Resource sharing between ramets of clonal plants is a well-known phenomenon, which allows stoloniferous and rhizomatous species to internally translocate water, mineral nutrients and carbohydrates from sites of high supply to sites of high demand. The mechanisms and implications of resource integration in clonal plants have extensively been studied in the past. Vascular ramet connections are likely to provide an excellent means to share substances other than resources, such as systemic defence signals and pathogens. The aim of this paper is to propose the idea that physical ramet connections of clonal plants can be used (1) to transmit signals, which enable members of clonal plant networks to share information about their biotic and abiotic environments, and (2) to facilitate the internal distribution of systemic pathogens in clonal plant networks and populations. We will focus on possible mechanisms as well as on potential ecological and evolutionary implications of clonal integration beyond resource sharing. More specifically, we will explore the role of physiological integration in clonal plant networks for the systemic transmission of direct and indirect defence signals after localized herbivore attack. We propose that sharing defence induction signals among ramets may be the basis for an efficient early warning system, and it may allow for effective indirect defence signalling to herbivore enemies through a systemic release of volatiles from entire clonal fragments. In addition, we will examine the role of clonal integration for the internal spread of systemic pathogens and pathogen defence signals within clonal plants. Clonal plants may use developmental mechanisms such as increased flowering and clone fragmentation, but also specific biochemical defence strategies to fight pathogens. We propose that clonal plant networks can act as stores and vectors of diseases in plant populations and communities and that clonal life histories favour the evolution of pathogens with a low virulence.

Many studies have focused on the ecology of seed dimorphism, the production of two seed types by a single plant. Morphology and seed size are usually correlated, but how morphology affects germination percentage and seedling growth is poorly understood. Here we explicitly separate these effects for nine populations of the dimorphic species Tragopogon pratensis subsp. pratensis. Larger seeds yielded higher germination percentages, yet seed morphology had no additional direct effect on germination. Neither seed size nor seed morphology affected seedling growth. Neither germination nor seedling growth varied among populations, but seed head varied significantly. Results show that germination is mainly controlled by seed size rather than by seed morphology. This study is one of the few to distinguish explicitly between seed size and seed morphology effects on ecological characteristics and suggests that seed dimorphism may exert its ecological effects predominantly through its correlated size.

Plant pathogens and insect herbivores are prone to share hosts under natural conditions. Consequently, pathogen-induced changes in the host plant can affect herbivory, and vice versa. Even though plant viruses are ubiquitous in the field, little is known about plant-mediated interactions between viruses and non-vectoring herbivores. We investigated the effects of virus infection on subsequent infestation by a non-vectoring herbivore in a natural genotype of Trifolium repens (white clover). We tested whether infection with White clover mosaic virus (WClMV) alters (1) the effects of fungus gnat feeding on plant growth, (2) the attractiveness of white clover for adult fungus gnat females, and (3) the volatile emission of white clover plants. We observed only marginal effects of WClMV infection on the interaction between fungus gnat larvae and white clover. However, adult fungus gnat females clearly preferred non-infected over WClMV-infected plants. Noninfected and virus-infected plants could easily be discriminated based on their volatile blends, suggesting that the preference of fungus gnats for non-infected plants may be mediated by virus-induced changes in volatile emissions. The compound b-caryophyllene was exclusively detected in the headspace of virus-infected plants and may hence be particularly important for the preference of fungus gnat females. Our results demonstrate that WClMV infection can 433-444 DOI 10.1007433-444 DOI 10. /s00442-012-2322 decrease the attractiveness of white clover plants for fungus gnat females. This suggests that virus infections may contribute to protecting their hosts by decreasing herbivore infestation rates. Consequently, it is conceivable that viruses play a more beneficial role in plant-herbivore interactions than generally thought.

No abstract