Inheritance of stress-mediated floral trait responses in Collinsia heterophylla

Background/Question/Methods

As climate change becomes imminent, unprecedented variations in temperature and water availability result in stressful conditions compromising a plant’s resources status. These abiotic variations do not have regular patterns resulting in parental and offspring generations experiencing different scenarios. To achieve optimal allocation of limited resources, flowering plants growing in stressful environments may exhibit altered reproductive traits that increase autonomous selfing. It is not very clear whether these altered traits are plastic responses or have a genetic basis. In mixed-mated plants, selfing is generally delayed and is a form of reproductive assurance. Advanced selfing in plants responding to abiotic stress allows for remobilization of resources from floral maintenance to seed production but is associated with inbreeding depression costs. Interaction between stress and inbreeding could determine the potential for a change in mating system. My research looks at the inheritance of stress-mediated floral trait responses in the annual flowering plant, Collinsia heterophylla where cross-pollination is facilitated by physical (herkogamy) and temporal (dichogamy) separation of stigma and anthers. Floral trait responses, reproductive functions and fecundity were determined in parental plants grown under temperature and water stress. Growing inbred offspring in the absence of stress allowed us to determine the interaction between stress and inbreeding. 

Results/Conclusions

Our results indicate that, in plants grown under abiotic stress, flower size, herkogamy, in vitro pollen tube length and pollen grains per flower decreased. While pollen viability remained relatively similar across treatments, ovule number and fecundity increased. Reduction in herkogamy facilitates self-pollination explaining the increased seed production under stress. Preliminary analyses suggest that the inbred offspring grown under normal conditions, do not inherit changes to flower size but reduced herkogamy continued to be expressed in the inbred offspring suggesting that stress mediated trait responses facilitating autonomous selfing could have a genetic bases enabling offspring to also increase incidences of selfing. Seed production in the inbred offspring however, was significantly reduced. Abiotic stress had negative effects on pollen functions but this was not enough to reduce seed production. However, combined effects of inbreeding depression and maternal stress, could have had increased unfavorable effects on pollen functions resulting in further reduced fecundity in the inbred offspring of stressed plants. We conclude that, while environmental stress elicits floral trait responses facilitating autonomous selfing, detrimental effects of inbreeding depression could slow the rate of change from a mixed-mating mode to a predominantly selfing  mode in Collinsia heterophylla.