Population-level and family-level inbreeding depression in a cleistogamous perennial

Cleistogamous species constitute strong evidence for the stability of mixed selfing and outcrossing but have been largely overlooked as theoretical and empirical systems for studying the forces thought to influence mating-system evolution. Inbreeding depression is expected to play a major role in the maintenance of outcrossing, yet reliable estimates of inbreeding depression for cleistogamous species are virtually nonexistent. We estimated both population- and family-level inbreeding depression for all life cycle stages for a population of the cleistogamous perennial Viola septemloba. Our estimate of cumulative inbreeding depression of 43% is substantially greater than two previous estimates for cleistogamous species, but it is not sufficient by itself to explain the maintenance of potentially outcrossed chasmogamous flowers.