Characterization of the mating system of a native perennial tetraploid herb, Silene stellata

Abstract

Premise of the StudyNursery pollination systems can range from obligate to facultative. In a system where generalists provide substantial pollination service, an important question is whether the cost of seed predation outweighs the benefit provided by the nursery pollinator to cause the plant to evolve toward more generalized pollination. Using a facultative system native to North America, we tested whether nursery pollinator vs. strictly mutualistic generalists affect mating‐system parameters of the host plant and explored the implications for long‐term coevolution.MethodsWe used paternity analyses with 11 microsatellite markers to characterize the mating system of Silene stellata when pollination service is primarily through the nursery pollinator Hadena ectypa and generalist moths.Key ResultsOur experimental population of S. stellata was predominantly outcrossing (average outcrossing rate t = 0.83), and mating‐system parameters were similar between pollinator groups. We detected significant correlations in both selfing and outcrossed paternity at the fruit and maternal family level, corresponding to limited pollen dispersal (mean = 3.9 m). Among individuals, variation in anther–stigma separation was positively associated with outcrossing rate, which suggests the importance of herkogamy in preventing selfing.ConclusionsCorrelated paternity suggests that seeds from the same fruit and/or plants are sired by a limited number of pollen donors, resulting from low pollen dispersal and potential male–male competition. The similar mating‐system parameters of the two pollinator groups suggest that selection for higher outcrossing in S. stellata is likely to be through floral design rather than through increased pollinator specialization with H. ectypa.

Variable and sexually conflicting selection onSilene stellatafloral traits by a putative moth pollinator selective agent

“…There is no significant difference in outcrossing rates between early and late flowering seasons and across years (∼83%, Zhou et al. 2018b).…”

“…The co-pollinating generalist moths are equally effective in pollen transfer (Reynolds et al 2012), and do not exhibit seed predation, thus are strict mutualists. There is no significant difference in outcrossing rates between early and late flowering seasons and across years (∼83%, Zhou et al 2018b).…”

“…Outcrossing rate is relatively high based on estimates from both pollinator exclusion experiments (>73%, Reynolds 2008) and mating system estimation using microsatellite markers (∼83%, Zhou et al. 2018b).…”

“…Because S. stellata is a predominantly outcrossing species and inbreeding depression is inferred to be high based on mating system estimates (Zhou et al. 2018b) and has been observed in the closely related S. virginica (Dudash and Fenster, 2001) and S. caroliniana (M. R. Dudash and C. B. Fenster, unpubl. data), we quantified selection only through outcrossing male fertility to test for conflicting selection on traits between sexual functions.…”

“…An individual plant at our study site usually produces multiple stems and on average produces approximately 40 flowers each flowering season (Reynolds et al 2012). Outcrossing rate is relatively high based on estimates from both pollinator exclusion experiments (>73%, Reynolds 2008) and mating system estimation using microsatellite markers (∼83%, Zhou et al 2018b).…”