The vanishing clone: karyotypic evidence for extensive intraclonal genetic variation in the peach potato aphid,Myzus persicae (Hemiptera: Aphididae)

Analysis of holocentric mitotic metaphase chromosomes of the peach‐potato aphid Myzus persicae (Sulzer) clone 33H revealed different chromosome numbers, ranging from 12 to 17 within each embryo, in contrast to the standard karyotype of this species (2n = 12). Chromosome length measurements revealed that the observed chromosomal mosaicism is the result of recurrent fragmentations of chromosomes X, 1 and 3 because of fragile sites or hot spots of recombination. Fluorescent in situ hybridization experiments showed that X chromosomes were frequently involved in recurrent fragmentations, in particular their telomeric end opposite to the nucleolar organizer region. Experiments to induce males showed that M. persicae clone 33H is obligately parthenogenetic. The reproduction by apomictic parthenogenesis, together with a high telomerase expression that stabilized the chromosomes involved in the fragmentations observed in the M. persicae clone 33H, appears to favour the stabilization of the observed chromosome instability. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 350–358.     

Fast chromosomal evolution and karyotype instability: recurrent chromosomal rearrangements in the peach potato aphid Myzus persicae (Hemiptera: Aphididae)

The occurrence of karyotype variations with respect to both chromosome number and structure has been frequently reported in aphids. Here, we review recent data attesting to the presence of recurrent chromosomal changes in the karyotype of the peach potato aphid Myzus persicae, where clones presenting metaphases with different chromosome number (from 12 to 17) have been observed, also comparing plates obtained within the same embryo. According to the available data, M. persicae autosomes 3 and 1 are the chromosomes mostly involved in changes compared to other autosomes, suggesting that they could have sites more susceptible to fragmentation. Chromosomal fissions involving the X chromosomes have also been observed, suggesting that they may have fragile sites located at the termini opposite to the nucleolar organizer regions‐bearing telomere. The presence of holocentric chromosomes and reproduction by apomictic parthenogenesis, together with a constitutive expression of telomerase, could explain the inheritance of the observed chromosomal instability in aphids. Considering that chromosomal changes may affect the host choice and could also favour speciation, it would be intriguing to confirm whether the observed karyotype variants have effects over short temporal and spatial scales.     

Segregation of autosomes during spermatogenesis in the peach-potato aphid (Myzus persicae) (Sulzer) (Hemiptera: Aphididae)

Most aphids are cyclic parthenogens, so are ideal models in studies of the mechanisms and consequences of sex and recombination. However, owing to a shortage of physical and genetic markers, there have been few studies of the most fundamental genetic processes in these organisms. For example, it is not known whether autosomal segregation during male spermatogenesis is in Mendelian proportions: we address that question here. The aphid Myzus persicae has a typical karyotype of 2n = 12 in females (XX), while males are XO (2n = 11). During male meiosis, only the spermatocytes with an X chromosome are viable. We hypothesized that assortment of autosomes might be non-random because chromosomal imprinting leading to elimination of the paternal autosomes is seen in the closely related coccoids. In other aphid models, we have observed segregation distortions at single microsatellite loci (Wilson, 2000). Such distortions may have nothing to do with 'selfish' behaviour, but may be caused by mutation accumulation causing fitness differentials. Thus single-locus distortions might be predicted to be more likely to be detected via the male lines of clones that have lost the ability to reproduce sexually (male-producing obligate parthenogenesis (androcyclic)). Using microsatellites we show that genetic imprinting or selfish autosome behaviour does not occur in male M. persicae. Generally, loci segregated in Mendelian proportions in both sexes of cyclically parthenogenetic (holocyclic) clones. However, in androcyclic clones, segregation distortions consistently involved the same two autosomes. This is consistent with linkage of markers to deleterious mutations associated with a loss of sexual reproduction.     

Microsatellite isolation, linkage group identification and determination of recombination frequency in the peach-potato aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae)

Fifteen polymorphic microsatellite markers were used to establish linkage groups and relative rates of recombination in male and female Myzus persicae (Sulzer) (Hemiptera: Aphididae) (peach-potato aphid). We cloned nine markers from M. persicae and for these we report primer sequences and levels of allelic diversity and heterozygosity in four Australian M. persicae populations. Of the remaining six loci, four loci, also cloned from M. persicae, were obtained from G. Malarky (Natural History Museum, London) and two loci from Sitobion miscanthi were used. Additionally, the primer sequences of locus M77, a locus monomorphic in M. persicae but polymorphic in the closely related Myzus antirrhinii, are presented. Eleven of the 15 polymorphic markers were autosomal and four were X-linked. A linkage analysis was performed on a European pedigree of aphids containing five families with between seven and 11 offspring each. There was no linkage between any loci in females. In males, several pairwise comparisons yielded no recombinant offspring. With the exception of locus M40, these observations were supported in a linkage analysis performed on larger families produced from Australian M. persicae crosses. Locus M40 showed segregation consistent with involvement in a translocation between autosomes 1 and 3 in European samples but not in the Australian samples. From the Australian crosses we report an absence of recombination in males but high recombination rates in females. One X chromosome and four autosomal linkage groups were identified and tentatively assigned to chromosomes. The relevance of achiasmate meiosis to the evolution of sex is discussed.     

黑麂和费氏麂四种卫星DNA的克隆特征和染色体定位

近年来,分子细胞遗传学研究已基本证实了染色体的串联融合(端粒-着丝粒融合)是麂属动物核型演化的主要重排方式。尽管染色体串联融合的分子机制还不清楚,但通过染色体的非同源重组,着丝粒区域的卫星DNA被认为可能介导了染色体的融合。以前的研究发现在赤麂和小麂染色体的大部分假定的串联融合位点处存在着非随机分布的卫星DNA。然而在麂属的其他物种中,这些卫星DNA的组成以及在基因组中的分布情况尚未被研究。本研究从黑麂和费氏麂基因组中成功地克隆了4种卫星DNA(BMC5、BM700、BM1.1k和FM700),并分析了这些卫星克隆的特征以及在小麂、黑麂、贡山麂和费氏麂染色体上的定位情况。结果表明,卫星I和IIDNA(BMC5,BM700和FM700)的信号除了分布在这些麂属动物染色体的着丝粒区域外,也间隔地分布在这些物种的染色体臂上。其研究结果为黑麂、费氏麂和贡山麂的染色体核型也是从一个2n=70的共同祖先核型通过一系列的串联融合进化而来的假说提供了直接的证据。     

Microsatellite variation in cyclically parthenogenetic populations of Myzus persicae in south-eastern Australia

We examined the population structure of the introduced aphid, Myzus persicae collected mainly from its primary host, Prunus persica, in south-east Australia. Myzus persicae has been present in Australia since at least 1893. Samples were collected in the spring of 1998 from two mainland and three Tasmanian localities and isofemale lines were established in the laboratory. The reproductive mode (life cycle), karyotype and 17-locus microsatellite genotype of each clone were determined. All populations showed significant population differentiation (F(ST) 0.058-0.202) even over small geographic distances (<50 km). All clones were karyotypically normal except for a subset of clones from one site that was exposed to the carbamate insecticide, Pirimor, the week prior to sampling. Those clones were heterozygous for an autosomal 1,3 translocation frequently associated in M. persicae with insecticide resistance. In contrast to other loci and despite being on different chromosomes, loci myz2(A) and M55(A) showed general and significant linkage disequilibrium. These loci may be affected by epistatic selection. We discuss the observed high clonal diversity, moderate but significant population differentiation, general conformance to Hardy-Weinberg equilibria and low linkage disequilibria with particular focus on the global population biology of M. persicae.     

Chromosomal polymorphism of mandarin vole,Microtus mandarinus (Rodentia)

The mitotic and meiotic chromosomes of mandarin vole, Microtus mandarinus Milne-Edwards, from Shandong Province of China were analyzed by conventional, G- and C-banding and Silver-staining techniques. We detected chromosomal polymorphism in the vole, exhibiting diploid chromosome numbers 2n = 48-50 and variable morphology of the 1st pair, one medium sized telocentric pair and the X chromosomes. Four types of karyotypes were revealed in the population. According to banding analysis, there were pericentric inversion, Robertsonian fusion and translocation in M. mandarinus karyotype evolution. The X displayed two different morphologies, which could be explained by prericentric inversion and a telocentric autosome translocation.     

Recent changes in the distribution of carboxylesterase genes and associated chromosomal rearrangements in Greek populations of the tobacco aphid Myzus persicae nicotianae

We present data on the frequency of amplified E4 and FE4 carboxylesterase genes in Myzus persicae s.l. clones collected during the years 2002–2007 and 2012 in Greece. Most clones were of the tobacco aphid, Myzus persicae nicotianae. Samples from 2012 were genotyped with microsatellite DNA markers and a number of them were karyotyped. Aphid clones with amplified FE4 genes predominated in all years, whereas E4 was present in only 3.5% of all samples and always occurred in clones with FE4. Most of the clones examined showed high carboxylesterase activity levels (R2 resistant category). The results showed marked changes in the frequencies of the two carboxylesterase genes in the tobacco aphid populations compared to published data that were collected in Greece in the mid 1990s, when E4 was recorded on its own in 20% of all samples and in 32% of samples from tobacco. A parallel change in karyotype was also observed because the A1,3 translocation, which had a worldwide association with amplified E4 genes in the 1990s, was not detected in the clones analyzed in 2012. Possible causes for these changes are discussed, although selection as a result of pest management practices appears to be the major one. Novel chromosomal rearrangements were also found in M. persicae nicotianae clones. These rearrangements could be a result of clastogenic effects of nicotine, which could persist because of the holocentric nature of aphid chromosomes. The results are discussed in relation to rapid evolution events that have taken place in the tobacco aphid in Greece during the last two decades. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 455–470.     

Analysis of clonal diversity of the peach–potato aphid, Myzus persicae (Sulzer), in Scotland, UK and evidence for the existence of a predominant clone

Clones of the peach–potato aphid, Myzus persicae (Sulzer), mostly from Scotland, UK were examined using an rDNA fingerprinting technique. Eighty patterns (genotypes) were found amongst the 276 clones. A large number of clones (30%) from all sample areas in Scotland exhibited the same simple pattern, suggesting the presence of a single M. persicae clone. There was no difference in genotype distributions between M. persicae collected from brassica or potato crops, suggesting that host-adapted genotypes have no advantage in the field. Different fingerprints were randomly distributed in the environment, although clones taken from the same leaf were more often the same fingerprint. Highly distinctive fingerprints, which were more widely distributed, suggest that this technique could be used to follow individual clones. In addition to the common clonal type, multiple fingerprint bands were found over successive years, implying that, in Scotland, local overwintering asexual populations are the most common source of M. persicae in the following year.     

High-density comparative BAC mapping in the black muntjac (Muntiacus crinifrons): molecular cytogenetic dissection of the origin of MCR 1p+4 in the X1X2Y1Y2Y3 sex chromosome system

The black muntjac (Muntiacus crinifrons, 2n = 8[female symbol]/9[male symbol]) is a critically endangered mammalian species that is confined to a narrow region of southeastern China. Male black muntjacs have an astonishing X1X2Y1Y2Y3 sex chromosome system, unparalleled in eutherian mammals, involving approximately half of the entire genome. A high-resolution comparative map between the black muntjac (M. crinifrons) and the Chinese muntjac (M. reevesi, 2n = 46) has been constructed based on the chromosomal localization of 304 clones from a genomic BAC (bacterial artificial chromosome) library of the Indian muntjac (M. muntjak vaginalis, 2n = 6[female symbol]/7[male symbol]). In addition to validating the chromosomal homologies between M. reevesi and M. crinifrons defined previously by chromosome painting, the comparative BAC map demonstrates that all tandem fusions that have occurred in the karyotypic evolution of M. crinifrons are centromere-telomere fusions. The map also allows for a more detailed reconstruction of the chromosomal rearrangements leading to this unique and complex sex chromosome system. Furthermore, we have identified 46 BAC clones that could be used to study the molecular evolution of the unique sex chromosomes of the male black muntjacs.     

Composition and epigenetic markers of heterochromatin in the aphid Aphis nerii (Hemiptera: Aphididae)

A detailed karyotype analysis of the oleander aphid Aphis nerii focusing on the distribution, molecular composition and epigenetic modifications of heterochromatin was done in order to better understand the structure and evolution of holocentric/holokinetic chromosomes in aphids. The female karyotype (2n = 8) consisted of 3 pairs of autosomes and a pair of X chromosomes that were the longest elements in the karyotype and carried a single, terminally located nucleolar organizer region. Males showed 2n = 7 chromosomes due to the presence of a single X chromosome. Heterochromatin was located in the X chromosomes only and consisted of 4 satellite DNAs that have been identified. A. nerii constitutive heterochromatin was enriched in mono-, di- and tri-methylated H3 histones and HP1 proteins but, interestingly, it lacked DNA methylation that was widespread in euchromatic chromosomal regions. These results suggest that aphid heterochromatin is assembled and condensed without any involvement of DNA methylation.     

Microsatellite marker analysis of peach-potato aphids (Myzus persicae, Homoptera: Aphididae) from Scottish suction traps

The peach-potato aphid Myzus persicae (Sulzer) is an important vector of plant viruses. A network of suction traps collects aerial samples of this aphid in order to monitor and help predict its spatial distribution and likely impact on virus transmission in crops. A suction trap catch is thought to be a good representation of the total aphid pool. Sensitive molecular markers have been developed that determine the genetic composition of the M. persicae population. In Scotland, UK, these were applied to field collections revealing a limited number of clones. Molecular markers are less successful when applied to specimens that have been preserved in an ethanol-based trap fluid designed to preserve morphology. An assessment of different DNA extraction and PCR techniques is presented and the most efficient are used to analyse M. persicae specimens caught in the Dundee suction trap in 2001, a year when exceptionally high numbers were caught. The results reveal that the majority of the M. persicae caught belonged to two highly insecticide resistant clones. In addition, it was possible to compare the relative frequencies of genotypes caught in the trap with those collected at insecticide treated and untreated field sites in the vicinity. These results indicate that, in addition to suction trap data, the ability to sample field sites provides valuable early warning data which have implications for pest control and virus management strategies.     

Effect of the antimicrobial peptide indolicidin on the green peach aphid Myzus persicae (Sulzer)

Abstract:  The green-peach aphid, Myzus persicae (Sulzer) (Hem., Aphididae), is a major agricultural pest of a wide range of host plants, causing damage by feeding and indirectly by transmitting viruses. In this study we tested the effect of the antimicrobial peptide indolicidin on M. persicae survival and on its essential bacterial endosymbionts. Artificial diet bioassays showed a significant dose-dependent lethal response of indolicidin on M. persicae survival (LD₅₀ of 209 ± 60  μ g/ml). Histological analysis of indolicidin-treated aphids revealed a lower number of distorted mycetocytes, whereas control aphids showed abundant number of rounded and filled mycetocytes. These results suggest that aphid survival could be affected via reduction of its endosymbionts. Thus, aphid control based on antimicrobial substances against endosymbionts could be a promising strategy that needs to be further explored.     

Lack of detectable genetic recombination on the X chromosome during the parthenogenetic production of female and male aphids

We used polymorphic microsatellite markers to look for recombination during parthenogenetic oogenesis between the X chromosomes of aphids of the tribe Macrosiphini. We examined the X chromosome because it comprises approximately 25 % of the genome and previous cytological observations of chromosome pairing and nucleolar organizer (NOR) heteromorphism suggest recombination, although the same is not true for autosomes. A total of 564 parthenogenetic females of Myzus clones with three distinct reproductive modes (cyclical parthenogenesis, obligate parthenogenesis and obligate parthenogenesis with male production) were genotyped at three informative X-linked loci. Also, parthenogenetically produced males from clones encompassing the full range of male-producing reproductive strategies were genotyped. These included 391 Myzus persicae males that were genotyped at three X-linked loci and 538 males from Sitobion clones that were genotyped at five informative X-linked loci. Our results show no departure from clonality in parthenogenetic generations of aphids of the tribe Macrosiphini: no recombinant genotypes were observed in parthenogenetically produced males or females.     

Numerical and structural variations of the X chromosomes and no. 2 autosomes in mandarin vole, Microtus mandarinus (Rodentia)

Here we describe our studies on Microtus mandarinus faeceus of Jiangyan in Jiangsu province of China. By karyotype and G-banding analysis we have found variation in chromosome number and polymorphisms of the X chromosome and the second pair of autosomes of the subspecies. Chromosome number of the subspecies is 2n=47-50. The subspecies has three kinds of chromosomal sex: XX, XO and XY, among which one of the X chromosomes is subtelocentric (X(ST)) and the other is metacentric (X(M)). After comparing karyotypes of different subspecies, we found the specific cytogenetic characteristics of Microtus mandarinus, that is they have three kinds of chromosomal sex: XX, XO and XY; X chromosomes are heteromorphic; the chromosome number of female individuals are one less than male individuals; chromosome number of XX individuals are equal to that of XO ones. We hypothesize that Robertsonian translocation is the main reason of the polymorphism of the second pair of autosomes and variety of chromosome number, and it also causes the chromosome number evolution in different subspecies of Microtus mandarinus.     

Performance of Myzus persicae (Hemiptera: Aphididae) clones on different host-plants and their host preference

The performance of eighteen clones of Myzus persicae (Sulzer) on pepper and tobacco plants at 20 degrees C and L16:D8 and the choice of young adult apterae between tobacco and pepper leaf-discs were examined. The clones were collected from weeds and peach in two tobacco-growing regions: Katerini, northern Greece and Karditsa, central Greece (only from weeds) and from Lehonia, central eastern Greece where tobacco is not cultivated. All clones did well on both hosts. However, the analysis of data revealed a significant effect of "region / host plant origin" on aphid performance. The mean values of adult weight, intrinsic rate of increase and fecundity of the clones collected in Lehonia and reared on tobacco were significantly lower than the observed values for clones from Katerini and Karditsa. Aphids from Lehonia had significantly higher mean values for developmental time on tobacco than clones from the other regions whereas the opposite was observed when aphids were reared on pepper. Aphids collected in Lehonia performed better on pepper than those originating from the tobacco-growing regions. A choice test revealed differences among the clones originating from different regions. Fifty three percent and 43% of aphids from weeds and peach from Lehonia, respectively, chose pepper. By comparison 41.5% and 40.0% of aphids from peach and weeds from Katerini, respectively and 49.5% of aphids from Karditsa preferred tobacco. The results are discussed in relation to host specialization in M. persicae.     

Temporal dynamics of genotypic diversity reveal strong clonal selection in the aphid Myzus persicae

Parthenogenetic organisms often harbour substantial genotypic diversity. This diversity may be the result of recurrent formations of new clones, or it may be maintained by environmental heterogeneity acting on ecological differences among clones. In aphids, both processes may be important because obligate and cyclical parthenogens can form mixed populations. Using microsatellites, I analysed the temporal dynamics of clonal diversity in such a population of the aphid Myzus persicae over a 1-year period. The frequency distribution of clonal genotypes was very skewed, with many rare and few common clones. The relative frequencies of common clones underwent strong and rapid changes indicative of intense clonal selection. Differences in their host associations suggest that these shifts may partly be caused by changes in the abundance of annual host plants. Other selective factors of potential importance are also discussed. New, sexually produced genotypes made a minor contribution to clonal diversity, consistent with the observed heterozygote excess characteristic of predominantly asexual populations in M. persicae.     

Isolation of the Drosophila melanogaster dunce chromosomal region and recombinational mapping of dunce sequences with restriction site polymorphisms as genetic markers.

Using the method of chromosomal walking, we have isolated a contiguous region of the Drosophila melanogaster X chromosome which corresponds to salivary gland chromosome bands 3C12 to 3D4. This five-band region contains approximately 100 kilobases of DNA, including those sequences comprising dunce, a gene which functions in memory and cyclic nucleotide metabolism. Genome blots of DNA from flies carrying several different chromosomal aberrations with breakpoints in the region have been probed with the isolated clones to map the breakpoints on the cloned DNA and to delimit dunce sequences. This has localized dunce to a 50-kilobase region. In addition, we have searched this 50-kilobase region for restriction site polymorphisms between X chromosomes from different Drosophila strains by genome blotting experiments, and we have followed the segregation of detected polymorphisms and dunce alleles after meiotic recombination. The data map one dunce mutation between two polymorphisms located 10 to 12 kilobases apart.     

对桃蚜高毒力的蜡蚧菌菌株筛选

【目的】桃蚜Myzus persicae是一种世界性的重要农作物害虫,近年来已对多种化学杀虫剂产生抗性。本研究旨在筛选对桃蚜具有高毒力且培养性状优良的蜡蚧菌菌株。【方法】选用蜡蚧菌属Lecanicillium 2个种的7个菌株,即刀孢蜡蚧菌L.psalliotae 3个菌株(HFLP006, HFLP021和HFLP025)和渐狭蜡蚧菌L.attenuatum 4个菌株(HFLA032, HFLA041, HFLA064和HFLA066),接种在SDAY平板上培养并观察菌落生长与产孢性状;以2.0×10⁷孢子/mL悬浮液用浸渍法测定对桃蚜无翅成蚜的致死率和致死中时(LT₅₀);进而用系列浓度(1.0×10⁴-1.0×10⁸孢子/mL) HFLP006和HFLA032菌株孢子悬浮液测定其对桃蚜无翅成蚜的致死中浓度(LC₅₀);利用体视显微镜逐日观察1.0×10⁸孢子/mL HFLP006菌株孢子悬浮液侵染后无翅成蚜的染病症状变化。【结果】在SDAY平板上7个...     

Host quality of different aphid species for rearing Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae)

This study aimed to evaluate the quality of the aphid Myzus persicae (Sulzer), Lipaphis erysimi (Kaltenbach) and Brevicoryne brassicae (L.) as hosts for the parasitoid Diaeretiella rapae (McIntosh). Parasitization by D. rapae was higher on M. persicae than on L. erysimi and B. brassicae. The time of development of D. rapae from egg to mummy or egg to adult male or female were shorter on M. persicae than on L. erysimi and B. brassicae. Moreover, D. rapae showed no significant differences in the emergence rate, sex ratio and longevity when reared on the three aphid species. Myzus persicae was the largest aphid host, with B. brassicae and L. erysimi being of intermediate and of small size, respectively. Diaeretiella rapae reared on M. persicae was larger than when reared on L. erysimi and B. brassicae, and females of D. rapae were significantly larger than males on M. persicae, but males of D. rapae were larger than females when reared on L. erysimi. No difference in size was detected between males and females in parasitoids reared on B. brassicae. Among the aphid species studied, M. persicae was found to be the most suitable to D. rapae.