Cryptic diversity begets challenges and opportunities in biodiversity research.

How many species of life are there on Earth? This is a question that we want to know but cannot yet answer. Some scholars speculate that the number of species may reach 2.2 billion when considering cryptic diversity and that each morphology-based insect species may contain an average of 3.1 cryptic species. With nearly two million described species, such high estimates of cryptic diversity would suggest that cryptic species are widespread. The development of molecular species delimitation has led to the discovery of a large number of cryptic species, and cryptic biodiversity has gradually entered our field of vision and attracted more attention. This paper introduces the concept of cryptic species, how they evolve, and methods by which they may be discovered and confirmed, and provides theoretical and methodological guidance for the study of hidden species. A workflow of how to confirm cryptic species is provided. In addition, the importance and reliability of multi-evidence-based integrated taxonomy are reaffirmed as a way to better standardize decision-making processes. Special focus on cryptic diversity and increased funding for taxonomy is needed to ensure that cryptic species in hyperdiverse groups are discoverable and described. An increased focus on cryptic species in the future will naturally arise as more difficult groups are studied, and thereby, we may finally better understand the rules governing the evolution and maintenance of cryptic biodiversity.

Marine-montane transitions coupled with gill and genetic convergence in extant crustacean.

Marine-terrestrial transition represents an important aspect of organismal evolution that requires numerous morphological and genetic innovations and has been hypothesized to be caused by geological changes. We used talitrid crustaceans with marine-coastal-montane extant species at a global scale to investigate the marine origination and terrestrial adaptation. Using genomic data, we demonstrated that marine ancestors repeatedly colonized montane terrestrial habitats during the Oligocene to Miocene. Biological transitions were well correlated with plate collisions or volcanic island formation, and top-down cladogenesis was observed on the basis of a positive relationship between ancestral habitat elevation and divergence time for montane lineages. We detected convergent variations of convoluted gills and convergent evolution of SMC3 associated with montane transitions. Moreover, using CRISPR-Cas9 mutagenesis, we proposed that SMC3 potentially regulates the development of exites, such as talitrid gills. Our results provide a living model for understanding biological innovations and related genetic regulatory mechanisms associated with marine-terrestrial transitions.

Taxonomic study of the genus Gammarus (Amphipoda, Gammaridae) from Xinjiang, China, with description of a new species.

A new species, Gammarus hoboksar Hou, sp. nov., is described from the Irtysh River basin of Xinjiang, China. The species differs morphologically from its congeners by calceoli of antenna II absent; merus and carpus of pereopods IIIIV with short setae; inner ramus of uropod III about 0.79 times the length of outer ramus, terminal article of outer ramus about 0.24 times the length of first article; telson cleft, with spines and setae on surface and three spines on distal end. Phylogenetic analysis based on 28S rRNA and COI gene sequences supported the species distinctness. A key to the genus Gammarus with nine species and a map of their distributions are provided.

Past climate cooling promoted global dispersal of amphipods from Tian Shan montane lakes to circumboreal lakes.

Climate changes have substantial impacts on the geographic distribution of montane lakes and evolutionary dynamics of cold-adapted species. Past climate cooling is hypothesized to have promoted the dispersal of cold-adapted species via montane lakes, while future climate warming is thought to constrain their distributions. We test this hypothesis by using phylogeographic analysis and niche modeling of the Holarctic crustacean Gammarus lacustris with global sampling comprised of 567 sequenced individuals and 3180 occurrence records. We found that the species arose in Tian Shan in Central Asia and dispersed into montane lakes along the Alps, Himalayas, Tibet, East Asia, and the North American Rocky Mountain ranges, with accelerated diversification rates outside Tian Shan. Climatically suitable regions for geographic lineages of G. lacustris were larger during cooling periods (LGM), but smaller during warming periods (Mid-Holocene). In the future (2070) scenario, potential distributions in the Himalayas, North Tibet, South Tibet and North America are predicted to expand, whereas ranges in East Asia, Europe and Tian Shan will decline. Our results suggest that Mid-Miocene-to-Pleistocene continuous cooling promoted multiple independent dispersal events out of Tian Shan due to increased availability of montane lakes via "budding" of lineages. Montane lakes are conduits through which cold-adapted amphipods globally dispersed, dominating circumboreal lakes. However, future climate warming is likely to force organisms to shift upward in altitude and northward in latitude, leading to a future change in local populations. These findings highlight the importance of conservation of montane lakes, especially in the context of climate change.

Chromosomal-level genome of a sheet-web spider provides insight into the composition and evolution of venom.

Spiders are the most abundant venomous predators in the world. Previous research related to spider venom has mostly relied on transcriptomes and proteomes, with only a few high-quality genomes available. This is far from consistent with the species diversity of spiders. In this study, we constructed a high-quality chromosome-level genome assembly of Hylyphantes graminicola, which contained 13 chromosomes, with a genome length of 931.68 Mb and scaffold N50 of 77.07 Mb. Integrating genome, transcriptome, and proteome profiling, we identified a total of 59 coding genes among nine toxin gene families. Among them, Group 7 allergen (ALL7) protein was reported in spider venom for the first time. Its coding genes had a predicted signal peptide and maintained high expression levels in the venom, suggesting that ALL7 plays an important role in venom and maybe is a type of newly discovered venom toxin in the spider. By implementing comparative genomics, we found a similar gene number of main toxin gene families in spiders and the scorpion genome with conservative evolutionary rates, indicating that these toxin genes could be an ancient (~400 million years) and a conserved "basic toolkit" for spiders and scorpions to perform primary defence functions. Obtaining high-quality chromosome-level genomes from spiders not only facilitates venom research and toxin resource application, but also can improve comparative genomic analysis in other important traits, like the evolution of silk or behaviour.

Ancient volcanos as species pumps: A case study of freshwater amphipods in Northeast Asia.

Volcano-tectonic processes have been viewed as primary drivers in the formation of present-day diversity. Volcanos associated with mountain uplifts drive allopatric speciation through vicariance and may impact the surrounding areas like species pump or species attractor. However, the application of these hypotheses to aquatic fauna has rarely been tested explicitly. We tested these hypotheses in the Changbai Mountains (Mts), which are one of the most typical, active volcanic ranges in Northeast (NE) Asia with a long and turbulent geological history. The Gammarus nekkensis species complex of amphipod crustaceans, widely distributed throughout NE Asia with poor dispersal abilities and a long evolutionary history, is a suitable model for testing hypotheses of species pump or species attractor. Phylogenetic and ancestral range reconstructions demonstrated that the studied amphipod originated from the Changbai Mts ~27 Ma and diverged into eastern (Clade I) and western (Clade II) clades, which corresponds well with the initial volcanic eruption of the Changbai Mts in the Late Oligocene. The subsequent diversifications of subclades CI-3, CII-1a and CII-2a were probably driven by second and third eruptions of the Changbai Mts during the Miocene. In particular, the Changbai lineages had spread to the Russian Far East multiple times since the Early Miocene, and widely colonized the region during the Pleistocene. Our discoveries suggest that the ancient volcanos of the Changbai Mts act as species pumps in NE Asia, resulted in burst of diversification around the Changbai Mts and subsequent dispersals into adjacent regions.

Cenozoic Tethyan changes dominated Eurasian animal evolution and diversity patterns.

Cenozoic tectonic evolution in the Tethyan region has greatly changed the landforms and environment of Eurasia, driving the evolution of animals and greatly affecting the diversity patterns of Eurasian animals. By combining the latest Tethyan paleogeographic models and some recently published Eurasian zoological studies, we systematically summarize how tectonic evolution in the Tethyan region has influenced the evolution and diversity patterns of Eurasian animals. The convergence of continental plates, closure of Tethys Sea, and Tethyan sea-level changes have directly affected the composition and spatial distribution of Eurasian animal diversity. The topographic and environmental changes caused by Tethyan tectonics have determined regional animal diversity in Eurasia by influencing animal origin, dispersal, preservation, diversification, and extinction. The ecological transformations resulted in the emergence of new habitats and niches, which promoted animal adaptive evolution, specialization, speciation, and expansion. We highlight that the Cenozoic tectonic evolution of the Tethyan region has been responsible for much of the alteration in Eurasian animal distribution and has been an essential force in shaping organic evolution. Furthermore, we generalize a general pattern that Tethyan geological events are linked with Eurasian animal evolution and diversity dynamics.

Floresorchestia xueli, a new terrestrial crustacean (Amphipoda, Talitridae) from Yunnan, China.

A new species, Floresorchestia xueli Tong Hou, sp. nov. is described from high altitude habitats of Yunnan, China. The species differs morphologically from its congeners by left mandible lacinia mobilis having four teeth; coxal gills complexly lobed and convoluted; epimeral plates IIIII without slits; telson with one slender facial spine and two terminal spines on each lobe. Analysis of DNA barcode sequences and niche distinctiveness support recognition of the new species.

Two species of Talitridae (Crustacea, Amphipoda) from Kenya.

Two species of the family Talitridae Rafinesque, 1815 are described from English Point Beach, Mkomani, Mombasa, Kenya. One new species Floresorchestia mkomani Bichang'a Hou, sp. nov. is reported and Gazia gazi Lowry Springthorpe, 2019 is redescribed. The new species is characterized by the five dentate lacinia mobilis on the left mandible in male and only four in female, pereopod IV dactylus thickened proximally and having a small protrusion towards the mid of its posterior margin, a sexually dimorphic pereopod VII, and the presence of vertical slits just above the ventral margin of epimera II and III. Detailed morphological characteristics, as well as comparisons with closely related species are provided. To ascertain the species delimitation, molecular evidence is availed in this paper. Type material is deposited in National Museums of Kenya (NMK).

A corrigendum to the phylogeny of the family Gammaridae (Crustacea: Amphipoda).

We stated an error in our previous DNA analysis of Gammaridae. The right position of Zenkevitchia in the phylogenetic tree is close to marine and American Gammarus spp., far from the Dinaric troglobiotic Typhlogammarus group of genera. The morphologically diverse Zenkevitchia group supports the necessity of some paraphyly in systematics.

Sarothrogammarusyiiruae, a new species of Amphipoda (Gammaridae) from China.

A relic amphipod of the Tethys, Sarothrogammarusyiiruae sp. nov., is described from Xinjiang, China. The new species is characterized by the absence of eyes; having the palm of the propodus without a mid-palmar spine on gnathopods I-II; a weakly concave coxal plate IV; narrow bases of pereopods V-VII; a peduncle of uropod I without a basofacial spine; uropod III longer than uropods I-II, a scale-like inner ramus, and a biarticulate outer ramus with distinct second article. Detailed morphological comparisons with related species are discussed. Genetic distances of the new and related species are provided as proof of species identification.

Three new remarkable amphipod species (Crustacea: Gammaridae) from springs and subterranean waters of Central Asia.

Three new species of the family Gammaridae-Gammarus troglomorphus, sp. n., G. parvioculatus, sp. n. from Lebap Province of Turkmenistan and Tadzocrangonyx alaicus, sp. n. from Batken Region of Kyrgyzstan are described and illustrated. Morphological studies of a closely related Turkmenistan population of G. cf. subaequalis-Garlyk, probably conspecific with Gammarus subaequalis Martynov, 1935 was provided. The affinity of new species to concerned taxa is discussed. To define phylogenetic position of mentioned species DNA barcode data are obtained. Gammarus troglomorphus and G. parvioculatus are close neighbors but exceedingly different morphologically. Gammarus troglomorphus is a troglobiont; G. parvioculatus is an eutroglophile, but with exception of slightly smaller eyes, not troglomorph. Both found only within small areas in the extreme East of Turkmenistan. Gammarus cf. subaequalis-Garlyk seems to extend from the same region far into the eastern Kyrgyzstan.

Bogidiellapingxiangensis, a new species of subterranean Amphipoda from southern China (Bogidiellidae).

A new species of subterranean amphipod, Bogidiellapingxiangensis Hou & Li, sp. n., is described from Xiongshizilong Cave in Pingxiang City, China. The new species is characterized by having the bases of pereopods III and V expanded; the inner ramus of pleopods I-III with one segment; the telson longer than wide and with the apical margin with a shallow U-shaped excavation. DNA barcode of the new species is documented as support of molecular differences between related species.

Four new Gammarus species from Tibetan Plateau with a key to Tibetan freshwater gammarids (Crustacea, Amphipoda, Gammaridae).

Four new species of the genus Gammarus are described and illustrated from Tibetan Plateau. Gammarus altussp. n. and G. limosussp. n. are characterized by pereopods III-IV with a few short setae and uropod III with marginal spines accompanied by short setae. Gammarus kangdingensissp. n. and G. gonggaensissp. n. are characterized by pereopods III-IV with long straight setae on posterior margins and inner ramus of uropod III 0.4 times as long as outer ramus. Detailed morphological comparisons with related species are discussed. A key to 15 Gammarus species from the Tibetan Plateau and a map of their distributions are provided.

Seven new freshwater species of Gammarus from southern China (Crustacea, Amphipoda, Gammaridae).

Seven new species of the genus Gammarus are described and illustrated from southern China. The new species Gammarus vallecula Hou & Li, sp. n., G. qinling Hou & Li, sp. n., G. zhigangi Hou & Li, sp. n. and G. jidutanxian Hou & Li, sp. n. are characterized by inner ramus of uropod III half the length of outer ramus. Gammarus longdong Hou & Li, sp. n. is characterized by inner ramus of uropod III 0.9 times as long as outer ramus. Gammarus mosuo Hou & Li, sp. n. is characterized by pereopods V-VII with long setae on anterior margins and both rami of uropod III armed with simple setae. Gammarus caecigenus Hou & Li, sp. n. can be distinguished from other species by eyes absent. DNA barcodes of the new species are documented as proof of molecular differences between species. A key to the new species and a map of their distributions are provided.

Tethyan changes shaped aquatic diversification.

The Tethys Ocean existed between the continents of Gondwana and Laurasia from the Triassic to the Pliocene. Analyses of multiple biogeographic and phylogenetic histories reveal that the subsequent breakup of the Tethys greatly influenced the distributions of many species. The ancestral Tethyan realm broke into five biogeographic provinces, including the present-day East Pacific, West Atlantic, East Atlantic, Mediterranean Sea, and Indo-West Pacific. Palaeogeographic maps illustrate the Mesozoic Atlantic opening, the Cenozoic closure of the Tethys, the Messinian Salinity Crisis, the mid-Miocene closure of the Central American Seaway, and Quaternary geological changes. Further, we consider Cenozoic sea-level changes and the formation of freshwater habitats. These reconstructions allow assessment of patterns of aquatic diversification for marine and freshwater animals, and comparison of vicariance and dispersal processes. Estimated divergence times indicate that fragmentation of the Tethys was responsible for the vicariant speciation of aquatic animals because these dates are consistent with associated tectonic events. The opening of the Atlantic Ocean during the Cretaceous is responsible for the earliest isolation between the West and East Atlantic. The mid-Miocene closure of the Tethys, which blocked global equatorial currents, appears to have isolated the Atlantic/Mediterranean Sea and Indo-West Pacific. Finally, formation of the Isthmus of Panama isolated East Pacific and West Atlantic marine organisms. Dispersals related to the Messinian Salinity Crisis and Quaternary sea-level changes influenced population structuring. Tethyan changes affected marine habitats, created new freshwater habitats, inland caves and ancient lakes along the Alps and Himalayas, and influenced anchialine caves at the edge of the ancient sea. The extensive new habitats provided opportunities for colonisation and rapid diversification. Future work should focus on testing the biological impact of the series of Tethyan changes.

A new terrestrial talitrid genus, Myanmarorchestia, with two new species from Myanmar (Crustacea, Amphipoda, Talitridae).

Myanmarorchestia Hou, gen. n. with two new species is described from terrestrial habitats in Myanmar. This new genus is characterised by 4-dentate lacinia on left mandible, simple gnathopod I in both sexes, weakly chelate gnathopod II in male, simplidactylate pereopods and complex and lobed gills. Myanmarorchestia peterjaegeri Hou, sp. n. closely resembles M. seabri Hou, sp. n. in gnathopod II merus and carpus protuberant on posterior margin; however, the former is distinguished from the latter by palp of maxilla I with two articles, coxal gills convoluted, and telson with nicks on surface. Additionally, DNA barcodes of the new species are obtained to confirm their distinctiveness.

Myanmarorchestia victoria sp. nov. (Crustacea, Amphipoda, Talitridae), a new species of landhopper from the high altitude forests in Myanmar.

Myanmarorchestia victoriasp. nov. is described from high altitude habitats in Myanmar. The new species differs morphologically from its congeners by palp of maxilliped narrow; sexually dimorphic gnathopod Ⅱ, propodus of male chelate and propodus of female mitten-shaped; and dimorphic uropod Ⅱ, outer ramus of male with small teeth distally, outer ramus of female with three distal spines. Analysis of DNA barcode sequences and niche distinctiveness support recognition of the new species.

Two new Gammarus species and a new name (Crustacea: Amphipoda: Gammaridae) from Northwest China.

Two new species of the genus Gammarus are described and illustrated from Northwest China. A new species name Gammarus tianshan nom. nov. is proposed to replace G. montanus Hou et al., 2004. Gammarus simplex sp. nov. from Altay, Xinjiang, is characterized by uropod III with simple setae on both rami and urosomite I only with setae on dorsal margin. Gammarus glaber sp. nov. from Qinghai, is characterized by uropod III with few simple and plumose setae. Detailed morphological description and differences from related species are discussed. A distribution map of the new species and related species is provided.

A new subterranean species of Pseudocrangonyx from China with an identification key to all species of the genus (Crustacea, Amphipoda, Pseudocrangonyctidae).

A subterranean species of Pseudocrangonyx elegantulus Hou, sp. n. is described from caves of Wulongdong National Forest Park in Henan Province, China. Pseudocrangonyx elegantulus is characterized by both male and female with calceoli on antenna II; urosomite III dorsal margin without armature; uropod III with peduncle 0.30 times as long as outer ramus and terminal article of the outer ramus a little shorter than adjacent spines; telson cleft 0.27 of its length. Phylogenetic analysis based on 28S and COI sequences supported the species distinctness. A key to the genus Pseudocrangonyx with 22 species and a map of their distributions are provided.