XVI International Botanical Congess
Populations of Chamerion angustifolium (fireweed) often contain diploid and tetraploid individuals, despite the expected barriers to tetraploid establishment. We examined the processes governing tetraploid establishment, including 1)viability and fertility differences among diploids and polyploids, 2) frequency-dependent fitness, and 3) reproductive isolation in natural populations. Tetraploids had lower fitness than diploids in a common garden but, in experimental populations,fitness of tetraploids was frequency-dependent and exceeded that of diploids when in the majority. Finally, intercytotype mating was low in the field, due to spatial structure of cytotypes and bee foraging behaviour, suggesting that reproductive isolation may be sufficiently strong to overcome any mating disadvantage.