An impact of non-native species invasions on the Caspian Sea biota.

The Caspian Sea is a large inland brackish basin, vulnerable to invaders due to its long isolation and considerable endemism among its native biota. A brief description of Caspian biota evolution until its modern state is given. The pathways and vectors of invasion and the ways of establishment of non-native species since the early 20th century are summarized. The newly established species are euryphilic, with high ecological plasticity, able to adapt to new environments and to affect their biodiversity. This review is based on unpublished field data, collected in 1999-2019 in the Northern, Middle and Southern Caspian, and on relevant published information. The arrival of non-native species occurred in three periods: (1) in the 1930s, deliberate introductions aimed at enriching commercial stocks and edible resources, (2) since 1952, the construction of the Volga-Don Canal led to the arrival of benthic foulers and macrophytes from ships; (3) since the early 1980s to present, ballast water tanks were mounted on ships, favoring the arrival of phyto- and zooplankton species. Most established non-native species reached the Caspian Sea via the Black Sea. They include both Black Sea native species and non-native species from the North Atlantic areas, which first arrived and established in the Black Sea. Few established non-native species came from brackish water; fresh water fishes were deliberately introduced to develop aquaculture. Though not numerous, these species became dominant in both benthos and plankton communities, where they replaced native Caspian species. Among them, the invading ctenophore Mnemiopsis leidyi, which had no predators, continues to thrive in the Caspian ecosystem, impoverishing its biodiversity and bio-resources. However, lately its natural predator, the ctenophore Beroe ovata, arrived and established in the Southern and Middle Caspian providing a chance for ecosystem recovery, as has already happened in the Black Sea.

High-quality genome of Diaphanosoma dubium provides insights into molecular basis of its broad ecological adaptation.

Diaphanosoma dubium Manuilova, 1964, is a widespread planktonic water flea in Asian freshwater. Although sharing similar ecological roles with species of Daphnia, studies on D. dubium and its congeners are still few and lacking a genome for the further studies. Here, we assembled a high quality and chromosome level genome of D. dubium by combining long reads sequencing and Hi-C technologies. The total length of assembled genome was 101.8 Mb, with 98.92 Mb (97.2%) anchored into 22 chromosomes. Through comparative genomic analysis, we found the genes, involved in anti-ROS, detoxification, protein digestion, germ cells regulation and protection, underwent expansion in D. dubium. These genes and their expansion helpfully explain its widespread geographical distribution and dominance in eutrophic waters. This study provides insight into the adaptive evolution of D. dubium at genomic perspectives, and the present high quality genomic resource will be a footstone for future omics studies of the species and its congeners.

Geography, ecology, and history synergistically shape across-range genetic variation in a calanoid copepod endemic to the north-eastern Oriental.

The center-periphery hypothesis (CPH) predicts that peripheral populations will have lower genetic variation than those at the center of a species' distribution. However, ecological margins do not always coincide with geographical edges when topographies are diverse. Historical climate changes can also strongly affect genetic variation. Here, we examined genetic variation in Phyllodiaptomus tunguidus, a calanoid copepod endemic to the north-eastern Oriental. This species was predicted to exhibit a complex pattern of genetic variation across its range due to the diverse topographies and stable climate history of the north-eastern Oriental. To test this, we used geographic distance to the center of the distribution, current ecological suitability, and climate during the last glacial maximum as geographical, ecological, and historical factors, respectively, in our analyses. We measured genetic diversity and population differentiation using mitochondrial and nuclear markers. This showed that P. tunguidus had 3 refugia during the last glacial maximum (LGM). Such a pattern of multiple refugia complicates the determination of the center and periphery of spatial genetic diversity. Both regression models and redundancy analyses failed to support the CPH. Instead, they showed that geographical, ecological, and historical factors together shaped population genetic structure in this species. Ecological factors explained significantly more genetic variation than did geographical and historical factors-however, all three factors interacted significantly to affect the pattern of genetic variation. The results extend our understanding of the CPH and the extent to which it can explain genetic variation across populations.

Extensive Carbon Contribution of Inundated Terrestrial Plants to Zooplankton Biomass in a Eutrophic Lake.

Organic carbon derived from terrestrial plants contributes to aquatic consumers, e.g., zooplankton in lakes. The degree of the contribution depends on the availability of terrestrial organic carbon in lake organic pool and the transfer efficiency of the carbon. Terrestrial organic carbon is poor-quality food for zooplankton with a mismatch of nutrition content and was incorporated to zooplankton with much lower efficiency than phytoplankton. Contributions of terrestrial carbon to zooplankton generally decrease with an increase in phytoplankton production, indicating a preferential incorporation of phytoplankton in previous investigations. However, in eutrophic lakes, the dominating cyanobacteria were of poor quality and incorporated to consumers inefficiently too. In that case, zooplankton in eutrophic wetlands, where cyanobacteria dominate the phytoplankton production and massive terrestrial plants are inundated, may not preferentially incorporate poor food-quality phytoplankton resource to their biomass. Therefore, we hypothesize that carbon contributions of terrestrial vegetation to zooplankton and to lake particulate organic pool should be similar in such aquatic ecosystems. We tested this hypothesis by sampling zooplankton and carbon sources in Ming Lake (Jinan University Campus, southern China) which was overgrown by terrestrial plants after drying and re-flooded. After 60 days of observations at weekly (or biweekly) intervals, applying stable carbon (13C), nitrogen (15 N), and hydrogen (2H) isotopic analysis and a stable isotope mixing model, we estimated the occurrence of extensive carbon contribution (≥ 50%) of flooded terrestrial plants to cladocerans and copepods. Contribution of inundated terrestrial plants to cladocerans was similar to that to lake particulate organic pool. Thus, our study quantified the role of terrestrial carbon in eutrophic wetlands, enhancing our understanding of cross-ecosystem interactions in food webs with an emphasis on the resource quality.

The Oracle of Delphia molecular phylogenetic approach to Greek Cordulegaster Leach in Brewster, 1815 (Odonata: Anisoptera: Cordulegastridae).

Taxonomy of the genus Cordulegaster Leach in Brewster, 1815 in Greece is not completely understood. The taxonomic status of the subspecies C. helladica buchholzi (Lohmann, 1993), C. helladica kastalia (Lohmann, 1993), and C. heros pelionensis Theischinger, 1979 was still unclear. We applied a molecular genetic approach using sequences of mitochondrial and nuclear DNA fragmentscytochrome c oxidase I (COI) and Internal Transcribed Spacer 1 (ITS1). This approach revealed that specimens presently assigned to C. heros pelionensis should be considered as conspecific to the nominate subspecific taxon making C. heros a monotypic species. Two major monophyletic lines were found within the Greek representatives of the species grouped around C. bidentata Selys, 1843: the clade of the European endemic C. bidentata and the clade composed of three species: C. helladica (Lohmann, 1993), C. buchholzi (stat. nov., raised to species level), and C. insignis Schneider, 1845. Cordulegaster helladica is restricted to the Peloponnese. Cordulegaster buchholzi is not restricted to the Cyclades as previously thought, but widespread from the Cyclades over the island Euboea to south-east mainland Greece reaching in the west near Mount Parnassos, where it hybridize with C. bidentata. Hybridization between C. bidentata and C. buchholzi was detected at the Castalian Spring, where in ancient times the Oracle of Delphi was located, and some kilometres east of the Castalian Spring. These hybrids had been formerly named C. helladica kastalia. In the case of C. insignis montandoni St. Quentin, 1971 we have investigated specimens some kilometres away from the type locality in Romania, which all revealed hybrids between C. bidentata and C. insignis. However, we do not know if specimens phenotypically looking like C. insignis from further west in the SE Balkans represent isolated population of C. insignis within the range of C. bidentata or belong to a broader hybrid zone between C. bidentata and C. insignis.

Modeling and Prediction of the Species' Range of Neurobasis chinensis (Linnaeus, 1758) under Climate Change.

Neurobasis chinensis is widely distributed in eastern tropical Asia. Its only congener in China, the N. anderssoni, has not been observed for decades. To protect N. chinensis, it is necessary to understand the ecological properties of its habitats and specie's range shift under climate change. In the present study, we modeled its potential distribution under one historical, current, and four future scenarios. We evaluated the importance of the factors that shape its distribution and habitats and predicted the historical and current core spatial distributions and their shifting in the future. Two historical core distribution areas were identified: the inland region of the Bay of Bengal and south-central Vietnam. The current potential distribution includes south China, Vietnam, Laos, Thailand, Myanmar, Luzon of Philippines, Malaysia, southwest and northeast India, Sri Lanka, Indonesia (Java, Sumatera), Bangladesh, Nepal, Bhutan, and foothills of the Himalayas, in total, ca. 3.59 × 106 km2. Only one core distribution remained, concentrated in south-central Vietnam. In a warming future, the core distribution, high suitable habitats, and even the whole range of N. chinensis will expand and shift northwards. Currently, N. chinensis mainly resides in forest ecosystems below 1200 m above sea level (preferred 500 m to 1200 m a.s.l.). Annual precipitation, mean temperature of driest quarter, and seasonality of precipitation are important factors shaping the species distribution. Our study provides systematic information on habitats and geographical distribution, which is useful for the conservation of N. chinensis.

Climate change and niche unfilling tend to favor range expansion of Moina macrocopa Straus 1820, a potentially invasive cladoceran in temporary waters.

Non-native species' introductions have increased in the last decades primarily due to anthropogenic causes such as climate change and globalization of trade. Moina macrocopa, a stress-tolerant cladoceran widely used in bioassays and aquaculture, is spreading in temporary and semi-temporary natural ponds outside its natural range. Here, we characterize the variations in the climatic niche of M. macrocopa during its invasions outside the native Palearctic range following introduction into the American continent. Specifically, we examined to what extent the climatic responses of this species have diverged from those characteristics for its native range. We also made predictions for its potential distribution under current and future scenarios. We found that the environmental space occupied by this species in its native and introduced distribution areas shares more characteristics than randomly expected. However, the introduced niche has a high degree of unfilling when displacing its original space towards the extension to drier and hotter conditions. Accordingly, M. macrocopa can invade new areas where it has not yet been recorded in response to warming temperatures and decreasing winter precipitation. In particular, temporary ponds are more vulnerable environments where climatic and environmental stresses may also lower biotic resistance. Supplementary Information: The online version contains supplementary material available at 10.1007/s10750-022-04835-7.

Complete mitochondrial genome of Ovalona pulchella (Branchiopoda, Cladocera) as the first representative in the family Chydoridae: Gene rearrangements and phylogenetic analysis of Cladocera.

Chydoridae are phytophilic-benthic microcrustaceans that make up a significant proportion of species diversity and play an important role in the littoral zone of freshwater ecosystems worldwide. Here, we provide the complete mitochondrial genome of Ovalona pulchella (King, 1853), determined by next-generation sequencing. The entire mitochondrial genome is 15,362 bp in length; this is the first sequenced mitochondrial genome in the family Chydoridae. The base composition and codon usage were typical of Cladocera species. The mitochondrial gene arrangement (37 genes) was not consistent with that of other Branchiopoda. Both maximum likelihood and Bayesian analyses supported each suborder and family of Branchiopoda as monophyletic groups. The relationships among the families were as follows: [(Leptestheriidae + Limnadiidae) + (Sididae + (Bosminidae + (Chydoridae + Daphniidae)))] + Triopsidae. The newly sequenced O. pulchella was most closely related to the family Daphniidae. The complete mitochondrial genome of O. pulchella also provides valuable molecular information for further analysis of the phylogeny of the Chydoridae and the taxonomic status of the Branchiopoda.

Geographic Variation of Phyllodiaptomus tunguidus Mitogenomes: Genetic Differentiation and Phylogeny.

Phyllodiaptomus tunguidus (Copepoda: Calanoida) is largely endemic to and widespread in freshwater in southern China, where it inhabits a complex landscape from lowland to highland across an elevation gradient of 2000m. A deep genetic differentiation can be expected between its most distant geographic populations. Here, we sequenced nine mitogenomes from diverse populations. All mitogenomes contained 37 genes, including 13 protein-coding genes (PCG), two rRNA genes, 22 tRNA genes and one control region. Their base composition, genetic distance and tRNA structure indeed revealed a wide differentiation between mitogenomes. Two P. tunguidus from Guangxi near Vietnam differed from the other seven by up to 10.1%. Their tRNA-Arg had a complete clover-leaf structure, whereas that of the others did not contain an entire dihydrouridine arm. The nine mitogenomes also differed in the length of rRNA. NJ, ML, and Bayesian analyses all split them into two clades, viz. the two P. tunguidus from Guangxi (Clade 1), and the other seven (Clade 2). Both the structure and phylogeny of the mitogenomes suggest that P. tunguidus has complex geographic origin, and its populations in Clade 1 have long lived in isolation from those in Clade 2. They currently reach the level of subspecies or cryptic species. An extensive phylogenetic analysis of Copepoda further verified that Diaptomidae is the most recently diverging family in Calanoida and that P. tunguidus is at the evolutionary apex of the family.

Mitogenomics of Cladocera (Branchiopoda): Marked gene order rearrangements and independent predation roots.

Cladocera (Crustacea: Branchiopoda) is a key group of invertebrates. Despite a long history of phylogenetic research, relationships within this group remain disputed. We here provide new insights based on 15 new mitochondrial genomes obtained from high-throughput sequencing (HTS) and 40 mitogenomes extracted from published HTS datasets. Together with 25 mitogenomes from GenBank, we generated a matrix of 80 mitogenomes, 44 of them belonging to Cladocera. We also obtained a matrix with 168 nuclear orthologous genes to further assess the phylogenetic result from mitogenomes based on published data and one new HTS data ofLeptodora. Maximum likelihood and Bayesian phylogenetic analyses recovered all Branchiopoda orders as monophyletic and supported a sister-group relationship between Anomopoda and Onychopoda, making the taxon Gymnomera paraphyletic and supporting an independent origin of predatory Haplopoda and Onychopoda. The nuclear phylogeny and topological tests also support Gymnomera as paraphyletic, and the nuclear phylogeny strongly supports a sister-group relationship between Ctenopoda and Haplopoda. We provide a fossil-calibrated time tree, congruent with a Carboniferous origin for Cladocera and a subsequent diversification of the crown group of Anomopoda, Onychopoda, and Ctenopoda, at least in the Triassic. Despite their long evolutionary history, non-Cladoceran Branchiopoda exhibited high mitogenome structural stability. On the other hand, 21 out of 24 gene rearrangements occurred within the relatively younger Cladocera. We found the differential base compositional skewness patterns between Daphnia s.s. and Ctenodaphnia, which might be related to the divergence between these taxa. We also provide evidence to support the recent finding that Spinicaudata possesses mitogenomes with inversed compositional skewness without gene rearrangement. Such a pattern has only been reported in Spinicaudata.

The mitochondrial genome of Diaphanosoma excisum Sars, 1885 (Crustacea: Branchiopoda: Cladocera) from Hainan Island, China.

Diaphanosoma excisum is the only Cladoceran in tropical freshwaters and parapatrically occurs with Diaphanosoma dubium in the transition between the tropics and subtropics. Here, we present the complete mitochondrial genome (MG) determined by next-generation sequencing and offer a phylogenetic analysis of D. excisum. The MG of D. excisum is 17,615 bp in size, including 13 protein-coding genes (PCGs), 2 ribosomal RNA, 23 tRNA, and 2 putative control regions. The MG has a biased A + T of 65.34% for base composition. Compared to D. dubium, the MG of D. excisum has one more tRNA-Met, one unknown extra putative control region and is different in the arrangement of its tRNAs. The MG sequence and tRNA order provide valuable molecular data for understanding the phylogeny and speciation of Diaphanosoma.

Miocene cladocera from Poland.

The Belchatów Lignite Mine of Poland is a treasure-cove for mid-to late Miocene plant and animal fossils, deposited in a slow-flowing river valley with swamps and oxbow lakes. Here, we report the finding of abundant fossil anomopod cladocerans. Some are three-dimensionally preserved, including the taxonomically important trunk limbs. They pertain to the families Chydoridae and Bosminidae, with species similar to but distinct from modern ones. All are members of the zooplankton, though some are littoral while others are pelagic in nature. Morphological stasis in these families is not outspoken as in the Daphniidae and the stasis hypothesis, based on ephippia only, is challenged. The absence of Daphnia is conspicuous and ascribed to a combination of fish predation and local water chemistry. Its place in the oxbow lakes is taken by at least two Bosmina species, one of which is undescribed. We consider this a case of paleo-competitive release. For Bosminidae, these are the first certified fossils predating the Pleistocene.

The mitochondrial genome of Phyllodiaptomus tunguidus Shen & Tai, 1964 (Copepoda, Calanoida) and its phylogeny.

The mitochondrial genome of Phyllodiaptomus diaptomus was sequenced and assembled via Next-Generation Sequencing (NGS) and iterative assembly with a reference seed. The genome is 16446 bp long, A + T biased (69.4%), with 13 protein-coding genes, 22 tRNAs, and 2 rRNA. All protein-coding genes are initiated by a typical "ATN" codon. ND1, ND2, ATP6 genes are terminated with "TAG", the other 10 genes are terminated with "TAA". This is the first complete mitogenome published in the Diaptomidae. It provides molecular information useful to a better understanding of the phylogeny of calanoids.

Cornigerius lacustris of Lake Hazar, Turkey, a synonym of Cornigerius maeoticus (Pengo) of the Ponto-Caspian (Cladocera: Onychopoda).

Cornigerius species are endemic to the Ponto-Caspian, with the exception of Cornigerius lacustris, which is endemic to freshwater Lake Hazar in the Euphrates basin. However, the barcoding fragment of the cytochrome c subunit I (COI) of animals from the type locality shows less than 1 % divergence with Black Sea and less than 2% with Caspian Lake C. maeoticus, the oldest and most widespread species of the genus. Black Sea and Caspian Lake animals show 1.5 % divergence. We therefore place the origin of the Hazar population in the Black Sea. Combined with a variable morphology, we also conclude that C. lacustris is a synonym of C. maeoticus, as already suspected by its describer. Dating the 'lacustris' population is difficult, but it has been there for at least a century.

Effect of algal and bacterial diet on metal bioaccumulation in zooplankton from the Pearl River, South China.

The biomagnification of metals (Cd, Co, Cr, Cu, Fe, Mn, Pb and Zn) and the metalloid As in aquatic systems is a global health concern. In this study, concentrations of fatty acid biomarkers in zooplankton were analyzed from the Pearl River, South China between September 2016 and July 2017. The objective was to examine how particulate matter, algae and bacteria food sources affect metal bioaccumulation using fatty acid facilitation. In the zooplankton fraction, positive correlations were observed between Pb concentration and Eicosapentaenoic acid (EPA), Zn and Docosahexaenoic acid (DHA) (diatoms and Cryptophyceae biomarkers), Fe with Palmitoleic acid (C16:1n-7, diatom marker), and a weak association of Mn with α-linolenic acid (C18:3n-3). Cu concentration in the zooplankton increased significantly with an endogenous biotic biomarker Stearic acid (C18:0, bacteria biomarker), while Cd concentrations increased with increasing Oleic acid (C18:1n-9, green alga biomarker) concentration. There was a positive correlation between Cr concentration and the sum of Pentadecylic and Margaric acids (C15:0 + C17:0, bacteria biomarkers). Seven of the nine metals examined showed associations with fatty acids in the zooplankton. The bioaccumulation of Co, Cu, Pb, Fe, Mn and Zn concentration was correlated to the individual biomasses of Brachionus calyciflorus, Filinia longiseta, Schmackeria forbesi, Limnoithona sinenisis, Thermocyclops brevifurcatus, and Diaphanosoma dubium. For selected zooplankton taxa, the algal biomasses of Euglenophyceae, Chlorophyceae, Cryptophyceae, and Bacillariophyceae were correlated. Zooplankton were affected by selected species of phytoplankton and bacteria numbers in the Pearl River. These results show that metal accumulation in zooplankton is not only correlated with diet but is also in part, species specific with metal type. Thus, the bioaccumulation or scavenging of metals across trophic levels is a fundamental and complex component of metal cycling in aquatic environments.

Daphnia diversity on the Tibetan Plateau measured by DNA taxonomy.

Daphnia on the Tibetan Plateau has been little studied, and information on species diversity and biogeography is lacking. Here, we conducted a 4-year survey using the barcoding fragment of the mitochondrial COI gene to determine the distribution and diversity of Daphnia species found across the Plateau. Our results show that species richness is higher than previously thought, with total described and provisional species number doubling from 5 to 10. Six of the taxonomic units recovered by DNA taxonomy agreed well with morphology, but DNA barcoding distinguished three clades each for the D. longispina (D. galeata, D. dentifera, and D. longispina) and D. pulex (D. pulex, D. cf. tenebrosa, and D. pulicaria) complexes. The sequence divergence between congeneric species varied within a large range, from 9.25% to 30.71%. The endemic D. tibetana was the most common and widespread species, occurring in 12 hyposaline to mesosaline lakes. The lineage of D. longispina is the first confirmed occurrence in west Tibet.

Checklist of the dragonflies (Odonata) of Iran with new records and notes on distribution and taxonomy.

Iran has a complex dragonfly fauna influenced by contacts and overlaps of different geographical zones. Its fauna is dominated by Eurosiberian taxa. However, the SE Province Sistãn-va-Baluchestãn is rich in oriental species, many of which having their western distribution limit in Iran. In NE-Iran, Irano-Turanian elements live and in the S- and SW-Iran African species are found. The Iranian Odonata fauna seems well studied, however, a closer look reveals many uncertainties and confusion, some records coming clearly from misidentification whereas other, which were missing proofs of correct identification remains to be confirmed. Even today, every new collecting trip reveals species new for Iran whereas species new for science are still detected, although rarely. In this checklist we include seven taxa new for Iran: Stylurus ubadschii (although a male of uncertain origin is recorded in Schmidt (1954), Ischnura senegalensis (although two uncertain records were published by Martin (1912) and Schmidt (1954), Coenagrion ponticum, C. lunulatum, C. pulchellum, Lestes macrostigma, and Calopteryx splendens tschaldirica. We critically checked all available data, including all published records. Fourteen taxa have been rejected, or placed in the category for need of confirmation. Till the end of 2017, 100 autochthonous taxa of dragonflies and two migratory species could be confirmed to be or have been present in Iran. We provide distribution maps, created after evaluation of published data and containing our own data from 12 trips to Iran, travelling over 35000 km in the country. Over 200 new localities are integrated. Taxonomic confusion is reduced by rejecting the following taxa for Iran: Calopteryx splendens mingrelica, C. hyalina, Erythromma najas, Aeshna cyanea, Gomphus davidi, and Sympetrum sinaiticum. We regard the taxa Gomphus amseli and G. schneiderii transcaspicus as synonyms of G. schneiderii, and Onychogomphus forcipatus lucidostriatus as a synonym of O. f. albotibialis.

Predation and reproductive performance in two pelagic typhloplanid turbellarians.

We investigated feeding and reproductive performance of coexisting pelagic turbellarians from experiments on predation rates of Mesostoma ehrenbergii and M. craci as a function of food (Daphnia similis, three levels) and temperature (4 levels) during 10 days. Flatworms were collected from the pelagic of a subtropical lake in Brazil. Growth was more rapid at higher temperatures: more prey were consumed, and more eggs produced. M. craci and particularly M. ehrenbergii fitted a linear mixed-effects model and showed a type II functional response. M. craci was the more stenothermic of the two. Intrageneric predation also occurred: M. ehrenbergii fed on M. craci, but not vice versa. After a first clutch of subitaneous eggs, M. ehrenbergii produced resting eggs only. In M. craci an intermediate type of eggs hatched some time after release, survived passage through the gut of M. ehrenbergii, but did not resist drying. By primarily selecting cladoceran prey, M. ehrenbergii can make coexistence of both flatworms possible. As population density of M. ehrenbergii increases, it turns to producing resting and non-viable subitaneous eggs, thus limiting its population size. In nature, these processes structure the zooplankton community, while avoiding extinction of prey and predator.

The mitochondrial genome of Atrocalopteryx melli Ris, 1912 (Zygoptera: Calopterygidae) via Ion Torrent PGM NGS sequencing.

The mitochondrial genome of Atrocalopteryx melli was sequenced and assembled via Next-Generation Sequencing (NGS) and iteratively assembly process with a reference seed. This genome is 15,562 bp long and A + T biased (71%), with 37 genes arranged in common order of Odonata. All protein-coding genes are initiated by typical "ATN" codon, and 9 genes are terminated with a complete stop codon, except nad4, nad5, cox2, and cox3, which are terminated with an incomplete codon "T(aa)". The S5 intergenic spacer is absent in this genome, supporting that lacking of S5 as a specific character for damselflies. The A + T rich region of A. melli is 267 bp longer than that of A. atrata. This mitogenome provides new molecular information for understanding of A. melli and Atrocalopteryx.

Species and hybrids in the genus Diaphanosoma Fischer, 1850 (Crustacea: Branchiopoda: Cladocera).

Cladocerans are well-studied planktonic crustaceans, especially those of the genus Daphnia in which interesting evolutionary questions have been addressed on speciation processes. The aim of the present study is to demonstrate that other genera of cladocerans show similar levels of cryptic diversity, intraspecific gene flow, and thus become useful model systems for comparison. In order to do so, we chose the genus Diaphanosoma, widespread in tropical and temperate areas. We started with a survey of species diversity in the genus Diaphanosoma in Asia using a morphological approach, then obtained sequences from a mitochondrial and a nuclear marker from multiple individuals of different species, performed tests on DNA taxonomy and molecular phylogenies, and assessed the role of hybridization in explaining the cases of mitonuclear discordance. The results are that cryptic diversity occurs in Diaphanosoma, and mitonuclear discordance was found in about 6% of the sequenced animals. Past hybridization is supported as the most likely explanation for the discordance: no evidence was found of first generation hybrids with heterozygous sequences. Our analysis on patterns of genetic diversity in Diaphanosoma supports similarities and differences with what is known in Daphnia.