Adaptive Flowering Time Variation in Perennial Helianthus Species Along a Northern Parallel Gradient.

The timing of anthesis is a critical life history event in many plant species in both natural and managed ecosystems. In many species flowering time is optimized to coincide with seasonal variations in resources such as light, precipitation, heat unit and nutrient availability.  The purpose of this study was to examine the range in flowering phenology of candidate species of Helianthus under investigation for perennial oilseed development and to determine the presence of underlying drivers promoting flowering time divergence.

We sampled plants consisting of the species H. maximiliani, H. nuttallii and H. giganteus from 71 sites across Southern Manitoba ranging from 49.0°-52.0°N. Individual plants were clonally propagated and established in replicated common gardens in 2012, with flowering phenology in the form of days to anthesis and flowering synchronicity being measured on each plant in the years 2013 and 2014.

Clinal variation in flowering time was observed across the latitudinal gradient across all species. Collection site of origin day length, elevation, historic heat unit accumulation, historic precipitation and combinations thereof were examined as potential drivers of population differentiation using simple linear and stepwise regression. Further investigation is underway to determine the genetic components of these observed patterns.