Intra- and inter-sexual competition of Populus cathayana under different watering regimes

1Previous studies have demonstrated that poplar is sexually dimorphic in its responses to environmental stresses and provided evidence of sex-related differences in protein composition, gene transcription and morphological and physiological processes. However, sexual competition of poplar has not yet been studied. We employed Populus cathayana males and females as a model to investigate intra- and intersexual competition under well-watered condition and drought stress. Our results indicated that competition significantly affected sexual dimorphism of P.cathayana under different watering regimes. Sexual competition was environment-dependent and modified by drought. In females, drought intensified the negative effect of intrasexual competition. Similar resource utilization patterns of females may aggravate pressure for resources under drought stress. Under intersexual competition, females showed a greater competitive ability than males under well-watered condition, while males showed a slight competitive advantage under drought stress. Intersexual competition seems to alleviate the sexual dimorphism of P.cathayana in response to drought stress, as females increase fitness and males decrease fitness compared with intrasexual competition. Sexual dimorphism in resource utilization patterns and niche segregation may contribute to sexual competition in a given environment. Sexual competition was found to affect competitive ability and fitness of both sexes, which may cause spatial segregation of sexes in P.cathyana populations.