Histochemical studies on the hyaline capsule of Holopedium gibberum Zaddach (Crustacea,Cladocera)

Summary The jelly capsule of the water flea Holopedium gibberum, was subjected to histochemical procedures for the visualization of acid mucopolysaccharides, amino acids, and proteins. The affinity of the capsule for azure A, alcian blue, colloidal iron, aldehyde fuchsin, and iron diamine reagents, at low pH, indicates the presence of a sulfated mucopolysaccharide. The presence of carboxyl groups, in addition, is indicated by alcian blue affinity in the combined aldehyde fuchsin-alcian blue and high-iron diamine-alcian blue procedures, as well as by the restoration of weak, but definite, basophilia after methylation-saponification pretreatment. The capsule remained alcianophilic in solutions of MgCl₂ as high as 0.4 molar. Cetylpyridinium blockade was removed by KCl solutions of 0.5–1.0 molar. The periodic acid-Schiff reaction was nil to very weak, in spite of extended oxidizing periods. None of the methods used for the visualization of amino acids or proteins gave unequivocally positive results. A possible origin of the capsular material is proposed.     

Allozyme variation among natural populations of Holopedium gibberum (Crustacea; Cladocera)

• 1 Holopedium gibberum, from twenty lakes in Rhode Island and Maine, were examined for allozyme variation at five loci to determine the pattern and degree of generic variation among sites and the genetic structure within individual lakes.
• 2 There were significant differences in allele frequencies among sites. Most populations were fixed for a particular allele at each locus. Only five lakes had polymorphic populations.
• 3 Polymorphic populations showed significant deviation from expected Hardy-Weinberg genotype frequencies. In each case, there was an excess of homozygotes.
• 4 Two lakes were examined for intra-lake allele frequency differences. In one lake there were no differences. The other lake exhibited significant allele frequency differences between stations at the north and south ends of the lake.
• 5 Populations were examined for the frequency distribution of composite genotypes over three loci. Most populations were dominated by one or two genotypes.
• 6 The results suggest sporadic sexual recruitment and a high degree of genetic isolation among these populations of H. gibberum. In these respects they resemble the permanent pond populations of Daphnia magna examined by Hebert (1974a).

     

Prevalence and inferred effects of microsporidia of Holopedium gibberum (Crustacea:Cladocera) in a Canadian Shield lake

Two species of microsporidial parasites are reported from Holopediungibberum in a small Canadian Shield lake. Seasonal changes inprevalence of the parasites were not attributable to changesin water temperature or to changes in size distribution of hostsover the season. Seasonal changes in resistance of hosts toparasitism, related to food stress may account for the patternin prevalence but it was more likely a consequence of host andparasite population dynamics and interplay. An examination ofH.gibberum fecundity and size structure indicated that microsporidiosisreduced birth rates and may have decreased survival of Holopedium.     

Coherence and horizontal movements of pathces of Holopedium gibberum (Cladocera)

The horizontal spatial dynamics of Holopedium gibberum in a small lake was followed during two summers. H. gibberum individuals aggregated into a single patch measured in tens of meters. Patch movement was extensive throughout the limnetic region, bore no apparent relationship to wind action, and patch structure remained cohesive regardless of weather conditions. Grazing activity by H. gibberum within the patch was intensive, reducing phytoplankton density to half that outside the patch.     

The taxonomic position of Asian Holopedium (Crustacea: Cladocera) confirmed by morphological and genetic analyses

Limnology - The cladoceran Holopedium gibberum Zaddach, 1855 (Ctenopoda: Holopediidae) was once thought to occur broadly in the northern hemisphere, but its cryptic sister species was recently...     

Life history variation within a parthenogenetic population of Daphnia parvula (Crustacea: Cladocera)

Summary Evidence for genetically determined life history variability within a population or a species is rare. In this three year experimental examination of a parthenogenetically reproducing population of the planktonic crustacean Daphnia parvula, we found evidence for a succession of clones or groups of clones that exhibited distinctive body size and reproductive differences that were maintained after numerous generations under standardized conditions in the laboratory. The D. parvula population reached maximum density in the fall and maintained relatively high densities through the winter and spring. Isolates from this fall-winter-spring period all had a larger body size at death and higher fecundity when compared with summer isolates under natural food and temperature conditions. These differences could not be accounted for by differences in temperature and food abundance among the seasons. An additional difference in these experiments was a shift in reproductive effort by the summer isolate which produced a higher proportion of its offspring in the first two broods. The shift in life history characteristics and a summer decline of the Daphnia parvula population was correlated with both an increase in inedible and perhaps toxic blue-green algae and an increase in a dipteran predator Chaoborus. Comparison of the survivorship curves for all of the seasonal life history experiments indicated that D. parvula survivorship was not lower during the summer discounting a toxic effect from blue-green algae. Positive population growth on natural food in the laboratory at this time indicated food was not limiting and that predation was the probable cause of the population decline.Laboratory life history experiments under standardized food and temperature conditions were run with D. parvula isolates from the spring and summer plankton. Genetically based differences as determined in these experiments were smaller body size, lower fecundity, smaller brood size, and shorter life span for the summer animals relative to spring animals. Thirty seven percent of the summer animals also reproduced at an earlier age under standardized conditions. The shift in reproductive effort to earlier broods by summer animals rnder natural conditions appeared to be a phenotypic response as the summer isolate did not produce a higher proportion of its offspring in early broods under standardized conditions.When estimates of predatory mortality were added to the life tables of the standardized experiments, the earlier reproduction of some of the summer animals allowed a population increase under a regime of intense predation. Life tables for the spring animals predicted a population decline under these circumstances. Predictable seasonal changes in biotic factors such as predation suggest a mechanism whereby diverse life history patterns with corresponding differences in r may be maintained within a population.     

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.     

Life history evolution and genome size in subtribe Oncidiinae (Orchidaceae)

• Background and Aims Within Oncidiinae, there are severalgroups of species that are effectively annuals, and we wishedto see if these species had smaller genome sizes than averagefor the subtribe. • Methods Fifty-four genome size estimates (50 of whichare new) for species in subtribe Oncidiinae (Orchidaceae) wereexamined for the first time in a phylogenetic context to evaluatehypotheses concerning genome sizes and life history traits. • Results and Conclusions Within the limits of still relativelysparse sampling, the species that are effectively annuals doappear to have smaller genome sizes than average. However, thegenome sizes of their immediate sister group are also small,indicating that changes in genome size preceded the change inlife history traits. Genome sizes and chromosome numbers alsodo not correlate; some slowly growing species have lower chromosomenumbers but large genomes and vice versa. Based on a surveyof the literature on orchids, it is also clear that epiphyticspecies have smaller genome sizes than do terrestrial species,which could be an effect of different water relations or thefact that most terrestrial orchids are geophytic or have distinctgrowth and dormancy phases.     

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.     

Life histories of some species of Chydoridae (Cladocera: Crustacea)

SUMMARY 1. Life history parameters of two species of Chydoridae ( Leydigia leydigi and Disparalona rostrata ) were studied in the field and in the laboratory.
2. For both species the number of juvenile instars was variable and tentatively related to initial size of neonate. Egg volume increased with increasing parent length and with decreasing temperature; possible advantages gained by the offspring are discussed in relation to invertebrate predation.
3. The life history strategy employed by the littoral Chydoridae is compared to that of large and small planktonic cladocerans. Small planktonic cladocerans and the Chydoridae (except the Eurycercinae and the Saycinae) produce large young relative to their size at maturity and mature early. However, unlike the small planktonic cladocerans, growth in the Chydoridae is curtailed after the onset of reproduction and in this they resemble the large planktonic cladocerans. This strategy may be related to vertebrate predation and the presence of vegetation in the habitat.     

Der Ankerapparat vonSida crystallina (Crustacea,Cladocera)

Zusammenfassung Die in eine Grundsubstanz eingebetteten Klebanker und Ankerfäden, mit deren Hilfe sichSida crystallina am Substrat befestigt, liegen auf der Epicuticula. Die Fäden sind mit der Epicuticula über Trennvorrichtungen verbunden. Die Sekretion der Ankerstrukturen durch die Epidermiszellen erfolgt zunächst in oberflächenparallelen Schichten. Später wird das Sekretionsfeld mit den Fadenenden nach hinten verschoben. Es folgt die Bildung der Trennstellen und schließlich die Sekretion der Cuticula. Nach der Häutung klappt die Ankerleiste in ihre funktionelle Stellung und die Procuticula skierotisiert.

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The anchor apparatus ofSida crystallina (Crustacea, Cladocera)II. Ultrastructure and formation

Summary Sida crystallina attaches itself to the substratum by adhesive anchors. Anchors and anchor threads are embedded in a matrix and situated on the epicuticle. The anchor threads are connected to the epicuticle by special junctions at which they can be separated. The new structures of the anchor organs, which are secreted by epidermal cells, are firstly laid down in layers parallel to the surface. Later the area of secretion becomes shifted backward. Then the junctions are formed and finely the secretion of the cuticle follows. After molting the anchor ledge turns out in its functional position and sclerotisation of the procuticle takes place.

     

Competition and Population Time Lags in Bosmina (Cladocera,Crustacea)

The competition between Bosmina coregoni and B. longirostris was studied by culturing of mixed and isolated populations in lake water. While interaction was detectable between the two species, they were capable of coexisting for at least 124 days. The pattern of predominance was found to depend on initial frequencies. The ratio of B. coregoni to B. longirostris in the pelagic zone of a mesotrophic lake could be explained on the basis of competition between either species. Birth, death, and population growth rates proved to be delayed functions of stock density, as was borne out by cross-correlation analysis of experimental population dynamics. Time lag estimates for all three rates varied for different phases of population oscillation. For accurate assessment of time lags, the phases of monotonous changes in density should have been separated from one another. The time lag estimated for the rate of population growth in mixed cultures was significantly higher for the superior competitor (B. coregoni). This estimate may well be predicted as an arithmetic mean value cf time lag estimates for birth and death rates. The duration of population growth (or decline) was correlated to the time lag of the death rate, whereas the amplitude was not correlated to any time lag at all.     

Redescription of Scapholeberis echinulata Sars 1903 (Crustacea,Cladocera)

Scapholeberis echinulata Sars is rediscribed, based on type material of Sars (S. echinulata), Daday (s. erinaceus) and the author's own samples. A differential diagnosis with Scapholeberis spinifera Nicolet and S. mucronata O. F. Müller, S. microcephala Sars, S. kingi Sars and S. aurita Fischer is given.     

Redescription of Diaphanosoma celebensis Stingelin, 1900 (Crustacea,Cladocera)

A rare species, Diaphanosoma celebensis (Stingelin, 1900) is redescribed from type material and material from the South of Vietnam. In comparative morphological aspect it is close to D. volzi, but it is relatively less specialized. D. celebensis is known from single locations in Indonesia, Sri Lanka, Vietnam. It probably also occurs in Malaysia. The size frequency and sex structure of a population from Vietnam is described.     

Revision of the Genus BosminaBAIRD, 1845 (Crustacea,Cladocera)

The genus Bosmina can be differentiated into four subgenera: 1. Bosmina s. str. BAIRD , 1845, 2. Eubosmina SELIGO , 1900, 3. Neobosmina LIEDER , 1957, and 4. Sinobosmina LIEDER , 1957. Subgeneric discrimination is based upon several features of the females (postabdominal claw, serration of the mucro, patterns of the lateral head pores) and, mainly, upon certain differences in the morphology of the male (postabdomen and, according to LILLJEBORG 1900, BURCKHARDT 1924 and KOŘINEK 1971, the first leg). The distribution of the Bosmina subgenera throughout the world varies: Bosmina s. str. is distributed worldwide (except for Australia?), Eubosmina is holarctic, Neobosmina has been found in Africa, the neotropical zone, Australia and Oceania, and Sinobosmina occurs in East and South-East Asia.     

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.     

First record of fossil Mesozoic Ctenopoda (Crustacea, Cladocera)

Pre-Pleistocene representatives of the crustacean order Ctenopoda Sars, 1865 are unknown. Here we describe Mesozoic fossil specimens of ctenopods from two localities in Mongolia: Khotont (Jurassic/Cretaceous boundary, about 145 Mya) and Khutel Khara (Lower Cretaceous, about 129 Mya). All specimens apparently belonged to the tribe Latonini Korovchinsky, 1986 of the subfamily Sidinae Baird, 1850. At the Khotont site, ctenopods were the most numerous microscopic animal fossils. We assigned these cladocerans to a new genus and species Archelatona zherikhini gen. nov., sp. nov. Our findings support a pre-Cretaceous origin for cladocerans.  © 2006 The Linnean Society of London, Zoological Journal of the Linnean Society , 2006, 146 , 269–274.     

Gene Conversion and Evolution of Daphniid Hemoglobins (Crustacea, Cladocera)

The extracellular hemoglobins of cladocerans derive from the aggregation of 12 two-domain globin subunits that are apparently encoded by four genes. This study establishes that at least some of these genes occur as a tandem array in both Daphnia magna and Daphnia exilis. The genes share a uniform structure; a bridge intron separates two globin domains which each include three exons and two introns. Introns are small, averaging just 77 bp, but a longer sequence (2.2–3.2 kb) separates adjacent globin genes. A survey of structural diversity in globin genes from other daphniids revealed three independent cases of intron loss, but exon lengths were identical, excepting a 3-bp insertion in exon 5 of Simocephalus. Heterogeneity in the extent of nucleotide divergence was marked among exons, largely as a result of the pronounced diversification of the terminal exon. This variation reflected, in part, varying exposure to concerted evolution. Conversion events were frequent in exons 1–4 but were absent from exons 5 and 6. Because of this difference, the results of phylogenetic analyses were strongly affected by the sequences employed in this construction. Phylogenies based on total nucleotide divergence in exons 1–4 revealed affinities among all genes isolated from a single species, reflecting the impact of gene conversion events. In contrast, phylogenies based on total nucleotide divergence in exons 5 and 6 revealed affinities among orthologous genes from different taxa. Received: 8 March 1999 / Accepted: 14 July 1999