Changes in floral shape: insights into the evolution of wild Nicotiana (Solanaceae)

Floral shape and size play a role in plant diversification and reproductive isolation. Different floral forms can rise by selective pressures by pollinators/ecological constraints and/or genetic drift. Nicotiana (Solanaceae) has c. 82 currently recognized species grouped in 13 sections. Nicotiana forgetiana and N. alata belong to section Alatae and present different floral traits related to their primary pollinators. These species co-occur in a region of plant endemism in southern Brazil marked by a mosaic between open grasslands and Araucaria forest. Here, we conducted a population-level sampling across the range of N. forgetiana and combined geometric morphometric analyses and ecological niche modelling to shed light on the patterns underlying intraspecific floral shape variation. Corolla shape and size varied significantly across the geographical distribution of N. forgetiana and 'rastroensis', a putative new species. These floral shape differences were related to variations in temperature, precipitation and elevation. We also observed a range of intermediate floral traits in two populations, and our results of geometric morphometric analyses reveal morphological overlap between N. alata and N. forgetiana. Moreover, we found that habitat suitability for both species was impacted by past climatic oscillations, with severe reduction for N. forgetiana during the Last Glacial Maximum. We discuss the results to shed light on the evolution of N. forgetiana.