Inbreeding Reduces Floral Longevity and Flower Size in the Mixed-Mating Biennial Sabatia angularis

Abstract

Premise of research. Inbreeding depression is well known to contribute to the maintenance of outcrossing in flowering plants because of its direct negative impacts on germination, survival, and fertility. Yet inbreeding depression could also impact fitness indirectly by affecting traits that govern biotic interactions. Relatively little is known about inbreeding depression on traits related to pollination success. Although often associated with pollinator attraction or reward, pollination success is also determined by floral longevity. Inbreeding depression in floral longevity has not been studied but has the potential to compound pollination disadvantages confronting inbred plants. Methodology. We investigated inbreeding depression for traits related to pollination success in the mixed-mating biennial Sabatia angularis L. (Pursh) (Gentianaceae). Under controlled, pollinator-free conditions, we performed crosses to create families of selfed and outcross seed and raised these plants to flower. We compared selfed and outcrossed individuals for the following traits: flower number, flower size, corolla longevity, stigma longevity, and plant height. We also considered whether inbreeding depression was influenced by flower number–longevity trade-offs or plant size. Pivotal results. Selfed plants produced significantly smaller flowers that lived for a significantly shorter amount of time than flowers of outcrossed plants, based on corolla and stigma longevity. Consistent with prior work, we found trade-offs between floral longevity and flower number and positive relationships between longevity and plant height. However, we did not detect inbreeding depression for flower number or plant size. Conclusions. We find novel evidence that inbreeding reduces both floral longevity and flower size. Although moderate, inbreeding depression for these traits could leave selfed plants at a disadvantage in pollen-limited environments, especially where rates of pollen export outpace deposition such that plants are forced to rely on pollinators for seed production. Our work contributes to our understanding of how inbreeding depression can alter plant-pollinator interaction outcomes and raises questions about its influence on reproductive allocation.