Genetic diversity and mating system comparisons between ray and disc achene seed pools of the heterocarpic species Heterotheca subaxillaris (Asteraceae)

We conducted a population genetic analysis of the heterocarpic species Heterotheca subaxillaris (Asteraceae, camphorweed) to determine whether there are mating system and, consequently, genotypic differences between ray and disc achene pools that correspond to ecological differences between achene morphs. No significant differences in levels of genetic diversity were detected between ray and disc achene pools of H. subaxillaris. A mixed mating system was measured overall (tm(TOTAL) = 0.648) and in separate ray (tm(RAY) = 0.736) and disc (tm(DISC) = 0.651) achene pools, and significant levels of inbreeding were detected in achene pools of most populations. We did not identify any relationships between the mating system of a floret and the dispersal traits of the achene morph it produces, nor did we identify a relationship between achene dispersal traits and the genotype of the seed contained within it. Our results indicate that frequent founder events and population bottlenecks promote high coancestry of individuals and significant levels of inbreeding within populations. Such high levels of inbreeding may impact the fitness of progeny from different achene morphs. However, differences in dispersal characteristics and seed provisioning between achene morphs may also shape progeny establishment success such that severity of inbreeding depression is reduced in H. subaxillaris and intermediate levels of self-fertilization can be evolutionarily stable.