Sex-specific effect of Microbotryum violaceum (Uredinales) spores on healthy plants of the gynodioecious Gypsophila repens (Caryophyllaceae).

Females of gynodioecious species need to have reproductive advantages to compensate for their lack of male function and assure their maintenance in natural populations. Females may be more fecund than hermaphrodites because they reallocate resources from male to female function, avoid selfing and inbreeding depression, or produce higher quality offspring by screening arriving pollen better. A novel type of female advantage is proposed that may be important for several species of gynodioecious Caryophyllaceae. The anther smut fungus Microbotryum violaceum generally sterilizes its infected hosts but even without infection, spore deposition can negatively affect the reproduction of healthy individuals. In Gypsophila repens, flowers of hermaphrodite plants experimentally pollinated with both fungal spores and pollen produced significantly fewer fruits and seeds than those that received pollen alone, whereas female reproduction was unaffected by spore deposition. This unexplored reproductive advantage of females is probably due to the larger stigmatic surface in pistillate flowers, that allows pollen germination despite the presence of spores. Because longer stigmas may also lead to increased spore deposition, these results raise questions regarding the infection probability for each sex, possible sex-specific defense mechanisms, and the general role of pathogens in the maintenance of females in natural gynodioecious populations.