Drivers of flower colour polymorphism in anemones along environmental gradients

• Applicant: Privatdozent Dr. Johannes Spaethe
• Subject Area: Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems ; Ecology and Biodiversity of Plants and Ecosystems
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 448791908

Flowers of animal-pollinated plants show impressive diversity in floral colour, a key advertisement trait of angiosperms attracting animal pollinators. Most flower populations are uniform in colour, thought to result from directional natural selection, often mediated by pollinators, which leads to fix a single flower colour in a population. Thus, the existence of species with stable colour variation is intriguing. Why within-population flower colour polymorphism exists and what maintains such natural variation when it does occur, is often unknown. Although the genetic basis of flower colours is well understood, there are only a handful of studies connecting environmental variation and pollinator-mediated selection with genetic divergence of flower colour polymorphism. To address this knowledge gap, we will study two closely related species of Anemone (A. pavonina and A. coronaria, Ranunculaceae) that show a distinct within- and between-population colour variation along environmental gradients. We aim to test for the roles of pollinators and abiotic environmental factors as selection agents that maintain it, using a combination of ecological experiments and molecular methods. We hypothesize that a specific flower colour is associated with tolerance to environmental stress: purple flowers are adapted to low temperatures in A. pavonina at the high altitudes of Mt. Olympus (Greece), and red flowers are adapted to drought in A. coronaria at the arid parts of a climate gradient (Israel). We also hypothesize that while the latter colour morphs are under selection by both pollinators and environmental stresses, the other morphs are experiencing random mating and void of directional selection (A. coronaria) , or are under pollinator selection (A. pavonina) and thus maintain polymorphic populations. To test these hypotheses we will grow plants of all colour morphs in reciprocal common gardens and in controlled environments that manipulate temperature or drought. In addition, we will monitor pollinators, and track pollen movement among colour morphs using quantum-dots pollen staining. Finally, we will sequence the whole transcriptome of different colour morphs under experimental climates to identify candidate genes for stress tolerance, and to identify co-expression of pigment synthesis genes and stress-tolerance genes. Altogether, the array of ecological experiment, pollinators’ observations and molecular study will reveal the mechanisms that maintain colour polymorphism in these Anemone species. The proposed study will uncover the evolutionary process that lead to floral colour polymorphism, and will shed light on mechanisms that manifest natural variation.

• DFG Programme: Research Grants
• International Connection: Israel
• International Co-Applicants: Professorin Dr. Tamar Keasar; Dr. Yuval Sapir