Document: FIS-3-39-18

Genetic Allee-effects in the rare clonal plant, Ranunculus reptans: Plant performance, plasticity, and developmental instability.

FISCHER, M.*, M.VAN KLEUNEN and B.SCHMID

Universität Zürich, Zürich, Switzerland ¹

Abstract:
We studied performance of and phenotypic variation among plants representing fourteen populations of the rare stoloniferous lake-shore plant, Ranunculus reptans, of known size and RAPD-variability (measured as molecular variance). To assess plant performance we grew vegetative offspring of 102 genotypes in a competition-free common environment similar to natural habitats. To assess plasticity in leaf and internode lengths we grew further replicates under competition by a grass. After eight weeks of growth without competition, plants from larger populations covering > 100 m² produced more rosettes than plants from smaller populations covering < 100m² (total number of rosettes +22.7%, p < 0.03; number of rooting rosettes +17.6%, p < 0.06; number of flowering rosettes +28.7%, p < 0.01). Similarly, plants representing populations with higher molecular variance had higher numbers of rosettes (p < 0.05 for the number of rooting rosettes). Under competition, longest leaves of daughter rosettes were shorter than in the competition-free environment. However, the relative reduction in leaf length was less pronounced for plants from larger than from smaller populations (p < 0.05) suggesting higher plasticity of plants from larger populations. Population size and molecular variance were weakly correlated with among-genotype CV in the numbers of rosettes. However, among-genotype CV in the length of the longest leaf of the first daughter rosette was smaller for populations with higher molecular variance (p < 0.05), suggesting that plants from genetically more diverse populations were more able to produce the optimum leaf phenotype. Within-genotype CV generally were smaller for genotypes from larger populations with higher molecular variance. This was significant for the relationship with molecular variance (MANOVA, p < 0.05) and indicates that genotypes representing populations with higher molecular variance are developmentally more stable. We conclude that there are genetically mediated Allee-effects in R. reptans. Observed smaller sexual and vegetative reproduction, plasticity, and developmental stability in plants from smaller populations may all negatively affect fitness and therefore compromise persistence of small populations of R. reptans.

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