Reproductive Plasticity In Two Subspecies Of A Cleistogamous Plant, Triodanis Perfoliata

Abstract

Dimorphic cleistogamy is an intriguing reproductive strategy in which a plant produces both closed (cleistogamous), obligately selfing flowers and open (chasmogamous) flowers. Phenotypic plasticity in the production of chasmogamous and cleistogamous flowers has been demonstrated in many cleistogamous species and has been argued to be adaptive. Two subspecies of Triodanis perfoliata (Campanulaceae) exhibit dimorphic cleistogamy but differ in allocation to cleistogamous and chasmogamous flowers. I hypothesized that the divergence in flower ratio evolved from a plastic response that allowed the species to persist in a new habitat. Supporting evidence of this hypothesis would be finding that when placed in an environment similar to T. perfoliata ssp. biflora, T. perfoliata ssp. perfoliata demonstrates traits typical of T. perfoliata ssp. biflora, the derived subspecies. I demonstrated that the habitats of the two subspecies differ in soil texture and light intensity. Many of these habitat differences are factors that have been shown to induce plastic responses in other dimorphic cleistogamous species. Using a series of growth room experiments I tested the hypothesis that chasmogamous and cleistogamous flower production is plastic in the two subspecies. Plasticity in response to light environment was tested by exposing plants of each subspecies to high and low light treatments while plasticity to soil type was tested using a reciprocal soil transplant. Flower production in both subspecies of Triodanis perfoliata was found to be phenotypically plastic in response to light. The proportion of chasmogamous flowers produced was three times higher in light than in shade for both subspecies. This response is the opposite of the expected response of T. p. ssp. perfoliata under the hypothesis that reproductive plasticity promoted divergence in T. p. ssp. biflora. In response to soil type no reproductive plasticity was observed in either subspecies of Triodanis perfoliata. Although the results did not support the hypothesis that plasticity allowed the divergence of these two subspecies, the finding of plasticity in chasmogamous flower production could provide insights into the maintenance of cleistogamy in Triodanis perfoliata.