Floral development & 3D-pollination syndromes in Aquilegia

The extraordinary diversity of angiosperms and their flowers it the results of the intricate co- evolutionary relationship with their animal pollinators. Many angiosperm groups are pollinated by a broad range of animals and have evolved strikingly different looking flowers. One such group is the genus Aquilegia (Columbines, Buttercup Family), species of which are pollinated either by bees (and bumblebees), hummingbirds or hawkmoths. Based on earlier studies, we know that bee pollination is most likely ancestral in this genus and that speciation was driven by repeated shifts to hummingbird and, subsequently, to hawkmoth pollination. One possible way by which morphological differences between derived species and their ancestors may occur, is through differential developmental patterns: relative to the ancestral species, development may be stopped prematurely (or prolonged), leading to a juvenilized (or hyperadult) morphology. The evolution of species through such changes in development is called heterochrony. Heterochrony has been recognized as an important process in animal evolution, but has rarely been studied in plants. Here, we investigate whether the differences among Columbine flowers can be explained with heterochrony. We hypothesize that some aspects of floral morphology such as, for instance, nectar spur length and curvature, are the result of heterochrony. In addition, we will test whether the repeated and independent evolution of similar flower morphologies in the group are paralleled by similar developmental patterns; in other words, whether morphological convergence of the adult floral form is linked to convergent patterns of floral development. We will first conduct field work in North America to fill in existing gaps in our knowledge of Columbine pollination. In order to investigate the three-dimensional (3D) shape of adult flowers collected in the field and their respective pollinators (museum specimens), we will apply micro computed tomography (micro-CT). The resulting high resolution 3D models will allow us to compare and quantify the 3D morphological fit of the different flowers and their pollinators in unprecedented detail. In a second step, we will harvest floral buds in different developmental stages from cultivated individuals and, again using micro- CT, describe and quantify developmental differences among the flowers of different species. Finally, with the help of a multidimensional mathematical approach, we will compare the developmental trajectories and test for heterochrony. This project is unique in that it addresses detailed 3D-shape properties of entire flowers and their pollinators and in that it makes a direct link between floral development and pollinator driven selection, two processes that are usually considered separately. Our work will allow for new insights into the interplay of developmental constraints and pollinator-mediated selection that shape flower evolution and angiosperm diversification. PR abstract_en 1|1

The extraordinary diversity of angiosperms (flowering plants) and their flowers results from their intricate co-evolution with animal pollinators. Many angiosperm groups are pollinated by a wide range of animals and have evolved distinct flower morphologies. The genus Aquilegia (columbines, Buttercup family) is a prime example, with species pollinated by bees, hummingbirds, or hawkmoths. Previous studies suggested that bee pollination is ancestral in this genus, and speciation was driven by shifts to hummingbird and later hawkmoth pollination. This project aimed to understand how floral morphology is shaped by the interaction between columbine flowers and their pollinators. We conducted our research in the USA, where many Aquilegia species occur. We closely observed floral visitors, which collect nectar from the long nectar spurs of the flowers, as well as pollen. Our observations revealed that more than a single pollinator types sometimes visit the same flowers; for example, both bees and hummingbirds pollinate Aquilegia eximia. We also analyzed floral scent and nectar composition, drawing conclusions about how pollinators influence floral chemistry. In the field, we collected hundreds of flowers and buds, preserved them in alcohol, and sent them to Austria. We scanned these samples in a tomography system to create 3D images, which we are now analyzing to understand how aspects of floral shape, such as nectar spur curvature, correlate with pollinator characteristics like hummingbird bill shape. This analysis will help us identify the selective pressures pollinators exert on floral features and explore how floral development (from buds to open flowers) varies across species with different pollinators. This project is unique in its focus on detailed 3D-shape properties of flowers and their pollinators, directly linking floral development with pollinator-driven selection-two processes often studied separately. Our work offers new insights into how developmental constraints and pollinator-mediated selection shape flower evolution and contribute to angiosperm diversification.