Mating systems in Nicotiana longiflora and N. plumbaginifolia: the effect of interspecific interactions

Abstract

The research presented here was focused on the effects of interactions between Nicotiana longiflora and N. plumbaginifolia on their mating systems. First, I conducted a series of observations and pollination experiments in natural populations to determine interpopulational variability in traits associated with mating system. Second, I determined if this variability also exists in the realized mating systems (i.e. outcrossing rates) and if it is affected by sympatry. Finally, I explore the importance of post-pollination mechanisms determining offspring paternity in natural population of both Nicotiana species. Results showed significant interpopulational variability in N. longiflora floral traits but not in the selfer N. plumbaginifolia. Sympatry showed a negative effect on N. longiflora fitness and N. plumbaginifolia outcrossing rate. An increase in genetic diversity was detected on sympatric N. plumbaginifolia populations, suggesting the occurrence of hybridization with N. plumbaginifolia being the maternal parent. Overall, this research strongly supports that interactions between N. longiflora and N. plumbaginifolia are occurring in sympatric natural populations at the present time. In sympatry, asymmetrical hybridization is a possibility, but a decrease in outcrossing rates in N. plumbaginifolia as well as strong preference for outcross pollen in N. longiflora might be acting as isolation mechanisms.