Genetic structure and genetic relatedness of a hatchery stock of Senegal sole (Solea senegalensis) inferred by microsatellites

Solea senegalensis is a fish species in an early stage of domestication. A commercial hatchery in southern Spain experienced a dramatic failure in spawning and embryo survival, after incorporation into the broodstock of fish reared in their hatchery. To assess the impact of management on the stock quality, a population genetics study was made of adult broodstock present at this hatchery in 2000. The broodstock was composed of a group of fish of wild origin and two more groups from F₁ progeny. A set of eight microsatellite loci was used to compare genetic variability among the three groups and to establish the relationships between pairs of individuals within each group.Individuals from F₁ origin showed a substantial reduction in genetic variability when compared to those from the wild. There was a greater than 50% decrease in the number of alleles per locus corrected by sample size and 16% and 26% reductions in H_e values in the two F₁ groups, respectively. The degree of genetic relationship between individuals, evaluated by the relatedness estimator, rxy, and by graphical approaches, revealed a high proportion, almost 75%, of full-sibs and half-sibs in both F₁ groups, which might account for the reduction in overall variability. The high proportion of siblings also suggests a reproductive pattern in this stock in which few individuals breed successfully. This mating behaviour, along with factors inherent to selection and management systems, might be responsible for the negative effects on the reproductive capacity of the stock.     

Accuracy of pastoralists' memory-based kinship assignment of Ankole cattle: a microsatellite DNA analysis

This study aimed to estimate the level of relatedness within Ankole cattle herds using autosomal microsatellite markers and to assess the accuracy of relationship assignment based on farmers' memory. Eight cattle populations (four from each of two counties in Mbarara district in Uganda) were studied. Cattle in each population shared varying degrees of relatedness (first-, second- and third-degree relatives and unrelated individuals). Only memory-based kinship assignments which farmers knew with some confidence were tested in this experiment. DNA isolated from the blood of a subsample of 304 animals was analysed using 19 microsatellite markers. Average within population relatedness coefficients ranged from 0.010 ± 0.005 (Nshaara) to 0.067 ± 0.004 (Tayebwa). An exclusion probability of 99.9% was observed for both sire-offspring and dam-offspring relationships using the entire panel of 19 markers. Confidence from likelihood tests performed on 292 dyads showed that first-degree relatives were more easily correctly assigned by farmers than second-degree ones (p < 0.01), which were also easier to assign than third-degree relatives (p < 0.01). Accuracy of kinship assignment by the farmers was 91.9% ± 5.0 for dam-offspring dyads, 85.5% ± 3.4 for sire-offspring dyads, 75.6% ± 12.3 for half-sib and 60.0% ± 5.0 for grand dam-grand offspring dyads. Herd size, number of dyads assigned and length of time spent by the herder with their cattle population did not correlate with error in memorizing relationships. However, herd size strongly correlated with number of dyads assigned by the herder (r = 0.967, p < 0.001). Overall, we conclude that memorized records of pastoralists can be used to trace relationships and for pedigree reconstruction within Ankole cattle populations, but with the awareness that herd size constrains the number of kinship assignments remembered by the farmer.     

关联和亲缘选择的概念·原理及其研究进展

就关联和亲缘选择的概念、原理作一总结,从模型建立、利他和协作方面综述了关联和亲缘的研究进展综述。     

Comparison of marker- and pedigree-based methods for estimating heritability in an agroforestry population of Vitellaria paradoxa C.F. Gaertn. (shea tree)

We implemented a regression-based method between pairwise relatedness estimated from markers and phenotypic similarity to estimate heritability of traits related to leaf size and morphology in a wild tree population (Vitellaria paradoxa C.F. Gaertn.: shea tree). We then compared the results with heritability estimated with a classical pedigree-based method. We tested both approaches in an agroforestry population of this tree species, a very important one and abundant in the Sudano-Sahelian zone of Africa. Twelve microsatellite loci were used to estimate pairwise relatedness after selection of estimator coefficients based on Monte Carlo simulation. The regression-based method applied to 200 individuals did not display a significant trend with physical distance between trees for relatedness as well as for actual variance of relatedness. In consequence, estimates of narrow-sense heritability of traits related to leaf size were not significant. The pedigree-based method using a progeny test with 39 families and 15 individuals per family from the same population showed high and significant estimates of narrow-sense heritability for the same traits (h² = 0.36–0.95), demonstrating a marked genetic variation within the population. This discrepancy between methods stresses the poor performance of the molecular marker-based method. This can be explained by the absence of fine-scale structure within the agroforestry population of shea trees, other parameters being consistent with recommended values. The regression-based method does not seem well adapted to the agroforestry tree population. New experiments in tree populations and theoretical approaches are needed to evaluate the real potential of the marker-based methods.     

Genetic analysis and molecular mapping of two dominant complementary genes determining resistance to sugarcane mosaic virus in maize

Recent work and publications in human population genetics involving very dense SNP datasets suggest that the use of these markers will become common in plant breeding. The experience of human geneticists futher suggests that attention will need to be paid to the very high degree of genomic heterogeneity of population genetic measures such as genetic diversity. Dense marker sets will also allow more precision of estimates of relatedness between individual plants or pure-breeding lines.     

岷江上游干旱河谷区植被多样性与环境因子的相关性研究

对岷江上游干旱河谷区植被多样性与环境因子相关研究表明：1）阴、阳坡灌、草丛植物群落物种α多样性指标均随海拔升高表现出明显的增加趋势,阳坡呈现出中间低两头高的海拔梯度格局;阴坡总体呈现直线上升的趋势。2）该区土壤肥力总体水平高低表现为：中上部〉中部〉下部〉中下部、阴坡〉阳坡。低海拔地区土壤破碎,土壤含水量和土壤肥力极低,高海拔地区的土壤水分含量和土壤肥力都相对较高,立地条件也较适宜植物的生长。3）植被多样性与环境因子的相关分析表明,海拔、坡向、坡度、土壤含水量、速效N、速效K、有机质、全N、全K与灌丛群落多样性和生物量均呈正相关关系,而pH值、速效P、全P、全Ca与多样性和生物量呈负相关关系。通过逐步回归分析和主成分分析筛选出环境主导因子为全N、速效P、土壤含水量和速效N。     

Phylogenetic diversity analyses reveal disparity between fungal and bacterial communities during microbial primary succession

Early community assembly of fungi and bacteria differ in many ways, including their contrasting successional trajectories. We examined if fungal and bacterial primary successional dynamics are phylogenetically constrained. Microbial communities were queried across a recently deglaciated forefront using three measures of phylogenetic diversity. We analyzed these data at the Kingdom (fungi) and Domain (bacteria) levels plus at less-inclusive taxonomic hierarchies (Phylum and Class) as well as selected, well-defined functional groups (N-fixing and photosynthetic bacteria). Fungi and bacteria differed in their phylogenetic distributions across successional age. Phylogenetic diversity estimates did not change over successional age for fungi, whereas bacteria were strongly structured phylogenetically over successional age. Further, our results suggest that analyses at Kingdom or Domain levels may prove inadequate to understand successional dynamics. Investigations should include both broad (Kingdom or Domain) and less inclusive groups (perhaps metabolically distinct taxa) to better dissect community dynamics.