The clonal structure of apomictic populations of Darwinula stevensoni from Northern Italy lacustrine and riverine habitats has been analysed by allozyme electrophoresis. Thirty two sites were sampled and a total of 748 individuals were analysed. Only one polymorphic locus, Gpi, turned out to have enough variation to be informative. Two thirds of all individuals were homozygous for the most frequent allele but the frequency of this genotype was significantly lower in rivers (16%) than in lakes (92%). As a consequence homozygous clonal females are dominant in lacustrine habitats while heterozygous clonal females are dominant in riverine ones. Differences in genetic structure between habitats were observed even at distances of a few meters. Allele and genotype frequencies are significantly different between Lake Montorfano and its outflow (River Seveso) and between Mantova lakes and their two tributaries, the River Mincio and Corniano Channel. The former is also the outflow of Lake Garda. By laboratory experiments, we previously reported difference between genotypes: homozygous females from Mantova lakes show significantly lower starvation tolerance than heterozygous females from River Mincio. We discuss the hypothesis that habitat segregation is related to this difference. Riverine females should be better adapted to low productivity ecosystems than lacustrine ones.
We report data on the coexistence of apomictic and amphimictic lineages of Eucypris virens within the same pond and discuss the role of intraspecific hybridation as a source of genetic variability. We describe the genetic structure of 36 populations of E. virens from Europe. Most (28) populations were made up of putative parthenogenetic females, in 8 populations from Spain and Sicily we found males. Using three polymorphic allozyme markers (MPI, PGM and GPI) we described at least 214 different multilocus genotypes (clones) in a total of 1151 analysed specimens and confirmed that parthenogenetic reproduction is apomictic. Most multilocus genotypes, 74 %, were limited to a single population indicating the absence of a single widespread 'clone'. In E. virens, genetic diversity was not affected by latitudinal dine or reproductive mode and was probably the result of several processes. Apomictic lineages were the likely result of at least two independent transitions from different sexual ancestors located in Southern Europe, in Central Spain and in Sicily. Transitions probably happened after the last glaciation. We found sympatric amphimictic and apomictic females in Extremadura (Western Spain) and reported evidence of gene flow between different lineages (intraspecific hybridation). Further genetic differentiation within and among populations reflects time of divergence and mutation accumulation. We found putative polyploid multilocus genotypes in all populations with males, further support for the coexistence of lineages with different reproductive modes. The presence of polyploid genotypes (14 %) is probably underestimated and this limits our ability to assess the role of hybridisation as a major route to parthenogenesis.
The ever-increasing use of paternity analysis to estimate the dispersal capability of forest trees calls for a quantitative evaluation of potential errors due to sampling design. Previous studies on optimal sampling strategies for seed trapping experiments suggested a link between sampling effort and error rate in the reconstruction of the seed dispersal kernel. We considered 92 papers on paternity analysis to quantitatively assess the sampling strategy used to study the characteristics of pollen dispersal patterns (pollen immigration rate, distribution of male reproductive success and estimates of pollen dispersal kernel parameters). For each studied stand we report data on the sampling effort (the total number of sampled seeds, the number of mother trees and the number of seeds per mother tree) and additional information on the studied species and characteristics of the sampling areas. The reviewed papers used a median of 8 mother trees (acting as pollen traps in paternity analysis studies), a median of 29 seeds per mother tree and a median of 240 total sampled seeds. These are values (especially the number of mother trees) lower than usually found in classical seed trapping studies, for which accuracy and precision of seed dispersal estimates had already been assessed. These findings underline the need of evaluating the consequences of realistic sampling efforts on the estimation of parameters describing the pollen dispersal pattern to provide the basis for meaningful guidelines to paternity analysis.
Una gestione sostenibile dei sistemi forestali deve garantire anche la conservazione della biodiversita genetica, base del potenziale evolutivo delle specie. Per stabilire in che modo e misura i trattamenti selvicolturali incidano sulla distribuzione della variabilita genetica delle popolazioni arboree, e necessario chiarire quali siano le dimensioni della popolazione entro cui avviene flusso genico e, quindi, a che livello di frammentazione si inizi ad osservare un effetto sulla diversita genetica delle popolazioni. A tal fine sono state analizzate 25 popolazioni di faggio ( Fagus sylvatica L.) dell’Italia centrale, classificate, in base al crescente grado di isolamento, come Marginali, Cacuminali e Abissali. Trenta alberi di ogni popolazione sono stati mappati e caratterizzati con 5 marcatori microsatellite. Non sono state rilevate differenze significative tra i tre gruppi di popolazioni per quanto riguarda l’erosione genetica. L’analisi dei dati ottenuti ha permesso di individuare un significativo incremento del valore di F SG nel gruppo delle popolazioni ad isolamento piu elevato. Dato confermato dall’analisi delle coordinate principali effettuata sulla matrice della distanza genetica a coppie delle popolazioni: il gruppo delle popolazioni Abissali presenta maggiore differenziamento rispetto alle popolazioni Marginali-Cacuminali che mostrano invece la tendenza a raggrupparsi insieme al centro del grafico.
We tested the constancy of linkage relationships of randomly amplified polymorphic DNA (RAPD) marker loci used to construct a population-based consensus map in material from an Italian stand of Picea abies (L.) Karst. in 29 individuals from three Norwegian populations. Thirteen marker loci linked in the Italian stand did show a consistent locus ordering in the Norwegian population. The remaining 16 unlinked marker loci were spread over different linkage groups and (or) too far apart both in the population map and in this study. The limited validity of RAPD markers as genomic "hallmarks" resilient across populations is discussed. We also investigated the reliability of RAPD markers; only 58% of the RAPD markers previously used to construct the consensus map in the Italian population were repeatable in the same material. Of the repeatable ones 76.3% were amplified and found polymorphic in 29 megagametophyte sibships from three Norwegian populations.
