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Developmental role of a coactivator MBF1 During gene activation, coactivators mediate the effect of DNA-binding transcription factors to RNA polymerase. Although coactivators are important for transcription, their in vivo roles are poorly understood. We show that an evolutionarily conserved but unique coactivator MBF1 cooperates with a bZIP transcription factor TDF (Tracheae defective) during the formation of the tracheal and nervous systems. MBF1 acts by bridging between TDF and the TATA-box binding protein (TBP). Transcription of a TDF-dependent reporter gene is reduced by 80% in mbf1 null mutant embryos. A recessive tdf allele becomes haploinsufficient in the mbf1-deficient embryos, causing severe lesions in the tracheal and central nervous systems. These data are the first genetic analysis of MBF1 function in a multicellular organism and demonstrate its crucial role in organogenesis. (Liu et al., Development 2003).
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| A mite species that consists entirely of haploid females. The dominance of the diploid state in higher organisms, with haploidy generally confined to the gametic phase, has led to the perception that diploidy is favored by selection. This view is highlighted by the fact that no known female organism within the Metazoa exists exclusively in a haploid state. Here, fluorescence microscopy and variation at nine microsatellite loci was used to show that the false spider mite, Brevipalpus phoenicis, consists of haploid female parthenogens. This reproductive anomaly is caused by infection by an undescribed endosymbiotic bacterium which results in feminization of haploid genetic males.
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| Extracellular adenosine is an important drosophila growth regulator We found a group of 6 related Drosophila proteins, named ADGF-A,-A2,-B,-C,-D,-E, similar to the enzyme adenosine deaminase. ADGFs have strong adenosine deaminase activity and they are also involved in the regulation of mitosis. They require their enzymatic function for the mitogenic activity. We proved that ADGFs function by modulating the level of extracellular adenosine. Closely related human protein CECR1 has been identified and it is implicated in the genetic diseases Cat-Eye Syndrome and DiGeorge Syndrome. The research on Drosophila ADGFs helps to explain the mechanism of those severe genetic human diseases.
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| Host specificity of herbivorous insects in tropical rainforests Our studies in Papua New Guinea, which included sampling tens of thousands of herbivorous insects from their host plants, testing their feeding preferences in the laboratory and - in case of larvae - their rearing to adults, demonstrated that there are relatively few strictly specialised herbivores in tropical rainforests. In particular, insects tend to feed on several closely related (congeneric) hosts, rather than being monophagous, i.e. limited to a single host plant species. This pattern of host preferences suggests that the extraordinarily speciose communities of tropical insects are not maintained by fine resource partitioning as has been often assumed.
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| Genetic transformation of the silkmoth Insect science cannot advance without genetic manipulations that would provide causal evidence of gene function. We report heritable germline transformation of the silkmoth Bombyx mori with the piggyBac transposon. The transgene is marked with a jellyfish gene for the green fluorescent protein (GFP). GFP is visible in the silkmoth eyes because it is regulated by the conserved Pax-6 protein, necessary for the eye development. Besides the selectable marker, we insert into the Bombyx chromosomes genes of interest under a heat-inducible hsp70 promoter from Drosophila. For the first time we show that a transgene can be induced by heat shock in vivo in a non-drosophilid insect, establishing a system for future transgenic studies.
See Uhlirova M., Asahina M., Riddiford L.M. and Jindra M. (2002) Heat-inducible transgenic expression in the silkmoth Bombyx mori. Dev. Genes Evol. 212, 145-151.
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| First report on semiochemical spacing in larvae of predators Our research revealed repellent effects of larval tracks on conspecific larvae in aphidophagous coccinellids. Searching behaviour of insects was monitored in double choice tests with the assistance of automatic video tracking system EthoVision. Larvae of the coccinellid Cycloneda limbifer Say (Coleoptera: Coccinellidae) effectively differentiated clean substrates from substrates with fresh tracks of conspecific first instars. Fourth instars walked significantly further and stayed longer on clean substrates than on those with tracks of first instars. These results indicate the presence of a deterring pheromone in tracks of larvae. The mode of action of repellent secretion of larvae is complementary to previously described semiochemical-mediated egg-spacing mechanism in coccinellids. Grown up coccinellid larvae may disperse away from potentially less suitable aphid colonies and thus contribute to a decline of the rate of cannibalism, especially of immobile prepupae and pupae. Active semiochemical spacing of larval predators is likely to adjust the distribution of voracious larvae to dynamic changes in prey-predator ratio. We suggest that the occurrence of immature heterospecific competitors in an aphid colony might be for some species even more hazardous than the presence of conspecific larvae. Thus, interspecific effects of larval tracks on active spacing of aphidophagous coccinellids deserve further attention. In: Růžička Z., Zemek R. (2007) Deterrent effects of larval tracks on conspecific larvae in Cycloneda limbifer. DOI 10.1007/s10526-007-9109-x BioControl.
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| Probable occurrence of recent permafrost in Bohemia Czech Republic occupies a keyposition in the research of scree slopes, related to its geological and geomorphological structure and position in the centre of Europe. Institute of Entomology participates in the reseach of microclimate and invertebrate communities in scree slopes. Interdisciplinary international SCREECOS (SCREe ECOSystem) project focuses on zoological, microclimatological and geophysical research of localities Kamenec and Klíč in North Bohemia. Cold-adapted northern and mountain spiders (Bathyphantes simillimus, Diplocentria bidentata, Lepthyphantes tripartitus) and mites (Rhagidia gelida) occur on lower margin of these scree slopes. Temperature measurements lasting several years and geophysical measurements (refraction seismic tomography, 2-dimensional DC resistivity tomography) give evidences for probable occurrence of sporadic permafrost in scree slope on Klíč Mt. (Gude et al. 2003).
Gude M., Dietrich S., Mäusbacher R., Hauck C., Molenda R., Růžička V. & Zacharda M. 2003: Probable occurrence of sporadic permafrost in non-alpine scree slopes in central Europe. In Phillips M., Springman S. M. & Arenson L. U. (eds.) Proceedings of the 8th International Conference on Permafrost. Lisse (NL), pp. 331-336.
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| Gene knock-down using RNAi delivered by a virus RNA interference (RNAi) allows gene silencing, and thus analyses of gene function, even in non-model organisms, where targeted mutagenesis is not feasible. The main problem is how to deliver the interfering double-stranded RNA, sufficient for a specific degradation of the target mRNA, into the organism's cells. We have solved this problem using a recombinant virus Sindbis. Once in host cells, the Sindbis RNA genome including an inserted foreign gene is replicated in both directions, such that resulting double-stranded RNA can trigger degradation of the endogenous mRNA for this gene and thereby silence it. We have for the first time demonstrated this process in vivo in the commercial silkworm. By silencing a gene for the transcription factor Broad-Complex (BR-C), we disrupted pupation of the silkworm (figure) and two classes of processes during metamorphosis: (i) differentiation of the adult wings, eyes and legs from their larval primordia, and (ii) programed death of the larval silk glands. These defects correspond to the effects of BR-C mutations in Drosophila and thus show that the role of BR-C in insect metamorphosis is evolutionarily conserved. In addition, our results have demonstrated the usefulness of the Sindbis virus as a vehicle for genetic "knock-outs" in non-model species. (Uhlirova et al. 2003; P.N.A.S. 100, 15607-15612).
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| Allee effects in plant and animal populations Ecologists commonly work with the concepts of competition and negative density dependence. Negative density dependence means that with increasing population size Darwinian fitness of each its member declines. Competition for common resources is one of the mechanisms causing such dependence. It appears, however, that especially at low population sizes where competition is weak this does not need to hold. In such a situation one can observe the opposite phenomenon, namely that with increasing population size Darwinian fitness of each its member increases. This phenomenon has been termed the Allee effect (after the U.S. ecologist W. C. Allee) and can even lead to the appearance of a critical population size necessary for the entire population to survive: if population size falls below that value, the population will go extinct with high probability. There are a variety of mechanisms that can create Allee effects, including the need to find mates, avoid predators or modify unfavorable (e.g. toxic) environment. Although the first studies on Allee effects go back at least to 1920’s, until recently, this phenomenon eked out on the margin of ecological theory, in the shade of negative density dependence. The situation has changed dramatically in the last ten years, mainly due to human-caused habitat destruction and subsequent emphasis on species conservation. We can thus observe an ever increasing number of studies considering Allee effects from an ever increasing range of disciplines, including population and community ecology, population genetics, evolutionary biology, conservation biology and population management, parasitology, or even social sciences. The book entitled Allee effects in ecology and conservation (Courchamp et al. 2008) presents a detailed view on this currently very important phenomenon, including its history, variety of underlying mechanisms, and implications for population and community ecology, evolution and population management (including pest control, conservation of endangered species, and species exploitation). Actually, much of what we know about these implications comes from mathematical models. This is also the case of Berec et al. (2007) which not only reviews populations for which we have evidence of a simultaneous operation of two or more mechanisms underlying Allee effects, but also shows, by means of a mathematical model, that their interaction can take various forms. For example, even if none of two present mechanisms leads to the appearance of a critical population density when alone, their interaction can lead to a critical density. If, on the contrary, both mechanisms lead to the appearance of a critical population density when alone, their interaction does so, too, yet the resulting critical density can be disproportionately larger than any of the single ones. It becomes obvious that due to such interactions, failing to take all present Allee effect mechanisms into account could have adverse consequences for the management of threatened or exploited populations. Allee effect also strongly affects dynamics of predator-prey interactions; it generally destabilizes the coexistence equilibrium of the two species (Boukal et al. 2007).
Berec, L., Angulo, E., Courchamp, F. 2007. Multiple Allee effects and population management. Trends in Ecology & Evolution 22:185-191
Boukal, D. S., Sabelis, M. W., Berec, L. 2007. How predator functional responses and Allee effects in prey affect the paradox of enrichment and population collapses. Theoretical Population Biology 72: 136-147
Courchamp, F., Berec, L., Gascoigne, J. 2008. Allee effects in ecology and conservation. Oxford University Press.
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| Illustrated Catalogue of Aphididae in the Korean Peninsula This book, as the first volume of the \"Illustrated Catalogue of Aphididae in the Korean Peninsula\", includes only one subfamily, Aphidinae, the major group of the family Aphididae.
It deals with 241 species, consisting of 206 species from the South Korea, and 116 species from the North Korea with 31 species new to the Korean Peninsula. There are 42 species found only in North Korea, 125 species found only in South Korea, and 81 species common in both North and South Korea. More than 180 colour photos of 89 species for live apterous viviparous female, alate viviparous female, fundatrix, and their damage symptoms (galls, pseudo-galls, or leaf curling etc.). The cooperative study was based mainly on collections of aphids stored in NIAST (Suwon, South Korea) and a large aphid collection deposited in the IE ASCR (Ceske Budejovice, Czech Republic).
Lee, S. H., Holman, J., and Havelka, J.
Illustrated Catalogue of Aphididae in the Korean Peninsula.
Part I, Subfamily Aphidinae (Hemiptera: Sternorrhyncha).
Insects of Korea, KRIBB & CIS, Series 9, 1-329.
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| The Lotka–Volterra predator-prey model with foraging-predation risk trade-offs The Lotka-Volterra predator-prey model is one of the earliest and, perhaps, the best known example used to explain why predators can indefinitely coexist with their prey. The population cycles resulting from this model (Figure A) can be found in every ecology textbook. Dr. Vlastimil Krivan, a mathematical ecologist at the Biology Center at Ceske Budejovice, shows that adaptive behavior of prey and predators can destroy these cycles and stabilize population dynamics at an equilibrium (Figure B).
The classical predator-prey model assumes that interaction strength is fixed, which means that coefficients describing interactions between prey and predators do not change in time. However, there is increasing evidence that individuals adjust their activity levels to maximize their Darwinian fitness. For example, a high predation risk due to large predator numbers leads to prey behaviors that make them less vulnerable. They can either move to a refuge or become vigilant. However, such avoidance behaviors usually also decrease animal opportunities to forage which leads to the so called foraging-predation risk trade-off. The present article shows that such a trade-off can have a strong bearing on population dynamics. In fact, while the classical Lotka-Volterra model has isoclines that are straight lines, the foraging-predation risk trade-off leads to prey (predator) isoclines with vertical (horizontal) segments. Rosenzweig and MacArthur in their seminal work on graphical stability analysis of predator-prey models showed that such isoclines have stabilizing effect on population dynamics because they limit maximum possible fluctuations in prey and predator populations. The present article shows that not only population fluctuations are limited, but they can even be completely eliminated. "Although mathematical models are caricatures of the real world, they can indicate the major mechanisms that regulate biodiversity," says V. Krivan.
Krivan, V. 2007. The Lotka-Volterra predator-prey model with foraging-predation risk trade-offs. American Naturalist 170: 771-782.
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| Sex-selective predation and predator-prey dynamics Given that many animals are sexually dimorphic and many predators hunt their prey based on its size, conspicuousness or behaviour, sex-selective predation should be widespread. In an article recently published in PloS ONE, David Boukal, Luděk Berec and Vlastimil Křivan from the Department of Theoretical Ecology highlight that this phenomenon is surprisingly poorly covered in the research on population dynamics. They combine a modelling approach with an extensive survey of known data to show that in most prey, male-biased predation will have a stabilizing effect on the predator-prey dynamics (that is, such predation may lead to a predator-prey equilibrium), while female-biased predation will usually be destabilizing and may lead to extinction of the populations. This ecological viewpoint might provide an alternative or supplementary explanation, other than sexual selection, as to why male-biased predation prevails in nature.
Boukal, D. S., Berec, L., Krivan, V. 2008. Does sex-selective predation stabilize or destabilize predator-prey dynamics? PloS ONE 3(7): e2687
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| First assessment of oviposition-deterring pheromone in an aphidophagous coccinellids For the first time, chemical nature of an oviposition-deterring pheromone was identified in predatory insects by the use of bioassay guided fractionation. Active oviposition-deterring component in tracks of the aphidophagous coccinellid, Cheilomenes sexmaculata larvae, was (Z)-pentacos-12-ene. The alkaloid coccinelline and saturated hydrocarbons that occur in larval tracks and in the extract of larvae were individually tested also, but proved to be inactive. Details of procedures and the synthesis and of (Z)-pentacos-12-ene were published in: Klewer N., Růžička Z., Schulz S., 2007: J. Chem. Ecol., 33: 2167-2170.
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