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.     

The attack of the clones: tracking the movement of insecticide-resistant peach-potato aphids Myzus persicae (Hemiptera: Aphididae)

Myzus persicae (Sulzer) collected in Scotland were characterized for four microsatellite loci, intergenic spacer fingerprints and the resistance mechanisms modified acetylcholinesterase (MACE), overproduced carboxylesterase and knockdown resistance (kdr). Microsatellite polymorphisms were used to define a limited number of clones that were either fully susceptible to insecticides or possessed characteristic combinations of resistance mechanisms. Within these clones, intergenic spacer fingerprints could either be very consistent or variable, with the latter indicating ongoing evolution within lineages, most likely derived from the same zygote. Two clones (termed A and B) possessed all three resistance mechanisms and predominated at sites treated with insecticides. Their appearance on seed potatoes and oilseed rape in Scotland in 2001 coincided with extensive insecticide use and severe control failures. Clones C, I and J, with no or fewer resistance mechanisms, were found in samples from 1995 and were dominant at untreated sites in 2001. A comparison of Scottish collections with those from other UK and non-UK sites provides insight into the likely origins, distribution and dynamics of M. persicae clones in a region where asexual (anholocyclic) reproduction predominates, but is vulnerable to migration by novel genotypes from areas of Europe where sexual (holocyclic) reproduction occurs.     

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.     

Clonal turnover of MACE-carrying peach-potato aphids (Myzus persicae (Sulzer), Homoptera: Aphididae) colonizing Scotland

Peach-potato aphids, Myzus persicae (Sulzer), collected in Scotland in the years 1995 and 2002-2004 were characterized using four microsatellite loci and three insecticide resistance mechanisms. From 868 samples, 14 multilocus genotypes were defined (designated clones A-N). Five of these (denoted A, B, H, M and N) carried modified acetylcholinesterase (MACE) resistance, the most recent resistance mechanism to have evolved in M. persicae. The current paper shows that the continued presence of MACE aphids is due to turnover, as clones A and B were replaced in field samples by clones H, M and N in later seasons. Thus, insecticide-resistant populations in Scotland can be attributed to multiple waves of rapid clone colonisations and not to the continued presence of stable resistant clones or mutation or sexual recombination in local populations. The MACE clones carried varying levels of the other insecticide resistance mechanisms, kdr and esterase. The presence of these mechanisms could alter the clones success in the field depending on insecticide spraying (positive selection) and resistance fitness costs (negative selection).     

Chromosomal localization of actin genes in the malaria mosquito Anopheles darlingi

Physical and genetic maps have been used for chromosomal localization of genes in vectors of infectious diseases. The availability of polytene chromosomes in malaria mosquitoes provides a unique opportunity to precisely map genes of interest. We report the physical mapping of two actin genes on polytene chromosomes of the major malaria vector in the Amazon, Anopheles darlingi (Diptera: Culicidae). Clones with actin gene sequences were obtained from a cDNA library constructed from RNA isolated from adult females and males of An. darlingi. Each of the two clones was mapped to a unique site on chromosomal arm 2L in subdivisions 21A (clone pl05‐A04) and 23B (clone pl17‐G06). The obtained results, together with previous mapping data, provide a suitable basis for comparative genomics and for establishing chromosomal homologies among major malaria vectors.     

Divergent ecology of sympatric clones of the asexual gecko,Lepidodactylus lugubris

We report differences in the thermal biology, elevational, temporal and geographic distributions of sympatric clones of the widespread asexual house gecko, Lepidodactylus lugubris. The two most common L. lugubris clones in Fiji, clones 2NA and 2NB, differ significantly in preferred temperature as measured in a laboratory heat gradient, but were similar in critical thermal maximum and minimum. Significant differences were found in the relative frequency of clones 2NA, 2NB, and a third Fijian clone, clone 3NB, at seven sites along an elevational gradient in Fiji. Clone 2NB was not collected at sites above 235 m, consistent with its higher preferred temperature, whereas clone 2NA was captured as high as 835 m. Clone 3NB was extremely rare at sealevel (1% of all individuals at three sites below 100 m), but predominated at the two highest-elevation sites (42% and 100%). Clones 2NA and 2NB did not differ significantly in their activity time or ambient activity temperature at low-elevation sites. Clone 3NB however, was active on significantly cooler nights at two of those sites. These significant inter-clonal differences in spatial and temporal distribution should allow a more complete utilization of resources by the assemblage of clones than by any single clonal genotype, and may promote coexistence of clones at a within-island and within-site scale. Clone 2NA, which is the most common clone in Fiji and has the broadest elevational distribution, also has the widest geographic distribution. It was the predominant clone at 27 of 34 sites surveyed in nine Pacific archipelagoes. This suggests that the ecological attributes that favor this clone in Fiji also favor it elsewhere in the Pacific despite differing environmental conditions and clonal composition in those areas.     

Influence of plant origin on propagation capacity and alkaloid biosynthesis during long-term <Emphasis Type="Italic">in vitro</Emphasis> cultivation of <Emphasis Type="Italic">Leucojum aestivum</Emphasis> L.

The investigation deals with in vitro clonal propagation of L. aestivum L. (summer snowflake), a threatened Amaryllidaceae plant species in Bulgaria used in the pharmaceutical industry as raw material for production of galanthamine-based medicines. Plants of known origin and with different alkaloid profile were taken from the living collection of the Institute of Botany, Sofia. Bulbs were used to initiate in vitro cultures and 24 clones were multiplied. The influence of the clone origin on the propagation coefficient, shoot and bulblet morphology, alkaloid profile and content of galanthamine, lycorine, and four related alkaloids was evaluated. Clones kept stable alkaloid profiles and for most of them, high regeneration rates were noted. Galanthamine content of some clones was commensurable with that of Bulgarian populations of L. aestivum of commercial importance. Five clones: four galanthamine-type and one lycorine-type were selected as promising for further investigation.     

Differences in adhesion, phagocytosis and virulence of clones from Entamoeba histolytica, strain HM1: IMSS

Orozco E., Suárez M. E. and Sánchez T. Differences in adhesion, phagocytosis and virulence of clones from Entamoeba histolytica, strain HM1: IMSS. International Journal for Parasitology15: 655–660. Clones isolated from Entamoeba histolytica, strain HM1: IMSS were tested for adhesion, phagocytosis and virulence after subculturing in liquid medium. Other clones were isolated from a subpopulation of strain HM1: IMSS, and highly phagocytic trophozoites were eliminated by irradiation, after incorporating bromodeoxiuridine into their DNA by phagocytosis of labelled bacteria. We thus obtained several clones from strain HM1: IMSS showing a different degree of phagocytosis. Some phagocytosis-deficient clones showed impairment in red blood cell adherence, while others showed a reduced intake of particles into their cytoplasm. The degree of phagocytosis always was associated with the virulence of the clone.     

Differentiation of Meloidogyne incognita and M. arenaria novel resistance phenotypes in Lycopersicon peruvianum and derived bridge-lines

Lycopersicon peruvianum PI 270435 clone 2R2 and PI 126443 clone 1MH were crossed reciprocally with three L. esculentum-L. peruvianum bridge-lines. The incongruity barrier between the two plant species was overcome; F₁ progeny were obtained from crosses between four parental combinations without embryo-rescue culture. Hybridity was confirmed by leaf and flower morphology and by the production of nematode-resistant F₁ progeny on homozygous susceptible parents. Clones of the five F₁ bridgeline hybrids were highly resistant to Mi-avirulent root-knot nematode (Meloidogyne incognita) at both 25°C and 30°C soil temperatures. However, only clones from PI 270435-3MH and PI 126443-1MH, and hybrids from PI 126443-1MH, were resistant to Mi-virulent M. incognita isolates at high soil temperature. Clones and hybrids from PI 270435-2R2 were not resistant to two Mi-virulent M. incognita isolates at high soil temperature. A source of heat-stable resistance was identified in bridge-line EPP-2, and was found to be derived from L. peruvianum LA 1708. Accessions of the L. peruvianum Maranon races, LA 1708 and LA 2172, and bridge-line EPP-2, segregated for heat-stable resistance to Mi-avirulent M. incognita, but were susceptible to Mi-virulent M. incognita isolates. Clone LA 1708-I conferred heat-stable resistance to M. arenaria isolate W, which is virulent to heat-stable resistance genes in L. peruvianum PI 270435-2R2, PI 270435-3MH, and PI 126443-1MH. Clone LA 1708-I has a distinct heat-stable factor for resistance to Mi-avirulent M. arenaria isolate W, for which the gene symbol Mi-4 is proposed. A Mi-virulent M. arenaria isolate Le Grau du Roi was virulent on all Lycopersicon spp. accessions tested, including those with novel resistance genes.     

Electrophoretic studies on populations of Myzus persicae in Scotland from October to December, 1976

Myzus persicae populations in Scotland were sampled during the last three months of 1976 and the individuals collected were classified into clones or groups of clones by electrophoretic analysis at three polymorphic loci. Samples from rape or mustard had a different range of clone compositions from samples from swede, cabbage or calabrese. The data provide further evidence in support of the oligogeneous population structure of this species during the period of the investigation.     

STRUCTURE OF CLONES OF NORTHERN PRICKLY ASH (XANTHOXYLUM AMERICANUM)

Clones of northern prickly ash (Xanthoxylum americanum) were excavated to expose their horizontal root structure and pattern of vegetative spread; stems and horizontal roots were mapped. Most of the root system was very shallow (< 10 cm deep). Stems and roots were aged from annual rings. The four clones studied ranged in age from 26 to 33 yrs. All root connections between shoots were maintained for the life of the clone. Clones were found to be single individuals in a physical as well as a genetic sense. There was virtually no overlap of adjacent clones; horizontal roots turned away or stopped growing when the border of another clone was encountered. No differences were found between male and female clones in above- or below-ground morphology. There was, however, a great deal of intrasexual variation among clones.     

Clone diversity of Eiseniella tetraedra (Oligochaeta: Lumbricidae) along regulated and free‐flowing boreal rivers

We have sampled populations of the parthenogenetic and polyploid earthworm Eiseniella tetraedra along the Ume, Vindel and Sävar Rivers in northern Sweden. The Vindel River is one of the last free‐flowing large rivers in NW Europe, while the Ume River, which flows parallel to it, is harnessed with twenty major dams. Clones were identified on the basis of overall enzyme phenotypes that were detected using starch gel electrophoresis. We found that clone pool diversity is higher along the Vindel River than along the Ume River and the clone pool similarity is, in a similar fashion, higher along the free‐flowing river. Evidently the dams stop effectively clone dispersal along the Ume River. Clone diversity is highest at the river mouth. The small free‐running Sävar River had also high clone diversity at the lower course of the river. Clone turnover between years is high. We found no evidence for parallel adaptation of clones along the two rivers.     

Life histories and habitat selection in Daphnia: divergent life histories of D. magna clones differing in phototactic behaviour

To test the hypothesis of co-adaptation of life histories and daytime vertical distribution (vertical migration behaviour) in Daphnia, life history characteristics were analysed for two positively, three negatively, and four intermediately phototactic Daphnia magna clones. Clones with different phototactic behaviour were found to have divergent life history strategies, with positively phototactic clones being good exploiters under the non-limiting conditions provided in the laboratory, i.e. low density (1 ind./1), high food concentration (6,5–7 10⁵ Scenedesmus cells/ml, restored daily) and high temperature (20° C). They realized a high intrinsic rate of increase at a small adult body size through rapid development, at a cost of producing small neonates. Negatively and intermediately phototactic clones had larger adult body sizes, and produced larger neonates that were more starvation-resistant than those of positively phototactic clones. Selection for high intrinsic rate of increase in intermediately phototactic clones was mediated through the production of large clutches.     

Barley yellow dwarf virus transmission and feeding behaviour of Rhopalosiphum padi on Hordeum bulbosum clones

A Hordeum bulbosum L. (Poaceae) clone A17 was identified, which showed complete resistance to Barley yellow dwarf virus (BYDV) and Cereal yellow dwarf virus (CYDV). It was not possible to infect plants of A17 with BYDV‐PAV, ‐MAV, or with CYDV‐RPV by the aphid vectors Rhopalosiphum padi (L.) or Sitobion avenae (Fabricius) (both Hemiptera: Aphididae). Plants of the A17 clone and of the BYDV‐susceptible H. bulbosum clone A21 revealed some resistance to R. padi compared to the susceptible winter barley cultivar Rubina [Hordeum vulgare L. (Poaceae)]. The development time to the imago was longer and the number of nymphs was reduced on both clones compared with cv. Rubina. The probing and feeding behaviour of R. padi on plants of the H. bulbosum clones was studied over 12 h and compared with that on plants of the barley cv. Rubina. Principal component analysis of the results of the feeding behaviour revealed a clear separation of the H. bulbosum genotypes from Rubina. On H. bulbosum the number of penetrations was higher but total feeding time was shorter. Significant differences were mainly found in the phloem feeding parameters for plants of both clones in comparison to Rubina, with the virus resistant A17 clone having the strongest effect and the susceptible A21 clone being intermediate. Most significant differences were found in parameters of the phloem salivation phase. On A17, an average of less than one (0.9) E1 phase per plant was observed (3.3 on A21 and 5.7 on Rubina) and its duration was reduced to less than 1 min (0.9 min) in comparison to 2.4 min on A21 and 5.7 min on Rubina. Also, the phloem feeding (E2) phase was clearly reduced on A17 plants with 0.5 E2 phases per test and a mean duration of 1.1 min in contrast with 2.9 and 3.5 E2 phases per test and 34.1 and 421.3 min for A21 and Rubina, respectively. These results point towards a phloem‐localized factor for aphid resistance in H. bulbosum, i.e., on A17 plants the phloem salivation time is too short for a successful infection by BYDV leading to vector resistance.     

Assessment of cues potentially mediating host selection of Leptoglossus occidentalis on Pinus contorta

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Aphid-transmitted viruses from lilies in Britain

Three aphid-transmitted viruses, tulip breaking, lily symptomless and cucumber mosaic, were obtained from lilies in Britain. Tulip breaking virus was detected by the leaf mottle produced in Lilium formosanum, cucumber mosaic virus by inoculation of sap to Nicotiana clevelandii and Chenopodium quinoa, and lily symptomless virus by electron microscopy of crude leaf extracts from symptomless L. formosanum. Liiy symptomless virus was transmitted by Myzus persicae, Macrosiphum euphorbiae, Aulacorthum solani and Aphis fabae. M. persicae, which in a small experiment appeared a more efficient vector than A. fabae, transmitted the virus in a non-persistent manner. This conflicts with the original report of transmission in a persistent manner by A. gossypii but no transmission by M. persicae. The possibility that there are two distinct viruses with similar pathological effects is discussed. Tulip breaking and lily symptomless viruses spread to bait plants of L. formosanum within a field planting of lilies in Scotland especially during July to September; lily symptomless virus was the more prevalent. No spread of cucumber mosaic virus was detected.     

Entamoeba Clone‐Recognition Experiments: Morphometrics,Aggregative Behavior,and Cell‐Signaling Characterization

Studies on clone‐ and kin‐discrimination in protists have proliferated during the past decade. We report clone‐recognition experiments in seven Entamoeba lineages (E. invadens IP‐1, E. invadens VK‐1:NS, E. terrapinae, E. moshkovskii Laredo, E. moshkovskii Snake, E. histolytica HM‐1:IMSS and E. dispar). First, we characterized morphometrically each clone (length, width, and cell‐surface area) and documented how they differed statistically from one another (as per single‐variable or canonical‐discriminant analyses). Second, we demonstrated that amebas themselves could discriminate self (clone) from different (themselves vs. other clones). In mix‐cell‐line cultures between closely‐related (E. invadens IP‐1 vs. E. invadens VK‐1:NS) or distant‐phylogenetic clones (E. terrapinae vs. E. moshkovskii Laredo), amebas consistently aggregated with same‐clone members. Third, we identified six putative cell‐signals secreted by the amebas (RasGap/Ankyrin, coronin‐WD40, actin, protein kinases, heat shock 70, and ubiquitin) and which known functions in Entamoeba spp. included: cell proliferation, cell adhesion, cell movement, and stress‐induced encystation. To our knowledge, this is the first multi‐clone characterization of Entamoeba spp. morphometrics, aggregative behavior, and cell‐signaling secretion in the context of clone‐recognition. Protists allow us to study cell–cell recognition from ecological and evolutionary perspectives. Modern protistan lineages can be central to studies about the origins and evolution of multicellularity.     

Intraspecific variation in zucchini yellow mosaic virus transmission by Myzus persicae and the impact of aphid host plant

Three isofemale lines of Myzus persicae (Sulzer), two lines collected from and reared on a brassicaceous host, and one line collected from and reared on a malvaceous host, were evaluated for their efficiency of transmitting Zucchini yellow mosaic virus (family Potyviridae, genus Potyvirus, ZYMV). In the first experiment, the transmission efficiencies of two clones from Brassicaceae (B1 and B2) were 52.0 and 60.8%, respectively, and these transmissions were not significantly different. In a second experiment, the transmission efficiencies of the clone on Malvaceae (M1) and clone B2 were significantly different at 35.6 and 55.7%, respectively. Further experiments evaluated host-related mechanisms that may have contributed to the differential transmissions observed between clones M1 and B2. Studies on short-term feeding showed that aphids continuously reared on okra, Abelmoschus esculentus (L.) Moench (malvaceous host), and those that were reared on okra and allowed a 24-h preacquisition feeding period on mustard, Brassica juncea (L.) Czern (brassicaceous host), had significantly lower transmission than aphids continuously maintained on mustard. Aphids reared on mustard and allowed a 24-h preacquisition feeding period on okra had intermediate transmission efficiency. In long-term host association studies, we found that aphids reared on mustard had significantly higher transmission efficiency than those reared on okra, and aphids reared first on okra and then switched to mustard had a transmission efficiency that was intermediate and not significantly different from the other two treatments. Our study reveals the existence of intraspecific variation in the transmission of ZYMV by M. persicae, and it suggests that to accurately assess the transmission capability of ZYMV by this species, multiple clones should be examined. Furthermore, the host plant on which the aphid is reared as well as the host plant on which it feeds just before virus acquisition contribute to ZYMV transmission efficiency of M. persicae.     

Identification of a Protein that Interacts with LeATL6 Ubiquitin‐protein Ligase E3 Upregulated in Tomato Treated with Elicitin‐Like Cell Wall Proteins of Pythium oligandrum

The expression of LeATL6, which encodes RING‐H2 zinc finger ubiquitin‐protein ligase E3, is highly induced in tomato roots treated with the elicitin‐like cell wall protein fraction (CWP) from the non‐pathogenic oomycete Pythium oligandrum, which enhances resistance to pathogens through a jasmonic acid (JA)‐dependent signalling pathway. In this study, the role of LeATL6 for CWP‐induced defence response was further analysed. To screen the putative target protein of LeATL6 for the CWP‐induced defence mechanism in tomato, we used a yeast two‐hybrid system to screen five clones encoding a protein that interacts with LeATL6. Four clones had a function associated with the ubiquitin‐proteasome system. Another positive clone encoded a protein sharing homology with S‐adenosylmethionine decarboxylase (SAMDC). In CWP‐treated tomato roots, SAMDC activity was clearly suppressed. Thus, the interaction of SAMDC with LeATL6 and the decreased SAMDC activity may be associated with JA‐dependent induced resistance in tomato treated with P. oligandrum.     

Growth and protection against oxidative stress in young clones and mature spruce trees (Picea abies L.) at high altitudes

Clones of Norway spruce (Picea abies L.) were grown for several years on an altitudinal gradient (1750 m, 1150 m and 800 m above sea level) to study the effects of environmental × genetic interactions on growth and foliar metabolites (protein, pigments, antioxidants). Clones at the tree line showed 4.3-fold lower growth rates and contained 60% less chlorophyll (per gram of dry matter) than those at valley level. The extent of growth reduction was clone-dependent. The mortality of the clones was low and not altitude-dependent. At valley level, but not at high altitude, needles of mature spruce trees showed lower pigment and protein concentrations than clones. In general, antioxidative systems in needles of the mature trees and young clones did not increase with increasing altitude. Needles of all trees at high altitude showed higher concentrations of dehydroascorbate than at lower altitudes, indicating higher oxidative stress. In one clone, previously identified as sensitive to acute ozone doses, this increase was significantly higher and the growth reduction was stronger than in the other genotypes. This clone also displayed a significant reduction in glutathione reductase activity at high altitude. These results suggest that induction of antioxidative systems is apparently not a general prerequisite to cope with altitude in clones whose mother plants originated from higher altitudes (about 650–1100 m above sea level, Hercycnic-Carpathian distribution area), but that the genetic constitution for maintenance of high antioxidative protection is important for stress compensation at the tree line. Received: 13 October 1998 / Accepted: 22 June 1999