ABSTRACT

Predicting the genetic and evolutionary consequences of disturbances such as population fragmentation requires an understanding of pollinator activities within and among population fragments and of the complex interactions of pollen transfer with plant breeding systems. We have been studying these issues using a set of Grevillea species which are visited by a wide range of potential pollinators including the introduced honeybee Apis mellifera. This series of case studies reveals the following points. There are striking differences between the levels of self-compatibility (estimated from hand-pollination experiments) and realised mating systems (based on genetic analyses), even within species. For a self-compatible species (Grevillea macleayana), the realised mating system varies among populations from random mating to almost complete selfing. In outcrossing species (e.g. G. mucronulata, G. sphacelata), allozyme analyses suggest that outcrossing must have been almost exclusively restricted to pollen exchange with immediate neighbours.

Patterns of pollinator visitation can explain some of this variation. Apis mellifera acts as a pollen thief in G. macleayana, reducing the level of seed set to below that observed following autogamy (all pollinators excluded).

Patterns of genetic subdivision do not always match predictions based on estimates of current mating systems. In G. macleayana, genetic variation [determined using randomly amplified polymorphic DNA (RAPD) markers] was partitioned within and among populations of established plants as expected for a highly outcrossed species, despite the fact that realised mating systems appear to be predominantly selfing. In contrast, for G. caleyi plants (which are in an environment recently fragmented by urban subdivision), amplified fragment length polymorphism (AFLP) markers revealed substantial genetic subdivision among population fragments.