Do sexually dimorphic traits explain light-associated spatial segregation of the sexes in the plant, Marchantía inflexa?

Plants have evolved many strategies (e.g. leaf anatomy or pigmentation) to mitigate tissue-damaging high light. Often, in vascular plants, these strategies have been linked to inter- and intra-specific distribution patterns along light gradients. Sometimes sex-specific distributions are linked to sexually dimorphic traits. In non-vascular plants with separate sexes, spatial segregation of the sexes (SSS) is common, but how light gradients and sexually dimorphic traits correlate with SSS is not well-understood. To test if sexually dimorphic traits lead to SSS along light gradients in non-vascular plants, we used Marchantia inflexa whose males are found in higher light than females. We grew 25 males and 25 females to sexual maturity in a greenhouse with one clone of each plant in low or high light and assessed traits in vegetative and sexual thalli (analogous to leaves). We expected that males compared to females would exhibit traits more consistent with high light acclimation (i.e. lower total chlorophyll and specific thallus area but higher chlorophyll a/b ratio, carotenoid/chlorophyll ratio, and dry matter content). Further, we predicted greater sex-differences in sexual thalli due to differences in sex function. For sexual thalli, males had higher carotenoid/chlorophyll ratios (consistent with expectation) while females had higher chlorophyll a/b ratios and dry matter content (opposite from expectations). Vegetative thalli were not sexually dimorphic. Overall, vegetative and sexual thalli differed more for males than females, but these differences were unrelated to light. For one trait (dry matter content), sexual and vegetative thalli differed more for females than males. These patterns do not clearly explain light-associated SSS. However, our results suggest that modifications (vegetative to sexual) of all but one trait are more tightly correlated with male than female sexual function. [ABSTRACT FROM AUTHOR]