“Dividing a maternal pie among half-sibs: genetic conflicts and the control of resource allocation to seeds in maize”
Aurélie Cailleau, Daniel Grimanelli, Elodie Blanchet, Pierre-Olivier Cheptou, and Thomas Lenormand (Nov 2018)
Sibling rivalry for maternal resource allocation: it also occurs in plants!
Offspring size is a key fitness trait, which often results from various, possibly conflictual, interactions among parents and offspring. In angiosperms, seed mass is most often thought to result from maternal control. Paternal genotype and sibling rivalry is thought to play little role in this resource allocation. In this paper, Cailleau et al. present both a large-scale experiment and a new method to partition how the maternal sporophyte and half-sibs with different paternal genomes influence resource allocation. They find that the paternal genotypes in seeds influenced resource allocation by interacting with both the maternal plant and half-sibs. This paternal genotype influences the resource allocated to seed, often eliciting a greater maternal allocation than that observed upon selfing. They also find that there is strong sibling rivalry: maternal resources are allocated entirely competitively, and seeds with different paternal genotypes show different competitive ability to take up this resource. Furthermore, the researchers find evidence that competition between seeds with different paternal genotypes entails a cost and reduces the overall amount of resources allocated to the ear. These findings provide a better view of the control of resource allocation to seeds, which is essential for conflict theories, and may prove useful to optimize yield.
Resource allocation to offspring is the battleground for various intra-familial conflicts. Understanding these conflicts requires knowledge of how the different actors (mother, siblings with different paternal genotypes) influence resource allocation. In angiosperms, resource to seeds is allocated post-fertilization and the paternally inherited genome in offspring can therefore influence resource allocation. However, the precise mode of resource allocation, and in particular the occurrence of sibling rivalry, has been rarely investigated in plants. In this paper, we develop a new method to analyze the resource allocation traits of the different actors (maternal sporophyte and half-sibs) using the data obtained from a large-scale diallel cross experiment in maize involving mixed hand pollination and colors markers to assess seed weight of known paternity. We found strong evidence for the occurrence of sibling rivalry: resources invested in an ear were allocated competitively and offspring with different paternal genotypes aggressively competed for this resource, entailing a measurable direct cost to the mother. We also show how resource allocation can be described for each genotype by two maternal (source effect, average sink responsiveness) and two offspring traits (ability to attract maternal resource, competitive ability towards siblings). We will discuss how these findings help understanding how genetic conflicts shape resource allocation traits in angiosperms.