Sprecher
Beschreibung
Among the seven families and ca. 4,000 living species of Laurales, unisexuality appears to have evolved multiple times across the order. To better understand the various pathways driving the evolution of sexual systems, the full morphological diversity of unisexual flowers and their associated sexual systems (e.g., monoecy vs dioecy) must be considered. Here, we reconstruct the evolution of sexual systems in Laurales using an undated and a new tip-dated phylogeny. We conducted Bayesian phylogenetic analyses using a morphological dataset of 62 floral characters that sampled 28 fossil flowers and 193 extant taxa of Laurales. To reconstruct the evolution of sexual systems, we tested four different character state transition models based on previous hypotheses of evolutionary transitions between sexual systems. Stochastic character mapping under the best-scoring model was used to reconstruct evolutionary transitions along the phylogeny. While phylogenetic placements of most Cretaceous fossil flowers differed between the undated and tip-dated analyses, results were robust between the two topologies when reconstructing sexual system evolution. Transitions to dioecy primarily occurred through two pathways: 1) direct transition from hermaphroditism to dioecy with structurally perfect and functionally unisexual flowers or 2) with an intermediate transition from hermaphroditism to monoecy with imperfect flowers before a transition to dioecy with imperfect flowers. Reversals to hermaphroditism were rare while reversals from dioecy to monoecy with imperfect flowers were frequently inferred. Our results indicate that Laurales has undergone numerous independent transitions to unisexuality through multiple pathways, suggesting that different molecular and evolutionary mechanisms have driven some of these transitions.