Dioecy, hermaphrodites and pathogen load in plants
Alex Williams, Janis Antonovics and Jens Rolff
A. Williams and J. Rolff (email@example.com), Dept of Animal and Plant Sciences, Univ. of Sheffield, Western Bank, S10 2TN,
UK. J. Antonovics, Dept of Biology, Univ. of Virginia, Charlottesville, VA 22904, USA.
Sex-specific 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 spe-
cies. We found that direct studies on differences 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 differences 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 her-
maphrodites had a higher average pathogen load than dioecious species, consistent with the idea that higher outcrossing
is beneficial to resistance to a greater diversity of pathogens. There was however no support for dioecious species also
having a greater variance in pathogen diversity. Our results are consistent with dioecy providing a benefit in terms of
pathogen resistance, but the data were insufficient to resolve if the male and female plants showed sex-specific invest-
ment in resistance.
Sex differences in parasite prevalence and intensity have
been documented in the plant and animal literature (Alex-
ander and Antonovics 1995, Poulin 1996). In vertebrates
(Poulin 1996) females are more immunocompetent than