Meeting Abstract
Fruits of the genus Elaeocarpus (Elaeocarpaceae) are notable for exhibiting structural coloration, but little is known about the evolutionary basis of this relatively rare trait in plants. Further, ultrastructural knowledge of these structurally colored fruits remains limited. We reconstructed the evolutionary history of structural color in Elaeocarpaceae using published phylogenetic hypotheses based on plastid and nuclear sequence data. We used scanning and transmission electron microscopy (EM), UV-VIS-NIR spectrophotometry, and theoretical optical modeling to confirm the structural origin of the blue structural color, as exemplified by the Blue Quandong (E. angustifolius). EM analyses shows that structural color in Elaeocarpus fruits is typically produced by a disordered multilayer ultrastructure within the epidermis, with theoretical modeling of the ultrastructure consistent with the measured reflectance spectrum. Ancestral state reconstruction reveals that the structural coloration trait is likely ancestral to this genus, with about 14 losses and 4 gains. Phylogenetic regression analyses also reveals that the presence of structural coloration is significantly correlated (Pagel’s λ 0.68, P < 0.001) with the extant geographical range of cassowaries (Casuarius spp.) but not with other ecological factors such as elevation, fruit size or shape, suggesting dispersal services provided by cassowaries and fruit pigeons (in the Southern Pacific) likely played a key role in both the evolution and maintenance of structural color in this genus. The results of this study can perhaps provide insights into exploitation of sensory preferences in the coevolution of plant-disperser mutualisms in forest ecosystems.
