Weed mating systems: Implications for management

Weeds have evolved an unrivalled diversity of sexual systems. The reproductive system is particularlyimportant in weed invasions because not only it affects the rate of production of new propagulesbut also regulates the evolutionary responses to the new environment. Similar to many other lifehistory traits, adoption of any sexual strategy is often accompanied by genetic and/or demographictrade-offs. On one extreme, hermaphroditism, particularly when coupled with selfing, has the demographicadvantage that allows even a single individual to reproduce, but this "reproductive assurance"will bring along the deleterious costs of inbreeding depression. On the other extreme of the breedingsystem, dioecy, maximizes outcrossing and thereby reduces the likelihood of inbreeding depression.Dioecy also has the benefit of optimizing the allocation of resources between male and female functionsby minimizing the competition between these two functions through sexual specialization, i.e.the so-call "division of labor" theory. Despite these advantages, a dioecious breeding system is subjectto several demographic handicaps: (۱) the two sexes must co-occur in the same habitat, (۲) the twosexes need to flower at the same time (or overlap) to ensure cross-fertilization, and (۳) the fecundity ofa dioecious population is also sensitive to the changes in the sex ratio and is likely to decline when thepopulation either becomes male-biased, i.e. ovule-limited, or female-biased, i.e. pollen-limited. Novelweed management strategies can be developed by better understanding of the above "cracks" in theevolution of mating systems. In this presentation, focusing on the dioicous mating system, I discusshow skewing the sex ratio towards one sex (sub-optimal sex ratio strategy) and reducing the floweringoverlap between the two sexes (phenological isolation strategy) can be exploited to reduce seed outputin dioicous weeds.

کلیدواژه ها:

Sex Ratio ، Environmental Sex Determination (ESD) ، Genetic Sex Determination(GSD) ، Secondary Sex Characters ، Flowering Overlap ، Gender Specializatio.