Dioecy, hermaphrodites and pathogen load in plants

Sex-specifi c investment in pathogen resistance and immunity has been widely reported in animals and to a much lesser degree in plants. Here, we investigated the incidence of fungal pathogens in dioecious versus hermaphroditic plant species. We found that direct studies on diff erences between males and females in disease resistance or pathogen incidence were rare or non-existent in plants, but if we made the prediction that if such diff erences exist (e.g. if males are less resistant than females), dioecious species should have a higher variation in pathogen diversity than hermaphrodites. Comparative studies on paired dioecious and hermaphrodite species from multiple plant families showed that hermaphrodites had a higher average pathogen load than dioecious species, consistent with the idea that higher outcrossing is benefi cial to resistance to a greater diversity of pathogens. Th ere was however no support for dioecious species also having a greater variance in pathogen diversity. Our results are consistent with dioecy providing a benefi t in terms of pathogen resistance, but the data were insuffi cient to resolve if the male and female plants showed sex-specifi c investment in resistance.