Ranked set sampling for replicated sampling designs

In practical ecological sampling studies, a certain design (such as plot sampling or line-intercept sampling) is usually replicated more than once. For each replication, the Horvitz-Thompson estimation of the objective parameter is considered. Finally, an overall estimator is achieved by averaging the single Horvitz-Thompson estimators. Because the design replications are drawn independently and under the same conditions, the overall estimator is simply the sample mean of the Horvitz-Thompson estimators under simple random sampling. This procedure may be wisely improved by using ranked set sampling. Hence, we propose the replicated protocol under ranked set sampling, which gives rise to a more accurate estimation than the replicated protocol under simple random sampling.     

Genetic diversity of heavy metal-tolerant populations in Silene paradoxa L. (Caryophyllaceae): a chloroplast microsatellite analysis

Eight populations of Silene paradoxa L. (Caryophyllaceae) growing in copper mine deposits, in serpentine outcrops or in uncontaminated soil in central Italy were studied. Genetic diversity was estimated using five polymorphic chloroplast microsatellite loci (cpSSR), identifying 27 different chloroplast haplotypes. The effective number of alleles, the haplotypic diversity and a stepwise mutational model-based parameter (DSH2) were computed. The effective number of alleles observed within populations from copper mine deposits was 20% that of the serpentine neighbouring populations, suggesting the occurrence of a founder effect. Moreover, 13 of the 27 different haplotypes scored were exclusive to only one population, indicating genetic isolation for all tolerant populations. Even the copper-tolerant populations appeared to have evolved independently. Finally, analysis of molecular variance (AMOVA) of the cpSSR markers gave statistical significance to the grouping of populations according to their geographical location. This study demonstrates that cpSSR markers could be a useful complementary tool to isoenzymes or random amplified polymorphic DNA markers for elucidating the pattern of genetic differentiation in heavy metal-tolerant populations.