Range expansion in asexual dandelions: selection for general-purpose genotypes?

1. Phenotypic plasticity and broad ecological tolerance are hypothesized as important traits in the range expansion of asexual species, because individual asexual lineages have to face spatial and temporal environmental variation with limited opportunity for genetic adaptation. The hypothesis that asexual lineages are general-purpose genotypes (GPG) has been previously tested, with mixed results, in species that have both sexual and asexual variants. Such comparisons can be confounded with intraspecific ploidy level differences that are often observed between the two reproductive types. 2. Avoiding the confounding effects of ploidy differences, we test whether northward range expansion selects for a GPG strategy in asexual lineages of the common dandelion (Taraxacum officinale), a species that shows geographic parthenogenesis. We compared the biomass of asexual lineages that were collected along a geographic transect from close to the asexuals' area of origin (central Europe, where asexuals descend from sexual ancestors in mixed populations) towards their northern distribution edge (Northern Europe, where only asexual lineages occur) in three different experimental environments: optimal, drought and shaded conditions. 3. The geometric mean performance across test environments did not differ significantly between plants from different regions along the transect. However, southern lineages typically showed larger differences in biomass between different test environments, mainly caused by a relatively high performance in the optimal environment. Northern and mid-latitude lineages showed more even performance across the different environments. 4. Synthesis. Our results suggest that phenotypic plasticity is important in the asexual range expansion of Taraxacum officinale and that range shifting in this species is accompanied by a change in phenotypic plasticity strategy from lineages with high ability to increase biomass in optimal growing conditions (master-of-some strategy) to lineages that maintain more constant performance in different environments (GPG or jack-of-all-trades strategy) from core to range edge.