Physiological and reproductive differences between hermaphrodites and males in the androdioecious plant Fraxinus ornus

Abstract

Androdioecy, the co-occurrence of males and hermaphrodites in a breeding population, is a rare reproductive system in the nature. This rarity may be the result of the large fitness gain required for male plants to be maintained by selection. Physiological, vegetative and reproductive characters of males and hermaphrodites of the androdioecious species Fraxinus ornus (Oleaceae) were compared, supporting the hypothesis that males compensate the fitness advantage of hermaphrodites with greater reproductive -but not vegetative- output, with concomitant differences in physiological capacities between the genders. Photosynthetic rate was similar between both genders, but hermaphrodites had lower water potential and carbon isotope discrimination than males. Photosynthesis rates decreased with decreasing water potentials more steeply in males than in hermaphrodites, indicating that hermaphrodites were more drought tolerant than males. Vegetative characters such as current year shoot growth or tree size did not differ between genders. Males produced 1.6 times more inflorescences than hermaphrodites. This difference was consistent across years and populations.