XVI International Botanical Congess

One hypothesis for why evolution does not occur in marginal populations is that the heritability of some critical trait(s) may be insufficient for natural selection to occur. This may be the result of 1) intense selection eroding genetic variation, 2) increased environmental heterogeneity in marginal habitats, or 3) an increase in within-parent maternal effects. I used the common Cocklebur (Xanthium strumarium) as a study organism to test the hypothesis that low heritability in marginal populations limits range expansion and to identify the causes for this lower heritability. Data from my previous research suggests that flowering and senescence time are two critical traits that limit Cocklebur's current range. Broad-sense heritabilities of these two traits were much lower in a marginal than in a more central population.