Annual dynamics of Zymoseptoria tritici populations in wheat cultivar mixtures: A compromise between the efficacy and durability of a recently broken-down resistance gene?

Cultivar mixtures slow polycyclic epidemics but may also affect the evolution of pathogen populations by diversifying the selection pressures exerted by their plant hosts at field scale. We compared the dynamics of natural populations of the fungal pathogen Zymoseptoria tritici in pure stands and in three binary mixtures of wheat cultivars (one susceptible cultivar and one cultivar carrying the recently broken-down Stb16q gene) over two annual field epidemics. We combined analyses of population “size” based on disease severity, and of population “composition” based on changes in the frequency of virulence against Stb16q in seedling assays with more than 3000 strains. Disease reductions were observed in mixtures late in the epidemic, at the whole-canopy scale and on both cultivars, suggesting the existence of a reciprocal protective effect. The three cultivar proportions in the mixtures (0.25, 0.5, and 0.75) modulated the decrease in (a) the size of the pathogen population relative to the two pure stands, (b) the size of the virulent subpopulation, and (c) the frequency of virulence relative to the pure stand of the cultivar carrying Stb16q. Our findings suggest that optimal proportions may differ slightly between the three indicators considered. We argue potential trade-offs that should be taken into account when deploying a resistance gene in cultivar mixtures: between the dual objectives “efficacy” and “durability,” and between the “size” and “frequency” of the virulent subpopulation. Based on current knowledge, it remains unclear whether virulent subpopulation size or frequency has the largest influence on interepidemic virulence transmission.     

Assessing the statistical training in animal science graduate programs in the United States: survey on statistical training

Statistical analysis of data and understanding of experimental design are critical skills needed by animal science graduate students (ASGS). These skills are even more valuable with the increased development of high-throughput technologies. The objective of this study was to evaluate the perceived statistical training of U.S. ASGS. A survey with 38 questions was shared across U.S. universities, and 416 eligible ASGS from 43 universities participated in this study. The survey included questions on the demographics and overall training, graduate education on statistics, and self-assessment on statistics and career path of ASGS. Several analyses were performed: relationship between perceived received education (PRE; i.e., how ASGS evaluated their graduate education in statistics) and perceived knowledge (PK; i.e., how ASGS evaluated their knowledge in statistics from their education); ranking of statistical topics based on PRE, PK, and confidence in performing statistical analyses (CPSA); cluster analysis of statistical topics for PRE, PK, and CPSA; and factors (demographic, overall training, interest in statistics, and field of study) associated with the overall scores (OS) for PRE, PK, and CPSA. Students had greater (P < 0.05) PRE than PK for most of the statistical topics included in this study. The moderate to high repeatability of answers within statistical topics indicates substantial correlations in ASGS answers between PRE and PK. The cluster analysis resulted in distinct groups of “Traditional” and “Nontraditional” statistical topics. ASGS showed lower (P < 0.05) scores of PRE, PK, and CPSA in “Nontraditional” compared with “Traditional” statistical methods. Several factors were associated (P < 0.05) with the OS of PRE, PK, and CSPA. In general, factors related to greater training and interest in statistics of ASGS were associated with greater OS, such as taking more credits in statistics courses, having additional training in statistics outside the classroom, knowing more than one statistics software, and more. This study provided comprehensive information on the perceived level of education, knowledge, and confidence in statistics in ASGS in the United States. Although objective measurements of their training in statistics are needed, the current study suggests that ASGS have limited statistical training on topics of major importance for the current and future trends of data-driven research in animal sciences.     

Effect of timing and duration of salt treatment during growth of a fragrant rice variety on yield and 2-acetyl-1-pyrroline, proline, and GABA Levels

In greenhouse experiments, Aychade, a fragrant rice variety, was grown under one level of salt solution (EC of 3800 ± 400 μS·cm(-1)) sufficient to induce salt stress in rice. Timing and duration of salt solution application varied according to the growth stages. 2-Acetyl-1-pyrroline (2AP), a characteristic flavor compound of fragrant rice as well as biogenetically related compounds, proline, and γ-aminobutyric acid (GABA) were quantified. Salt treatments induced 2AP synthesis in the leaves, but the increase was often higher in the vegetative phase. This increase was correlated with proline level but not with that of GABA. Interestingly the grains from all the salt treated plants contained significantly higher levels of 2AP (733-998 μg·kg(-1)) than those from the control (592 μg·kg(-1)). The highest 2AP synthesis occurred when the plants were subjected to salt treatment during whole vegetative or reproductive phases. However in the latter case crop yield decreased significantly.     

Effects of brood size manipulation and common origin on phenotype and telomere length in nestling collared flycatchers

Background

Most species of brown macroalgae recruit exclusively sexually. However, Fucus radicans, a dominant species in the northern Baltic Sea, recruits new attached thalli both sexually and asexually. The level of asexual recruitment varies among populations from complete sexual recruitment to almost (> 90%) monoclonal populations. If phenotypic traits have substantial inherited variation, low levels of sexual activity will decrease population variation in these traits, which may affect function and resilience of the species. We assessed the level of inherited variation in nine phenotypic traits by comparing variation within and among three monoclonal groups and one group of unique multilocus genotypes (MLGs) sampled in the wild.

Results

Of the nine phenotypic traits, recovery after freezing, recovery after desiccation, and phlorotannin content showed substantial inherited variation, that is, phenotypic variation in these traits were to a large extend genetically determined. In contrast, variation in six other phenotypic traits (growth rate, palatability to isopod grazers, thallus width, distance between dichotomies, water content after desiccation and photochemical yield under ambient conditions) did not show significant signals of genetic variation at the power of analyses used in the study. Averaged over all nine traits, phenotypic variation within monoclonal groups was only 68% of the variation within the group of different MLGs showing that genotype diversity does affect the overall level of phenotypic variation in this species.

Conclusions

Our result indicates that, in general, phenotypic diversity in populations of Fucus radicans increases with increased multilocus genotype (MLG) diversity, but effects are specific for individual traits. In the light of Fucus radicans being a foundation species of the northern Baltic Sea, we propose that increased MLG diversity (leading to increased trait variation) will promote ecosystem function and resilience in areas where F. radicans is common, but this suggestion needs experimental support.     

Arable weed decline in Northern France: Crop edges as refugia for weed conservation?

The maintenance of biodiversity in agro-ecosystems is often viewed as an insurance against an uncertain future, yet, there is increasing evidence of biodiversity loss in agricultural landscapes. Here, we examined long term trends in the arable weed flora of North-East France by revisiting 158 arable fields initially surveyed in the 1970s. We assessed changes in species richness, density and frequency of occurrence in weed communities as well as for subgroups that are recognised for their conservation value. We also evaluated the importance of crop edges as potential refugia for the threatened arable weeds. Among the 121 species recorded in both surveys, 40% had significantly declined in frequency while 10% had significantly increased. At the field level, we recorded a 42% decline in species richness and a 67% decline in species density. Trends were comparable for weed species of particular conservation value. In the 2000s survey, crop edges harboured levels of weed diversity that were intermediate between those found in field cores in the 1970s and in the 2000s survey. Our results indicated that many species of conservation value had disappeared or seriously decreased in the field core but still persisted in the crop edge. The consequences of this general decline and possible conservation options are discussed in the light of the results.     

Comparison of morphological traits and molecular markers to analyse diversity and structure of alfalfa (<Emphasis Type="Italic">Medicago sativa</Emphasis> L.) cultivars

Diversity and structure of populations may differ substantially between morphological traits and molecular markers. Explanations of such discrepancies are crucial for further progress in breeding as well as for the maintenance of genetic resources. Our objective was to compare indices of among-cultivars differentiation for morphological traits (Q_ST) and molecular markers (F_ST) in alfalfa (Medicago sativa), a legume forage species. Ten cultivars representing the Northern and Southern types commonly grown in Europe were investigated. For each cultivar, 40 genotypes were analysed with 16 SSR markers and four morphological traits measured in two locations and several cuts. Q_ST values were in general high (0.02–0.39) compared to the differentiation observed with molecular markers (F_ST = 0.01), especially for growth habit, indicating that morphological traits were more efficient to structure the diversity than molecular markers. For morphological traits, a clear separation of Northern and Southern cultivars was observed, whereas for molecular markers, no clear structure was detected. Nevertheless, the grazing type cultivar Luzelle was separated from the rest of the cultivars for both morphological traits and molecular markers. Although pairwise differences between cultivars were significant for both morphological traits and molecular markers, the main part of the variation was found within cultivars. This large within-cultivar variation may be explained, besides the outcrossing reproductive mode and autotetraploid genetics, by the recent history of M. sativa domestication in Europe and the frequent seed exchanges. Selection for morphological traits (Q_ST > F_ST) was achieved without modification of within-cultivar neutral diversity.     

Modelling historical mesocosm data: Application of a fish bioenergetics model in semi‐natural conditions

Developing ecological models for accurately predicting the dynamics of a population and individual physiological processes in field conditions is a challenging task for ecosystem management and ecological risk assessment. Here, we propose to assess the relevance of a dynamic energy budget (DEB) model calibrated using data previously generated from laboratory experiments for adult three‐spined sticklebacks (Gasterosteus aculeatus) living in semi‐natural conditions. We compared different ways of integrating different data sets such as temperature and prey abundance obtained in mesocosm experiments to assess the predictive capacity of the model. By this study, we provide recommendations for developing an appropriate environmental scenario (e.g. natural variations of food and temperature) for using a DEB model in a field context. We conclude that a DEB model calibrated with laboratory data can be used to predict the physiological processes of an organism living in semi‐natural conditions, but that the reproductive behaviour of the organism can affect the predictions. At last, we suggest that further studies on the feeding behaviour may be necessary for immature organisms.     

Responses to 19 generations of litter size selection in the Nebraska Index line. I. Reproductive responses estimated in pure line and crossbred litters

Our objective was to estimate responses in reproductive traits in the Nebraska Index line (I) after 19 generations of selection for increased litter size. Responses were estimated in dams producing pure line, F1, and three-way cross litters. A total of 850 litters were produced over six year-seasons, including 224 pure line litters, 393 F1 litters produced from I and C females mated with Danbred NA Landrace (L) or Duroc-Hampshire (T) boars, and 233 litters by F1 L x I and L x C females mated with T boars. Contrasts of means were used to estimate the genetic difference between I and C and interactions of line differences with mating type. Farrowing rates of lines I (u = 91.0%) and C (u = 92.8%) did not differ. Averaged across all genetic groups, mean number born alive per litter was 10.1 pigs, and number and weight of pigs weaned per litter, both adjusted for number nursed and weaning age of 12 d, were 9.7 pigs and 34.4 kg, respectively. Averaged across mating types, direct genetic effects of I were greater than C (P < 0.05) for total born (3.53 pigs), number born alive (2.53 pigs), number of mummified pigs (0.22 pig), and litter birth weight (2.14 kg). The direct genetic effect of line I was less than C (P < 0.05) for litter weaning weight (-1.88 kg). Interactions of line effects with crossing system were significant (P < 0.05) for total number born, number of stillborn pigs, number weaned, and litter weaning weight. In pure line litters, I exceeded C by 4.18 total pigs and 1.76 stillborn pigs per litter, whereas the estimate of I-C in F1 litters was 2.74 total pigs and 0.78 stillborn pig per litter. The contrast between I and C for number weaned and litter weaning weight in pure litters was 0.32 pig and -0.28 kg, respectively, compared with 0.25 pig and -2.14 kg in F1 litters. Crossbreeding is an effective way to use the enhanced reproductive efficiency of the Index line.     

External Phosphorus Load Estimates and P-Budget for the Hydroelectric Reservoir of Bort-les-Orgues,France

This paper presents two methods used to estimate the externalphosphorus load for the hydroelectric reservoir ofBort-Les-Orgues (in France's `Massif Central' region). The Pload calculated from export coefficients (150 t yr^-1) agreedwith field measurements taken during a one-year survey carriedout from March 1996 to February 1997 (121 t yr^-1). Exportcoefficients represent a good option for estimating phosphorusloads of other reservoirs in the region of Bort-Les-Orgues,provided that they display similar characteristics. Theseexternal load estimates are greater than the maximum permissibleload for a mesotrophic lake calculated from the OECD equations(40 t yr^-1); thus, a yearly reduction of about 60 t shouldideally be achieved. This target, however, is probably tooambitious, and measures to reduce both point and non-pointsources must be implemented for the reservoir to tbe mesotrophic.Moreover, Bort-Les-Orgues is a tourist area. As such, thepresence of algal blooms (a regular occurrence on the lake) dueto an excess of P in the lake's water inflow could actuallyexert a negative impact on regional economy.