Differences in heritable trait variation among populations of varying size in the perennial herb Phyteuma spicatum

Habitat fragmentation may affect trait evolution in plants through changes in the environment. Evolutionary change, however, may be limited when fragmented populations suffer from genetic or environmental deterioration. In this study, we examined the potential of plants in fragmented populations to respond to altered selective pressures by estimating the amount of heritable variation in several phenotypic traits, using Phyteuma spicatum as study species. We grew offspring of plants of ten natural populations of varying size under common environmental conditions and assessed if population trait means or heritability estimates were related to the size and abiotic environmental conditions of the populations of origin. All traits differed significantly among populations and maternal families, suggesting that genetic effects were responsible for the observed trait variation. Narrow-sense heritabilities (h ² ) ranged between 0 and 1.13, depending on trait and population of origin. Size and/or environmental conditions of the populations of origin affected means and h ² -estimates of some of the measured traits. Heritabilities for flowering duration and mean seed mass decreased with decreasing population size, suggesting that plants in small populations may have a reduced capacity to respond and adapt to changes in the environment which alter selective pressures on these traits. Still, mean h ² -estimates were in some cases low, and patterns were generally quite variable. Further studies are therefore needed to gain more conclusive insights into the adaptive potential of small plant populations. Such knowledge is important if we want to understand how habitat fragmentation and associated changes in the environment affect trait evolution.