EVOLUTIONARY SIGNIFICANCE OF AWN LENGTH VARIATION IN A CLONAL GRASS OF FIRE-PRONE SAVANNAS
We investigated the selective advantage of continuous variation of awn length in the clonal grass Hyparrhenia diplandra (Poaceae) in a West African tropical savanna (Ivory Coast) that burns every year. This species is apomictic, so all seeds produced by one mother plant have the same genotype. H. diplandra produces diaspores with a hygroscopic awn whose length varies within and among plants. In other grass species, awns play a significant role in secondary dispersal on the ground and in seed burial. Using an experimental approach, we quantified (1) the environmental and genetic components of awn length variation, (2) the influence of awn length variation on seed burial depth, (3) the effect of awn length on seed germination and seedling survival rates in burned and unburned plots, and (4) the potential role of fire intensity in selecting diaspores with different awn lengths. Awn length varied from 35 to 70 mm and was highly heritable (h2 = 0.63). Variation within individuals was not related to flowering p...