Pollen dispersal in star cactus ( Astrophytum asterias)

Gene flow occurs via seeds and pollen in plants. In cases where seed dispersal is limited, pollen dispersal can have a substantial impact on the genetic makeup of plant populations. We examined pollen dispersal in Astrophytum asterias, an endangered cactus occurring in southern Texas and northern Mexico. Fluorescent dye was used in this study as a pollen analogue to track the distribution of pollen dispersal within a 1.9 hectare patch of star cactus. Approximately 80% of all recipient plants were located within 30 m of the source plant. Mean dispersal distance was ∼17 m. The longest dispersal event recorded was 142.2 m. Dispersal distances between source and recipient plants were used to calculate estimates of genetic neighborhood size and area using Wright's neighborhood model. These neighborhood estimates (neighborhood size = 41.8 individuals, neighborhood area = 0.094 hectares) indicate potential for population subdivision within the larger patch due to restricted pollen dispersal.