Quantitative genetics in a fragmented landscape, a study of heritable floral traits in Oenothera harringtonii

Background/Question/Methods

Habitat fragmentation can alter the conditions of plant populations, introducing novel selective pressures. The ability of a population to respond to environmental change can be inferred by assessing the population’s genetic diversity and the heritability of traits thought to be under selection.  In plants, floral traits have been shown to have significant heritabilities, especially those associated with pollination success. The goal of this study was to assess whether floral traits in the annual Oenothera harringtonii (Onagraceae) varied by populations and determine whether this variation was heritable. The six traits measured for this moth pollinated species were corolla diameter, floral flare, herkogamy, floral tube length, nectar volume and nectar concentration. Additionally, we compared plants from fragmented and non-fragmented populations to determine if habitat changes are leading to shifts in floral traits. We conducted a common garden experiment with offspring from 115 maternal lines from 10 populations (five each from fragmented and non-fragmented populations). Floral traits were measured for both generations (maternal – field, offspring – common garden). We performed parent-offspring regressions to estimate trait heritability. We used mixed-effects models to create nested ANOVAs to obtain genetic variance components and test for the role of habitat fragmentation on the mean differences for each trait.

Results/Conclusions

We found significant heritability for three floral traits (corolla diameter, floral tube length and floral flare) and significant mean differences by habitat fragmentation were also found for three traits (floral flare, herkogamy and nectar volume). Our results show a significant environmental and genetic component in local adaptation of O. harringtonii populations studied.  Although there was high genetic variance found within sibling group, there was also substantial variation between maternal lines and populations which suggest genetic differences for these floral traits exists at the population level. Variation in floral traits between fragmented populations and non-fragmented populations for three floral traits suggest there are differences in selective pressures in these two habitat types but cannot specify a key driver of local adaptation. Future studies should focus on identifying whether pollinator-mediated selection can explain these differences. The results of this project can serve as a guide for future research on the ecology of Oenothera harringtonii and its conservation.