Conspecific pollen precedence and its contribution to speciation in Triodanis perfoliata

Abstract

Speciation is the process by which one species diverges into two distinct species. To fully understand speciation, it is important to understand reproductive isolation. Reproductive isolation, the inability of two individuals to mate and produce viable offspring, restricts gene flow between populations allowing them to diverge as distinct species. Reproductive isolation can be caused by several factors or mechanisms. Some of these factors that are unique to plants include different temporal flowering patterns, different pollinators, and conspecific pollen precedence, or the preference for conspecific pollen for fertilization in the presence of both conspecific and heterospecific pollen. This study asks whether conspecific pollen precedence contributes to reproductive isolation between subspecies of Triodanis perfoliata. Triodanis perfoliata is a weedy species of plant that has two subspecies, Triodanis perfoliata subsp. perfoliata and Triodanis perfoliata subsp. biflora, that grow sympatrically in eastern North Carolina. Based on experimentation, it has been shown that these subspecies can breed and produce viable hybrid offspring; however, the two subspecies have distinct sets of traits. The question remains as to what factors contribute to isolation of the two subspecies. In this experiment, plants were raised that were produced by mixed pollinations. Using morphological traits, hybrid and pure offspring were identified in the offspring generation, and these identities were verified by AFLP (Amplified Fragment Length Polymorphism) genetic markers. If the frequency of the hybrid and pure individuals in the offspring of mixed pollination deviates from the null expectation of a 1:1ratio, we will conclude that conspecific pollen precedence contributes to reproductive isolation, providing insight into speciation mechanisms in the study species.