4–3.4 mm; cl 4.9–6.6 mm, same data as for holotype. Paratypes: 6 males (FU, 2018-11-27-05) tl 18.4–25.1 mm, cl 4.4–5.9 mm, rl 2.5–3.0 mm; 9 females (3 ovigerous) (FU, 2018-11-27-06), tl 17.5–25.0 mm, cl 4.5–6.0 mm, rl 2.4–3.1 mm; cl 5.0–6.3 mm, same data as for holotype. Two samples from (FU, 2018-11-27-05) and three samples from (FU, 2018-11-27-06) were sequenced.
Caridina sinanensis Xu, Li, Zhang and Guo 2020. Holotype: Adult male (FU, 2019-01-25-01), tl 16.7 mm, cl 4.8 mm, rl 1.5 mm; a cave river at Pengjiaao, Tangtou Town, Sinan County, Guizhou Province, southwestern, China (27°44'10"N, 108°11'58"E, alt. 294.7 m), January 25, 2019. Paratypes: 1 male (FU, 2019-01-25-02) cl 5.4 mm; 1 male (FU, 2019-01-25-03) cl 6.8 mm; 1 male (FU, 2019-01-25-04) cl 4.8 mm; 2 males (FU, 2019-01-25-05), cl 4.2–6.2 mm; 20 females (9 ovigerous) (FU, 2019-01-25-05), cl 4.9–6.6 mm.
Body and appendages without coloration, translucent. Rostrum slender, slightly elevated at base, reaching to base of 3rd segment of antennular peduncle to end of scaphocerite; straight, slightly sloping downwards, sometimes with tip turned upwards; rostral formula 6–10+11–27/4–15. First pereiopod carpus 0.83–0.91 × as long as chela, 2.3–2.7 × as long as high; chela 2.2–2.5 × as long as broad; fingers 1.1–1.4 × as long as palm. Second pereiopod carpus 1.3–1.4 × as long as chela, 5.4–5.6 × as long as high; chela 2.4–2.6 × as long as broad; fingers 1.6–1.8 × as long as palm. Third pereiopod propodus 3.8–4.0 × as long as dactylus, 13.6–14.4 × breadth, with 8–11 thin spines on the posterior and lateral margins. Fifth pereiopod propodus 4.0–4.7 × as long as dactylus, 17.6–20.5 × breadth, with 17–20 thin spines on the posterior and lateral margins, dactylus terminating in one claw, with 50–55 spinules on flexor margin. Endopod of male subrectangular, slightly wider proximally, length 0.39–0.46 × exopod length, 2.0–2.2 × proximal breadth, ending broadly rounded; inner margin slightly concave, bearing spine-like setae, outer margin slightly convex, proximally 1/3 bearing nearly equal length short spine-like setae, distally 2/3 bearing nearly equal length long spine-like setae, and top bearing nearly equal length stout spine-like setae; appendix interna well developed, arising from distal 1/3 of endopod, beyond the end of endopod, distally with cincinulli. Appendix masculina rod-shaped and gradually tapering into a triangular tip, reaching about 0.48–0.51 × length of endopod, with numerous long spined setae on proximal and distal regions; endopod reaching about 0.76–0.79 × length of exopod; appendix interna well developed, reaching about 0.58–0.78 × length of appendix masculina, with cincinulli distally. Uropodal diaeresis with 10–12 movable spinules. Females carry 10–15 eggs, size of undeveloped eggs (without eyespots) 0.83–0.88 × 1.18–1.26 mm.
Body
(Figs
Rostrum
(Figs
Eyes
(Figs
Carapace
(Figs
Antennule
(Fig.
Antenna
(Fig.
Mouthparts
characteristic of the genus. Mandible with well-developed incisor and molar processes; left incisor process with a single short sharp outer tooth, two long stout inner teeth, 7 curving setae followed by a patch of long setae; molar process stout and with triturative surface (Fig.
First pereiopod
(Fig.
Second pereiopod
(Fig.
Caridina incolor sp. nov. A carapace and cephalic appendages, lateral view B second pereiopod C third pereiopod D dactylus of third pereiopod E fourth pereiopod F dactylus of fourth pereiopod G fifth pereiopod H dactylus of fifth pereiopod I first male pleopod J second male pleopod K distal margin of telson A–K paratype (FU, 2018-11-27-02).
Third pereiopod
(Fig.
Fourth pereiopod
(Fig.
Fifth pereiopod
(Fig.
First four pereiopods with epipod. Branchial formula typical for the genus.
First pleopod
(Fig.
Second pleopod
(Fig.
Telson
(Fig.
Females carry 10–15 eggs, size of undeveloped eggs (without eyespots) 0.83–0.88 × 1.18–1.26 mm.
Coloration
(Fig.
Caridina incolor sp. nov. is named after the colorless and transparent body color.
Caridina incolor sp. nov. might be more closely related to the epigean species than to its supposed cave congeners. It is morphologically similar to C. guiyangensis Liang, 2002, from Guiyang, Guizhou Province in the long rostrum and indentation, the shape of endopod of the male first pleopod and appendix masculina. Although no molecular comparison with C. guiyangensis could be accomplished, C. incolor sp. nov. can easily be distinguished from the latter by the reduced eyes, colorless body and appendages (versus developed eyes and pigmentation in C. guiyangensis); the long stylocerite, reaching to the end of the antennule basal segment (versus reaching 0.85 × of basal segment in C. guiyangensis); the long penultimate segment of the 3rd maxilliped, which is distinctly longer than the basal segment and distal segment (versus penultimate segment as long as basal segment and distinctly shorter than distal segment in C. guiyangensis); absence of a projection on the base of the inner margin of male first pleopod endopod (vs. with projection in C. guiyangensis); and relatively large eggs, size of undeveloped eggs 0.83–0.88 × 1.18–1.26 mm (versus 0.63–0.75 × 1.05–1.13 in C. guiyangensis). In comparison to other cave species within Caridina, C. sinanensis Xu, Li, Zhang & Guo, 2020, is most similar in sharing the long 6th abdominal segment, and the variably pigmented cornea. However, the new species differs from the latter by possessing a relatively long and slender rostrum which reaches beyond the end of the 3rd antennular peduncle segment (versus stouter, reaching to the end of the 2nd segment in C. sinanensis); the long stylocerite, reaching to the end of the basal segment of the antennule (versus reaching 0.75–0.88 × of basal segment in C. sinanensis); and completely different shape of the endopod of the 1st pleopod and appendix masculina of the 2nd pleopod in males (Fig.
We analyzed 47 COI sequences in total. Five specimens of Caridina incolor sp. nov. were used in the molecular phylogenetic analysis shown in Figure
Threats to cave shrimp are of concern due to the uniqueness of the habitat and increasing anthropogenic activities. Based on the information available, the Yaoshui Cave and its faunas are potentially at risk from excessive levels of external disturbance. Daqikong scenic area is famous for its marvelous primeval forests, steep canyons, spectacular caves, and underground rivers. Over the years, tourism to the region has improved the welfare of local residents and has become a major industry in this area. Moreover, new recreational trails and amusement facilities have been built in the scenic area. It is almost inevitable that these new projects will put great pressure and impact on caves and their faunas. In addition, land development and agriculture lead to habitat degradation and groundwater pollution, which also has a negative impact on the survival of this species.
So far, no freshwater shrimps are protected by the national legislation. The Announcement of the Ministry of Agriculture and Rural Areas of China has failed to categorize the strictly endemic cave species as Endangered (CITES Appendix aquatic wild species of China, no. 69, 2018). Caridina incolor sp. nov. is new to science and the conservation status remains unassessed. Using the criteria provided by the
The Yaoshui Cave, which is home to two unique and range-restricted species (atyid shrimp, Caridina incolor sp. nov., and loach fish, Oreonectes daqikongensis) is biologically significant without question. These strictly-adapted cave species must be considered as important units for conservation, and devising an effective conservation strategy is clearly an urgent priority. It has also become obvious that there is a need to collect more baseline data, such as the exact population size, structure, natality, and mortality rates. Regular monitoring may be necessary to ensure populations are sustained in the face of further anthropogenic disturbances. Equally important, a captive breeding program of these cave species should be developed. In addition, we propose that non-invasive and non-destructive projects, such as eco-tourism, should be promoted. Last but not least, we also appeal to local farmers to lower the usage of agricultural pesticides, herbicides, and fertilizers to help reduce the amount of hazardous chemicals that are leeched into the groundwater.
This study was supported by the Special Fund for Central Public Welfare Research Institutes (grant no. PM-zx097-201904-134), the Running Cost for Key Laboratory of Utilization and Breeding of Aquatic Resources in Tropical and Subtropical Areas, Ministry of Agriculture and Rural Affairs (grant no. 9020190008) and the Investigation on Crustaceans in Priority Area of Mangrove Diversity Protection in Guangxi Zhuang Autonomous Region (grant no. kh19051). We thank Wenjian Chen and Xiaozhuang Zheng for their assistance in collecting samples. We also appreciate Dr. Chao Huang (Independent researcher) and Erdong Xia (Stevens Institute of Technology/Chinese Academy of Forestry) for improving the manuscript. Thanks are also due to subject editor Célio Magalhães and two reviewers Werner Klotz and Valentin de Mazancourt (Muséum national d’Histoire naturelle) for providing their valuable suggestions, which greatly improved the manuscript.