Petunia is a genus of flowering plants endemic to South American grasslands. Species of this genus exhibit variation in flower colour and shape, attracting bees, hawkmoths or hummingbirds. This group of plants is thus an excellent model system for evolutionary studies of diversification associated with pollinator shifts. Petunia secreta is a rare species that can be found in just few sites in the south of South America. P. secreta displays several key morphological traits that are associated with attracting bees, such as pink petals, but it also presents characteristics that are attractive to other pollinators.

In a recent study published in AoBP, Rodrigues et al. aimed to identify the legitimate pollinator of P. secreta and to assess the importance of floral traits in pollinator attraction in this Petunia species. To determine the legitimate pollinator field observations were conducted, with all floral visitors recorded and evaluated. Nectar volume and sugar concentration were also measured. To characterize morphological cues for pollinators, the ultraviolet (UV)-light response was assessed in detached flowers, and floral pigments and pollen volatile scents were characterised for four different Petunia species that present different pollination syndromes. P. secreta shares a recent ancestor with a white hawkmoth-pollinated species, P. axillaris, but has flavonols and anthocyanin pigments responsible for a pink corolla colour and UV-light responses that are common to bee-pollinated Petunia species. This study indeed showed that a solitary bee in the genus Pseudagapostemon was the most frequent pollinator of P. secreta, and these bees collect only pollen as a reward. However, different functional groups of pollinators were found to visit P. secreta, including hummingbirds. The variation in colour, nectar and pollen scent of different co-occurring species of Petunia can provide information on the specific signals that guide pollinators and may contribute to reproductive isolation. This study presents the first field observations of the pollination ecology of P. secreta. The authors suggest further study of the pollinator attractants from Petunia is essential to investigate the potential interaction between olfactory and other signals in Petunia species and detect which are the most important compounds in mutualistic interactions.

Researcher highlight

Loreta Freitas obtained a BSc. in Biology from the Pontifical Catholic University of Rio Grande do Sul, Brazil and a PhD in plant molecular evolution at the Federal University of Rio Grande do Sul (UFRGS), Brazil. Loreta currently holds a full professor position in Genetics at UFRGS.

Loreta is a plant geneticist interested in identifying plant evolutionary processes. She works mainly with Solanaceae species, and has investigated phylogenetic relationships, phylogeographic patterns, population genetics, and ecological features that promote diversification and speciation.