Reproductive success of the gynodioecious Lobelia spicata Lam. (campanulaceae): Female frequency, population demographics, and latitudinal patterns

Premise of research. In gynodioecious species, female plants are often at a disadvantage due to their reliance on hermaphroditic pollen donation and lower attractiveness to pollinators. They may compensate for these disadvantages through greater reproductive output and progeny fitness; however, the level of female advantage may vary based on population demographics (i.e., female frequency and gender morph density), geographic location, and abiotic conditions (i.e., temperature and precipitation). Methodology. In 2008 and 2009, data on latitude, longitude, mean temperature and mean precipitation from May to July (growing season), female frequency, female density, hermaphrodite density, reproductive output (i.e., fruit set, seed number per fruit, seed biomass), seed germination, and female advantage in reproduction were collected for 11 populations of the gynodioecious prairie species Lobelia spicata Lam. (Campanulaceae) in Illinois. Pivotal results. Female plants were found to produce greater fruit sets, greater number of seeds per fruit, and heavier, better-germinating seeds than hermaphrodites, though these gender differences in reproduction varied among populations and between sampling years. Female frequency impacted the gender-based reproductive measur'ements; in particular, it was negatively correlated with fruit set. Female frequency within L. spicata populations was negatively correlated with latitude, with temperature the most likely driving force. Conclusions. Abiotic conditions such as high temperatures seem to favor the success of female plants within populations of L. spicata, either directly through differential resource allocation between genders or indirectly as a covariate for some other environmental factor (e.g., pollinator abundance/behavior), though experimental data are needed to support this assertion.