diversity Article Ganxiao Dong: A Hotspot of Cave Biodiversity in Northern Guangxi, China Sunbin Huang 1,2 , Guofu Wei 3, Hengsong Wang 4, Weixin Liu 1,* , Anne Bedos 5, Louis Deharveng 5 and Mingyi Tian 1 1 Department of Entomology, College of Plant Protection, South China Agricultural University, 483 Wushan Road, Guangzhou 510642, China; [email protected] (S.H.); [email protected] (M.T.) 2 Mécanismes Adaptatifs et Évolution (MECADEV), UMR 7179 CNRS-MNHN, Muséum National d’Histoire Naturelle, CP50, 57 rue Cuvier, 75005 Paris, France 3 Protection Centre of Huanjiang World Natural Heritage, Huanjiang, Hechi 547100, China; [email protected] 4 School of Karst Science, Guizhou Normal University, 116 Baoshanbeilu, Yunyan, Guiyang 550001, China; [email protected] 5 Institut de Systématique, Évolution, Biodiversité (ISYEB), UMR 7205 CNRS, Muséum National d’Histoire Naturelle, Sorbonne Université, EPHE, 45 rue Buffon, 75005 Paris, France; [email protected] (A.B.); [email protected] (L.D.) * Correspondence: [email protected] Abstract: Located in the core zone of Mulun National Nature Reserve in northern Guangxi, the limestone cave Ganxiao Dong harbours the richest cave fauna currently known in China. In total, 26 species of cave invertebrates have been recognized so far, in spite of limited sampling efforts. Of them, 20 are troglobionts or stygobionts, including one snail, four millipedes, three spiders, one harvestman, three isopods, two springtails, two crickets, one non-glowing sticky worm, and three Citation: Huang, S.; Wei, G.; Wang, trechine beetles. Six other species are troglophiles. The most remarkable characteristic of this fauna is H.; Liu, W.; Bedos, A.; Deharveng, L.; its high number of troglomorphic species, especially among millipedes, crickets and beetles. Tian, M. Ganxiao Dong: A Hotspot of Cave Biodiversity in Northern Keywords: biodiversity; cave; hotspot; Huanjiang; Guangxi; South China Karst; troglomorphy Guangxi, China. Diversity 2021, 13, 355. https://doi.org/10.3390/ d13080355 1. Introduction Academic Editor: The World Heritage Property of South China Karst is a cluster of seven karsts, i.e., Spyros Sfenthourakis Shilin (stone forest) in Yunnan, Shibing and Maolan in Guizhou, Jinfoshan and Wulong in Chongqing, as well as Guilin and Huanjiang in Guangxi (https://whc.unesco.org/ Received: 4 June 2021 en/list/1248/, accessed on 1 July 2021). The Huanjiang Karst component is located in Accepted: 28 July 2021 Published: 2 August 2021 the Guangxi Zhuang Autonomous Region within the boundaries of the Mulun National Nature Reserve. Actually, Maolan and Mulun are the same karst unit across the border Publisher’s Note: MDPI stays neutral between Guizhou and Guangxi, and the karst unit is totally included in national nature with regard to jurisdictional claims in reserves. The Huanjiang karst is a large Fengcong (peak cluster) landscape covered with published maps and institutional affil- primary forest and hundreds of scattered caves. The cave biodiversity in this karst has iations. been recently investigated and shown to be very rich [1–3]. The cave which will be dealt with in this paper, Ganxiao Dong, is located in the Mulun karst. The Huanjiang Karst World Natural Heritage Site is located in Huanjiang Maonan Autonomous County, northern Guangxi, with a total area of 115.59 km2. The area is a typical tropical-subtropical karst landscape with the main landform of so-called peak- Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. cluster depression (Figure1), as well as other landforms, for example, dolines, fossil This article is an open access article valleys and cave systems. Geographically, Huanjiang Karst belongs to the slope zone distributed under the terms and from the Yunnan-Guizhou plateau to the hilly basin of Guangxi, decreasing in elevation conditions of the Creative Commons from 1028 m a.s.l. in the northwest to 250 m a.s.l. in the southeast. The topography of Attribution (CC BY) license (https:// the area is fragmented due to the erosion-denudation of the eastern Gubin River and the creativecommons.org/licenses/by/ western Dagou River and the fault structure in the area, making it a typical area for the 4.0/). development of conical peak-cluster karst landforms in the mid-subtropical zone [4,5]. Diversity 2021, 13, 355. https://doi.org/10.3390/d13080355 https://www.mdpi.com/journal/diversity Diversity 2021, 13, x 2 of 16 Diversity 2021, 13, 355 2 of 16 Dagou River and the fault structure in the area, making it a typical area for the develop- ment of conical peak-cluster karst landforms in the mid-subtropical zone [4,5]. FigureFigure 1.1. Fengcong peak cluster landscapeslandscapes inin HuanjiangHuanjiang Karst,Karst, Hechi,Hechi, Guangxi,Guangxi, China.China. ForestForest coveragecoverage exceedsexceeds 95%95% andand predominantlypredominantly isis comprisedcomprised ofof aa mixedmixed evergreenevergreen andand deciduous broad-leaved broad-leaved forest. forest. The The humid humid subtropical subtropical climate, climate, the diverse the diverse karst karst hab- habitatsitats and and the theenclosed enclosed island-l island-likeike environment environment are areconducive conducive to the to growth the growth and andreproduc- repro- ductiontion of living of living organisms. organisms. Likewise, Likewise, there there are are hundreds hundreds of of limestone limestone caves caves distributed inin thisthis area,area, suchsuch asas CaveCave GanxiaoGanxiao Dong,Dong, Cave Dongtu Dong, Cave Mashan Dong and so on. XuXu Xiake,Xiake, thethe firstfirst karstologistkarstologist andand cavercaver ofof ChinaChina (1587–1641),(1587–1641), exploredexplored oror locatedlocated moremore thanthan 270270 caves in Guangxi. After this pioneering work, nothing significantsignificant was pub- lishedlished onon thethe karstkarst ofof ChinaChina forfor aboutabout 300300 years.years. ModernModern cavecave explorationexploration andand karstologykarstology developeddeveloped rapidlyrapidly fromfrom thethe 1970s1970s onwards,onwards, firstfirst throughthrough manymany foreignforeign expeditions,expeditions, thenthen throughthrough increasingincreasing efforts efforts of of Chinese Chinese cavers. cavers. Speleologically, Speleologically, the the most most impressive impressive result result of thisof this activity activity is theis the exploration exploration of theof the Shuanghe Shuanghe cave cave system system in in Guizhou, Guizhou, today today the the largest larg- inest China in China and and Asia Asia with with over over 300 300 km km of passages of passages (Jean (Jean Botazzi, Botazzi, pers. pers. comm.) comm.) ResearchResearch on cave cave biology biology in in Chinese Chinese caves caves be begangan in in1960 1960 with with the thedescription description of five of fivemillipedes millipedes and andone onecentipede centipede by Loksa by Loksa [6], followed [6], followed in 1981 in 1981 by that by thatof the of cave the cave fish Ore- fish Oreonectesonectes anophthalmus, anophthalmus, describeddescribed by by Zheng, Zheng, the the first first of of a along long series. series. The The first first cave beetlebeetle waswas described in in 1991 1991 (Sinaphaenops (Sinaphaenops mirabilissimus mirabilissimus UénoUéno & Wang, & Wang, 1991), 1991), the thefirst firstcave cave Col- Collembolalembola in 1993 in 1993 (Sinella (Sinella trogla trogla ChenChen && Christiansen, Christiansen, 1993) 1993) and and the the first first cave woodlice inin Sinoniscus cavernicolus 19951995 ((Sinoniscus cavernicolus SchultzSchultz 1995).1995). AllAll thesethese animalsanimals werewere collectedcollected inin thethe cavescaves ofof Guangxi or Guizhou, but none of them is from the Mulun karst. Guangxi or Guizhou, but none of them is from the Mulun karst. These zoological groups, fish, millipedes, woodlice, springtails and beetles, together These zoological groups, fish, millipedes, woodlice, springtails and beetles, together with spiders, represent today the bulk of the cave diversity of Chinese caves, with tens of with spiders, represent today the bulk of the cave diversity of Chinese caves, with tens of new species described since then. Three of these groups have been particularly studied in new species described since then. Three of these groups have been particularly studied in the Mulun karst: millipedes, woodlice and beetles. the Mulun karst: millipedes, woodlice and beetles. Millipedes are the most common terrestrial medium- to large-size invertebrates in the Millipedes are the most common terrestrial medium- to large-size invertebrates in caves of South China Karst [7]. However, the diversity of cave millipedes in China has been the caves of South China Karst [7]. However, the diversity of cave millipedes in China has revealed and recognized only during the last few decades. Approximately 350 millipede been revealed and recognized only during the last few decades. Approximately 350 mil- species from China have been named at present, including at least a third only known lipede species from China have been named at present, including at least a third only from caves [8]. In Mulun, the first cave millipede, Eutrichodesmus similis, reported by known from caves [8]. In Mulun, the first cave millipede, Eutrichodesmus similis, reported Golovatch et al., 2009, was described from Gui Dong and Shenlong Dong. Since this date, 16by speciesGolovatch of Diplopoda et al., 2009, have was been described reported from from Gui this Dong karst and [8]. Shenlong Dong. Since this date,Oniscid 16 species isopods of Diplopoda are the