Flowers are classic models in the ecology and evolution of species interactions. Because of their function as reproductive signals in plants, flower signals are expected to be under a suite of selection pressures related to their role in speciation, reinforcement, and prolonged coexistence with close relatives. Here, we investigate how time since speciation and coexistence with close relatives shaped the macroevolutionary trajectories of floral size and scent in a group of closely related and frequently co-occurring species: the California Jewelflowers (genus Streptanthus s.l.).
Results/Conclusions
We found phylogenetic signal in flower size and weak phylogenetic signal in scent complexity (the number of scent compounds species emitted in their floral blends). Flower size similarity was positively related to phylogenetic relatedness. In contrast, scent similarity (the degree of shared compounds) was negatively correlated with species relatedness, consistent with scent composition diverging rapidly near or at speciation. Scent ranged from highly similar to dissimilar in allopatric species, but species with some or no range overlap had streongly dissimilar scents. Because the vast majority of these species have pre-zygotic reproductive isolation, scent divergence in sympatry suggests that reproductive interference or similar processes may shape scent evolution.