Increased seed dispersal potential towards geographic range limits in a Pacific coast dune plant

• Dispersal may be favoured at geographic range edges by unstable populationand metapopulation dynamics. However, dispersal may also evolve in response togeographic variation in other life-history traits, especially the mating system. Here,increased dispersal at range margins was tested for with a range-wide analysis ofseed dispersal and mating system traits in Abronia umbellata, a plant endemic toPacific coastal dunes of North America.• Seeds disperse within winged anthocarps. Anthocarps from 34 populations variedwidely in wing size (mass-corrected wing index). Wing index correlated negativelywith threshold wind velocity for dispersal in wind tunnel tests, suggesting that wingsfacilitate tumbling over open sandy substrate. As predicted, wing index increasedand threshold velocity decreased towards both range limits.• Flower size, herkogamy and self-incompatibility declined towards range limits,indicating a shift to self-fertilization, and flower size and wing index correlatednegatively. However, the increase in wing index towards range limits remained afterstatistically controlling flower size.• These results are consistent with selection favouring dispersal at range margins.The evolutionary lability of dispersal across the range may affect the interactionbetween selection and gene flow in the establishment and maintenance ofgeographic range limits.Source type: Electronic(1