Genetic structure of the annual weedSenecio vulgarisin relation to habitat type and population size

Abstract

Throughout the world, the highly selfing annual common groundsel, Senecio vulgaris (Asteraceae) is a common weed. Recently, it has also colonized ecological compensation areas in agro-ecosystems. We investigated the genetic structure of S. vulgaris using random amplified polymorphic DNA (RAPD) profiles of 80 plants from nine populations representing three habitat types in two regions in Switzerland. RAPD variation among regions (19.8%), among populations within regions (19.2%) and within populations (61.1%) was highly significant (ANOVA; P < 0.001). Gene flow estimated from the observed differentiation among populations (PhiST = 0.382) was low (assuming Wright's island model, Nem = 0.404). Genetic distances between pairs of populations were significantly correlated with geographical distances (Mantel test; r = 0.37, P < 0.03). Molecular variance obtained with AMOVA was lowest in the small populations in compensation areas (1.13), intermediate in vineyard populations (2.49), all located in northern Switzerland and highest in the larger vegetable field populations from western Switzerland (3.41; P < 0.05). Overall, there was a positive correlation of molecular variance and population size (P < 0.05), as expected under genetic drift. However, molecular variance was negatively correlated with population size among populations in ecological compensation areas, suggesting that selection was also important. We also applied triazine herbicide to leaves of three offspring of each of the 80 plants. Plants from populations of compensation areas showed higher mean levels and reduced variation in the resistance to triazine herbicide than plants from vineyards and vegetable fields. This suggests that compensation areas were colonized from adjacent corn fields, in which there has been selection for herbicide resistance. We discuss the implications of our results for the biological control of S. vulgaris.

Phenotypic plasticity in Carlina vulgaris: effects of geographical origin, population size, and population isolation

“…Even if large and non-isolated populations in general have higher genetic diversity, there is no obvious reason why they should show overall stronger or more adaptive responses than less diverse populations (cf. Mu¨ller-Scha¨rer and Fischer 2001;Vergeer et al 2003), just as large and non-isolated populations of high genetic diversity do not necessarily have higher mean fitness than small and isolated populations of low diversity (Ouborg et al 1991;Lammi et al 1999;Eisto et al 2000). If selection operates on plasticity (Bradshaw 1965;Schlichting 1986), its strength and direction may be more dependent on fitness-relevant habitat factors than on population size or isolation, and in a spatially heterogeneous habitat, genotypes with different response patterns will be able to coexist (Sultan and Bazzaz 1993a;Sultan 1995;Leiss and Mu¨ller-Scha¨rer 2001).…”

Two lineages ofTrifolium alpinum(Fabaceae) in the Pyrenees: evidence from random amplified polymorphic DNA (RAPD) markers

“…We used random amplified polymorphic DNA (RAPD) molecular markers to elucidate the effect of historical and ecological factors on the pattern of genetic variation of T. alpinum in the Pyrenees. They have proven to be valuable tools to investigate species phylogeography (Gabrielsen et al, 1997;Comes & Abbott, 2000;Segarra-Moragues & Catalan, 2003) and to analyze genetic structure of plant populations (Muller-Scharer & Fischer, 2001;Kwon & Morden, 2002;Pearson et al, 2002). We investigated fine-scale genetic diversity in 40 populations of T. alpinum by considering three hierarchal levels: 1) within populations, 2) among populations collected within a same region (defined as river catchments) and 3) among group of populations from the different regions.…”

High RAPD but no cpDNA sequence variation in the endemic and endangered plant, Heptacodium miconioides Rehd. (Caprifoliaceae)

“…As expected, low genetic variation was observed in small populations, due to small sampling sizes. Similarly, reduced genetic variation in smaller populations has been reported for 11 of 16 plant taxa mentioned in a review by Frankham (1996) and in some species studied since then, such as Senecio vulgaris (Mueller-Scharer and Fischer 2001). These relationships were usually interpreted as results of genetic drift (Chen 2000).…”