PS 20-195 - Investigating latitudinal trends in stigma/style exsertion (outcrossing behaviour) for five North America Lobelia species using citizen science
Lobelia floral development is protandrous and occurs through a ‘pollen-pump’ mechanism where the style is exserted from within a fused stamen tube, pushing mature pollen out prior to stigma lobe opening. Protandry is considered an outcrossing enhancing breeding system due to the temporal separation of staminate and pistillate floral phases. However, Lobelia inflata has been found to be obligately selfing (< 99%) at the northern extent of its species range, assumed to be the result of the style remaining enclosed within the stamen tube throughout floral development. Yet, anecdotal evidence suggests that stylar exsertion, and consequently outcrossing, occurs in southern areas of the L. inflata range. This potential latitudinal gradient in outcrossing behaviour may be the result of selection for selfing at range edges because of the dynamics of dispersal to new habitats. We used iNaturalist citizen science data to track the occurrence of stylar exsertion in L. inflata, and four congenerics, by analyzing observation photographs for evidence of visible stigmatic surfaces. We tracked the presence/absence and the number of flowers with visible stigmas across observations to determine whether latitude or environmental factors might affect outcrossing behaviour in L. inflata and its congenerics.
Results/Conclusions
In preliminary results, we have found that the occurrence and proportion of flowers demonstrating visible stigmas/styles was significantly predicted by the presence of fruit (senesced flowers) for all five Lobelia species. We also found that stigma/style visibility was lowest in L. inflata (~21% of all observations) when compared to congenerics (~42 – 80% of observations) and stigma/style visibility in observations of L. inflata and one other congeneric decreased at northern latitudes. Moreover, the proportion of flowers in each observation that demonstrated visible stigmas/styles also significantly decreased at northern latitudes for L. inflata and two congenerics. This preliminary evidence suggests that expression of protandry in L. inflata does indeed exist on a latitudinal gradient which would indicate that outcrossing may be more common in southern areas of the species range. However, this trend does not seem to be consistent across all the studied species.
