Nototribic Pollination Reduces Heterospecific Pollen Deposition and Dampens Its Negative Impact on Seed Production in Calceolaria Species

Abstract

Premise of research. Nototriby has evolved independently many times in different plant families, possibly for the advantage in the prevention of heterospecific pollen contact in pollinator-sharing environments. However, differences in pollen deposition and their consequences have received little attention, especially in highly specialized systems. Methodology. A systematic stigma collection was performed to estimate the proportion of heterospecific and conspecific pollen in two Calceolaria species with different pollination modes (i.e., nototribic and sternotribic) inhabiting a high mountain valley in Chile. Then, with the previous information, a manipulative pollen donor-receipt experiment was conducted to determine the impact of heterospecific pollen deposition in female reproductive success in both species (seed production). Pivotal results. The two Calceolaria species were prone to receive pollen from some plants of the surrounding community, mainly Adesmia emarginata. However, in the nototribic species (C. filicaulis), only 10% of the total pollen deposition belonged to heterospecific plant species, while in the sternotribic species (C. cavanillesii), more than 60% was heterospecific. Concomitant with this, the hand cross-pollination experiment showed that seed production of C. cavanillesii was more affected by A. emarginata pollen deposition than C. filicaulis pollen. Conclusions. Nototribic morphology can be an effective prepollination barrier to the deposition of heterospecific pollen. However, when this barrier is overcome, its impact may be affected by different factors, such as the foraging behavior of their main pollinator species and a rejection or tolerance mechanism to foreign pollen receipt developed by plant species. Future studies should consider assays to determine the mechanisms behind these findings and their generality to other species of the genus Calceolaria.