scholarly journals Eutrophic status influences the impact of pesticide mixtures and predation on Daphnia pulex populations

2021 ◽  
Author(s):  
Talles Bruno Oliveira dos Anjos ◽  
Francesco Polazzo ◽  
Alba Arenas‐Sánchez ◽  
Laura Cherta ◽  
Roberto Ascari ◽  
...  
Keyword(s):  
Daphnia Pulex ◽  
Pesticide Mixtures ◽  
The Impact

The effect of transposon Pokey insertions on sequence variation in the 28S rRNA gene of Daphnia pulex

Genome ◽  
2008 ◽  
Vol 51 (12) ◽  
pp. 988-1000 ◽  
Author(s):  
Shiona K. Glass ◽  
Anna Moszczynska ◽  
Teresa J. Crease
Keyword(s):  
Sequence Variation ◽  
Insertion Site ◽  
Daphnia Pulex ◽  
Rrna Genes ◽  
Rrna Gene ◽  
28S Rrna ◽  
Intraindividual Variation ◽  
Rdna Array ◽  
The Impact ◽  
Host Genes

The goal of this study was to determine the impact of breeding system and the presence of the transposon Pokey on intraindividual variation in 28S rRNA genes. We PCR-amplified, cloned, and sequenced 1000 nucleotides downstream of the Pokey insertion site in genes with and without insertions from 10 obligately and 10 cyclically parthenogenetic isolates of Daphnia pulex. Variation among genes with Pokey insertions was higher than variation among genes without insertions in both cyclic and obligate isolates. Although the differences were not quite significant (p = 0.06 in both cases), the results suggest that Pokey insertions are likely to inhibit the homogenization of their host genes to some extent. We also observed that the complement of 28S rRNA alleles differed between genes with and without inserts in some isolates, suggesting that a particular inserted gene can persist for substantial periods of time and even spread within the rDNA array, despite the fact that insertions are deleterious. This apparently contradictory pattern can be explained if homogenization of rRNA genes occurs primarily by gene conversion, but copies with Pokey inserts can occasionally increase in frequency within arrays owing to unequal crossing over events that do not originate in the inserted genes themselves.

The impact of two Chaoborus species on a zooplankton community

1990 ◽  
Vol 68 (5) ◽  
pp. 981-985 ◽  
Author(s):  
Neil A. MacKay ◽  
Stephen R. Carpenter ◽  
Patricia A. Soranno ◽  
Michael J. Vanni
Keyword(s):  
Chlorophyll A ◽  
Daphnia Pulex ◽  
Zooplankton Community ◽  
Chlorophyll A Concentration ◽  
Chaoborus Flavicans ◽  
Chaoborus Americanus ◽  
Diaptomus Oregonensis ◽  
Herbivore Responses ◽  
The Impact

The responses of a zooplankton community to Chaoborus predation were studied in large in situ mesocosms in Peter Lake. Chaoborus flavicans, the native chaoborid, significantly reduced the density of the dominant grazer, Daphnia pulex, in relation to controls that lacked Chaoborus. Chaoborus americanus, a species found only in fishless bogs, reduced Da. pulex densities far more than the chaoborid found in Peter Lake, C. flavicans. Chaoborus americanus also significantly reduced the dominant copepod, Diaptomus oregonensis, in relation to both the control and the C. flavicans treatment. Chlorophyll a concentration did not differ among treatments, indicating that herbivore responses could not be explained by changes in food levels. Our results show that Chaoborus predation can greatly affect a zooplankton community, especially daphnids.

scholarly journals Cladocera from the Sediment of High Arctic Lake in Svalbard (Norway)

2021 ◽  
Vol 23 (2) ◽  
pp. 13-20
Author(s):  
Vartika Singh ◽  
Sophia Barinova
Keyword(s):  
Hot Spots ◽  
Surface Sediments ◽  
Daphnia Pulex ◽  
High Arctic ◽  
Freshwater Ecosystems ◽  
Climate Conditions ◽  
Chydorus Sphaericus ◽  
Cladoceran Remains ◽  
The Impact ◽  
Palaeoenvironmental Conditions

Abstract The High Arctic Region’s freshwater ecosystems serve as hot spots to study the impact of extreme warming conditions on the biota. The cladoceran remains have been recovered from the surface sediments of a non-marine water body near Ny-Alesund, Svalbard, Norway. The cladoceran (crustaceans) belongs to the Chydorus sphaericus group Frey, 1980 and Daphnia pulex Leydig, 1860. The ecology of the species suggests that they lived in a well-developed ecosystem with Water Quality Class 3. This study has implications for understanding the response of the present-day biota experiencing the changing climate conditions and using these remains for assessing palaeoenvironmental conditions.

scholarly journals Pesticide Mixtures, Endocrine Disruption, and Amphibian Declines: Are We Underestimating the Impact?

2006 ◽  
Vol 114 (Suppl 1) ◽  
pp. 40-50 ◽  
Author(s):  
Tyrone B. Hayes ◽  
Paola Case ◽  
Sarah Chui ◽  
Duc Chung ◽  
Cathryn Haeffele ◽  
...  
Keyword(s):  
Endocrine Disruption ◽  
Amphibian Declines ◽  
Pesticide Mixtures ◽  
The Impact

Vertical distributions and zooplankton predation in a small temperate pond

1981 ◽  
Vol 59 (9) ◽  
pp. 1720-1725 ◽  
Author(s):  
Guy E. Melville ◽  
Edward J. Maly
Keyword(s):  
Daphnia Pulex ◽  
Predation Rate ◽  
Invertebrate Predation ◽  
Chaoborus Americanus ◽  
Vertical Distributions ◽  
Zooplankton Communities ◽  
The Impact ◽  
Predation Rates

Depth-specific sampling in a small Quebec pond between April and October 1977 revealed that instars of Daphnia pulex less than 1.41 mm in length and instars of Diaptomus leptopus greater than 0.64 mm in length consistently had vertical distributions which were different from those of late instars of their predator Chaoborus americanus. Experiments were done to determine to what extent these distributions affected the rate of predation by Chaoborus. Vertical and horizontal 25-L enclosures, 1.4 m long, and 2.5-L enclosures, all containing Chaoborus–prey pairs, were introduced into a pond for 3-day periods weekly from July to September. Predation rates in vertical enclosures were considerably lower than those in small and horizontal enclosures. These results suggest that distributions of Diaptomus and Daphnia in vertical enclosures significantly reduce predation on them by Chaoborus. In horizontal and small enclosures where overlap of predator and prey was increased, predation rate of Chaoborus was higher. Results are discussed in relation to the impact of invertebrate predation on zooplankton and the structure of zooplankton communities.

Formation of Lunar Craters and Bright Rays as a Result of Meteorite Impacts

1962 ◽  
Vol 14 ◽  
pp. 415-418
Author(s):  
K. P. Stanyukovich ◽  
V. A. Bronshten
Keyword(s):  
Explosive Charge ◽  
The Moon ◽  
Meteorite Impacts ◽  
The Earth ◽  
Lunar Craters ◽  
The Impact

The phenomena accompanying the impact of large meteorites on the surface of the Moon or of the Earth can be examined on the basis of the theory of explosive phenomena if we assume that, instead of an exploding meteorite moving inside the rock, we have an explosive charge (equivalent in energy), situated at a certain distance under the surface.

The Geosciences Applied to Lunar Exploration

1962 ◽  
Vol 14 ◽  
pp. 169-257 ◽  
Author(s):  
J. Green
Keyword(s):  
Lunar Surface ◽  
Probable Mechanism ◽  
Point Of View ◽  
Lunar Exploration ◽  
Geological Model ◽  
Apply Geophysics ◽  
Surface Features ◽  
The Impact

The term geo-sciences has been used here to include the disciplines geology, geophysics and geochemistry. However, in order to apply geophysics and geochemistry effectively one must begin with a geological model. Therefore, the science of geology should be used as the basis for lunar exploration. From an astronomical point of view, a lunar terrain heavily impacted with meteors appears the more reasonable; although from a geological standpoint, volcanism seems the more probable mechanism. A surface liberally marked with volcanic features has been advocated by such geologists as Bülow, Dana, Suess, von Wolff, Shaler, Spurr, and Kuno. In this paper, both the impact and volcanic hypotheses are considered in the application of the geo-sciences to manned lunar exploration. However, more emphasis is placed on the volcanic, or more correctly the defluidization, hypothesis to account for lunar surface features.

Asteroid and Comet Impact Speeds upon Mars: Significance for Panspermia and the Supply of Organics

1997 ◽  
Vol 161 ◽  
pp. 197-201 ◽  
Author(s):  
Duncan Steel
Keyword(s):  
Probability Distributions ◽  
Regions Of Interest ◽  
Significant Fraction ◽  
Organic Chemicals ◽  
Impact Speed ◽  
The Mean ◽  
The Impact

AbstractWhilst lithopanspermia depends upon massive impacts occurring at a speed above some limit, the intact delivery of organic chemicals or other volatiles to a planet requires the impact speed to be below some other limit such that a significant fraction of that material escapes destruction. Thus the two opposite ends of the impact speed distributions are the regions of interest in the bioastronomical context, whereas much modelling work on impacts delivers, or makes use of, only the mean speed. Here the probability distributions of impact speeds upon Mars are calculated for (i) the orbital distribution of known asteroids; and (ii) the expected distribution of near-parabolic cometary orbits. It is found that cometary impacts are far more likely to eject rocks from Mars (over 99 percent of the cometary impacts are at speeds above 20 km/sec, but at most 5 percent of the asteroidal impacts); paradoxically, the objects impacting at speeds low enough to make organic/volatile survival possible (the asteroids) are those which are depleted in such species.

Organic Syntheses During the Impact of a Comet with a Gaseous Planet

1997 ◽  
Vol 161 ◽  
pp. 189-195
Author(s):  
Cesare Guaita ◽  
Roberto Crippa ◽  
Federico Manzini
Keyword(s):  
Polymeric Material ◽  
Molecular Form ◽  
Parent Compound ◽  
Blue Filter ◽  
Organic Syntheses ◽  
The Impact

AbstractA large amount of CO has been detected above many SL9/Jupiter impacts. This gas was never detected before the collision. So, in our opinion, CO was released from a parent compound during the collision. We identify this compound as POM (polyoxymethylene), a formaldehyde (HCHO) polymer that, when suddenly heated, reformes monomeric HCHO. At temperatures higher than 1200°K HCHO cannot exist in molecular form and the most probable result of its decomposition is the formation of CO. At lower temperatures, HCHO can react with NH3 and/or HCN to form high UV-absorbing polymeric material. In our opinion, this kind of material has also to be taken in to account to explain the complex evolution of some SL9 impacts that we observed in CCD images taken with a blue filter.

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