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  • 1
    Electronic Resource
    Electronic Resource
    The role of density in sex determination in Daphnia magna (Crustacea, Cladocera) (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 23 (1990), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY. 1. Cladocerans are generally believed to exhibit environmental sex determination; however, the evidence for this assertion is equivocal. Particularly, no studies have been performed which isolate potential effects of the environment on the sex of offspring (and hence sex ratio) from effects on the induction of sex (with the necessary appearance of males). We report the findings of a study of Daphnia magna Straus which is able to make this distinction.2. We examined the sexes of broods produced by asexually reproducing females collected from high and low densities of D. magna in naturally occurring populations. We looked for an effect of density, a factor frequently implicated in male induction, on offspring sex.3. We could find no effect of density on brood sex. Our results may indicate a true absence of interaction or may arise from our sampling procedure obscuring an interaction. More detailed field observations are suggested as a means of further examining the role of density in sex determination in Cladocera.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2427.1990.tb00279.x
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  • 2
    Electronic Resource
    Electronic Resource
    Methods for the activation of the resting eggs of Daphnia (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 17 (1987), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY. 1. The conditions required to initiate development of resting eggs of thirty-six clones of Daphnia representing seven species were investigated.2. The temperature of both dark incubation and subsequent light treatment are shown to affect hatch success. By varying these parameters the majority of resting eggs from each test clone were stimulated to develop. Arctic clones required a low hatching temperature (7°C), whereas clones from warmer climates hatched best at 14–21°C.3. Variation in hatching cues existed between conspecific individuals from different collection sites. These differences suggest that research determining macro- and microgeographic patterns in hatching phenology would be fruitful.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2427.1987.tb01057.x
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  • 3
    Electronic Resource
    Electronic Resource
    The adaptive significance of cyclomorphosis in Daphnia: more possibilities (1978)
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 8 (1978), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY. Morphological variability in Daphnia populations has often been uncritically ascribed to phenotypic plasticity. For instance, detailed study revealed that the ‘cyclomorphic species’D. carinata s. l. was a complex of nine species. Several of these species often cohabit and seasonal change in their relative frequencies causes phenotypic cycles which mimic true cyclomorphosis. Intraspecific genetic variation in head shape also seems widespread and is likely to be important in explaining phenotypic changes in many single species populations.The hypothesis that helmet formation in Daphnia is primarily related to predator avoidance is not supported by work on the D. carinata group. Seasonal trends in species composition can be explained without reference to differential predation. Natality differences exist between species with disparate head size suggesting that helmet formation may have direct effects on fitness. Two possibilities are considered. The length of the anterior adductor muscle is directly correlated with helmet size and such variation may affect swimming efficiency. In addition the laminar design of helmets suggests a role in gas exchange.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2427.1978.tb01452.x
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  • 4
    Electronic Resource
    Electronic Resource
    Cyclomorphosis in natural populations of Daphnia cephalata King (1978)
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 8 (1978), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY. Daphnia cephalata King is a major component of the zooplankton in freshwater ponds of eastern Australia. Phenotypic variation in head shape both within and between populations is striking. Some of this variation is ontogenetic, but among individuals of similar size head length still varies by a factor of two. The causes of this variation have been investigated by analysing head size in thirty-four populations of D. cephalata over a 17-month period. An annual cycle in crest size, apparently related to seasonal changes in mean temperature, was evident when the data were pooled. Large differences in head size were commonly observed, however, among samples collected simultaneously. Some of this variation was correlated with local differences in resource availability, which were due, in part, to local variation in Daphnia density. Other consistent interpopulation differences in head size were related to stable environmental differences among sites and probably also to genetic differences among populations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2427.1978.tb01429.x
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  • 5
    Electronic Resource
    Electronic Resource
    A test for the production of sexual pheromones by Daphnia magna (Crustacea: Cladocera) (1983)
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 13 (1983), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY. (1) Swarming in the Cladocera has often been associated with periods of sexual reproduction and this has led to the suggestion that members of opposite sex are attracted to one another. The most plausible mechanism by which this could occur is through the production of pheromones. The present experiments aimed to determine if Daphnia magna Straus produce such chemicals.(2) No evidence was found for the presence of sexual pheromones. The behaviour of both males and females was unaffected by the presence of sexually receptive animals of the opposite sex.(3) It is suggested that the cited relationship between sexual reproduction and swarming may be due to the fact that sexual reproduction occurs during periods of high population density. It is during such periods that swarming behaviour would be most apparent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2427.1983.tb00007.x
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  • 6
    Electronic Resource
    Electronic Resource
    Ecological differences among clones of Daphnia pulex Leydig (1981)
    Springer
    Oecologia 51 (1981), S. 162-168 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Natural populations of Daphnia pulex that reproduce by obligate parthenogenesis include a number of clones. Studies on two common and two rare clones from southwestern Ontario revealed significant differences in their intrinsic rates of increase, competitive abilities, rates of ephippial egg production, and lifespans. Environmental factors such as temperature and food type had large inluences on the rate of increase of each clone. Differences in rates of increase among clones were most pronounced at temperatures higher than those encountered in nature. In general, the covariance of life history traits among clones was high. The outcome of competitive encounters between clones was deterministic and in most cases was unaffected by temperature. Clones with high rates of increase tended to be better competitors than those with low rates of increase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00540595
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  • 7
    Electronic Resource
    Electronic Resource
    Prey preference and utilization by Mesostoma lingua (Turbellaria, Rhabdocoela) at a low arctic site (1986)
    Springer
    Hydrobiologia 135 (1986), S. 251-257 
    Details
    ISSN: 1573-5117
    Keywords: Mesostoma lingua ; rhabdocoel ; arctic ; zooplankton ; predation ; prey preference
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The rhabdocoel Mesostoma lingua is a common inhabitant of rock bluff ponds in the area of Churchill, Manitoba. Unlike most flatworms it has the ability to prey actively on zooplankton. Among the zooplankton, Mesostoma prefers Daphnia pulex, Simocephalus vetulus, and Diaptomus tyrrelli. Larger calanoid copepods are difficult to capture and take much longer to consume. Growth in Mesostoma is maintained when individuals consume 0.5 Daphnia day−1 and is maximal at 4 Daphnia day−1. In comparison, Mesostoma maintained growth only when offered the copepod Diaptomus victoriaensis at the rate of 8–10 individuals-day−1. Mesostoma may be an important agent in structuring pond zooplankton communities in the arctic, producing a shift in dominance away from cladocerans such as Daphnia toward larger calanoid copepods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00006537
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  • 8
    Electronic Resource
    Electronic Resource
    Shifts in postembryonic somatic ploidy levels in Daphnia pulex (1999)
    Springer
    Hydrobiologia 394 (1999), S. 29-39 
    Details
    ISSN: 1573-5117
    Keywords: endopolyploidy ; development ; ontogeny ; endomitosis ; ploidy ; modulation ; Cladocera
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Although the presence of polyploid cells in somatic tissues of the cladoceran Daphnia has been reported, the nature of ploidy level shifts through life has not been investigated. This study examined the effects of growth and age on ploidy level variation across 10 instars in Daphnia pulex. The transition from mitotic to endomitotic cycles occurred during embryogenesis in all tissues, but the timing of it appeared to be tissue-specific. Lower than expected DNA estimates for the 4C and 8C ploidy classes suggested an underreplication of the genome during the first two endomitotic cycles, while complete replication seemed to occur in subsequent cycles. Polyploid cells underwent from four to seven endomitotic cycles over the 13 postembryonic instars, with ploidy levels reaching a maximum of 2048C in the labrum. The number of polyploid cells in all tissues, except the digestive tract, remained uniform beyond the fourth instar. Three patterns of ploidy level increments were observed i n the various tissues. Polyploid cells in the epipodite and rostrum exhibited age-related shifts, reaching asymptotic levels, while those in the digestive tract similarly reached asymptotic levels but then re-entered the mitotic cycle to enable tissue growth. Finally, ploidy level shifts in both the labrum and the epidermis were affected by age and food levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003567012950
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  • 9
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    Complementary molecular information changes our perception of food web structure (2014)
    National Academy of Sciences
    Details
    Publication Date: 2014-01-21
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 10
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    Nuclear genomes distinguish cryptic species suggested by their DNA barcodes and ecology (2017)
    National Academy of Sciences
    Details
    Publication Date: 2017-07-17
    Description: DNA sequencing brings another dimension to exploration of biodiversity, and large-scale mitochondrial DNA cytochrome oxidase I barcoding has exposed many potential new cryptic species. Here, we add complete nuclear genome sequencing to DNA barcoding, ecological distribution, natural history, and subtleties of adult color pattern and size to show that a widespread neotropical skipper butterfly known as Udranomia kikkawai (Weeks) comprises three different species in Costa Rica. Full-length barcodes obtained from all three century-old Venezuelan syntypes of U. kikkawai show that it is a rainforest species occurring from Costa Rica to Brazil. The two new species are Udranomia sallydaleyae Burns, a dry forest denizen occurring from Costa Rica to Mexico, and Udranomia tomdaleyi Burns, which occupies the junction between the rainforest and dry forest and currently is known only from Costa Rica. Whereas the three species are cryptic, differing but slightly in appearance, their complete nuclear genomes totaling 15 million aligned positions reveal significant differences consistent with their 0.00065-Mbp (million base pair) mitochondrial barcodes and their ecological diversification. DNA barcoding of tropical insects reared by a massive inventory suggests that the presence of cryptic species is a widespread phenomenon and that further studies will substantially increase current estimates of insect species richness.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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