Variable Investment into Cleistogamous Reproduction in Populations of Two Grass Species from Eastern North America

Premise of research. A self-fertilizing mating system can be important for colonization and persistence in diverse habitats. This study uses life history theory to generate hypotheses and compare mixed mating strategies in two caespitose grass species native to eastern North America: the annual Triplasis purpurea, which colonizes sandy beaches, and the perennial Danthonia compressa, which colonizes woodland edges. Methodology. Both species produce open, potentially outcrossed chasmogamous (CH) spikelets on emergent panicles and self-fertilizing, axillary cleistogamous (CL) spikelets enclosed by leaf sheaths along flowering tillers. Individuals from three populations per species were collected. Fecundity and mass of seeds from CH and CL panicles were determined. Plant parts were separated and dried to constant mass. Aboveground allocation to CH and CL seeds as a proportion of shoot mass and investment into cleistogamy based on its proportion of total fecundity or reproductive allocation was calculated. Pivotal results. Both species had similar sizes in the field based on tiller numbers and shoot mass. However, CL fecundity and allocation were much greater in T. purpurea than in D. compressa. Axillary CL seeds weighed more than CH seeds but only in D. compressa. Populations of T. purpurea showed phenotypic variation in CH and CL fecundity and allocation-based CL investment. Danthonia compressa populations varied in allocation to chasmogamy and cleistogamy and in fecundity- and allocation-based CL investment; a young experimental population (27 mo) had the highest CL investment. There was no evidence of a trade-off between CH and CL fecundity or allocation in either species. Conclusions. Colonizing annual grasses such as T. purpurea rely on CL seed production as reproductive assurance in sparsely populated, recently disturbed habitats. Although fecundity and reproductive allocation to chasmogamy and cleistogamy are lower in perennial D. compressa, heavier axillary CL seeds that are minimally dispersed maintain populations within less disturbed, more vegetated competitive habitats.