Paolo Maria Bisol

Grape downy mildew spread and mite seasonal abundance in vineyards: evidence for the predatory mites Amblyseius andersoni and Typhlodromus pyri

Abstract Mite populations, in particular those belonging to the Phytoseiidae family were monitored in a commercial vineyard comprising two varieties (Prosecco and Pinot gris). On Prosecco, densities of Amblyseius andersoni , and to a lesser extent of Typhlodromus pyri increased when downy mildew symptoms occurred on a high number of leaves. On Pinot, A. andersoni was the dominant species and its densities markedly increased when downy mildew spread. A. andersoni populations were significantly larger on leaves with downy mildew symptoms than on leaves without symptoms and their densities were positively correlated to the extent of leaf surface showing symptoms. The effect of downy mildew on T. pyri populations was less marked. There were no relationships between downy mildew spread and spider mite abundance ( Panonychus ulmi ). Untreated plots or plots treated with folpet to control downy mildew were monitored in an experimental vineyard colonized by A. andersoni . A. andersoni populations increased when downy mildew symptoms spread and their densities were significantly higher in the control than on folpet plots. In another experimental vineyard, T. pyri densities were significantly higher in the control (severely infected by downy mildew) than on copper hydroxide plots. Isoelectric focusing electrophoresis (IEF) was employed to detect downy mildew in mites and glucose phosphate isomerase (GPI) was selected from among different enzymes. A stain corresponding to downy mildew in addition to the phytoseiid intrinsic stains was detected in a high proportion of A. andersoni and T. pyri collected from infected leaves. Downy mildew stains were not detected in P. ulmi females collected from infected leaves. Most A. andersoni and T. pyri females confined on symptomatic leaves became positive to IEF a few hours later.

GENETIC VARIABILITY IN DEEP-SEA ORGANISMS

Four species of deep-sea marine invertebrates, coming from the vicinity of the Rockall Trough (Shetland-Faroe Channel), have been studied by means of gel electrophoresis. The degree of genetic polymorphism found would seem to indicate absence of correlation with the particular environmental factors which characterize the sampled area. The results suggest that the adaptive strategies of organisms belonging to different phyla are different.

Studies on differential fitness of PGI genotypes with regard to temperature in Gammarus insensibilis (Crustacea: Amphipoda)

This paper deals with an experimental study of survival, combined with estimates of biochemical activity, of different genotypes at the PGI (phosphoglucose isomerase) locus in Gammarus insensibilis, in relation to temperature. Samples were collected in the lagoon of Venice during 1987. No mortality occurred at 10°C whereas at 27°C, where mortality reached the value of 50%, heterozygotes exhibited significantly higher survival than homozygotes. Experiments conducted in order to evaluate the PGI biochemical activity of homo- and heterozygote genotypes at three different temperatures (4°, 20° and 37°C) showed in all genotypes an increased activity from 4° to 20°C and a fall of activity from 20° to 37°C. Heterozygotes exhibited higher activity at all temperatures tested. The difference between homo- and heterozygotes became more obvious at 37°C. Our results suggest that in G. insensibilis the PGI locus, as already shown in other organisms, may be subject to selection and that the heterozygous genotypes possess superior fitness. The biochemical bases of the observed differences between genotypes are briefly discussed.

Characterization of Coastal Sites by Applying Genetic and Genotoxicity Markers in Mytilus Galloprovincialis and Tapes Philippinarum

Electrophoretic profiles of allozyme loci (Odh, Gpi, Idh, Pgm, 6Pgd) and early markers of genetic damage have been studied in parallel in Mytilus galloprovincialis and Tapes philippinarum from three coastal zones concerning the Venice Lagoon (off-shore. Malamocco outlet, inner industrial district). The selected species are filter-feeding bivalves inhabiting the water column and bottom sediments. respectively. In general. heterozygosity values were higher in clams than in mussels. Interestingly, heterozygote deficiency was detected in both species. particularly in samples from the industrial area where significant levels of DNA adducts. cytogenetic alterations and DNA strand breaks were also detected. Further work is necessary to extend these data and to investigate the relationships between long-lasting exposure to toxic and genotoxic contaminants and changes in the genetic structure of native mollusc populations.

Low variation at allozyme loci and differences between age classes at microsatellites in grass goby (Zosterisessor ophiocephalus) populations

Allozymes and microsatellites were used to assess the level and distribution of genetic variation in grass goby population samples collected from the Venice Lagoon between October 2001 and May 2002. Eighteen enzymatic loci were examined in 434 individuals, 14 of which resulted to be monomorphic, and 4 (GPI-B*, LDH-B*, PGM-A*, PGM-B*) showed 2 alleles scored in 6 individuals only. Comparison with previous data suggests that genetic variation has been eliminated in the Venice Lagoon population during the last few years at three loci. In contrast, analysis of 11 microsatellites in a subset of 192 individuals revealed substantial molecular variation. Analysis of molecular variance showed a lack of genetic differentiation inside the lagoon with respect to site and date of collection, sex, and level of pollution. Significant variation in allelic frequencies was found at microsatellite loci when small (one year old) males were compared to large males (two and three years old), suggesting that a complex population dynamics occurs in this species. The very low level of polymorphism of allozymes could be due to the evolutionary history of the species, or, considering the difference between small and large males, could be the result of recent effects of drift. The second hypothesis is supported by the comparison with previous allozyme studies of the species in the same area, that suggests that loss of heterozygosity at three loci occurred in the last 10 years.

PERMANENT GENETIC RESOURCES: Isolation and characterization of microsatellite loci in the Mediterranean shore crab Carcinus aestuarii (Decapoda, Portunidae)

We characterized nine polymorphic microsatellites in the Mediterranean shore crab Carcinus aestuarii (Decapoda: Portunidae). Microsatellites were isolated from a partial genomic library enriched for multiple motifs. All loci were polymorphic, with number of alleles ranging from two to 16 and a mean observed heterozygosity of 0.75. Seven loci were in Hardy–Weinberg equilibrium, and two showed weak heterozygote deficiency. No linkage disequilibrium was found between loci. In addition, we tested Hardy–Weinberg and linkage equilibrium of three Carcinus maenas loci, already reported to cross‐amplify in C. aestuarii. These molecular markers will be potentially useful to investigate genetic structure of this species.

A study of enzyme polymorphism in the Antarctic amphipod Paramoera walkeri Stebbing

SummaryStudies concerning the evaluation of the genetic structure and the mechanisms of genetic adapation to the Antarctic environment were carried out on two population samples (A and B) of the amphipod Paramoera walkeri Stebbing collected in two different areas of the Terranova Bay during the Italian Antarctic Expedition 1987/1988. The analyses of the level of genetic variability were conducted on starch gel. The electrophoretic results on the twenty two loci examined reveal a very low amount of genetic polymorphism in both populations with an average observed heterozygosity of 0.6% in population A and 0.7% in population B. The two populations can be considered part of a single breeding unit on the basis of the Student test for paired observations since the differences in single-locus heterozygosity for seven polymorphic loci are not significant (P>0.70). A possible explanation of the observed low genetic polymorphism is discussed in terms of genetic adaptation, as suggested by some results obtained in studies on enzyme activity carried out at the level of the PGI locus.

Environmental Factors, Genetic Differentiation, and Adaptive Strategies in Marine Animals

Recent advances in oceanographic research have revealed an impressive spatial and temporal heterogeneity in a number of biotic and abiotic features at different scales. However, the possibility of bringing physical and biological observations in the marine realm into harmony is often precluded by the inadequacy of methods for a correct determination of marine species, particularly at the level of secondary producers. Laboratory and field investigations show that many taxonomic entities, previously considered as “good” species, are instead clusters of reproductively isolated sibling species, or species in statu nascendi among which gene-flow may be reduced. Certain physical conditions play an active role in creating barriers to gene-flow. Populations of the same species from different geographic and/or ecological origin may exhibit genetic differentiation affecting a broad spectrum of characters. Some of these inherited differences are adaptive and maintained by natural selection. Similar genetic changes may be induced also by the impact of man on the environment. The relevance of both long term and short term effects on recruitment is briefly discussed.

Characterization of novel microsatellite markers in the Antarctic silverfish Pleuragramma antarcticum and cross species amplification in other Notothenioidei

We characterized nine polymorphic microsatellites by an enriched library from the Antarctic silverfish Pleuragramma antarcticum, a key species in the high Antarctic zone of the Southern Ocean. The number of alleles scored ranged from 7 to 39, whereas the observed and expected heterozygosity ranged from 0.4000 to 0.9750 and from 0.3943 to 0.9782, respectively. Cross-amplification was tested in the 3 species of the genus Chionodraco (Channichthyidae). These new microsatellites could potentially be useful in further investigations on P. antarcticum for which many questions on population structure and exposition to global environment change are still open to debate.

Polimorfismi enzimatici in copepodi del genere Acartia delta laguna di Venezia

In the framework of a study on the relationships between the ecological features of estuarine environments, the population dynamics and the genetic structure of the species which inhabit them, the populations of the following two planctonic Copepods from the lagoon of Venice were studied:Acartia clausi Giesbrecht andAcartia margalefi Alcaraz. Twelve isozymes (16 loci) of the first species and nine (12 loci) of the second were analyzed, by means of electroforetic methods, in samples of the inner and outer lagoon and from the adjacent sea. The mean genetic variability appears very similar in the two species;A. clausi shows a value of observed heterozigosity between 0,07 and 0,08,A. margalefi between 0,07 and 0,09. The data obtained suggest forA. clausi the condition typical for a single large population, whereasA. margalefi appears splitted in slightly-diversified, relatively isolated, subpopulations. The possible causes of such diversification are briefly discussed.RiassuntoNello studio dellie relazioni intercorrenti tra le caratteristiche ecologiche degli ambienti estuarini, la struttura genetica e la dinamica di popolazioni delle specie che li abitano, sono state prese in esame due specie di Copepodi planctonici presenti nella laguna di Venezia:Acartia clausi Giesbrecht eAcartia margalefi Alcaraz. Con tecniche elettroforetiche sono stati analizzati 12 sistemi enzimatici (16 loci) délia prima e 9 (12 loci) délia seconda in alcuni campioni provenienti da diverse zone della laguna e del mare prospiciente. La variabilità genetica media stimata è molto simile nelle due specie:A. clausi mostra un valore di eterozigosi media compreso tra 0,07 e 0,08 a seconda del campione. InA. margalefi le variazioni risultano comprese tra 0,07 e 0,09. I dati ottenuti suggeriscono, perA. clausi, l’esistenza di un’unica popolazione che occupa un vasto areale, mentreA. margalefi si presenta frazionata in subpopolazioni diversiricate e relativamente isolate tra di loro. Le possibili cause di tale diversificazione vengono brevemente discusse.