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Jim Hardie - One of the best experts on this subject based on the ideXlab platform.
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the effect of temperature on the photoperiodic clock and counter of a scottish clone of the vetch aphid Megoura viciae
Journal of Insect Physiology, 2000Co-Authors: Marlies Vaz Nunes, Jim HardieAbstract:Photoperiodic response curves were determined for a Scottish clone of the vetch aphid, Megoura viciae Buckton, at three temperatures: 12.5, 15, and 17.5 degrees C. Critical night lengths (CNLs) for ovipara (sexual female) induction were 6 h, 7 h and 8 h, respectively. High incidences of ovipara production were observed in all night lengths longer than the CNL including continuous darkness (DD), as well as in continuous light (LL) at 12.5 and 15 degrees C. At the same three temperatures, the number of long- or short-night cycles required for half of the experimental aphids to be ovipara producers (i.e. the required day number, RDN) was determined. The RDN for long-night cycles (LD12:12) could not be determined at 12.5 degrees C, but was temperature compensated between 15 and 17.5 degrees C. The RDN for short-night cycles (LD20:4) could not be determined at any temperature. However, as induction of oviparae was always 100% in 12.5 degrees C, 94-100% in 15 degrees C and dropped from 100% to between 47 and 71% in 17.5 degrees C, it seems that short-night accumulation was temperature dependent. When fourth-stadium larvae were transferred from LD20:4 at 20 degrees C to the same light-dark cycle at 15 degrees C, the aphids, when adult, switched to the production of oviparae after about 4 weeks. First-born progeny kept in LD20:4 and 15 degrees C switched to the production of oviparae about 7 days after the moult to adult. Thus, the photoperiodic response can be directly affected by temperature, irrespective of photoperiod. Model-generated response curves using the 'double circadian oscillator model' for photoperiodic time measurement (Vaz Nunes, M., 1998. A double circadian oscillator model for quantitative photoperiodic time measurement in insects and mites. Journal of Theoretical Biology 194, 299-311) closely resembled the observations. Differences between these data and the results of previous experiments with an English clone of M. viciae could be accounted for by differences in the photoperiodic clocks (damping rate and period) as well as the photoperiodic counters.
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two opsin genes from the vetch aphid Megoura viciae
Insect Molecular Biology, 2000Co-Authors: Nong Gao, Russell G Foster, Jim HardieAbstract:The cDNAs of two opsins (Megopsin1 and Megopsin2) from the vetch aphid, Megoura viciae, have been sequenced and encoded for gene products with 378 and 371 amino acid residues, respectively. Phylogenetic analysis reveals that Megopsin1 falls into the insect long-wavelength opsin group and Megopsin2 is a member of the insect UV-wavelength opsins. Both opsins share the key features of G-protein-coupled receptors and the specific motifs of photopigments. In situ hybridization demonstrated that the transcripts of Megopsin1 and Megopsin2 were expressed in the retinula cells of the compound eyes.
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the putative brain photoperiodic photoreceptors in the vetch aphid Megoura viciae
Journal of Insect Physiology, 1999Co-Authors: Nong Gao, Russell G Foster, M Von Schantz, Jim HardieAbstract:In an attempt to identify the brain photoreceptors that mediate the photoperiodic response of the vetch aphid, Megoura viciae, we utilised immunocytochemical techniques and employed 20 antibodies directed against invertebrate and vertebrate opsins and phototransduction proteins. A sub-set of these antibodies (to Drosophila rhodopsin 1: RH1-1; vertebrate cone opsins: COS-1; CERN-874; CERN-933; vertebrate rod opsin: CERN-901; vertebrate arrestin: AB-Arr; vertebrate transducin+arrestin+rhodopsin kinase+cGMP phosphodiesterase: CERN-911; and vertebrate cellular retinoid binding protein: CRALBP) consistently labelled an anterior ventral neuropile region of the protocerebrum. These anatomical findings, coupled with previous localised illumination and micro-lesion studies, provide strong evidence that this region of the aphid brain houses the photoperiodic photoreceptors. The present study also confirms that the medial (Group I) neurosecretory cells are not the photoperiodic photoreceptors.
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peripheral odour perception by adult aphid forms with the same genotype but different host plant preferences
Journal of Insect Physiology, 1995Co-Authors: Jim Hardie, J H Visser, P G M PironAbstract:As adults, the summer (alate virginopara) and autumn (gynopara) winged forms of the black bean aphid, Aphis fabae, utilise different host plants, the bean Vicia faba, and the spindle tree, Euonymus europaeus, respectively. Electroantennograms (EAGs) were recorded from the antennae of these aphid forms, reared from a single clone, to thirty five plant volatiles and to paraffin oil extracts from leaves of the two host plants. The EAG peak responses were normalised against the adjacent responses to a standard stimulus ((E)-2-hexenal at log 2 dilution). The comparison of different parameters of the EAG responses, i.e. peak, rise and decay, reveals that peripheral olfactory perception of most volatiles is not significantly different between these two forms. In addition, the responses of adult wingless virginoparae to thirteen of the plant volatiles show, with one exception, similar peripheral perception. The results indicate that any odour discrimination between the two alternative host plants by their respective colonisers is not perceived at the level of the peripheral olfactory receptors. The EAG response profile of A. fabae differs from that of the vetch aphid, Megoura viciae, which also colonises bean.
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a model for the photoperiodic counter in the aphid Megoura viciae
Journal of Insect Physiology, 1993Co-Authors: Marlies Vaz Nunes, Jim HardieAbstract:The photoperiodic counter in the aphid Megoura viciae was analysed by means of a previously developed general model of the photoperiodic counter mechanism in insects and mites. It was shown that the counter in M. viciae accumulated long scotophases as well as short scotophases. It could further be shown that the inductive strength, or “value”, of long and short scotophases depended to a certain extent on photophase duration: long, 12-h scotophases accompanied by long photophases (> 18 h) decreased in value, whereas the inductive strength of short, 8-h scotophases decreased when accompanied by short photophases (< 16 h). Sensitivity to photoperiod changed slightly during the 10-day postnatal sensitive period at 15°C. Although sensitivity to short-night cycles (16 h light-8 h dark) showed a maximum at around day 7 and thereafter decreased sharply, sensitivity to long-night cycles (12 h light-12 h dark) did not appear to change. In M. viciae the “required day number”, which is the number of long- or short-night cycles required to elicit a 50% response, could only be determined at 12 and 15°C, as at higher temperatures (17 and 20°C) the long-night response (ovipara-production) was attenuated. For the low temperatures it was found that the accumulation of short-night cycles was far more temperature sensitive than that of long-night cycles. The observed attenuation of the long-night response at the higher temperatures could be explained in terms of the model, by assuming that the “minimally required induction sum” (Smin) is extremely sensitive to temperature, with a temperature coefficient much higher than the temperature coefficients of the photoperiodic values of both long-night cycles and short-night cycles.
U. Bianchi - One of the best experts on this subject based on the ideXlab platform.
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patterns of dnase i sensitivity in the holocentric chromosomes of the aphid Megoura viciae
Genome, 1998Co-Authors: Gian Carlo Manicardi, D. Bizzaro, Mauro Mandrioli, U. BianchiAbstract:Using the in situ nick translation technique, we looked for the presence of DNase I sensitive sites in Megoura viciae chromosomes, to study the distribution of active or potentially active genes in...
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chromosomal localization of a highly repeated ecori dna fragment in Megoura viciae homoptera aphididae by nick translation and fluorescence in situ hybridization
Chromosome Research, 1996Co-Authors: D. Bizzaro, Gian Carlo Manicardi, U. BianchiAbstract:To investigate the genome of the aphidMegoura viciae at molecular level, we have studied total DNA by agarose gel electrophoresis after cleavage with different restriction endonucleases.EcoRI digestion produced a highly repeated DNA fragment, about 600 bp long. The contribution of thisEcoRI element to the total genome ofM. viciae was estimated at about 6% by means of densitometric scanning of agarose gel photographs. The chromosomal localization of this fragment, investigated by fluorescentin situ hybridization (FISH), constantly showed one large and two narrower fluorescent bands located on the X chromosome, all corresponding to C-positive heterochromatic areas. These results are in full accordance with the data obtained byin situ nick translation experiments carried out afterEcoRI digestion, and clearly demonstrate that a substantial amount ofM. viciae heterochromatin consists ofEcoRI fragments which are mainly located on the X chromosome. Using theEcoRI restriction fragment as a molecular probe may prove to be a practical tool for the investigation of taxonomic and evolutionary relationships in this group of insects.
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chromosomal localization of a highly repeated ecori dna fragment in Megoura viciae homoptera aphididae by nick translation and fluorescence in situ hybridization
Chromosome Research, 1996Co-Authors: D. Bizzaro, Gian Carlo Manicardi, U. BianchiAbstract:To investigate the genome of the aphid Megoura viciae at molecular level, we have studied total DNA by agarose gel electrophoresis after cleavage with different restriction endonucleases. EcoRI digestion produced a highly repeated DNA fragment, about 600 pb long. The contribution of this EcoRI element to the total genome of M. viciae was estimated at about 6% by means of densitometric scanning of agarose gel photographs. The chromosomal localization of this fragment, investigated by fluorescent in situ hybridization (FISH), constantly showed one large and two narrower fluorescent bands located on the X chromosome, all corresponding to C-positive heterochromatic areas. These results are in full accordance with the data obtained by in situ nick translation experiments carried out after EcoRI digestion, and clearly demonstrate that a substantial amount of M. viciae heterochromatin consists of EcoRI fragments which are mainly located on the X chromosome. Using the EcoRI restriction fragment as a molecular probe may be a practical tool for the investigation of taxonomic and evolutionary relationships in this group of insects.
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Heterochromatin heterogeneity in the holocentric X chromatin of Megoura viciae (Homoptera, Aphididae).
Genome, 1996Co-Authors: Gian Carlo Manicardi, Ermanno Galli, D. Bizzaro, U. BianchiAbstract:Holocentric chromosomes, prepared by spreading embryo cells obtained from Megoura viciae parthenogenetic females, have been C-banded, enzymatically digested in situ using the specific endonucleases DdeI (C↓TNAG), DraI (TTT↓AAA), Tru9I (TT↓AA), and CfoI (GCG↓C), and subsequently stained with Giemsa, DAPI, CMA3, and AgNO3. We observed that the X chromosome had the best defined banding patterns. In the M. viciae X chromosome there is a certain amount of heterogeneity in heterochromatic DNA composition. In fact, the GC-rich NOR-associated heterochromatin differs from other heterochromatic bands that are characterized by AT-rich DNAs. Our data also indicate that, in M. viciae holocentric chromosomes, all heterochromatic blocks are accessible to in situ enzyme attack, the only limit to the digestion being the presence or absence of recognition targets. This is an interesting point, since, in monocentric chromosomes, it is well known that in situ endonuclease digestion is heavily affected not only by DNA base co...
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cytological and electrophoretic analysis of dna methylation in the holocentric chromosomes of Megoura viciae homoptera aphididae
Genome, 1994Co-Authors: Gian Carlo Manicardi, D. Bizzaro, Paola Azzoni, U. BianchiAbstract:Chromosomal and purified DNA methylation patterns were determined in the holocentric chromosomes of Megoura viciae by treatment with MspI and HpaII. Both enzymes produced a clear C-like banding pattern but widely digested one telomere of the X chromosome, which appeared as heterochromatic after C-banding treatment and brightly fluorescent after chromomycin A3 staining. Quantitative microfluorometric evaluations of DNA extraction performed on cytological preparations showed that both isoschizomers resulted in the same DNA extraction (about 30%). Contrary to what was found by in situ endonuclease treatment, the electrophoretic patterns of purified and digested DNA showed that digestion with MspI was slightly more extensive than that with HpaII in a zone of fragments ranging from 23 to 9 kb. This result indicates that aphid chromatin is not wholly unmethylated. The discrepancy between electrophoretic and cytological data has been explained by taking into consideration that DNA fragments with high molecular w...
D. Bizzaro - One of the best experts on this subject based on the ideXlab platform.
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NOR heteromorphism within a parthenogenetic lineage of the aphid Megoura viciae
Chromosome Research, 1999Co-Authors: Mauro Mandrioli, Gian Carlo Manicardi, D. Bizzaro, Umberto BianchiAbstract:In parthenogenetic females of a clone of the aphid Megoura viciae (Homoptera, Aphididae), more than 50% of the cells show heteromorphism between homologous NORs which are located on one telomeric region of the two X chromosomes. Using different techniques, such as staining with the CG-specific fluorochrome chromomycin A3, silver staining and in-situ hybridization with an rDNA probe, we have shown that the observed heteromorphism is due to an unequal distribution of ribosomal genes between homologous NOR regions. The total number of rDNA genes per individual aphid remained constant. Moreover, the analysis of cells from single embroys has shown that the observed heteromorphism is not only intraclonal but also intraindividual. These data, together with the finding of X chromosomes connected by chromatin bridges between their NORs, allow us to suggest that mitotic unequal crossing over could be the main cause of NOR heteomorphism in this taxon.
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patterns of dnase i sensitivity in the holocentric chromosomes of the aphid Megoura viciae
Genome, 1998Co-Authors: Gian Carlo Manicardi, D. Bizzaro, Mauro Mandrioli, U. BianchiAbstract:Using the in situ nick translation technique, we looked for the presence of DNase I sensitive sites in Megoura viciae chromosomes, to study the distribution of active or potentially active genes in...
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chromosomal localization of a highly repeated ecori dna fragment in Megoura viciae homoptera aphididae by nick translation and fluorescence in situ hybridization
Chromosome Research, 1996Co-Authors: D. Bizzaro, Gian Carlo Manicardi, U. BianchiAbstract:To investigate the genome of the aphidMegoura viciae at molecular level, we have studied total DNA by agarose gel electrophoresis after cleavage with different restriction endonucleases.EcoRI digestion produced a highly repeated DNA fragment, about 600 bp long. The contribution of thisEcoRI element to the total genome ofM. viciae was estimated at about 6% by means of densitometric scanning of agarose gel photographs. The chromosomal localization of this fragment, investigated by fluorescentin situ hybridization (FISH), constantly showed one large and two narrower fluorescent bands located on the X chromosome, all corresponding to C-positive heterochromatic areas. These results are in full accordance with the data obtained byin situ nick translation experiments carried out afterEcoRI digestion, and clearly demonstrate that a substantial amount ofM. viciae heterochromatin consists ofEcoRI fragments which are mainly located on the X chromosome. Using theEcoRI restriction fragment as a molecular probe may prove to be a practical tool for the investigation of taxonomic and evolutionary relationships in this group of insects.
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chromosomal localization of a highly repeated ecori dna fragment in Megoura viciae homoptera aphididae by nick translation and fluorescence in situ hybridization
Chromosome Research, 1996Co-Authors: D. Bizzaro, Gian Carlo Manicardi, U. BianchiAbstract:To investigate the genome of the aphid Megoura viciae at molecular level, we have studied total DNA by agarose gel electrophoresis after cleavage with different restriction endonucleases. EcoRI digestion produced a highly repeated DNA fragment, about 600 pb long. The contribution of this EcoRI element to the total genome of M. viciae was estimated at about 6% by means of densitometric scanning of agarose gel photographs. The chromosomal localization of this fragment, investigated by fluorescent in situ hybridization (FISH), constantly showed one large and two narrower fluorescent bands located on the X chromosome, all corresponding to C-positive heterochromatic areas. These results are in full accordance with the data obtained by in situ nick translation experiments carried out after EcoRI digestion, and clearly demonstrate that a substantial amount of M. viciae heterochromatin consists of EcoRI fragments which are mainly located on the X chromosome. Using the EcoRI restriction fragment as a molecular probe may be a practical tool for the investigation of taxonomic and evolutionary relationships in this group of insects.
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Heterochromatin heterogeneity in the holocentric X chromatin of Megoura viciae (Homoptera, Aphididae).
Genome, 1996Co-Authors: Gian Carlo Manicardi, Ermanno Galli, D. Bizzaro, U. BianchiAbstract:Holocentric chromosomes, prepared by spreading embryo cells obtained from Megoura viciae parthenogenetic females, have been C-banded, enzymatically digested in situ using the specific endonucleases DdeI (C↓TNAG), DraI (TTT↓AAA), Tru9I (TT↓AA), and CfoI (GCG↓C), and subsequently stained with Giemsa, DAPI, CMA3, and AgNO3. We observed that the X chromosome had the best defined banding patterns. In the M. viciae X chromosome there is a certain amount of heterogeneity in heterochromatic DNA composition. In fact, the GC-rich NOR-associated heterochromatin differs from other heterochromatic bands that are characterized by AT-rich DNAs. Our data also indicate that, in M. viciae holocentric chromosomes, all heterochromatic blocks are accessible to in situ enzyme attack, the only limit to the digestion being the presence or absence of recognition targets. This is an interesting point, since, in monocentric chromosomes, it is well known that in situ endonuclease digestion is heavily affected not only by DNA base co...
Gian Carlo Manicardi - One of the best experts on this subject based on the ideXlab platform.
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NOR heteromorphism within a parthenogenetic lineage of the aphid Megoura viciae
Chromosome Research, 1999Co-Authors: Mauro Mandrioli, Gian Carlo Manicardi, D. Bizzaro, Umberto BianchiAbstract:In parthenogenetic females of a clone of the aphid Megoura viciae (Homoptera, Aphididae), more than 50% of the cells show heteromorphism between homologous NORs which are located on one telomeric region of the two X chromosomes. Using different techniques, such as staining with the CG-specific fluorochrome chromomycin A3, silver staining and in-situ hybridization with an rDNA probe, we have shown that the observed heteromorphism is due to an unequal distribution of ribosomal genes between homologous NOR regions. The total number of rDNA genes per individual aphid remained constant. Moreover, the analysis of cells from single embroys has shown that the observed heteromorphism is not only intraclonal but also intraindividual. These data, together with the finding of X chromosomes connected by chromatin bridges between their NORs, allow us to suggest that mitotic unequal crossing over could be the main cause of NOR heteomorphism in this taxon.
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patterns of dnase i sensitivity in the holocentric chromosomes of the aphid Megoura viciae
Genome, 1998Co-Authors: Gian Carlo Manicardi, D. Bizzaro, Mauro Mandrioli, U. BianchiAbstract:Using the in situ nick translation technique, we looked for the presence of DNase I sensitive sites in Megoura viciae chromosomes, to study the distribution of active or potentially active genes in...
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chromosomal localization of a highly repeated ecori dna fragment in Megoura viciae homoptera aphididae by nick translation and fluorescence in situ hybridization
Chromosome Research, 1996Co-Authors: D. Bizzaro, Gian Carlo Manicardi, U. BianchiAbstract:To investigate the genome of the aphidMegoura viciae at molecular level, we have studied total DNA by agarose gel electrophoresis after cleavage with different restriction endonucleases.EcoRI digestion produced a highly repeated DNA fragment, about 600 bp long. The contribution of thisEcoRI element to the total genome ofM. viciae was estimated at about 6% by means of densitometric scanning of agarose gel photographs. The chromosomal localization of this fragment, investigated by fluorescentin situ hybridization (FISH), constantly showed one large and two narrower fluorescent bands located on the X chromosome, all corresponding to C-positive heterochromatic areas. These results are in full accordance with the data obtained byin situ nick translation experiments carried out afterEcoRI digestion, and clearly demonstrate that a substantial amount ofM. viciae heterochromatin consists ofEcoRI fragments which are mainly located on the X chromosome. Using theEcoRI restriction fragment as a molecular probe may prove to be a practical tool for the investigation of taxonomic and evolutionary relationships in this group of insects.
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chromosomal localization of a highly repeated ecori dna fragment in Megoura viciae homoptera aphididae by nick translation and fluorescence in situ hybridization
Chromosome Research, 1996Co-Authors: D. Bizzaro, Gian Carlo Manicardi, U. BianchiAbstract:To investigate the genome of the aphid Megoura viciae at molecular level, we have studied total DNA by agarose gel electrophoresis after cleavage with different restriction endonucleases. EcoRI digestion produced a highly repeated DNA fragment, about 600 pb long. The contribution of this EcoRI element to the total genome of M. viciae was estimated at about 6% by means of densitometric scanning of agarose gel photographs. The chromosomal localization of this fragment, investigated by fluorescent in situ hybridization (FISH), constantly showed one large and two narrower fluorescent bands located on the X chromosome, all corresponding to C-positive heterochromatic areas. These results are in full accordance with the data obtained by in situ nick translation experiments carried out after EcoRI digestion, and clearly demonstrate that a substantial amount of M. viciae heterochromatin consists of EcoRI fragments which are mainly located on the X chromosome. Using the EcoRI restriction fragment as a molecular probe may be a practical tool for the investigation of taxonomic and evolutionary relationships in this group of insects.
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Heterochromatin heterogeneity in the holocentric X chromatin of Megoura viciae (Homoptera, Aphididae).
Genome, 1996Co-Authors: Gian Carlo Manicardi, Ermanno Galli, D. Bizzaro, U. BianchiAbstract:Holocentric chromosomes, prepared by spreading embryo cells obtained from Megoura viciae parthenogenetic females, have been C-banded, enzymatically digested in situ using the specific endonucleases DdeI (C↓TNAG), DraI (TTT↓AAA), Tru9I (TT↓AA), and CfoI (GCG↓C), and subsequently stained with Giemsa, DAPI, CMA3, and AgNO3. We observed that the X chromosome had the best defined banding patterns. In the M. viciae X chromosome there is a certain amount of heterogeneity in heterochromatic DNA composition. In fact, the GC-rich NOR-associated heterochromatin differs from other heterochromatic bands that are characterized by AT-rich DNAs. Our data also indicate that, in M. viciae holocentric chromosomes, all heterochromatic blocks are accessible to in situ enzyme attack, the only limit to the digestion being the presence or absence of recognition targets. This is an interesting point, since, in monocentric chromosomes, it is well known that in situ endonuclease digestion is heavily affected not only by DNA base co...
Marlies Vaz Nunes - One of the best experts on this subject based on the ideXlab platform.
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the effect of temperature on the photoperiodic clock and counter of a scottish clone of the vetch aphid Megoura viciae
Journal of Insect Physiology, 2000Co-Authors: Marlies Vaz Nunes, Jim HardieAbstract:Photoperiodic response curves were determined for a Scottish clone of the vetch aphid, Megoura viciae Buckton, at three temperatures: 12.5, 15, and 17.5 degrees C. Critical night lengths (CNLs) for ovipara (sexual female) induction were 6 h, 7 h and 8 h, respectively. High incidences of ovipara production were observed in all night lengths longer than the CNL including continuous darkness (DD), as well as in continuous light (LL) at 12.5 and 15 degrees C. At the same three temperatures, the number of long- or short-night cycles required for half of the experimental aphids to be ovipara producers (i.e. the required day number, RDN) was determined. The RDN for long-night cycles (LD12:12) could not be determined at 12.5 degrees C, but was temperature compensated between 15 and 17.5 degrees C. The RDN for short-night cycles (LD20:4) could not be determined at any temperature. However, as induction of oviparae was always 100% in 12.5 degrees C, 94-100% in 15 degrees C and dropped from 100% to between 47 and 71% in 17.5 degrees C, it seems that short-night accumulation was temperature dependent. When fourth-stadium larvae were transferred from LD20:4 at 20 degrees C to the same light-dark cycle at 15 degrees C, the aphids, when adult, switched to the production of oviparae after about 4 weeks. First-born progeny kept in LD20:4 and 15 degrees C switched to the production of oviparae about 7 days after the moult to adult. Thus, the photoperiodic response can be directly affected by temperature, irrespective of photoperiod. Model-generated response curves using the 'double circadian oscillator model' for photoperiodic time measurement (Vaz Nunes, M., 1998. A double circadian oscillator model for quantitative photoperiodic time measurement in insects and mites. Journal of Theoretical Biology 194, 299-311) closely resembled the observations. Differences between these data and the results of previous experiments with an English clone of M. viciae could be accounted for by differences in the photoperiodic clocks (damping rate and period) as well as the photoperiodic counters.
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a pacemaker slave model for the photoperiodic clock in the vetch aphid Megoura viciae
Journal of Insect Physiology, 1994Co-Authors: Marlies Vaz NunesAbstract:Abstract Recent investigations into the photoperiodic clock of Megoura viciae indicated that night-length measurement in this aphid is accomplished by a circadian-based oscillator mechanism, despite its typical “hourglass” responses in Nanda-Hamner and Bunsow experiments. To reconcile these apparently contradicting observations, it is suggested here that although long-night determination is executed in a repetitive manner, this is not true for short-night determination. To test this hypothesis, the previously developed “coupled oscillator model” has been modified such that once a scotophase has exceeded the critical night length (as in the Nanda-Hamner experiments) it will always be determined as “long”, no matter whether a subsequent “photo-inducible phase” coincides with darkness or with light. In this respect the modified model differs from all known circadian-clock models. Model-generated responses are compared with a variety of experimental results previously observed with Megoura and the validity of the model as a description of the photoperiodic clock-counter mechanism in Megoura is discussed.
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a model for the photoperiodic counter in the aphid Megoura viciae
Journal of Insect Physiology, 1993Co-Authors: Marlies Vaz Nunes, Jim HardieAbstract:The photoperiodic counter in the aphid Megoura viciae was analysed by means of a previously developed general model of the photoperiodic counter mechanism in insects and mites. It was shown that the counter in M. viciae accumulated long scotophases as well as short scotophases. It could further be shown that the inductive strength, or “value”, of long and short scotophases depended to a certain extent on photophase duration: long, 12-h scotophases accompanied by long photophases (> 18 h) decreased in value, whereas the inductive strength of short, 8-h scotophases decreased when accompanied by short photophases (< 16 h). Sensitivity to photoperiod changed slightly during the 10-day postnatal sensitive period at 15°C. Although sensitivity to short-night cycles (16 h light-8 h dark) showed a maximum at around day 7 and thereafter decreased sharply, sensitivity to long-night cycles (12 h light-12 h dark) did not appear to change. In M. viciae the “required day number”, which is the number of long- or short-night cycles required to elicit a 50% response, could only be determined at 12 and 15°C, as at higher temperatures (17 and 20°C) the long-night response (ovipara-production) was attenuated. For the low temperatures it was found that the accumulation of short-night cycles was far more temperature sensitive than that of long-night cycles. The observed attenuation of the long-night response at the higher temperatures could be explained in terms of the model, by assuming that the “minimally required induction sum” (Smin) is extremely sensitive to temperature, with a temperature coefficient much higher than the temperature coefficients of the photoperiodic values of both long-night cycles and short-night cycles.