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Diapausing Eggs (diapausing + egg)
Selected AbstractsTransgenerational plasticity for sexual reproduction and diapause in the life cycle of monogonont rotifers: intraclonal, intraspecific and interspecific variation in the response to crowdingFUNCTIONAL ECOLOGY, Issue 3 2004T. SCHRÖDER Summary 1In monogonont rotifers parthenogenetic reproduction allows population growth, and mictic (sexual) reproduction leads to the production of diapausing eggs. When amictic females are exposed to a mixis stimulus, they produce mictic daughters, whose eggs develop into males or, if fertilized, into diapausing eggs. Experiments showed that mictic offspring production is initiated by crowding in females of Brachionus angularis Gosse 1851, Epiphanes senta (O.F. Müller 1773) and Rhinoglena frontalis Ehrenberg 1853, just as it is in Brachionus calyciflorus Pallas 1766 and B. plicatilis Müller 1786. 2In B. calyciflorus, B. angularis, E. senta and R. frontalis, the propensity of amictic females to respond to crowding by producing mictic female offspring is low in the stem female hatching from a diapausing egg, but then increases after some generations. In many cases, only few mictic offspring are produced by crowded females of the second to the fifth generation, but the maximal response occurs only in later generations. Delayed sexual reproduction in early generations from the resting egg may be advantageous, because it first favours rapid population growth and later on maximizes resting egg production. However, it may be disadvantageous, if unpredictable environmental variation causes a population decline when sexual reproduction is still suppressed. 3The extent to which sexual reproduction is delayed varies among and within species. When strains from populations in temporary and permanent habitats were compared, sexual reproduction was significantly delayed in strains from temporary habitats in all species, whereas in B. calyciflorus and R. frontalis mixis was not significantly delayed in strains from permanent habitats. In E. senta mixis was significantly delayed in clones from both habitat types. 4Within all strains there was significant variation among clones in the propensity to produce mictic offspring, the extent to which sexual reproduction was delayed in the first generations after the stem female hatched, or both. [source] To sink or float: the fate of dormant offspring is determined by maternal behaviour in DaphniaFRESHWATER BIOLOGY, Issue 3 2008LUSARCZYK, MIROS Summary 1As the ephippia (chitinous shells enclosing diapausing eggs) of pelagic crustaceans of the genus Daphnia have been occasionally reported to float at the water surface, we considered that this might be an adaptation promoting their passive dispersal. We investigated the mechanisms by which ephippia appear at the water surface. 2While field surveys revealed that floating Daphnia ephippia are often numerous in various freshwater habitats, laboratory tests showed that newly formed ephippia are not buoyant initially. Once transferred to the surface by whatever means, however, they may remain there due either to surface tension or gas absorption. 3Video recordings showed that all ephippia at the water surface in laboratory vessels were shed there by ephippial females when moulting (despite the attendant risk of exposure to UV radiation). This implies that the moulting behaviour of female Daphnia may determine the fate of their dormant offspring, predetermining whether they remain in the natal environment (when the ephippium is released into the water column) or disperse (when it is deposited at the water surface). 4Our findings reveal a potential mechanism underlying the high dispersal capacity of freshwater cladocerans inhabiting island-like aquatic habitats. [source] Two hundred years of a diverse Daphnia community in Lake Naivasha (Kenya): effects of natural and human-induced environmental changesFRESHWATER BIOLOGY, Issue 8 2004Joachim Mergeay Summary 1. We used fossil diapausing eggs extracted from 210Pb-dated sediment cores to reconstruct historical changes in the Daphnia community of Lake Naivasha, a climate-sensitive lake in Kenya which over the past 200 years has experienced a series of well-documented natural and anthropogenic environmental changes. 2. Contiguous sampling and analysis of four cores yielded ephippial capsules of eight Daphnia species. Only two of these had been recorded previously in live collections from Lake Naivasha, and one species is new to science. The four more common species (Daphnia barbata, D. laevis, D. magna, and D. pulex) show striking differences in abundance patterns and population dynamics through time. Four other species (D. lumholtzi, D. curvirostris, D. longispina s.l., and Daphnia sp. nov. type Limuru.) appear to have been present only occasionally. Nevertheless, between 1895 and 1915 seven species of Daphnia inhabited Lake Naivasha simultaneously. 3. Despite considerable natural environmental change associated with climate-driven lake-level fluctuations, the Daphnia community of Lake Naivasha has been severely affected by human activities over the past century, especially the introduction of exotic fishes and water-quality changes because of agricultural soil erosion. The recent reappearance of large-bodied Daphnia species (D. magna, D. barbata, D. lumholtzi, Daphnia sp. nov. type Limuru) after 20,110 years of absence can be explained by their release from fish predation, following a dramatic increase in turbidity caused by excess clastic sediment input from eroded catchment soils. The small-bodied species D. laevis has fared less well recently, presumably because the benefit of lowered predation pressure is counteracted by more pronounced negative effects of increased turbidity on this species and loss of submerged macrophyte beds which formerly served as predation refuge. 4. Our results suggest that, despite considerable environmental instability and the absence of specialised zooplanktivores, top-down control of fish on large zooplankton is important in Lake Naivasha. Predation pressure from fish has led to clear-cut shifts in local Daphnia species composition, but failed to drive the larger taxa to extinction. [source] Transgenerational plasticity for sexual reproduction and diapause in the life cycle of monogonont rotifers: intraclonal, intraspecific and interspecific variation in the response to crowdingFUNCTIONAL ECOLOGY, Issue 3 2004T. SCHRÖDER Summary 1In monogonont rotifers parthenogenetic reproduction allows population growth, and mictic (sexual) reproduction leads to the production of diapausing eggs. When amictic females are exposed to a mixis stimulus, they produce mictic daughters, whose eggs develop into males or, if fertilized, into diapausing eggs. Experiments showed that mictic offspring production is initiated by crowding in females of Brachionus angularis Gosse 1851, Epiphanes senta (O.F. Müller 1773) and Rhinoglena frontalis Ehrenberg 1853, just as it is in Brachionus calyciflorus Pallas 1766 and B. plicatilis Müller 1786. 2In B. calyciflorus, B. angularis, E. senta and R. frontalis, the propensity of amictic females to respond to crowding by producing mictic female offspring is low in the stem female hatching from a diapausing egg, but then increases after some generations. In many cases, only few mictic offspring are produced by crowded females of the second to the fifth generation, but the maximal response occurs only in later generations. Delayed sexual reproduction in early generations from the resting egg may be advantageous, because it first favours rapid population growth and later on maximizes resting egg production. However, it may be disadvantageous, if unpredictable environmental variation causes a population decline when sexual reproduction is still suppressed. 3The extent to which sexual reproduction is delayed varies among and within species. When strains from populations in temporary and permanent habitats were compared, sexual reproduction was significantly delayed in strains from temporary habitats in all species, whereas in B. calyciflorus and R. frontalis mixis was not significantly delayed in strains from permanent habitats. In E. senta mixis was significantly delayed in clones from both habitat types. 4Within all strains there was significant variation among clones in the propensity to produce mictic offspring, the extent to which sexual reproduction was delayed in the first generations after the stem female hatched, or both. [source] Selection of low investment in sex in a cyclically parthenogenetic rotiferJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 10 2009M. J. CARMONA Abstract Cyclical parthenogens, which combine asexual and sexual reproduction, are good models for research into the ecological and population processes affecting the evolutionary maintenance of sex. Sex in cyclically parthenogenetic rotifers is necessary for diapausing egg production, which is essential to survive adverse conditions between planktonic growing seasons. However, within a planktonic season sexual reproduction prevents clonal proliferation. Hence, clones with a low propensity for sex should be selected, becoming dominant in the population as the growing season progresses. In this context, we studied the dynamics of the heritable variation in propensity for sexual reproduction among clones of a Brachionus plicatilis rotifer population in a temporary Mediterranean pond during the period the species occurred in plankton. Clonal isolates displayed high heritable variation in their propensity for sex. Moreover, the frequency of clones with low propensity for sex increased during the growing season, which supports the hypothesized short-term selection for low investment in sex within a growing season. These results demonstrate (1) the inherent instability of the cyclical parthenogenetic life cycle, (2) the cost of sexual reproduction in cyclical parthenogens where sex produces diapausing eggs and (3) the role of the association between sexual reproduction and diapause in maintaining sex in these cyclical parthenogens. [source] New microsatellite primers for Daphnia galeata mendotaeMOLECULAR ECOLOGY RESOURCES, Issue 4 2004JENNIFER A. FOX Abstract In order to study genetic changes in populations of Daphnia galeata mendotae, I characterized seven polymorphic microsatellite loci. Primers to amplify these loci were tested on individual eggs from the resting egg bank of Onondaga Lake, NY. Levels of polymorphism and cross-amplification in D. g. galeata indicate that they will be useful markers for ecological genetic studies on both adults and diapausing eggs of these species. [source] | ||||||||||||||||||||||