But a small proportion of self-fertilising pollen is tolerated. The technique picked out those seeds where the genes differed from the parent plant, and so must have been contributed by pollen from another plant. From this information it was possible to work out the degree of inbreeding and outcrossing in the population. The team now also has evidence that this lack of outcrossing directly affects the fertility of the plants. Each daisy flower can produce one seed.
Germination rates can also be lower.
Young thinks there may be at least two mechanisms working to cause this drop in fertility. Not only are there fewer plants with which to breed, but smaller populations, with a less showy display, may have difficulty in attracting pollinators such as bees. In addition, the researchers have stumbled on another, unrelated difficulty for several small daisy populations in Victoria. Some individuals have undergone a genetic change, acquiring an extra set of chromosomes. While this may not affect their growth, it decreases dramatically their ability to produce fertile offspring when they mate with normal plants.