The role of phenotypic plasticity and pollination environment in the cleistogamous, mixed mating breeding system of Triodanis perfoliata

Abstract

The role of variable pollination environments in maintaining mixed mating systems is an active area of research. Dimorphic cleistogamy, in which a plant reproduces by both open, facultative outcrossing chasmogamous (CH) flowers and closed, cleistogamous (CL) flowers presents an excellent opportunity to study mixed mating. For example, plastic responses in allocation to an optimal floral type could serve as an adaptive strategy that maintains mixed mating under variable pollination environments. We tested for pollen limitation and plastic responses in allocation to different floral types under manipulated pollination conditions in the dimorphic cleistogamous, mixed mating annual, Triodanis perfoliata. Using a field population, we quantified pollen limitation, auto-fertility and plastic responses in the breeding system by measuring allocation to flower number and seed set of floral types. We found no evidence for pollen limitation for CH flowers, and CH flowers had low efficacy of autonomous selfing. Importantly, we found that T. perfoliata alters floral number following changes in pollination conditions, with pollen-supplemented plants having lower relative CH flower number than non-supplemented plants. Breeding system plasticity may allow for benefits from outcrossing through CH flowers, but also increased overall fitness through relatively cheap CL reproduction. After CH flowers receive pollen, subsequent production of CH flowers was reduced, which may be due to resource limitation. Our findings did not support a theoretical model predicting increased CH flowers with high pollination levels. These results increase our understanding of the role of pollination services and resource allocation in the maintenance of mixed mating systems, which also warrants further investigation.

The influence of environmental factors on breeding system allocation at large spatial scales

“…Ecological studies at different spatial and temporal scales can detect different components of the genetic or plastic basis of traits such as cleistogamy. Our results expand upon previous work in Triodanis which used greenhouse experiments to examine how differences in soil and light conditions influence reproductive allocation (Colbert 2015), and a field study which examined the role of pollination in the plasticity of cleistogamy (Ansaldi et al 2018). Colbert (2015) found that light increased the proportion of CH flowers, but soil did not influence reproductive plasticity.…”

“…Drawing general conclusions about the role of abiotic parameters in trait variation across CL species can be problematic. For example, soil moisture can interact with other factors that influence cleistogamy, such as pollination (Albert et al 2011; Munguía-Rosas et al 2012; Ansaldi et al 2018). Additionally, the strength of response is likely to vary with plant life history, with annuals experiencing stronger selection than perennials on traits that maximize reproduction (Jasieniuk and Lechowicz 1987).…”

Low levels of inbreeding depression and enhanced fitness in cleistogamous progeny in the annual plantTriodanis perfoliata

“…But the extent to which CL flower and fruit production are relatively less costly, as well as the value of CL flowers in providing reproductive assurance will vary with species. In T. perfoliata, CH reproduction is not pollen limited, and CL fruits produce only 10-50% the seeds of CH fruits, depending on pollination conditions, so reproductive assurance via CL flowers may not be as important in this species (Ansaldi et al 2018).…”

“…Experimental floral manipulations showed that some of the selfing is delayed, and may occur as the stigma curls back towards the style in the later stages of anthesis to make contact with self-pollen present on the style (Goodwillie et al 2018). However, pollination studies in both field and greenhouse indicate that autonomous selfing results in only about 60% as many seeds as flowers that have been supplemented with self-pollen (Ansaldi et al 2018;Goodwillie et al 2018).…”

“…flowers; (average % chasmogamy  1 SE=  15%(Ansaldi et al 2018)). With this reduced genetic load, CL flowers could be maintained because selfing would not result in the loss of fitness, and would produce the low estimates of inbreeding depression that we found in this study.Estimates of inbreeding depression can be influenced by whether the study is conducted in the greenhouse or the field, but the effects of the conditions on estimates of inbreeding depression is controversial.…”