Missions

Phenotypic integration is defined as the study of trait covariation at different organizational scales. It is a central question of several research fields: evolutionary biology, genetics, functional ecology, ecophysiology, crop science, and plant biology more broadly (Pigliucci, 2003). A trait is said integrated when it results from the effect of one or several other traits considered at “lower degrees of phenotypic integration” (Arnold 1983, Violle et al., 2007). Yet, we still lack quantification of phenotypic integration in plants in particular, which would have tremendous impacts from both applied and theoretical perspectives. One reason is that the study of phenotypic integration in comparative ecology has largely been led independently of the study of trait inheritance in evolutionary biology.
A direct consequence of trait stratification in an integrated phenotype is that the more integrated traits are expected to exhibit stronger non-additive inheritance, that is a deviation of the offspring from the mean parental phenotype. Empirical studies on plant hybrids generally support this idea: performance-related traits such as fruit and seed production exhibit stronger deviation to the parents compared to morphological traits (e.g., plant biomass and height, leaf width), which in turn exhibit more deviation than developmental traits (e.g., flowering time, number of leaves).
The linkage between phenotypic integration and trait inheritance can be explained by the multiplicative effect of traits across organizational scales. For instance, grain yield is the product of the number of fruits per individual, the number of seeds per fruit and seed weight. Consequently, it was observed that phenotypic deviation (compared to their parents) of total grain yield in barley hybrids was disproportionately higher than the deviation of the underlying components. Thus, a possible - but so far neglected - solution to understand phenotypic integration is to compare the intensity of non-additive inheritance between traits at different organizational levels (cell, tissue, organ, organism). This question also echoes a major caveat of current approaches in functional ecology: the widespread focus on single functional traits rather than whole phenotype has strongly limited our understanding of the functioning of organisms and beyond.
Myriads of multivariate methods developed as part of the field have brought partial solutions to this issue only. For instance, the multiplicative effect of traits on phenotypic integration can be captured by allometric relationships, which have been found to explain, and even predict, trait inheritance and hybrid vigour in Arabidopsis thaliana (Vasseur et al., 2019). Insights on phenotypic integration from genetics and evolutionary biology would contribute to the emergence of new questions in functional ecology (Vasseur et al., 2022). In this context, the use of model species (e.g., Arabidopsis thaliana, crop species) is a very promising avenue. Moreover, studying phenotypic integration through trait covariance such as allometric relationships can, in turn, help to model and predict trait inheritance.

By studying a large set of already-acquired trait measurements in hybrids and parents in model species (Arabidopsis thaliana, sorghum, and maize), the hired postdoc will compare the degree of non-additive inheritance among multiple traits at different scales. Trait covariation network will be compared between species and genotypes to explore frontier questions from functional ecology, genetics, and evolutionary biology. Moreover, the postdoc will examine trait-trait relationships between different organizational scales in order to explain, and ultimately predict, hybrid phenotype and performance. Taking advantage of the mathematical formalization developed in the field of plant allometry, the postdoc will examine trait-trait relationships from the cell to the whole organism. This represents a cutting-edge perspective of the project, with key consequences for our understanding of the physiological mechanisms of plant performance and trait inheritance. Moreover, predicting trait inheritance is a key challenge in crop science, with important outcomes for plant breeders.

Key references
Arnold, S. J. (1983). Morphology, performance and fitness. American Zoologist, 23(2), 347-361.
Pigliucci, M. (2003). Phenotypic integration: studying the ecology and evolution of complex phenotypes. Ecology letters, 6(3), 265-272.
Violle, C., Navas, M. L., Vile, D., Kazakou, E., Fortunel, C., Hummel, I., & Garnier, E. (2007). Let the concept of trait be functional!. Oikos, 116(5), 882-892.
Vasseur, F., Fouqueau, L., de Vienne, D., Nidelet, T., Violle, C., & Weigel, D. (2019). Nonlinear phenotypic variation uncovers the emergence of heterosis in Arabidopsis thaliana. PLoS biology, 17(4), e3000214.
Vasseur, F., Westgeest, A. J., Vile, D., & Violle, C. (2022). Solving the grand challenge of phenotypic integration: allometry across scales. Genetica, 150(3-4), 161-169.

Activités

Phenotypic data at different organizational scales in Arabidopsis thaliana, maize and sorghum are already available in the host laboratory. These data include cellular traits (e.g., cell size, total RNA and ribosomal RNA concentration, abundance in mitochondria and chloroplasts), leaf traits (e.g., leaf area, fresh and dry mass, width and length, number of cells, epidermal cell area and stomata density, specific leaf area, and leaf dry matter content), as well as whole-plant traits (e.g., leaves and stem biomass, plant height, number of leaves, leaf angle, flowering time, reproductive output). These phenotypic data have been collected on large set of genotypes in the three focal species (c. 300 genotypes per species, including inbred and hybrid lines). Moreover, additional traits can be collected on frozen tissue if needed during the postdoc.
Trait inheritance will be compared between organizational scales and species. Heterosis (i.e. trait deviation from mean parental value) will be measured using the classical quantitative genetics framework. In addition, trait relationships will be investigated, using in particular models and equations from the field of allometry. Finally, multivariate approaches will be used to depict phenotypic integration (PCA, hypervolume, structural equation modelling, and network analysis).

Compétences

We look for a motivated candidate, with strong interest in functional ecology, evolutionary biology and genetics. We are open to applications of candidates from various fields. Curiosity and creativity are two main required qualities for this work, combined with competencies in statistical analyses, rigour and organizational skills. We particularly expect a postdoc with a good experience (and a taste) for scientific writing. Previous experience in allometry, genomics and/or modelling will be appreciated.

Contexte de travail

The postdoctoral fellow will be assigned to the Centre d'Ecologie Fonctionnelle et Evolutive (CEFE, UMR5175, CNRS Montpellier; https://www.cefe.cnrs.fr/fr/) within the ECOPAR team, and will be supervised by François Vasseur and Cyrille Violle. The postdoc will be funded within the framework of an ERC project led by François Vasseur (PHENOVIGOUR project).

Contraintes et risques

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Informations complémentaires

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