Partial revision of the neustonic genus Scapholeberis Schoedler, 1858 (Crustacea: Cladocera): decoding of the barcoding results

Spring and autumn fauna of Cladocera (Crustacea: Branchiopoda) in the center of East Asia plain: Hunan and Hubei Provinces of China

Cladoceran (Crustacea: Branchiopoda) fauna of Hunan and Hubei provinces of China was studied in April 2014 and October 2018. 49 species of Cladocera were found, Anthalona sanoamuangae Sinev & Kotov, 2012 was recorded for China for the first time. Eight species were newly recorded for central China, taxonomic status of four species was clarified. Among the observed species, 19 taxa are predominantly Boreal, 13 species are recorded predominantly in south part of temperate zone and subtropics, and 17 species are mainly tropical. Significant difference was revealed between the spring and autumn fauna: Boreal species were the most frequent in spring, whereas subtropical and tropical species became more common in autumn. Species diversity and composition of the cladoceran fauna in the center of East Asia plain is discussed.

Phylogeography and genetic diversity of the Scapholeberis kingii species complex (Cladocera: Daphniidae) in China

There is increasing interest in the diversity and phylogeography of aquatic invertebrate zooplankton in the Eastern Palearctic, yet this topic remains largely unexplored in China. Here, we investigated the lineage diversity and phylogeography of an important cladoceran taxon, the Scapholeberis kingii (Cladocera: Daphniidae) species complex, members of which live in the surface layers of freshwater ecosystems. We identified only the S. smirnovi morphospecies from this species complex in 29 of 491 Chinese water bodies examined. Its phylogenetic position was verified using both a mitochondrial (mitochondrial cytochrome c oxidase subunit I; COI) and a nuclear marker (the nuclear large subunit ribosomal RNA gene; 28S). Pronounced geographical separation among three S. smirnovi mitochondrial lineages was observed in China: only a single lineage (Lineage A) was present in the Eastern Plain, whereas Lineages B and C were restricted to the Inner Mongolia-Xinjiang Plateau and the Qinghai-Tibetan Plateau respectively. This deep mtDNA divergence and the substantial genetic differentiation among S. smirnovi populations from different regions is likely a result of the rapid uplift of the Qinghai-Tibetan Plateau and associated ecological changes. This study contributes to an understanding of the genetic diversity of the S. kingii complex, a key component of neustonic zooplankton.

Genome Assembly of a Relict Arabian Species of Daphnia O. F. Müller (Crustacea: Cladocera) Adapted to the Desert Life

The water flea Daphnia O.F. Müller 1776 (Crustacea: Cladocera) is an important model of recent evolutionary biology. Here, we report a complete genome of Daphnia (Ctenodaphnia) arabica (Crustacea: Cladocera), recently described species endemic to deserts of the United Arab Emirates. In this study, genome analysis of D. arabica was carried out to investigate its genomic differences, complexity as well as its historical origins within the subgenus Daphnia (Ctenodaphnia). Hybrid genome assembly of D. arabica resulted in ~116 Mb of the assembled genome, with an N50 of ~1.13 Mb (BUSCO score of 99.2%). From the assembled genome, in total protein coding, 5374 tRNA and 643 rRNA genes were annotated. We found that the D. arabica complete genome differed from those of other Daphnia species deposited in the NCBI database but was close to that of D. cf. similoides. However, its divergence time estimate sets D. arabica in the Mesozoic, and our demographic analysis showed a great reduction in its genetic diversity compared to other Daphnia species. Interestingly, the population expansion in its diversity occurred during the megadrought climate around 100 Ka ago, reflecting the adaptive feature of the species to arid and drought-affected environments. Moreover, the PFAM comparative analysis highlights the presence of the important domain SOSS complex subunit C in D. arabica, which is missing in all other studied species of Daphnia. This complex consists of a few subunits (A, B, C) working together to maintain the genome stability (i.e., promoting the reparation of DNA under stress). We propose that this domain could play a role in maintaining the fitness and survival of this species in the desert environment. The present study will pave the way for future research to identify the genes that were gained or lost in this species and identify which of these were key factors to its adaptation to the harsh desert environment.

Mitochondrial Lineage Diversity and Phylogeography of Daphnia (Daphnia) (Crustacea: Cladocera) in North-East Russia

The variability of the 12S gene fragment of the mtDNA for taxa belonging to subgenus Daphnia (Daphnia) O.F. Müller, 1776 (Crustacea: Cladocera) in NE Russia is studied, and their phylogenetic analysis performed. We identified (based both on morphological and molecular data) nine species belonging to four species complexes, namely: (A) D. longispina s.l.: (1) D. longispina O.F. Müller, 1776; (2) D. dentifera Forbes, 1893; (3) D. galeata Sars, 1864; (4) D. umbra Taylor, Hebert et Colbourne, 1996; (B) D. cristata s.l.: (5) D. cristata Sars, 1862; (6) D. longiremis Sars, 1862; (C) D. curvirostris s.l.: (7) D. curvirostris Eylmann, 1887; (D) D. pulex s.l.: (8) D. pulex Leydig, 1860; (9) D. middendorffiana Fischer, 1851. Rare arcto-mountainous taxon D. umbra was found in the mountains of the Sakha (Yakutia) Republic for the first time. Species diversity in NE Asia is relatively low, and the most revealed taxa are trans-Beringian. We also performed a phylogeographic analysis of D. dentifera and D. pulex s.l., the two most common species in NE Russia. Our new data allow us to assume that the daphniids of NE Asia have undergone various evolutionary scenarios during the Pleistocene period: survival is within some local refugia, and re-colonization from these areas and from North America through the Beringian land bridge, etc. We agree with previous authors who revealed that the patterns in the studied species groups are relatively recent (of Late Pleistocene or even Holocene age), although the main phylogenetic daphniid lineages (mainly congruent with the biological species) are very old. Our results provide convincing evidence for the hypothesis that NE Russia is a very important source of modern haplotypic diversity for the cladocerans.

Aquatic Organisms Research with DNA Barcodes

Since their inception, DNA barcodes have become a powerful tool for understanding the biodiversity and biology of aquatic species, with multiple applications in diverse fields such as food security, fisheries, environmental DNA, conservation, and exotic species detection. Nevertheless, most aquatic ecosystems, from marine to freshwater, are understudied, with many species disappearing due to environmental stress, mostly caused by human activities. Here we highlight the progress that has been made in studying aquatic organisms with DNA barcodes, and encourage its further development in assisting sustainable use of aquatic resources and conservation.