Abstract
Viola pubescens is a perennial, mixed breeding herb that produces both chasmogamous and cleistogamous flowers at different times of the season. Once bud type is specified, it does not convert from one form to the other. While temporal production of the two flowers is known to be influenced by environmental factors, the specific environmental cues that signal emergence of each flower type have not been empirically studied. To investigate the environmental parameters driving seasonal development of chasmogamous versus cleistogamous flowers, a native V. pubescens population was examined during the spring and summer of 2016 and 2017. Measurements of light quantity, canopy cover, photoperiod, temperature, soil moisture, soil pH, and the number of chasmogamous and cleistogamous buds were collected on either a weekly or biweekly basis. Independent zero-inflated negative binomial (ZINB) regressions were used to model the odds of bud production (0 versus 1 bud) and bud counts (≥ 1 bud) as a function of the environmental variables. Results of the ZINB models highlight key differences between the environmental variables that influence chasmogamous versus cleistogamous bud development and counts. In addition to the ZINB regressions, individual logistic regressions were fit to the bud data. The logistic models support results of the ZINB models and, more crucially, identify specific environmental thresholds at which each bud type is probable. Collectively, this work offers novel insight into how environmental variables shape temporal development of chasmogamous and cleistogamous flowers, suggests distinct threshold values that may aid in selectively inducing each flower type, and provides insight into how climatic change may impact mixed breeding species.
Highlights
IntroductionEnvironmental impact on chasmogamous and cleistogamous flowering in Viola pubescens flowers (Fig 1A), and closed, self-pollinating cleistogamous flowers (Fig 1B) [1,2,3,4,5,6]
The present study highlights the environmental impacts of light quantity, photoperiod, temperature, and soil moisture on chasmogamous and cleistogamous bud development and the seasonal transition from chasmogamous to cleistogamous budding in a native Viola pubescens population
The opposite relationships between environmental variables and bud likelihood support that chasmogamous and cleistogamous buds develop in response to distinct environmental cues
Summary
Environmental impact on chasmogamous and cleistogamous flowering in Viola pubescens flowers (Fig 1A), and closed, self-pollinating cleistogamous flowers (Fig 1B) [1,2,3,4,5,6]. For these mixed breeding species, chasmogamous and cleistogamous flowers can exhibit spatial separation, as seen in Amphicarpaea bracteata, where aerial chasmogamous flowers are isolated from subterranean cleistogamous flowers [5,7]. When and whether chasmogamous or cleistogamous flowers dominate depends on growth conditions, offering an alternative mating strategy in variable environments [6,14,15,16]
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