Have male trees of the tropical rain forest evolved to minimize the interactions with mycorrhizal symbionts?

Abstract

While arbuscular mycorrhizal fungi improve plant performance they demand large shares of the plant's assimilated carbon, therefore resource allocation trade-offs may drive the commonly observed sexual dimorphism in mycorrhizal colonization in dioecious species. Here we looked for evidence of the evolutionary reduction of mycorrhizal colonization in males of 15 tropical rain forest plants including palms (Chamaedorea) and trees, light-demanding and shade-tolerant species. For none of the analyzed species there was evidence of spatial segregation of the sexes. Most of the tree species had no seasonal variability in mycorrhizal colonization and males had lower mycorrhizal colonization than females in over 70% of the tree species. In contrast, there were no differences between the sexes of the Chamaedorea species. Chamaedorea species had ticker roots and lower specific root length than trees, and seasonal patterns of mycorrhizal colonization correlated with the life-histories of the plants. Based on phylogenetically independent contrast, mycorrhizal colonization of male trees correlated negatively with a metric of sexual differentiation of mycorrhizal colonization between sexes. Our results suggest an evolutionary reduction in the intensity of mycorrhizal interactions in male plants, presumably driven by resource allocation trade-offs as the origen of sexual dimorphs in mycorrhizal colonization.