Estimates of species diversity of free-living marine isopod crustaceans on coral reefs

 A core group of isopod crustacean genera appears to be present at many coral reef sites. Within these genera, however, species show high local endemicity. Based on the estimated percentage of endemism for the Atlantic (19% for individual sites, 90% for the tropical western Atlantic as a unit), the Indian Ocean (50%), the eastern-central Pacific (80%), and the western Pacific (40%), it is estimated that there are some 5,000 to 13,000 isopod species in the world’s coral reefs, and that some 2,000 to 6,000 of these are endemics. (At present, approximately 4,400 species of marine and 560 species of freshwater isopods have been described.) Based on the crudely estimated relative abundances of other peracaridan crustaceans in coral reefs (compared to isopods), the total diversity of reef amphipods, tanaidaceans, cumaceans, and mysidaceans is approximately 54,500 species. Accepted: 29 August 1997     

Olive genetic diversity assessed using amplified fragment length polymorphisms

 Amplified fragment length polymorphism (AFLP) analysis was used to study the genetic variation within and among populations of genus Olea. A group of genotypes, all of them cultivated varieties of a single species, Olea europaea, was compared with wild olives and with a group of individuals belonging to different Olea species. Five primer combinations were used which produced about 290 polymorphic bands. The data obtained were elaborated with the Nei’s genetic similarity coefficient, applying different clustering methods and the Principal Coordinate Analysis. Cultivars, wild olives and North-West African species formed groups clustering together at a similarity level of 0.56, while the Olea species from East Africa and Asia grouped separately. Species from the Indian Ocean and Australia showed the highest diversity. We hypothesize that cultivars and wild plants are different forms of the same O. europaea species. The Olea from East Africa and Asia may be assigned to a different species, while the role of O. laperrini as well as that of O. maroccana as an intermediary form is confirmed. Received: 30 April 1998 / Accepted: 13 August 1998     

Breeding bird assemblages of eastern Mediterranean shrublands: composition, organisation and patterns of diversity

The patterns of α-diversity and the structure and organisation of breeding bird assemblages were studied in four vegetation stages (characteristic of Mediterranean shrublands) on an eastern Mediterranean island (Crete, Greece): low phrygana, tall phrygana, low maquis and tall maquis. Phrygana differed significantly from maquis, in regard to the community metrics, composition and the homogeneity of bird assemblages. Moreover, detrended correspondence analysis ordered the census plots along a continuum of increasing vegetation height. On the other hand, within-maquis differences were few, while no significant differences were found within phrygana stages. Based upon the observed patterns, we recognise three vegetation groups: (1) phrygana, with low α-diversity and abundance and homogenous bird assemblages; (2) low maquis with relatively high α-diversity and heterogenous bird assemblages; and (3) tall maquis with relatively high α-diversity and heterogenous assemblages in which “woodland” bird species contribution is prominent.     

Benthic microalgal diversity enhanced by spatial heterogeneity of grazing

This study presents model experiments on the effect of the spatial pattern of herbivory on primary producer diversity. Microalgal biofilms (periphyton) were exposed to different mixtures of two benthic herbivores, the isopod Idothea chelipes and the gastropod Littorina littorea. The herbivores are similar in their feeding selectivity but differ strongly in the spatial pattern of grazing. Idothea did not increase the spatial heterogeneity of algal cell densities beyond the level of ungrazed controls (<1 order of magnitude between local minima and maxima at the 1 mm² scale). Littorina grazing, in contrast, created a pronounced spatial heterogeneity with maximum:minmum ratios of almost 3 orders of magnitude. When algae were exposed to mixtures of both gazers, the spatial heterogeneity of microalgal cell densities increased with an increasing proportion of Littorina in the herbivore mixture. Algal species richness, diversity and evenness also increased with increasing proportions of Littorina, and was highly significantly correlated with the spatial heterogeneity of cell densities. Received: 25 May 1999 / Accepted: 14 September 1999     

The effects of long-term nitrogen loading on grassland insect communities

Just as long-term nitrogen loading of grasslands decreases plant species richness and increases plant biomass, we have found that nitrogen loading decreases insect species richness and increases insect abundances. We sampled 54 plots that had been maintained at various rates of nitrogen addition for 14 years. Total insect species richness and effective insect diversity, as well as herbivore and predator species richness, were significantly, negatively related to the rate of nitrogen addition. However, there was variation in trophic responses to nitrogen. Detritivore species richness increased as nitrogen addition increased, and parasitoids showed no response. Insect abundances, measured as the number of insects and insect biovolume (an estimate of biomass), were significantly, positively related to the rate of nitrogen addition, as were the abundances of herbivores and detritivores. Parasitoid abundance was negatively related to the rate of nitrogen addition. Changes in the insect community were correlated with changes in the plant community. As rates of nitrogen addition increased, plant species richness decreased, plant productivity and plant tissue nitrogen increased, and plant composition shifted from C₄ to C₃ grass species. Along this gradient, total insect species richness and effective insect diversity were most strongly, positively correlated with plant species richness. Insect biovolume was negatively correlated with plant species richness. Responses of individual herbivores varied along the nitrogen gradient, but numbers of 13 of the 18 most abundant herbivores were positively correlated with their host plant biomass. Although insect communities did not respond as strongly as plant communities, insect species richness, abundance, and composition were impacted by nitrogen addition. This study demonstrates that long-term nitrogen loading affects the entire food chain, simplifying both plant and insect communities. Received: 18 May 1999 / Accepted: 5 January 2000     

Levels of genetic diversity at different stages of the domestication cycle of interior spruce in British Columbia

Concerns over the reductionist nature of the domestication of forest-tree species focus on the possibility of potential genetic erosion during this process. To address these concerns, genetic diversity assessments in a breeding zone the Province of British Columbia “interior” spruce (Picea glauca×engelmanni) program was conducted using allozyme markers. Genetic-variation comparisons were made between natural and production (seed orchard) populations as well as seed and seedling crops produced from the same breeding zone’s seed orchard. The natural population sample consisted of a total of 360 trees representing three stands within each of three watersheds present in the Shuswap-Adams low-elevation zone of interior British Columbia. Small amounts of genetic differentiation were observed among the nine natural populations (4%) and this was attributable to extensive gene flow Consequently, the sum of these nine populations was considered as a baseline for the genetic variation present in the breeding zone. The comparisons between the seed orchard and the breeding zone produced a similar percentage of polymorphic loci while the expected hetrozygosity (0.207 vs 0.210) and the average number of alleles per locus (2.7 vs 2.4) were slightly lower in the seed orchard. A total of seven natural populations’ rare alleles were not present in the orchard population, while one allele was unique to the orchard. The %P increased to 70.6% in the seedlot, but dropped to the natural populations level (64.7%) in the plantation. The observed increase in %P was a result of pollen contamination in the orchard. It is suspected that the reduction in the plantation was caused by an unintentional selection in the nursery. Simulated roguing in the orchard did not drastically reduce even if up to 50% of the orchard’s clones were rogued. However, roguing was associated with a reduction in the average number of alleles per locus (i.e., sampling effect). Received: 2 January 1996 / Accepted: 24 May 1996     

Soil nitrogen availability and nitrification in Mediterranean shrublands of varying fire history and successional stage

The short-term effect of a single fire, and the long-term effect of recent fire history and successional stage on total and mineral N concentration, net nitrogen mineralization, and nitrification were evaluated in soils from a steep semi-arid shrubland chronosequence in southeast Spain. A single fire significantly increased soil mineral N availability and net nitrification. Increasing fire frequency in the last few decades was. associated with a sharp decrease in surface soil organic matter and total N concentrations and pools, and with changes in the long-term N dynamic patterns. The surface-soil extractable NH₄ ⁺:NO₃ ^– ratio increased throughout the chronosequence. All net mineralized N in laboratory incubations from all sites was converted to nitrate, suggesting that allelochemic inhibition of net nitrification is probably not important in this system. Net nitrification in samples during incubation increased through the sere. The maximum rate of net nitrification (k_max) increased through the first three stages of the sere. A linear relationship was found between total soil N and N mineralization, and both k_max and net nitrification for the first three stages of the sere, suggesting that total N and ammonification are likely to be the control mechanisms of nitrification within the sere. The oldest site exhibited the lowest specific k_max and the highest, potential soil respiration rate suggesting that a lower N quality and increasing competition for ammonium might also limit nitrification at least in the long-unburned garrigue site.     

The genetic diversity of annual wild soybeans grown in China

Annual wild soybeans (Glycine soja), the ancestors of cultivated soybeans (G. max), are important sources of major genes for resistance to pests, diseases and environmental stresses. The study of their genetic diversity is invaluable for efficient utilization, conservation and management of germplasm collections. In this paper, the number of accessions, the variation of traits, the genetic diversity indexes (Shannon index) and the coefficient of variation were employed to study the geographical distribution of accessions, genetic diversity of characters and genetic diversity centers of annual wild soybean by statistical analysis of the database from the National Germplasm Evaluation Program of China. Most annual wild soybeans are distributed in Northeast China, and the number of accessions decreases from the Northeast to other directions in China. The genetic diversity indexes (Shannon index) were 0.49, 0.74, 0.02, 0.55, 1.45, 2.41, 1.27 and 1.89 for flower color, sootiness of seed coat, cotyledon color, pubescence color, hilum color, leaf shape, stem type and seed color, respectively. Coefficients of variation were 7.1%, 28.7%, 76.43% and 18.2% for protein content, oil content, 100-seed weight and days to maturity, respectively. Three genetic diversity centers, the Northeast, the Yellow River Valley and the Southeast Coasts of China, are proposed based on the geographical distribution of the number of accessions, genetic diversity and the multivariate variation coefficient. Based on these results and Vavilov’s theory of crop origination, two opposing possible models for the formation of the three centers are proposed, either these centers are independent of each other and the annual wild soybeans in these centers originated separately, or the Northeast center was the primary center for annual wild soybeans in China, while the Yellow River Valley center was derived from this primary center and served as the origin for the Southeast Coast center. Received: 25 June 2000 / Accepted: 18 October 2000     

Combining genetic gain and diversity by considering average coancestry in clonal selection of Norway spruce

 Genetic relationship within a population can be measured by average coancestry. This can also be expressed as an effective number which represents the relative genetic diversity of the population. The goal of breeding can be formulated to maximise genetic value minus average coancestry times a constant (the “penalty constant”). An iterative search algorithm can then be used to find the best selections for meeting this goal. Two such algorithms, one for a fixed number of selections and the other for a variable optimum number, were applied to select a mixture of field-tested Norway spruce clones with known parents. The results were compared with those from the conventional method of restricting parental contributions to the selected population as a means to control diversity. Coancestry-adjusted selection always yielded more gain than restricted selection at a given effective population size (except under circumstances where the methods were equivalent). Expressed another way, at any given level of gain, coancestry-adjusted selection maintained a larger effective population size than did restricted selection. The relative superiority of coancestry-adjusted selection declined when the effective population size approached the lowest value, that at which no penalty or restriction was applied. The method was extended by the second search algorithm to optimise the selected number of clones. The optimal number of clones can be rather large when diversity is heavily valued, but the reduction in genetic gain becomes large. Received: 7 April 1997 / Accepted: 9 June 1997     

Sequences of colonization,diversity, biomass,and productivity of macroinvertebrates on artificial substrates in a freshwater canal

The sequence of colonization, species diversity (% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaaca% qGKbaaaaaa!36E5!\[\overline {\text{d}} \]), biomass, and productivity of macroinvertebrates on artificial substrates was determined in a relatively constant environment freshwater canal. Three substrates were removed weekly during a 16 week test period. Community structure of benthic macroinvertebrates was determined at the onset and end of the test period and compared with substrate community structure. Calopsectra sp. was the dominant early colonizing organism; Dicrotendipes sp. and Dicrotendipes modestus were also abundant. In late collections other chironomids, ephemeropterans, gastropods, oligochaetes, amphipods, and trichopterans occurred. Trichopterans were generally dominant in numbers and biomass in later collections. A total of 104 were collected on the substrates.Collection diversity (% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaaca% qGKbaaaaaa!36E5!\[\overline {\text{d}} \]) began at 3.42 (week 1), decreased to 2.72 in the third week, and then continually increased for the remainder of the test period to 4.43. Cumulative diversity had a similar trend, decreasing from 3.42 (week 1) to 3.06 in the fourth week, and then increasing to 4.05. Neither collection % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaaca% qGKbaaaaaa!36E5!\[\overline {\text{d}} \] or cumulative % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaaca% qGKbaaaaaa!36E5!\[\overline {\text{d}} \] reached an asymptote in the 16 week period.Collection biomass began at 0.0867 g/0.26 m² for week one and was 1.0575 g/0.26 m² at the end of the test period. Biomass increased linearly for seven weeks, fluctuated widely until week 14, then increased sharply for the remainder of the test period. Productivity ranged from –3.42 g/m²/wk in the eighth week to 5.10 g/m²/wk in the last collection. Biomass and productivity were greatly affected by the presences or absences of a relatively few large organisms.One hundred two taxa were collected from the benthic samples, 34 not being present on the substrates. Limodrilus hoffmeisteri was the dominant benthic organism, while Calopsectra sp. and Polypedilum sp. were also abundant. The February benthic diversity % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaaca% qGKbaaaaaa!36E5!\[\overline {\text{d}} \] was 4.54 and the June % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaaca% qGKbaaaaaa!36E5!\[\overline {\text{d}} \] was 4.05.     

Interacting influence of mycorrhizal symbiosis and competition on plant diversity in tallgrass prairie

In tallgrass prairie, plant species interactions regulated by their associated mycorrhizal fungi may be important forces that influence species coexistence and community structure; however, the mechanisms and magnitude of these interactions remain unknown. The objective of this study was to determine how interspecific competition, mycorrhizal symbiosis, and their interactions influence plant community structure. We conducted a factorial experiment, which incorporated manipulations of abundance of dominant competitors, Andropogon gerardii and Sorghastrum nutans, and suppression of mycorrhizal symbiosis using the fungicide benomyl under two fire regimes (annual and 4-year burn intervals). Removal of the two dominant C₄ grass species altered the community structure, increased plant species richness, diversity, and evenness, and increased abundance of subdominant graminoid and forb species. Suppression of mycorrhizal fungi resulted in smaller shifts in community structure, although plant species richness and diversity increased. Responses of individual plant species were associated with their degree of mycorrhizal responsiveness: highly mycorrhizal responsive species decreased in abundance and less mycorrhizal responsive species increased in abundance. The combination of dominant-grass removal and mycorrhizal suppression treatments interacted to increase synergistically the abundance of several species, indicating that both processes influence species interactions and community organization in tallgrass prairie. These results provide evidence that mycorrhizal fungi affect plant communities indirectly by influencing the pattern and strength of plant competitive interactions. Burning strongly influenced the outcome of these interactions, which suggests that plant species diversity in tallgrass prairie is influenced by a complex array of interacting processes, including both competition and mycorrhizal symbiosis. Received: 7 April 1999 / Accepted: 30 July 1999     

Marine molluscs and fish as biomarkers of pollution stress in littoral regions of the Red Sea, Mediterranean Sea and North Sea

The intensive development of industry and urban structures along the seashores of the world, as well as the immense increase in marine transportation and other activities, has resulted in the deposition of thousands of new chemicals and organic compounds, endangering the existence of organisms and ecosystems. The conventional single biomarker methods used in ecological assessment studies cannot provide an adequate base for environmental health assessment, management and sustainability planning. The present study uses a set of novel biochemical, physiological, cytogenetic and morphological methods to characterize the state of health of selected molluscs and fish along the shores of the German North Sea, as well as the Israeli Mediterranean and Red Sea. The methods include measurement of activity of multixenobiotic resistance-mediated transporter (MXRtr) and the system of active transport of organic anions (SATOA) as indicators of antixenobiotic defence; glutathione S-transferase (GST) activity as an indicator of biotransformation of xenobiotics; DNA unwinding as a marker of genotoxicity; micronucleus test for clastogenicity; levels of phagocytosis for immunotoxicity; cholinesterase (ChE) activity and level of catecholamines as indicators of neurotoxicity; permeability of external epithelia to anionic hydrophilic probe, intralysosomal accumulation of cationic amphiphilic probe and activity of non-specific esterases as indicators of cell/tissue viability. Complete histopathological examination was used for diagnostics of environmental pathology. The obtained data show that the activity of the defensive pumps, MXRtr and SATOA in the studied organisms was significantly higher in the surface epithelia of molluscs from a polluted site than that of the same species from control, unpolluted stations, providing clear evidence of response to stress. Enhanced frequency of DNA lesions (alkaline and acidic DNA unwinding) and micronucleus-containing cells was significantly higher in samples from polluted sites in comparison to those from the clean sites that exhibited genotoxic and clastogenic activity of the pollutants. In all the studied molluscs a negative correlation was found between the MXRtr levels of activity and the frequency of micronucleus-containing hemocytes. The expression of this was in accordance with the level of pollution. The complete histopathological examination demonstrates significantly higher frequencies of pathological alterations in organs of animals from polluted sites. A strong negative correlation was found between the frequency of these alterations and MXRtr activity in the same specimens. In addition to these parameters, a decrease in the viability was noted in molluscs from the polluted sites, but ChE activities remained similar at most sites. The methods applied in our study unmasked numerous early cryptic responses and negative alterations of health in populations of marine biota sampled from the polluted sites. This demonstrates that genotoxic, clastogenic and pathogenic xenobiotics are present and act in the studied sites and this knowledge can provide a reliable base for consideration for sustainable development. Received: 2 March 1999 / Received in revised form: 2 August 1999 / Accepted: 3 August 1999     

Molecular diversity at the major cluster of disease resistance genes in cultivated and wild Lactuca spp.

Diversity was analyzed in wild and cultivated Lactuca germplasm using molecular markers derived from resistance genes of the NBS-LRR type. Three molecular markers, one microsatellite marker and two SCAR markers that amplified LRR-encoding regions, were developed from sequences of resistance gene homologs at the main resistance gene cluster in lettuce. Variation for these markers were assessed in germplasm including accessions of cultivated lettuce, Lactuca sativa L. and three wild Lactuca spp., L. serriola L., L. saligna and L. virosa L. Diversity was also studied within and between natural populations of L. serriola from Israel and California; the former is close to the center of diversity for Lactuca spp. while the latter is an area of more recent colonization. Large numbers of haplotypes were detected indicating the presence of numerous resistance genes in wild species. The diversity in haplotypes provided evidence for gene duplication and unequal crossing-over during the evolution of this cluster of resistance genes. However, there was no evidence for duplications and deletions within the LRR-encoding regions studied. The three markers were highly correlated with resistance phenotypes in L. sativa. They were able to discriminate between accessions that had previously been shown to be resistant to all known isolates of Bremia lactucae. Therefore, these markers will be highly informative for the establishment of core collections and marker-aided selection. A hierarchical analysis of the population structure of L. serriola showed that countries, as well as locations, were significantly differentiated. These differences may reflect local founder effects and/or divergent selection. Received: 7 March 1999 / Accepted: 25 March 1999     

A mini core subset for capturing diversity and promoting utilization of chickpea genetic resources in crop improvement

A core collection is a chosen subset of large germplasm collection that generally contains about 10% of the total accessions and represents the genetic variability of entire germplasm collection. The purpose of a core collection is to improve the use of genetic resources in crop improvement programs. In many crops the number of accessions contained in the genebank are several thousands, and a core subset consisting of 10% of total accessions would be an unwieldy proposition. In this article we have suggested a two-stage strategy to select a chickpea mini core subset consisting of only about 1% of the entire collection held in trust at ICRISAT’s genebank (16,991 accessions). This mini core subset still represents the diversity of the entire core collection. The first stage involves developing a representative core subset (about 10%) from the entire collection using all the available information on origin, geographical distribution, and characterization and evaluation data of accessions. The second stage involves evaluation of the core subset for various morphological, agronomic, and quality traits, and selecting a further subset of about 10% accessions from the core subset. At both stages standard clustering procedure was used to separate groups of similar accessions. A mini core subset consisting 211 accessions from 1,956 core subset accessions, using data on 22 morphological and agronomic traits, was selected. Newman- Keuls’ test for means, Levene’s test for variances, the chi-square test and Wilcoxon’s rank-sum non-parametric test for frequency distribution analysis for different traits indicated that the variation available in the core collection has been preserved in the mini core subset. The most important phenotypic correlations which may be under the control of coadapted gene complexes, were also preserved in the mini core. This mini core subset, due to its drastically reduced size, will prove to be a point of entry to proper exploitation of chickpea genetic resources. Received: 20 August 2000 / Accepted: 25 September 2000     

Genetic diversity within and among maize populations: a comparison between isozyme and nuclear RFLP loci

 In order to compare the potential of enzyme and DNA markers to investigate genetic diversity within and among populations, ten maize populations were characterized for (1) 20 isozyme loci and (2) restriction fragment length polymorphism (RFLP) for 35 probe-enzyme combinations. Each population was represented by a sample of at least 30 individuals. The average number of alleles detected per locus was clearly higher for RFLPs (6.3) than for isozymes (2.4). Similarly, total diversity was higher for RFLPs (0.60) than for isozymes (0.23). This difference is consistent with observations on inbred-line collections and can be related to the fact that many variations at the DNA level do not change the amino-acid composition or the global charge of proteins. By contrast, the magnitude of population differentiation, relative to the total diversity, was similar for isozymes (23%) and RFLPs (22%). This suggests that the isozyme and RFLP loci considered in this study are subject to similar evolutionary forces, and that both are mostly neutral. However, RFLPs proved clearly superior to isozymes both to (1) identify the origin of a given individual and (2) reveal a relevant genetic structure among populations. The higher polymorphism observed for RFLP loci and the greater number of these loci contributed to the superior discriminative ability of the RFLP data. Received: 1 June 1997 / Accepted: 3 November 1997     

QTLs for agronomic traits from a Mediterranean barley progeny grown in several environments

In order to identify quantitative trait loci (QTLs) controlling agronomic trait variation and their consistency under Mediterranean conditions in barley, a progeny of 167 recombinant inbred lines (RILs) and the parents Tadmor and Er/Apm, originating from the Mediterranean basin, were grown under Mediterranean conditions in 1995, 1996, 1997 and 1999. For the 2 first years (M95 and G96), one replicate was grown, but for the latter (M97 and M99) two rainfed (rain) and two irrigated (ir) replicates were produced. M95, G96, M97rain, M97ir, M99rain and M99ir were considered as six different environments and were compared in terms of their meteorological conditions and water supply. Grain yield and yield components were assessed, as well as heading date and plant height. Highly significant differences were noted between environments. QTLs were obtained from each environment separately and from a multiple environment analysis (simple interval mapping and simplified composite interval mapping). Despite heterogeneity between environments, numerous QTLs were common to several environments. This was particularly true for traits like plant height and thousand-grain weight. The most reliable QTLs which explained the largest part of the phenotypic variation were obtained for plant height on chromosomes 3 (3H) and 6 (6H). The multiple-environment analysis provided an opportunity to identify consistent QTLs for agronomic traits over six Mediterranean environments. A total of 24 consistent QTLs were detected. Out of these, 11 presented main effects, seven presented QTL×E interaction, and six presented both effects. In addition, 18 of the consistent QTLs were common to other published work and six seemed specific to this study. These latter QTLs could be involved in Mediterranean adaptive specificities or could be specific to the studied genetic background. Finally, when the rainfed and the irrigated environments of M97 were considered separately, a total of 16 QTLs presenting main effects over the two water conditions were identified, whereas five QTLs seemed dependent on the water conditions. Received: 31 January 2001 / Accepted: 19 February 2001     

The meiofaunal community structure of a Mediterranean lagoon (Gialova lagoon, Ionian Sea)

The higher taxonomic structure of a meiofaunal community was investigated in an Eastern Mediterranean lagoon (Gialova lagoon, Ionian Sea). Seven stations were sampled on a seasonal basis during 1995–1996. Stations within the lagoon were found to support a maximum of 14 meiofaunal taxa with densities ranging from 17 to over 2000 individuals per 10 cm². Nematodes were not always the most abundant taxa, although they dominated about half of the total 28 samples. Uni- and multivariate analyses were employed to study the community structure. The distribution pattern of the meiofaunal community varied both across the lagoon and over the seasons. On the basis of the spatial differences a meiofaunal coenocline, correlated with the degree of isolation, was observed, composed of mainly two zones: one defined by the area close to the marine channel and the other the more isolated area in the inner lagoon. Meiofaunal distribution pattern was not clearly correlated to one environmental variable, but rather to many, and spatial and seasonal effects could be seen. Received: 2 March 1999 / Received in revised form: 6 December 1999 / Accepted: 9 December 1999