An Exploration of Factors Driving Patterns of Hybridization in Triodanis

Premise of research. Elucidating and preserving biodiversity are essential components of biological research, yet many natural processes limit our ability to define basic patterns of biodiversity. Hybridization is a common process in flowering plants with a range of outcomes that influence our understanding of species ecology and evolution. In many systems, factors that facilitate or prevent successful hybridization are poorly understood. Here, we investigate potential mechanisms driving patterns of hybridization between Triodanis biflora and Triodanis perfoliata. These species exhibit dimorphic cleistogamy, with T. biflora producing relatively fewer open flowers and thus with less potential to contribute to hybrid gene flow.Methodology. We conducted a large-scale field study across hybrid zones to synthesize our understanding of factors that could influence patterns of hybridization in this system. We examined potential variation in pollinator visitation, microhabitats, and breeding system allocation among parental individuals and putative hybrids. We also examined the occurrence of hybrids via genetic data and subsequently quantified morphological differences between parental taxa and confirmed hybrids.Pivotal results. Across multiple field sites, there is no evidence for microhabitat (i.e., soil texture, light availability) or pollinator visitation rates for consistently limiting gene flow. However, congruent with previous work, our data support the theory that variation in breeding system between T. biflora and T. perfoliata may play a role in driving patterns of hybridization.Conclusions. In this system, we find few barriers for hybridization and strong genetic evidence for gene flow between T. biflora and T. perfoliata, but variation in the breeding system may be the key driver in shaping the magnitude as well as the overall patterns of hybridization in this study system. Our research, combined with multiple previous studies, emphasizes the importance of natural history studies for elucidating these patterns.