Provenance and fitness in weeds

Genetic introgression from distant provenances reduces fitness in local weed populations Geobotanisches Institut 01/09/2000 
Journal of Applied Ecology, 37: 647-659 (2000). British Ecological Society.
Keller, M., Kollmann, J. and Edwards, P.J.


Seed mixes of wildflowers are widely used to create new native grasslands within intensively farmed agricultural landscapes. Seed mixes are usually commercially produced and may be used a long distance from their place of native origin. The authors, in this study, aimed to evaluate the effects of genetic introgression of "foreign" provenances on the fitness of local weed populations. The species studied were Corncockle (Agrostemma githago), Common Poppy (Papaver rhoeas) and White Campion (Silene alba). These three species are commonly included in wildflower seed mixes in Switzerland. Plants of local (Swiss) origin were back-crossed with plants of Hungarian, German and English origin (plus one US Silene source). The study revealed negative outbreeding effects in all the Papaver backcrosses and in one Agrostemma F2 backcross (Swiss x German). Other negative effects were observed in some of the hybrids, including lower survival and decrease in seed mass.
The authors conclude that the results suggest that only plants of relatively local origin should be used in wildflower mixtures, although they argue it is not possible to specify precisely over what distance seed can be safely transferred. The same recommendation is also valid for schemes to reinvigorate endangered plant populations.
Outbreeding depression is the reduced fitness in hybrid offspring. The authors identify two main causes: (1) loss of local adaptation - due to inheriting traits which are not well adapted to the new environment; (2) loss of intrinsic co-adaptation - caused by disruption of co-adapted gene complexes.
The authors can be contacted at Geobotanisches Institut, ETH, Zürichbergstrasse 38, 8044 Zürich, Switzerland.



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