Use of GGEbiplot methodology and Griffing's diallel method for genetic analysis of partial resistance to phoma black stem disease in sunflower

Abstract

The objectives of the present study were to estimate the general combining ability (GCA) and specific combining ability (SCA) for partial resistance to phoma black stem and to identify the most promising combination for the selection of improved breeding lines. The response of five parental genotypes and their F1 hybrids to a phoma black stem isolate (MA6) were evaluated in a diallel programme under controlled growth chamber conditions. Significant GCA and SCA indicate that both additive and non-additive gene effects contributed in the inheritance of partial resistance to phoma black stem, however, the Baker ratio showed that the additive genetic effects were more important than nonadditive ones. It is recommended that the GGEbiplot methodology could be an excellent tool for visualizing entry by tester (diallel) data. By using this technique to analyse black stem severity data, interaction among the sunflower genotypes in providing partial resistance to phoma black stem was clearly identified. Based on GGEbiplot presentation and Griffing's diallel analysis, the mutant line ‘M6-54-1’ showed the largest GCA, indicating contribution towards partial resistance, and the genotype B454/03 presented the smallest GCA, indicating contribution towards susceptibility. Our results show that the F1 hybrids ‘SDR18×B454/03’ and ‘M6-54-1×B454/03’ showing heterosis for partial resistance to phoma black stem come from the crosses between a susceptible genotype ‘B454/03’ and two partially resistant genotypes (SDR18 and M6-54-1), originated from different breeding programmes. We conclude therefore that these genotypes possess at least some different resistance genes, which were expressed in the hybrids and led to the observed effects.     

Linkages between below and aboveground communities: Decomposer responses to simulated tree species loss are largely additive

Inputs of aboveground plant litter influence the abundance and activities of belowground decomposer biota. Litter-mixing studies have examined whether the diversity and heterogeneity of litter inputs affect decomposer communities in ways that can be predicted from monocultures. They have mainly attempted to detect non-additive effects of litter mixing, although individual species effects (additivity) as well as species interactions (non-additivity) may alter decomposition rates. To determine potential impacts of plant species loss on aboveground-decomposer linkages, we assessed both additive and non-additive effects of litter mixing on decomposer communities. A full-factorial litterbag experiment with leaves from four deciduous tree species was conducted, to assess responses of bacteria, fungi, nematodes, and microarthropods. Data were analyzed using a statistical method that first looked for additive effects based on the presence or absence of species and then any significant species interactions. We observed almost exclusively additive effects of all four litter species on decomposer biota, with each species exerting effects on different aspects of the community. These results imply that the consequences of species loss for the decomposer community will be largely predictable from knowledge of single species litter dynamics. The two species at opposite ends of the quality spectrum exerted the most effects. High-quality Liriodendron tulipifera supported a more diverse arthropod community and drove bottom-up effects on the decomposer food web. Low-quality Rhododendron maximum had negative effects on most groups of biota. Litter of mid-quality species exerted fewer effects. The influence of litter species richness on the Tylenchidae (nematodes) was the only non-additive effect of litter mixing. Together, these data demonstrate an effect of plant community composition on decomposer biomass, abundance, and diversity, confirming a link between above and belowground communities. We were able to identify the species to which the decomposer community is most sensitive, aiding predictions of the consequences of the loss of these dominant species on the decomposer community, with potential feedbacks for organic matter and nutrient turnover.     

The practical use of semiparametric models in field trials

This article examines the practical use of semiparametric models in the analysis of field trials—that is, models with parameterized treatment effects and additive terms derived by a data-driven approach using a locally weighted running line smoother (loess). We discuss graphical methods to identify spatial structure in the data and model selection procedures to choose the degree of smoothing. Once the spatial part of the model has been chosen, hypotheses about the treatment effects may be tested. Semiparametric models are used to analyze two barley field trials exhibiting spatial trends. The first has a single experimental treatment and a row-column design. The second has a split-plot design, and we use a semiparametric model which accounts for the randomization at the different strata of this design. We compare the semiparametric analyses with classical analyses of variance and with alternative spatial models. We find that semiparametric models give a good insight into spatial variation in the field and can improve the precision of parameter estimates.     

Genetic properties of drought tolerance indices in sunflower

Abstract

The objective of the present study was genetic analysis of yield-based drought tolerance indices using the diallel method. Twenty-one genotypes of sunflower (Helianthus annuus L.) derived from a half diallel cross between six inbred lines were evaluated in both stress and non-stress conditions using a randomized complete block design for each one. Eight drought tolerance indices comprising stress tolerance index (STI), mean productivity (MP), geometric mean productivity (GMP), harmonic mean (HM), stress susceptibility index (SSI), tolerance index (TOL), yield index (YI) and yield stability index (YSI) were calculated based on grain yield under stress and non-stress environments. Significant genotypic differences were observed in TOL, GMP, MPSTI, HM and YI. Diallel analyses revealed the importance of both additive and non-additive gene effects in GMP, STI, HM and YI. However, the Baker ratio supported the predominance of an additive effect in their expression. Our results demonstrated that SSI, YSI, TOL and MP are not reliable indices to select drought tolerant genotypes in sunflower breeding programmes because of their low heritability. Indices such as GMP, STI, HM and YI were moderately heritable and are usually able to select high-yielding genotypes in both environments and could be usefully employed in drought tolerance breeding programmes of sunflower.     

Genetic Effects on Grain Characteristics of <Emphasis Type="Italic">indica</Emphasis> Black Rice and their Useson Indirect Selections for some Mineral Element Contents in Grains

Complete diallel crosses with Oryza sativa L., six varieties of black rice and one variety of aromatic white rice were conducted to study the seed, maternal and cytoplasmic genetic effects on grain characteristics such as 100-grain weight, length, width and shape and their genetic correlations with Fe, Zn, Mn and P mineral contents in kernels by using the genetic model on quantitative traits of seed in parents and their F₁s and F₂s. The seed genetic effects were found more important than the maternal genetic effects for grain characteristics, and seed additive effects constituted a major part of their genetic effects. The heritabilities of seed effects were high for 100-grain weight, width and shape and moderate for grain length. Single seed selection based on the 100-grain weight, width and shape was advocated in early generations, whereas single plant and seed selection based on grain length were advocated in late generations. Significant genetic correlations including seed additive, dominance, cytoplasmic, maternal additive and dominance between 100-grain weight, length, width and shape and Fe, Zn, Mn and P mineral contents were observed. Indirect selection of grain characteristics may be one of the breeding methods to select for higher contents of Fe, Zn, Mn and P in black pericarp indica rice.     

Genotype-by-environment interaction of elite heat and drought tolerant bread wheat (Triticum aestivum L.) genotypes under non-stressed and drought-stressed conditions

ABSTRACT

The selection of relatively high and stable yielding genotypes is key in wheat breeding programs to improve yield performance under heat and drought-stressed environments. This study determined grain yield response and stability among elite heat and drought tolerant bread wheat genotypes under simulated drought-stressed (DS) and non-stressed (NS) environments to select promising parents for breeding. Twenty-four elite bread wheat genotypes selected from the International Maize and Wheat Improvement Centre (CIMMYT) drought and heat tolerant nursery were assessed under NS and DS conditions using a 7?×?4 alpha-lattice design under rainout shelter (RS) and glasshouse (GH) environments. Grain yield data was subjected to analysis of variance (ANOVA), the additive main effect and multiplicative interaction (AMMI) and genotype and genotype-by-environment (GGE) biplot analyses. ANOVA and AMMI revealed highly significant (p?≤?0.001) differences among test genotypes (G), environments (E) and G?×?E interaction effects suggesting differential responses for selection. The GGE biplot explained 83.76% of total variation and aided in selection of high-yielding and stable heat and drought tolerant wheat genotypes such as LM13, LM22, LM95 and LM100. These selections are recommended for breeding for yield gains under heat and drought-stressed environments.     

Simulating the effects of using different types of species distribution data in reserve selection

In a perfect world, systematic conservation planning would use complete information on the distribution of biodiversity. However, information on most species is grossly incomplete. Two main types of distribution data are frequently used in conservation planning: observed and predicted distribution data. A fundamental question that planners face is - which kind of data is better under what circumstances? We used simulation procedures to analyse the effects of using different types of distribution data on the performance of reserve selection algorithms in scenarios using different reserve selection problems, amounts of species distribution known, conservation targets and costs. To compare these scenarios we used occurrence data from 25 amphibian and 41 reptile species of the Iberian Peninsula and assumed the available data represented the whole truth. We then sampled fractions of these data and either used them as they were, or converted them to modelled predicted distributions. This enabled us to build three other types of species distribution data sets commonly used in conservation planning: “predicted”, “transformed predicted” and “mixed”. Our results suggest that reserve selection performance is sensitive to the type of species distribution data used and that the most cost-efficient decision depends most on the reserve selection problem and on how much we have of the species distribution data. Choosing the most appropriate type of distribution data should start by evaluating the scenario circumstances. While there is no one best approach for every scenario, we discovered that using a mixed approach usually provides an acceptable compromise between species representation and cost.     

An assessment of the Fosberg and Ellenberg methods of classifying vegetation for conservation purposes

This paper describes a field trial of two rapid-survey methods of classifying vegetation for conservation purposes. The work was carried out by staff and students of the Conservation Course at University College, London, on Majorca in the spring of 1971. A brief review of the two methods is followed by an account of the difficulties encountered with their use in the field and of their theoretical advantages and disadvantages. It was concluded that both methods offer a quick, repeatable approach to vegetation classification which requires little previous knowledge. Fosberg's method was considered the more logical because Ellenberg's includes habitat data which may lead to circularity of argument. Ellenberg's was found to be the easier to use in the field, but this is possibly because it has been principally developed in temperate regions. Both methods offer a very useful framework for an ecological inventory of an area but are subject to practical difficulties when the vegetation has to be mapped.     

Evaluation of <Emphasis Type="Italic">Rubus</Emphasis> genetic resources on their resistance to cane disease

Raspberry cane disease, caused by a complex of fungi, is amongst the most devastating problems for raspberry production. Using resistant or highly tolerant genotypes is a promising strategy. However, until now, cultivars with good field resistance for German fruit growers as well as the primary causal pathogens of cane disease present in the eastern part of Germany, Saxony state are still unknown. The primary objective of this study was to identify the primary disease causing organisms and resistant Rubus germplasm for future breeding efforts. From 2012 to 2014, we evaluated the degree of susceptibility to cane diseases on 213 raspberry cultivars at two different locations using a rating scale. We also identified the main fungi growing on infected canes. Our results suggest that Fusarium avenaceum is the main fungus causing cane disease in Saxony. The Rubus hybrid cultivars ‘Tayberry’ (2n?=?6x?=?42), ‘Buckingham Tayberry’ (2n?=?6x?=?42) and ‘Dorman Red’ (2n?=?2x?=?14) displayed the highest levels of field resistance at both locations. Moreover, we established an in vitro assay for resistance evaluation which correlates significantly with field data and is particularly suitable for quick assessment of resistance against F. avenaceum in breeding material. Future breeding programs, aiming at cultivars with enhanced resistance towards cane diseases can use the presented data for parental selection and may employ our in vitro F. avenaceum inoculation method for parental testing and progeny selection.     

Non-additive effects vary with the number of component residues and their mixing proportions during residue mixture decomposition: A microcosm study

Poplar leaf litter and crop residues (leaves and stems) of two main crops (soybean and maize) collected from semiarid agroforestry systems of Northeast China were used in our microcosm study. The aims were to examine whether non-additive effects (synergistic or antagonistic) between poplar leaf litter and crop residues exist during decomposition and to identify the influence of residue mixing proportion on the incidence of non-additive effects of residue mixture for the same plant residues. We determined residue decomposition rate by measuring mass loss and N release. Synergistic effects between poplar leaf litter and crop residues were more common than additive effects in terms of mass loss and N release. Moreover, the interactive effects between tree leaf litter and crop residues on decomposition varied with the number of component residues and their mixing proportion. Three-residue mixtures produced synergistic effects on mass loss and N release, although two-residue mixtures showed an additive effect in some cases. In addition, as compared with equal proportion, mixing residues with unequal proportion increased the incidence of non-additive effects during decomposition of residue mixture. These findings highlight that residue decomposition dynamics in ecosystems should be assessed on the basis of plant residue mixtures and their mixing proportions, which may help us better understand nutrient dynamics and guide our decisions on nutrient management.     

GENETIC ANALYSIS OF CHLORIDE CONCENTRATION IN ORIENTAL TOBACCO GENOTYPES

A high chloride concentration in oriental tobacco leaf has a detrimental effect on tobacco quality and its burning properties. In order to determine the inheritance of chloride concentration in oriental tobacco leaf, eight tobacco genotypes showing genetic variability for chloride concentration on the basis of our previous investigation were crossed in a diallel program. Parental genotypes and their F1 hybrids were evaluated in greenhouse experiment using randomized complete block design with three replications. Each replication consisted of two pots (one plant per pot). Cultivation took place in plastic plant pots which contained 10 kg soil from the fields of the northwest Iran where the oriental tobacco type is planted. Standard agrotechnical practices for this tobacco type were applied during growth. Tobacco was harvested when it reached technical maturity then it was sun-cured. Percentage of chloride in cured leaves was determined as defined by CORESTA (Cooperation Center for Scientific Research Relative to Tobacco, Paris, France). Analysis of variance was performed to determine the effect of genotypes on chloride concentration and showed significant variability among genotypes for this trait. Diallel analysis showed that general combining ability (GCA) and specific combining ability (SCA) effects for chloride concentration were highly significant indicating that both additive and dominant gene effects were important in controlling the chloride concentration. However, the mean square for specific combining ability was greater than those of general combining ability that shows the predominance of the non-additive genetic effects in controlling the chloride concentration. Therefore, the interpopulational breeding strategy using the heterosis effect could give superior gains to this character.     

基因型×环境互作下小麦氮代谢相关性状的遗传和相关性分析

【目的】选育氮高效的小麦品种,可有效提高氮素利用效率和生产效率,对环境安全至关重要。本文分析了小麦氮代谢相关性状的遗传效应,为小麦氮高效品种选育提供理论依据。【方法】选用7个小麦品种及其组配的12个杂交组合,进行田间盆栽试验。设置3个氮水平,利用基因型与环境互作的加性-显性遗传模型,对氮代谢相关的10个性状进行遗传与相关性分析。【结果】株高、开花期和成熟期单茎干物重、开花期氮素积累量、籽粒氮素积累量和氮素吸收总量主要受加性效应控制,花后氮素同化量受显性×环境互作效应影响较大,氮素利用效率、氮素生理效率以加性×环境互作效应为主。10个性状狭义遗传力总体不高(平均值为0.56),广义遗传力总体较高(平均值为0.881)。互作广义遗传力均达到1%显著水平,表明不同的氮水平对遗传表达有较大影响。氮素利用效率、氮素生理效率和开花期氮素积累量的互作狭义遗传力较大,表明不同氮水平对这些性状的选择效果不同。通过加性效应预测值得出,亲本DK138和JN10的氮素利用效率和氮素生理效率的加性效应为显著正效应。大多数组合的显性主效应与不同氮水平下的显性×环境互作效应在方向上不尽一致,表明小麦氮高效杂交后代的选择宜考虑特定的氮水平条件。显性效应预测值表明,组合JN10×W9903的氮素生理效率显性效应值最大且达到显著水平,是氮素生理效率较高的组合。相关分析表明,两两性状间以加性遗传相关为主。氮素生理效率与株高呈加性正相关关系,达到10%显著水平。除株高和谷氨酰胺合成酶活性外,氮素利用效率与其他性状间以显性环境互作相关为主。氮素利用效率与氮素生理效率之间的显性×环境互作相关系数达到10%显著水平。氮素利用率与氮素生理效率的表现型和基因型相关系数为正值且达1%显著水平。【结论】通过性状分析表明,株高在一定程度上可以作为氮素生理效率的间接选择性状,氮素利用效率与氮素生理效率这两个性状进行协同改良。品种DK138和JN10可作为亲本以提高后代的氮素利用效率和氮素生理效率。杂交组合LM14×W9903表现出良好的后代选育利用潜力。     

Nitrogen Status of Pollen Donor Affects Kernel Set and Yield Components in Corn

ABSTRACT

Nitrogen (N) status of corn plants influences yield performance through adjustment of yield components. Physiological function of corn pollen produced under N-stressed conditions has not drawn enough attention in genotype selection and breeding programs. The object of this study was to assess effects of N nutrition of the pollen donor on kernel set and yield components of the pollen recipient in a field trial by using a restricted pollination procedure. Pollen from plants receiving 0 and 240 kg N ha^?1 was manually applied to plants receiving 0, 80, 160, and 240 kg N ha^{? 1} during silk emergence. The high rate of N fertilizer applied to the pollen donor significantly increased kernel number, kernel weight, harvest index, and aboveground biomass in the pollen recipient. The effect of N nutrition of the pollen donor was similar at all N levels that were applied to the pollen recipient so the interaction was not significant for any of the variables.     

Joint Modeling of Spatial Variability and Within-Row Interplot Competition to Increase the Efficiency of Plant Improvement

Trials in the early stages of selection are often subject to variation arising from spatial variability and interplot competition, which can seriously bias the assessment of varietal performance and reduce genetic progress. An approach to jointly model both sources of bias is presented. It models genotypic and residual competition and also global and extraneous spatial variation. Variety effects were considered random and residual maximum likelihood was used for parameter estimation. Competition at the residual level was examined using two special simultaneous autoregressive models. An equal-roots second-order autoregressive (EAR(2)) model is proposed for trials where competition is dominant. An equal-roots third-order autoregressive (EAR(3)) model allows for competition and spatial variability. These models are applied to two yield data sets from an Australian sugarcane selection program. One data set is in the paper and the other is in supplementary material available online. To determine the effect of simultaneously adjusting for spatial variability and interplot competition on selection, the percentages of superior varieties in common in the top 15% for the joint model and classical approaches were compared. Agreement between the two approaches was 45 and 84%. Hence, for some trials there are large differences in varieties advanced to the next stage of selection.     

Associating SSR Markers with Soybean Resistance to Iron Deficiency Chlorosis

Abstract

Iron deficiency chlorosis (IDC) causes soybean yield loss to growers when certain varieties are planted on calcareous soils. Planting IDC‐resistant varieties is the best management practice, although they may still exhibit chlorosis under certain environmental conditions. Environmental variation for chlorosis expression impedes progress in improving IDC resistance. Breeders could use molecular marker‐assisted selection (MAS), an environment‐independent tool, to improve soybeans' resistance to IDC. Our objective was to determine the efficiency of simple sequence repeat (SSR) markers in selecting for IDC resistance in soybean. A breeding population was developed using parents differing in IDC resistance and yield potential. The population was advanced to the F₂ and F_2:4 generations. Foliar chlorosis data were recorded for parents and F_2:4 lines in replicated field tests planted on calcareous soils at two Iowa locations in 2000 and 2001. Chlorosis scores between parents and F_2:4 lines varied according to location and year. Genotypic data were obtained on individual F₂ plants, and association between chlorosis scores and allele segregation was tested by single‐factor analysis of variance using 2001 data. Three SSR markers were associated (P ≤ 0.1) with chlorosis scores at each location; however, the identity of the markers associated with chlorosis scores was different at each location. In addition, two SSR markers associated with IDC resistance were examined for their efficacy in improving breeding efficiency. Preliminary data presented herein demonstrate the importance of environment on expression of this soil‐stress factor and the potential of using SSR markers as an environment‐independent selection tool for breeding IDC resistance in soybean.     

Can an introduced predator trigger an evolutionary trap in a colonial seabird?

Animals use environmental cues, social information and behavioural decision-making rules moulded by natural selection to decide where to breed. We assessed whether the presence of an alien nest predator, the Black Rat (Rattus rattus) is used by a colonial seabird, the Cory’s shearwater (Calonectris diomedea), as an environmental cue in the selection of breeding sites. We compared potential habitat preference using quality of breeders and nest fidelity as response to nest predation between two sub-colonies with different habitat characteristics, breeding success and predation pressure. Quality of individuals was better in the predated habitat and birds did not perceive the presence of predators signalling differences in predation risk and in turn of breeding success. This failure of perception could be at two levels: in the selection of habitat for first breeding and in the breeding dispersal following a reproductive failure. Preference for the sub-colony with higher predation risk suggests the presence of an evolutionary trap. In fact, the introduction of alien predators probably transformed the behaviour of shearwaters in a maladaptive response due to a mismatch between the new environmental factors and their behavioural and evolutionary algorithms. This can be a common pattern in other species with little behavioural plasticity, evolved in stable environments free of predators.     

A General Bayesian Estimation Method of Linear–Bilinear Models Applied to Plant Breeding Trials With Genotype × Environment Interaction

Statistical analyses of two-way tables with interaction arise in many different fields of research. This study proposes the von Mises–Fisher distribution as a prior on the set of orthogonal matrices in a linear–bilinear model for studying and interpreting interaction in a two-way table. Simulated and empirical plant breeding data were used for illustration; the empirical data consist of a multi-environment trial established in two consecutive years. For the simulated data, vague but proper prior distributions were used, and for the real plant breeding data, observations from the first year were used to elicit a prior for parameters of the model for data of the second year trial. Bivariate Highest Posterior Density (HPD) regions for the posterior scores are shown in the biplots, and the significance of the bilinear terms was tested using the Bayes factor. Results of the plant breeding trials show the usefulness of this general Bayesian approach for breeding trials and for detecting groups of genotypes and environments that cause significant genotype × environment interaction. The present Bayes inference methodology is general and may be extended to other linear–bilinear models by fixing certain parameters equal to zero and relaxing some model constraints.     

蚕豆6×6双列杂交子代主要性状的遗传效应分析

为提高蚕豆优势组合的选配效率,以6个蚕豆材料(P1~P6)为亲本,采用Griffing完全双列杂交配制30个组合,分析亲本和F₁的9个主要农艺性状的杂种优势、配合力和遗传力。结果表明,蚕豆产量相关农艺性状的杂种优势明显,分枝数、单株荚数、单株粒数、每荚粒数、百粒重和单株产量的超亲优势为正值,株高、始荚高和主茎节数的超亲优势为负值。配合力效应分析表明,P1和P2为选育大粒高产的优良亲本,P1×P2和P4×P6符合高产的育种目标,P2×P5和P2×P6符合大粒的育种目标;遗传力分析表明,百粒重、每荚粒数和单株粒数的广义遗传力和狭义遗传力均较高,可以相对稳定地遗传给后代,且这3个性状主要受加性效应控制,适宜进行早代选择,其他性状主要受非加性效应影响;主要性状与单株产量的相关分析表明,蚕豆育种应将单株荚数和单株粒数作为重点目标;通径分析表明,在育种过程中应重点关注分枝数、株高、百粒重、每荚粒数等农艺性状。本研究为蚕豆育种进程中的亲本选配和后代选择提供了一定的理论依据。     

耐低氮小麦基因型筛选指标的研究

以12个小麦基因型为研究对象,采用溶液培养与田间试验的方法,设低氮胁迫和正常供氮2个水平,对耐低氮小麦基因型的筛选指标进行了探讨,为氮高效基因型小麦育种提供理论依据。结果表明,小麦植株干重在低氮胁迫和正常供氮条件下都有较大的基因型变异(变异系数CV分别为29.03%和18.21%);在所有调查性状的相对值中,相对植株干重(低氮胁迫/正常供氮)基因型变异较大(CV为22.76%)。相关性分析表明,相对植株干重与相对株高、相对植株吸氮量和相对氮利用效率间呈极显著正相关(P0.01),且溶液培养试验中相对植株干重和田间试验中相对子粒产量(不施氮/施氮)间呈极显著正相关(r=0.77**,n=12)。因此,以小麦苗期相对植株干重作为筛选指标,然后进行田间验证,是筛选耐低氮小麦基因型行之有效的途径。     

Models for Jointly Estimating Abundances of Two Unmarked Site-Associated Species Subject to Imperfect Detection

In ecological field surveys, it is often of interest to estimate the abundance of species. It is frequently the case that unmarked animals are counted on different sites over several time occasions. A natural starting point to model these data, while accounting for imperfect detection, is by using Royle’s N-mixture model (Biometrics 60:108–115, 2004). Subsequently, many multivariate extensions have been proposed to model communities as a whole. However, these approaches are used to study species richness and other community-level variables and do not focus on the relationship between two site-associated species. Here, we extend the N-mixture modelling framework to model two site-associated species abundances jointly and propose to measure the influence of one species’ abundance on the populations of the other and study how this changes over time and space. By including a new parameter in the abundance distribution of one of the species, linking it to abundance of the other, our proposed model treats extra variability as an effect induced by an associated species’ abundance and allows one to study how environmental covariates may affect this. Using results from simulation studies, we show that the model is able to recover true parameter estimates. We illustrate our approach using data from bald eagles and mallards obtained in the 2015 survey of the North American Breeding Bird Survey. By using the joint model, we were able to separate overdispersion from mallard-induced variability and hence what would be accounted for with a dispersion parameter in the univariate framework for the eagles was explained by covariates related to mallard abundance in the joint model. Our approach represents an attractive, yet simple, way of modelling site-associated species populations jointly. Conservation ecologists can use the approach to devise management strategies based on the strength of association between species, which may be due to direct interactions and/or environmental effects affecting both species’ populations. Also, mathematical ecologists can use this framework to develop tools for studying population dynamics under different scenarios. Supplementary materials accompanying this paper appear on-line.