Life-history traits and population differentiation in a clonal plant: implications for establishment, persistence and weediness

Abstract: Clonality is wide-spread among plants, and clonal plants dominate many habitats and include many highly invasive species. Clonal growth incurs both advantages and costs and clonal plants often have reduced sexual reproduction compared to non-clonal plants which could be expected to lower genetic variation and hence evolutionary potential. However, clonal plants have revealed similar levels of genetic variation as non clonal plants in the majority of species studied. This thesis includes studies of life-history traits such as resource sharing, storage, growth, seed germination and seedling performance, as well as studies of the partitioning of genetic variation using leaflet shape analysis. The study organism used; Aegopodium podagraria, is a clonal herb with vigorous vegetative reproduction by means of underground rhizomes. In its natural distribution range it is a noxious garden weed and it has been reported to be invasive in natural areas in many places where it has been introduced. I have compared weedy (garden) and natural (forest) populations in northern, central and southern Sweden. Sampling was mainly performed by collecting rhizome pieces and propagating them in the green house, but in some populations we were able to collect seeds as well. The aim has been to investigate the relation between variation of life history traits in A. podagraria and the available genetic variation that may be the bases for this variation. A further aim has been to understand what makes plants like A. podagraria such persistent weeds, and how it is able to thrive in so many different habitats and climatic regions. Aegopodium podagraria from forest populations were found to be more negatively affected by severing of rhizomes than plants from garden populations indicating a higher dependence on sharing in forest clones. Furthermore, it seemed that harsh climatic conditions in combination with heterogeneous light availability had caused a higher degree of storage in plants from forests in North Sweden than plants from garden habitats in North Sweden as well as from both types of habitats in South Sweden. Sexual reproduction was found in the field, and in a common garden study a high percentage of seeds produced seedlings that developed rhizomes and began to spread vegetatively during their first growing season. Sexual reproduction in natural populations of A. podagraria is in agreement with the considerable variation within and between populations revealed using multivariate leaflet shape analysis. I conclude A. podagraria combines the advantages of clonal growth, resource sharing, longevity and vigorous vegetative spread of genets, with enough sexual reproduction to maintain a genetic base for adaptation to new types of habitats and different regions.

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