The systematics of Australian Daphnia (Cladocera: Daphniidae). Multivariate morphometrics

Forty nine characters were measured in each of 76 male and 200 female Daphnia including specimens from all eleven taxa described from the genus in Australia, except D. jollyi. Separate multivariate analyses (cluster, principal components and discriminant) of males and females each revealed only five morphological groups in the genus corresponding to the species D. occidentalis, D. lumholtzi, D. cephalata, D. nivalis, and a conglomerate of all other taxa described from the D. carinata complex, D. carinata (sensu lato). Interpretation of the male results was straightforward, but that for females was not because of the occurrence of an environmentally induced seasonal change in morphology (cyclomorphosis) in females. Log transformations of the female data successfully isolated the effects of cyclomorphosis. The seasonal morphs formed two groups which were further differentiated into taxonomic groups.     

The systematics of Australian Daphnia (Cladocera: Daphniidae). Electrophoretic analyses of the Daphnia carinata complex

Genetic variation at eleven allozyme loci was scored in approximately 1600 individual Daphnia. The samples included representatives of all nine taxa described from the D. carinata complex in Australia. Principal coordinates and cluster analyses revealed only three groups of genotypes within the complex, corresponding to the taxa D. cephalata, D. nivalis, and a conglomerate of all other taxa described from the complex, D. carinata (sensu lato). These results are consistent with recent multivariate morphological analyses of the complex.     

Daphnia (Cienodaphnia) menucoensis (Anomopoda; Daphniidae): a new species from athalassic saline waters in Argentina

Daphnia (Ctenodaphnia) menucoensis n. sp. is described from various localities in arid and semiarid Argentina. D. menucoensis has no ocellus, and a characteristic head, fornices, ephippium and denticular arrangement of postabdomen in females and males. The species belongs to a group, along with D. mediterranea, D. dolichocephala Negrea 1984, and D. salina, sharing ecological and morphological characteristics.     

Naturally occurring interspecific hybridization inSimocephalus (Cladocera,Daphniidae): its potential significance

Among the Cladocera, the occurrence of interspecific hybrids in nature has been reported frequently but rarely adequately documented. During the course of a survey of the genetic variation and population structure of several species ofSimocephalus in ponds in southern Ontario, Canada, readily distinguishable congeners often co-occurred in a pond. Occasionally, clones were recovered that were intermediate in phenotype (as determined from both morphological and electrophoretic analyses) between two species. Two different hybrid clones have been examined in detail to determine the parentals involved in the crosses. Evidence from field and laboratory studies is presented to document the hybrid nature of these clones. Factors favouring formation and long-term survival of hybrids in littoral zone and pelagic species are discussed.     

Differences in demographic parameters among electrophoretic clones of Daphnia obtusa Kurz (Crustacea: Cladocera)

In an 18-month electrophoretic study, a Daphnia obtusa population that recently colonized Lake Orta (a large, severely polluted lake in Northern Italy) showed no genetic variation.Populations from other localities were sampled. From clones established by single females, genotype differences were determined by two life table experiments (using Lake Orta and Lake Maggiore water as a culture medium).As expected, in the Lake Orta water the colonizing clone (LO) had longer survival, produced more newborns and had a larger rate of increase than the other clones. In the Lake Maggiore water the LO clone still fared better than the other clones.     

Notes on Cladocera and Copepoda from high altitude lakes in the Mount Everest Region (Nepal)

The paper deals with Cladocera and Copepoda species from eight high altitude lakes in the Khumbu area. In all lakes, an endemic known diaptomid of the palearctic genus Arctodiaptomus is found. The dark and large Daphnia tibetana occurs in five of the lakes sampled, characterized by the persistence of the spine in adults (parthenogenetic and ephippial females, males). Apparently, this is an unknown feature of this species. The literature on the diagnostic traits of the different morphs described is reviewed. In addition, a transparent and smaller-sized Daphnia species occurs in two lakes. This is a D. longispina characterized by the absence in adults of the carapace spine (var. aspina Weretschagin, 1911). The presence of these two species is discussed in relation to water transparency, colour, and vertical distribution. Two hypotheses on the evolution of cuticular pigmentation in Daphnia are examined. In addition to these mostly dominant species, a macrothricid also typical of high altitude lakes in the Alps was found (Macrothrix hirsuticornis) together with two cosmopolitan Chydoridae.     

Photoperiod and temperature as inducers of gamogenesis in a dicyclic population of Scapholeberis armata Herrick (Crustacea: Cladocera: Daphniidae)

The induction of gamogenesis in a dicyclic population of Scapholeberis armata from a small pond at 40° N in Pennsylvania, USA, was studied. Animals were collected at the time of gamogenesis in mid-October (fall) 1988 and early June (spring) 1989). 10 clones were established from isolated females for each season and maintained at low density under standard conditions of 20 °C and 13.5L/10.5D, with Chlamydomonas reinhardtii diluted with pond water to 3 · 105 cells ml^–1 as a food source. For each clone, mothers of pairs of test animals were acclimated to 4 sets of conditions: 20 °C/15.5L (spring), 15 °C/11.5L (fall), 20 °C/11.5L (control), and 15 °C/15.5L. Test animals were observed bidaily or daily for up to 37 days. Occurrence of molts and of parthenogenetic broods or ephippia was recorded. At short photoperiod, ephippial females developed, usually after one or more parthenogenetic broods, among both spring and fall animals. The response was stronger (higher % sexual females) among fall clones, and was enhanced in both groups by 15 °C water. No animals responded to long photoperiod in warm or cool water. It is likely that additional factors, such as prior photoinduction, rapid depletion of food supply, and increased inter-animal contact due to high population density are required for the induction of spring gamogenesis. Differences in the responsiveness of spring and fall clones to inducing conditions suggest some differences in genotypes of spring and fall subpopulations in this pond. It is proposed that variable responses among genotypes to factors inducing gamogenesis may be the basis for the differences and clines in the timing of gamogenesis found among ecologically and latitudinally separated populations.     

On the taxonomy of theDaphnia hyalina-galeata complex (Crustacea: Cladocera)

Populations of theDaphnia hyalina-galeata complex from Central, North and South Europe have been compared morphologically. The main purpose of this investigation is delimitation of the critical speciesDaphnia galeata, based on a thorough examination of the original materials from G. O. Sars' collection, and taking into account hitherto overlooked or insufficiently appreciated characters. According to their morphology and ecology,Daphnia hyalina, Daphnia galeata andDaphnia cucullata have to be treated taxonomically as separate species. In view of the short and high antennula mound and other morphological characteristics,Daphnia gracilis Hellich andDaphnia hyalina lacustris sensu Lilljeborg belong to the speciesDaphnia galeata. In the common range ofDaphnia galeata andDaphnia cacullata there occurs quite frequently an intermediary form, which according to genetic evidence is a hybrid of these two species. Although apparently this hybrid form is stabilized genetically to a large extent and is capable of identical reproduction, it should not be considered as a species in the usual sense.The present work intends to put the notoriously confused systematics of theDaphnia hyalina-galeata complex on a firm basis. It concludes with a key, which should enable also non-specialists to identify uniquely the three species and the hybrid form in question.     

Study of the in vitro development of the parthenogenetic egg of daphnia carinata king (Cladocera: Daphnidae)

The embryonic development of Daphnia carinata King was studied under laboratory conditions. Detailed observations were made at frequent intervals and conspicuous morphological changes were recorded. The results were compared with those of other allied tropical and temperate forms. While the basic pattern of development is similar to that of other daphnids, the duration of the total period of development as well as of the individual stages in this species differed from those of other tropical and temperate forms.     

Diurnal vertical migration of Daphnia hyalina Leydig, 1860 (Crustacea: Cladocera) in Lake Bled (Slovenia) in relation to temperature and predation

Diurnal vertical migration (DVM) of Daphnia hyalina in Lake Bled was most intense during summer stratification. The extent of DVM varied with the size of the animal and its reproductive state. Migration distances were shortest in immature specimens and longest in ovigerous females. During daytime, ovigerous females stayed deeper in the water column than females without ova or immatures. The daytime temperature of water at the median depth of the ovigerous females did not exceed 10 °C, even in the warmest season. At night they migrated upward to an environment which was warmer by as much as 9 °C.Laboratory observations indicate that specimen's size and water temperature determine the velocity of passive sinking, such that morning descent of the different groups of Daphnia can be explained by passive sinking alone.Our hypothesis is that the distribution of different groups of D. hyalina in Lake Bled is influenced by two types of predators: fish (Perca fluviatilis L. and Rutilus rutilus (L.)) and larvae of Chaoborus flavicans (Meig.), the latter appearing in the epilimnion during the night. Fish predation has a key-role at the beginning of thermal stratification. Supposing that in spring the gene pool of Daphnia consists of a mix of different genotypes, distributed at different depths during the day, fish predation combined with a presence of fish chemicals favored genotypes with a lower day-depth during the spring/summer period.     

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.     

Occurrence of Cladocera (Crustacea) in subterranean waters in Yugoslavia

Contrary to some localities in France and Spain, Cladocera occur in hypogean waters in Yugoslavia very sporadically. Beside the stygobitic species, Alona hercegovinae from caves and Alona smirnovi from interstitial waters, particularly some other Chydoridae seem to be suited for hypogean life. Chydorus sphaericus, reputed as one of the most euryoecious cladocerans, occurs also the deepest in interstitial waters as well as in caves. Other species, found in hypogean waters are Simocephalus vetulus, Ilyocryptus sordidus, Eurycercus lamellatus, Chydorus ovalis, Leydigia leydigi, Acroperus harpae and Biapertura affnis.     

Daphnia (Ctenodaphnia) Mediterranea: A new species of hyperhaline waters,long confused with D. (C.) Dolichocephala Sars, 1895.

A very particular form of Daphnia (Ctenodaphnia), adapted to life in epicontinental hyperhaline waters of Mediterranean arid regions had long been confused with Daphnia (Ctenodaphnia) dolichocephala Sars, 1895. In this paper the morphological and ecological differences between the two taxa are pointed out and comparison is made with another closely related Rumanian form (Daphnia cf. mediterranea) and with the related Spanish species (D. atkinsoni and D. chevreuxi). The Daphnia of saline environments is described here as Daphnia (Ctenodaphnia) mediterranea. The most important differential characters of this new species are: 1) the short and widely rounded rostrum; 2) dorsal ridge of the female extends to the anteriormost part of the head; 3) elliptical ephippium with a ride anterior margin; convex shape and separate from the dorsal ridge; 4) males possessing a very long antennule base that reaches the distal limit of the head.     

Effect of previous feeding conditions on survival in Daphnia pulicaria (Crustacea: Cladocera)

Survival of natural Daphnia populations without previous acclimatization in filtered water under laboratory conditions (starvation) was used as a parameter describing the actual competitive ability of populations in periods of food limitation. Two populations (1 and 2) of Daphnia pulicaria Forbes coming from two enclosures with a low (< 1 mgC l^–1) and a high (about 3 mgC l^–1) seston level were examined in their resistance to starvation. Juveniles of both populations survived better than adult females in the conditions without seston as well as in the control experiment, despite their much lower biomass. Animals from population 1 had lower mortality than those from population 2 in all variants of the experiment. The results confirm the hypothesis that the ability of daphnids to starve depends also on adaptation to previous feeding conditions.     

Daphnia (Ctenodaphnia) hispanica sp. nov., a new daphnid (Cladocera) from Spain

Daphnia (C.) hispanica n. sp. has thoracic limbs of A D. (C.) atkinsoni type and is very similar toD. chevreuxi Richard, 1896. With this speciesD. (C.) hispanica shares the presence of a soft accessory seta on the outer side of the trunk of the first thoracic limb, apparently unique among the genusDaphnia. Although other morphological characteristics are very similar in this two species, a detailed comparison reveals that they can easily be separated as different species. The most useful features in differentiating both species are:D. (C.) hispanica has a dorsal crest in the head, its rostrum is longer, its accesory seta of the first thoracic limb is more developed, the juveniles are not helmeted and its male postabdomen lacks individual denticles on the anal and preanal margin.The new species is, up to now, restricted to Spain and inhabits the temporary and low mineralized waters of the steppe regions.     

Significance of head and carapace pores inCeriodaphnia (Crustacea,Cladocera)

Twelve species ofCeriodaphnia were examined by light and scanning electron microscopy for the presence of head and carapace pores. Rostral pores, similar to those in the Scapholeberinae (Dumont & Pensaert, 1983) were found in all species, situated just anterior to or between insertions of the antennules. With two exceptions, the pattern of reticulations around the pores was distinctive for each species. Oval ‘head pores’ or fenestrae occur consistently on the anterior surface of the cervical notch of juvenile and adultC. dubia, cf.dubia (from Australia),lacustris, andreticulata. The patterns of reticulations around a fenestra are unique to each species. It appears thatC. cornuta (s.l.) in the Americas has a fenestra, whereas AustralianC. cornuta (s.s.) has none. Minute pores often occur bilaterally anterior and posterior to the cervical notch in heavily reticulated individuals of several species but are not constant enough to be taxonomically useful. Well-defined small pores are situated within narrow reticulations just medial to the ventral and posterior valve margins ofC. dubia, lacustris, andreticulata. These open into carapace glands of unknown, perhaps secretory, nature. Similar glands have been observed in related taxa. Such glands and marginal pores occur only occasionally or not at all in otherCeriodaphnia. Other small pores sometimes occur among reticulations of the head, fornix, and lateral and antero-ventral surfaces of the valves. They are found more often in juvenile or heavily reticulated individuals. As yet no consistent pattern to their occurrence among species has emerged. Head and carapace pores inCeriodaphnia may be most useful in identifying species rather than in determining species groups or evolutionary patterns within the genus.     

Recycling of food byDaphnia magna Straus (Cladocera): A possible role in swarming

Daphnia magna is a filter feeder able to recycle part of its food. The fraction of the ingestion that consists of recycled food increases with the filtering impact, without leading to a decrease in growth efficiency. Swarming creates locally a high filtering impact and recycling of food might be one of its benefits.     

Development and characterization of eight polymorphic microsatellite markers for Daphnia atkinsoni (Crustacea: Ctenodaphnia)

A microsatellite‐enriched genomic library was developed for the water flea Daphnia atkinsoni Baird, 1859, a dominant species of intermittent wetlands in Europe. Eight polymorphic microsatellite markers were successfully optimized. Characterization of 77 individuals from Belgium and Spain showed moderate (in the former) to high (in the latter) levels of polymorphism with two to 11 alleles per locus and an observed heterozygosity ranging from 0 to 0.87. Some of these microsatellite markers were successfully amplified in three other Daphnia species (D. magna n = 4, D. similis n = 6; D. obtusa n = 6).