Continuous inbreeding affects genetic variation, phenology, and reproductive strategy in ex situ cultivated Digitalis lutea

Abstract

Premise: Ex situ cultivation is important for plant conservation, but cultivation in small populations may result in genetic changes by drift, inbreeding, or unconscious selection. Repeated inbreeding potentially influences not only plant fitness, but also floral traits and interactions with pollinators, which has not yet been studied in an ex situ context.

Methods: We studied the molecular genetic variation of Digitalis lutea from a botanic garden population cultivated for 30 years, a frozen seed bank conserving the original genetic structure, and two current wild populations including the source population. In a common garden, we studied the effects of experimental inbreeding and between-population crosses on performance, reproductive traits, and flower visitation of plants from the garden and a wild population.

Results: Significant genetic differentiation was found between the garden population and the wild population from which the seeds had originally been gathered. After experimental selfing, inbreeding depression was only found for germination and leaf size of plants from the wild population, indicating a history of inbreeding in the smaller garden population. Moreover, garden plants flowered earlier and had floral traits related to selfing, whereas wild plants had traits related to attracting pollinators. Bumblebees visited more flowers of outbred than inbred plants and of wild than garden plants.

Conclusions: Our case study suggests that high levels of inbreeding during ex situ cultivation can influence reproductive traits and thus interactions with pollinators. Together with the effects of genetic erosion and unconscious selection, these changes may affect the success of reintroductions into natural habitats.

Keywords: Digitalis lutea; Plantaginaceae; biotic interactions; ex situ cultivation; flower longevity; flower size; inbreeding depression; pollinator visitation; rapid evolution; selfing syndrome.