Wide variation in selfings rates among natural populations of monkeyflower
Variation in selfing rates within and among populations of hermaphroditic flowering plants may reflect both genetic and ecological factors. This important component of plant mating systems can strongly influence the evolution of reproductive strategies and the genetic structure of populations. We explored how the selfing rate in 13 natural populations of the perennial wildflower Mimulus ringens is influenced by pollinator visitation, an ecological factor, and floral display, a trait with a genetic component that also responds to environmental variation. We found substantial variation among populations in selfing rate (0.13-0.55). Selfing rates increased strongly and significantly with floral display size, among as well as within populations. Selfing rates also increased at sites with lower pollinator visitation. However, selfing rates were not correlated with floral morphology. Overall, these results suggest that two aspects of plant-pollinator interactions can influence selfing rate: pollinator visitation, and floral display, which can influence geitonogamous pollinator movements.
flowering phenology and patterns of flower deployment varies widely within and among populations in a common garden
The timing and duration of flowering (flowering phenology) is crucial to reproductive success because it determines the number and identity of potential mates. However, most studies examine singular components of flowering phenology in natural populations, such as date of flowering onset or total flower number, and fail to account for temporal variation in flowering schedules among individuals. Studies of among-plant variation in patterns of flower deployment can provide important insights concerning mating patterns, especially the extent of among-flower, within-plant self-fertilization.
In this study, we raised individual plants grown from seed from 9 natural populations of Mimulus ringens in a common garden. M. ringens is a wetland perennial native to central and eastern North America, and plants produce flowers that last for only half a day. We recorded the daily floral display for the duration of the flowering period for 20 individuals from each of the 9 populations. We then analyzed the components of flowering phenology, including date of flowering onset, total flower number, flowering duration, and flowering synchrony. Individual flowering schedules and components vary widely within and among populations in the common garden. Plants that flower early also flower for longer and therefore have greater fecundity. Within populations, individuals are asynchronous in their peak flowering, which may reduce mate diversity and effective population size.
In this study, we raised individual plants grown from seed from 9 natural populations of Mimulus ringens in a common garden. M. ringens is a wetland perennial native to central and eastern North America, and plants produce flowers that last for only half a day. We recorded the daily floral display for the duration of the flowering period for 20 individuals from each of the 9 populations. We then analyzed the components of flowering phenology, including date of flowering onset, total flower number, flowering duration, and flowering synchrony. Individual flowering schedules and components vary widely within and among populations in the common garden. Plants that flower early also flower for longer and therefore have greater fecundity. Within populations, individuals are asynchronous in their peak flowering, which may reduce mate diversity and effective population size.
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Recorded talk for Virtual Asilomar 2021
Disentangling the role of ecological and genetic factors on AMONG-POPULATION variation in selfing rates
Most flowering plants are hermaphroditic, yet the proportion of ovules fertilized by self pollen (selfing rate) varies widely among species, ranging from predominant self-fertilization to mixed-mating to nearly exclusive outcrossing. Selfing rates also vary widely among populations within species, but the evolutionary mechanisms for this among-population variation are not well understood. One possibility is that differences among populations may largely be due to ecological context, reflecting differences in pollinator community composition or pollinator foraging behavior. Alternatively, among-population differences in selfing rate may reflect heritable differences in floral traits that influence self-pollen receipt. I hypothesize that a history of increased inbreeding may have purged genetic load in these many-flowered populations, leading to reduced inbreeding depression and evolution of floral traits that promote self-fertilization. This research utilized a common garden study to determine the relative contribution of the environment and genetic factors on population selfing rate. If differences in selfing rate are similar in the common garden and in the natural populations, this suggests that the differences in selfing may be evolved responses rather than the ecological consequences of display size influencing pollinator behavior.
Influence of resource limitation on plasticity in branching architecture and flowering patterns
For angiosperms, the degree to which an individual’s flowering coincides with that of its conspecifics can have important consequences for reproductive success and fitness. Yet, how flowering patterns evolve, and to what extent they are influenced by environmental factors, remains an open question. Flowering often varies widely within and among populations, which may result in reduced mating opportunity if plants vary in the timing of flowering onset. Additionally, although large floral displays may potentially attract more pollinators, they may also promote transfer of self pollen among flowers on the same plant. In populations with substantial inbreeding depression, selection should favor plants that produce small floral displays over many days because they would suffer fewer costs associated with among-flower selfing. This temporal pattern of flower deployment may be achieved through differences among plants in branching architecture, which may also be influenced by phenotypic plasticity under different environmental conditions. My research explores how branching architecture influences patterns of flower deployment, and the role of phenotypic plasticity in shaping flowering and branching patterns as a consequence of resource limitation.
examining the effect of pollen layering on germination success using scanning electron microscopy
Angiosperm reproduction occurs when pollen grains are transported from the anthers to a stigma. The pollen grains adhere, hydrate, and develop tubes, which grow down through the style to fertilize the ovules. Deposition does not guarentee fertilization, however: pollen grains require access to stigma fluids for hydration and they need space on the stigmatic surface to germinate pollen tubes. When pollen is deposited during sequential pollinator visits, early arriving pollen may occlude the stigma surface, restricting access of later arriving pollen grains to the stigma surface. As a result, later arriving pollen grains fail to hydrate and germinate, and are therefore unlikely to contribute to reproduction. To test this, I collected stigmas from monkeyflower plants that were open pollinated and therefore received multiple pollinator visits. Then, using a scanning electron microscope (SEM), I counted the layers of deposited pollen and categorized pollen grains in the top layer as unhydrated, hydrated but not germinated, and germinated (pollen tube visible). Although pollen deposition frequently exceeded 6 layers, there was no significant difference in the proportion of pollen grains that successfully germinated in the top layer regardless of total layer number. This suggests that the timing of pollen arrival may have little influence on successful pollen germination.