Groundwater Cladocera: A synopsis

A review is given of our present knowledge on the Cladocera that live in subterranean waters. Besides species that are accidentally or passively transported to caves and wells, at least one groundwater habitat, namely that of river gravels, is inhabited by species that either do not occur at the surface at all, or are only rarely thrown up by springs. Such species are now known from three continents.     

Cladocera: Predators and prey

Among the freshwater zooplankton community, Cladocera represent one of the most common elements of pelagic populations. Being almost exclusively filter feeders and algae users and, at the same time, the favourite prey of invertebrate and vertebrate predators, Cladocera represent the most important group in the plankton community of lakes as regards energy transfer along the food chain. Because of their short generation times and their high reproductive efficiency, predation by invertebrates, usually, has only a limited role in controlling their density. However, at high densities, invertebrate predators can provide an effective control of Cladocera populations. The intensive research on selective predation by vertebrates has demonstrated that this activity can be responsible, together with competitive interactions, for the dominance of different groups in the planktonic community: large Cladocera dominate when predation is low, Rotifera and small Crustacea dominate at high predation levels and high nannoplanktonic densities. These evidences on the role of vertebrate predation in structuring aquatic environments has greatly contributed to our better understanding of aquatic ecosystem functioning. In particular, it seems that the removal of large filter-feeding herbivorous Cladocera by zooplanktivorous fish can lead to worsening environmental conditions in eutrophicating lakes. In this respect, Cladocera appear to be the key group among zooplanktonic organisms, and their interactions the key factors in aquatic food chain management.     

Genotypic characteristics of the Cladocera

Work on the genetics of cladocerans reproducing by cyclic parthenogenesis has indicated that populations usually include a large number of genotypes, whose frequencies are in close approximation to Hardy-Weinberg equilibrium. Less diverse genotypic arrays and pronounced instability in genotype frequencies occur only in permanent populations exposed to limited ephippial recruitment. Genetic diversification among local cladoceran populations is greater than in most other organisms as a consequence of the inefficiency of passive dispersal. Genotypic characteristics of cladocerans reproducing by obligate parthenogenesis are markedly different from those of cyclic parthenogens. Local populations include few clones, but genetic distances between them are often large and accompanied by significant ecological and morphological divergence. When considered over their entire range, cladoceran taxa reproducing by obligate asexuality are the most genotypically diverse asexual organisms known. This diversity has originated from the spread of a sex-limited meiosis suppressor through species that originally reproduced by cyclic parthenogenesis. The confused state of cladoceran taxonomy is partially a consequence of the presence of such obligately asexual groups, but also results from the occurrence of hybridization and sibling species. The genome size of cladocerans is exceptionally small and is associated with a large amount of endopolyploidy. Somatic tissues in adult cladocerans show a range in nuclear DNA content from 2–2048 c. DNA quantification studies have additionally revealed the frequent occurrence of polyploid clones in obligately asexual taxa.     

福建淡水枝角类及其区系

本文记录了福建淡水枝角类7科25属71种,其中25种为福建新纪录.文章分析了福建淡水枝角类的区系特点,并与邻近地区进行了比较.     

福建淡水枝角类及其区系

本文记录了福建淡水枝角类７科２５属７１种,其中２５种为福建新记录,文章分析了福建淡水枝角类的区系特点,并与邻近地区进行了比较。     

The evolution of groundwater Cladocera

Cladocera occur in various types of groundwater, but are most common in the underflow of rivers. Numerous surface water species occasionally venture into groundwater; some chydorids are more common in groundwaters than in surface waters; at least three groups within Alona, finally, have evolved exclusive groundwater species. The latter show few obvious adaptations to the subterranean habitat, except loss of an eye or total blindness. Some, however, have conserved an array of primitive characters (e.g. on the end-claw of the postabdomen, and the setation of the valve rims) which suggest that the physical protection and relative constancy of the hyporheic has permitted the survival of some ancient taxa.     

Osmoregulatory capacity of the Cladocera

Within the order Cladocera are found almost all varieties of osmotic regulation, which make it possible for them to live in waters of a wide range of salt concentrations. Many Cladocera are very powerful osmoregulators and are comparable to the teleosts and decapod crustaceans in their abilities. The variety of osmoregulatory capacities within the cladocerans are illustrated and discussed. The function of mitochondrion-rich ion transporting cells found in nuchal glands or on epipodites are diseussed and the physiological mechanisms involved in osmoregulation are compared with similar mechanisms in other crustaceans and in teleosts. Data is provided on osinotic regulation in eggs and embryos in open and elosed brood chambers. Other topics include the occurrence of physiological races in some species, recent changes in osmoregulatory abilities following man-induced changes in salinity, the effects of temperature on osmoregulation and the effects of pH.     

Cladocera in space and time: Analysis of lake sediments

Shells of Bosminidae and Chydoridae are quantitatively preserved in lake sediments. The chronological deposition of these remains provides the means for longterm observation of these Cladocera, both in terms of species and communities. Chydorid analysis, as based on subfossil assemblages, is an analysis of community and provides direct observation of community dynamics over extended periods of time. It has proved to be a valuable method to obtain information on the influence of environmental factors and time on community characteristics. Morphological variation inBosmina (Eubosmina) has been followed for some thousand years. This is of special interest for the evaluation of taxonomic rank (species, forms) if closely related taxa have co-existed. Bosmina successions, as well as shifts in the chydorid fauna, are related to environmental change. Thus, cladoceran analysis of lake sediments provides information on the developmental history of lakes and allows observation of the effects of longterm environmental changes, such as climatic changes and eutrophication.     

A revision of the Scapholeberinae (Crustacea: Cladocera)

The group of hyponeustonic daphniid cladocera previously known under the generic name Scapholeberis is raised to the rank of a subfamily (Scapholeberinae) and contains two genera, Megafenestra n.gen. (2 species), and Scapholeberis s.s. (7 species and one subspecies). The characters upon which this revision is based are: structure of the rostrum, structure of the first antennae, structure of trunk limbs 1, 2, and 5, presence and nature of headpore(s), structure of the ventral rim of the valves, armature of the distal rim of the valves, structure of the postabdomen and its end-claws. Males were examined in all but two species, and proved to be more primitive than females and much less diagnostic than in the Chydoridae. It also appeared that the shape and armature of the postabdomen are less important taxonomical tools than heretofore supposed. In more than half of the species, it is of generalised shape and hardly usable beyond the species-group level. The same, although less drastically, holds true for the P1 of males. Of greatest diagnostic value at the species level are the shape of the rostrum and the armature of the valve margins. A phylogeny of the subfamily is proposed, with Megafenestra as the more primitive genus, closely allied to Ceriodaphnia, and within Scapholeberis, S. mucronata as the most apomorphic species. In biogeographical respect, no species is cosmopolitan, although their ranges may be of continental dimensions. Species and populations appear to concentrate in the temperate and continental climate belts of the northern hemisphere, but more research in the southern hemisphere is needed. A key for the identification of all species is given.     

Two-egged ephippia in the chydorid Cladocera

SUMMARY. With a single reported exception, the ephippia of all specialized chydorid cladocerans hitherto described contain a single egg. Ephippia the European Chydorus ovalis and the North American species currently listed as C. cf. sphaericus have been found persistently, and so far invariably, to contain two eggs. The alternative strategies of producing 1-and 2-egged ephippia are briefly considered. Anomalous 1-egged ephippia of Daphnia (family Daphniidae) are also mentioned.     

Altitudinal distribution of tropical planktonic Cladocera

The altitudinal distributions of planktonic Cladocera in Africa in three latitudinal bands: 0–10 °, 10–20 ° and 28–31 ° are described. Some species have altitudinal ranges of 2000 m within a latitudinal band of 10 °. It is possible to distinguish tropical species which do not extend up to high altitudes, particularly at higher latitudes. At the lowest latitudes, some species are found only at high altitudes, but occur at progressively lower altitudes with increasing latitude: Daphnia pulex and D. obtusa are good examples. A study in South America, with a smaller database, gives similar results.     

Cladocera (Crustacea) from Nicaragua

Thirty-one Cladocera taxa are recorded from lakes, rivers and ponds of Western Nicaragua. They include Alona bromelicola sp. nov. found in water accumulations in epiphytic Bromeliads. The Cladocera recorded are neotropical and circumtropical. Other invertebrates found are also listed.     

The evolutionary history of the Chydoridae (Crustacea: Cladocera)

Although much is known about the evolutionary history of the pelagic 'cladocerans', there is little information on benthic families such as the Chydoridae. In this study, we examine the phylogenetic history of 37 chydorid species using sequence variation in two mitochondrial genes, COI and 16S rDNA, and one nuclear gene, 18S rDNA. The four recognized subfamilies of chydorids (Eurycercinae, Saycinae, Aloninae and Chydorinae) were well supported, being separated by large sequence divergences of 14.3–16.4%. By contrast, the existing taxonomic system appears to be less clear at a generic level, since many genera (e.g. Alona , Chydorus , Pleuroxus ) consist of an amalgam of distantly related species. However, among those genera which are monophyletic, levels of divergence are very high, suggesting that they originated somewhere in the mid-Palaeozoic. The factors involved in promoting diversification in this group are discussed.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 79, 629–643.     

河北白洋淀的枝角类和桡足类

白洋淀在河北省中部,位于东经115°38′～116°07′,北纬38°43′～39°02′之间;是华北平原最大和最典型的淡水湖泊湿地.湖内浮游动物种类丰富,但不同时期由于种种原因其种类又存在着差异.笔者于2005～2007年曾17次对白洋淀8个样点枝角类和桡足类进行了调查.