Influence of the Parasitism by the Thistle Gallfly Urophora cardui on the Genotypic and Genetic Diversity of the Host plant species Cirsium arvense (Diptera: Tephritidae)

Abstract

Several studies in controlled conditions have demonstrated that the parasitic Gallfly Urophora cardui (Linnaeus 1758) has profound negative effects on life history traits of its host Cirsium arvense. Such negative effects may affect the neutral genotypic and genetic diversity of natural populations of the host plant. To test this hypothesis, eight populations of C arvense with different history of infestation by U cardui were investigated. Half of the populations were in the last five years infested by U cardui, whereas the other half was not. Genotypic and genetic diversity was investigated with AFLP markers. Contrary to what expected, average genotypic diversity, clonal evenness and molecular variance did not differ between infested and not-infested populations (0.73 ± 0.21 versus 0.78 ± 0.26 for clonal diversity; 0.58 ± 0.27 versus 0.71 ± 0.34 for clonal evenness). Molecular variance due to infestation state of populations was not significant (1.81 ± 1.05 versus 2.22 ± 0.82) and explained < 5 % of the total variance. Hence, the results suggest that selection imposed by U cardui on C arvense was weaker , on a population and/or metapopulation scale than it was supposed in experimental studies. This can be explained by the complex spatio-temporal population dynamics of the C arvense-U cardui system (e.g numerous extinction/colonization events). Within each population, no significant correlation between the genetic dissimilarity matrix of C arvense shoots and the corresponding 'infestation state' matrix was found. In this study, C arvense shoots appear to be randomly infested by U cardui.