Morphological variation in a biotically patchy environment : evidence from a pasture population of Trifolium repens l.

The relationship between morphological variability and biotic environmental heterogeneity was studied in a pasture population of Trifolium repens. It had been argued that the unexpectedly high levels of variation in T. repens could be maintained by diversifying selection. The mosaic of neighbours (perennial grasses) with which T. repens coexists constitutes a prominent element of biotic patchiness that may lead to sorting among T. repens genotypes on the basis of neighbour-specific compatibilities. A variation study was conducted on a set of 400 individuals of T. repens collected on a neighbour-specific basis from a 43 year old pasture and grown for one season under common garden conditions. A significant proportion of the variation in a set of twelve morphological characters was accounted for by the neighbour with which the individual of T. repens had been growing in the field. The actual amount of variation accounted for, however, was low (6-19%). It was concluded that although diversifying selection could be operating in the pasture, it is not of primary importance in the maintenance of variation in this population. A repeat study was carried out after the plants had spent two years in the common garden. None of the earlier among-neighbour differences in morphology were retained. I concluded that the original results reflected developmental differences carried over from the pasture.Science, Faculty ofBotany, Department ofGraduat