Sexual differences and sex ratios of dioecious plants under stressful environments

Dioecious plants exhibit sexual dimorphism in both sexual features (reproductive organs) and secondary sex characteristics (vegetative traits). Sexual differences in secondary traits, including morphological, physiological and ecological characters, have been commonly associated with trade-offs between the cost of reproduction and other plant functions. Such trade-offs may be modified by environmental stressors, although there is evidence that sexually dimorphic responses to stress do not always exist in all plant species. When sexual dimorphism exists, sexually different responses appear to depend on the species and stress types. Yet, further studies on dioecious plant species are needed to allow the generalization of stress effects on males and females. Additionally, sexual dimorphism may influence the frequency and distribution of the sexes along environmental gradients, likely causing niche differentiation and spatial segregation of sexes. At the present, the causes and mechanisms governing sex ratio biases are poorly understood. This review aims to discuss sex-specific responses and sex ratio biases occurring under adverse conditions, which will advance our knowledge of sexually dimorphic responses to environmental stressors.