A role for environmental niche divergence in the rapid radiation of Nicotiana section Suaveolentes (Solanaceae).

Nicotiana sect. Suaveolentes is a group that has undergone recent and rapid radiation, a clade that originated ca. six millionyears ago and has since rapidly speciated throughout Australia, with a few taxa on Pacific Islands and one in Namibia (Africa). Post-tetraploidisation, species in N. sect. Suaveolentes vary in genome size and chromosome number (2.7 to 5.8 pg/1C nucleus; n = 15 to24), which offers a novel opportunity to explore how underlying (and variable) polyploid genome structure may contribute to nicheevolution during rapid radiation. Thus, we test whether there is a relationship between genome structure, and environmental nichevariables, to observe if closely related taxa share more similar niches than more distantly related taxa in the section. We also test whichenvironmental niche variables shape genome sizes or chromosome numbers of N. sect. Suaveolentes and could therefore play a po-tential role in speciation. We find that the species overall are undergoing niche divergence, which is likely a significant contributingfactor to their radiation. Although genome sizes are conserved, we find they have a relationship with environmental niches, specifi-cally edaphic, climatic and topographic variables, and therefore have a role in diversification. However, we do not find environmentalrelationships with chromosome number, which suggests this trait does not influence environmental niche evolution. This studydeepens our understanding of niche evolution and the drivers of rapid speciation in Nicotiana, with potential implications in the night-shade family, Solanaceae. It also highlights the potential importance of genome size in angiosperm niche evolution anddiversification.