Abstract
The clonal weed Solanum carolinense exhibits plasticity in the strength of its self-incompatibility (SI) system and suffers low levels of inbreeding depression (δ) in the greenhouse. We planted one inbred and one outbred plant from each of eight maternal plants in a ring (replicated twice) and monitored clonal growth, herbivory, and reproduction over two years. Per ramet δ was estimated to be 0.63 in year one and 0.79 in year two, and outbred plants produced 2.5 times more ramets than inbred plants in the spring of year two. Inbred plants also suffered more herbivore damage than outbred plants in both fields, suggesting that inbreeding compromises herbivore resistance. Total per genet δ was 0.85 over the two years, indicating that S. carolinense is unlikely to become completely self-compatible, and suggesting that plasticity in the SI system is part of a stable mixed-mating system permitting self-fertilization when cross pollen limits seed production.
Highlights
Self-fertilization is common in plants—it has been estimated that half of all flowering plant species self-pollinate 20% or more of the time [1]—and has pronounced effects on fitness
Inbreeding depression, defined as the reduction in fitness of selfed progeny relative to outbred progeny, is a major factor influencing the evolution of plant mating systems: most models of mating system evolution predict a threshold level of inbreeding depression (0.5 in the simplest cases) below which the transmission advantage of selfing favors alleles that increase the selfing rate and above which the reduced fitness of inbred offspring favors alleles that promote outcrossing (e.g., [5,6,7,8])
We directly explored the effects of inbreeding depression on plant fitness under field conditions in the herbaceous perennial weed Solanum carolinense, a species that exhibits plasticity in the strength of its selfincompatibility (SI) system [28,29]
Summary
Self-fertilization is common in plants—it has been estimated that half of all flowering plant species self-pollinate 20% or more of the time [1]—and has pronounced effects on fitness. Inbreeding depression, defined as the reduction in fitness of selfed progeny relative to outbred progeny, is a major factor influencing the evolution of plant mating systems: most models of mating system evolution predict a threshold level of inbreeding depression (0.5 in the simplest cases) below which the transmission advantage of selfing favors alleles that increase the selfing rate and above which the reduced fitness of inbred offspring favors alleles that promote outcrossing (e.g., [5,6,7,8]). Studies that examined inbreeding depression under both greenhouse and field conditions have generally reported higher levels of inbreeding depression in the field (e.g., [10,11,12]), suggesting that inbred plants may exhibit increased vulnerability to a variety of biotic and abiotic stresses that exhibit considerable natural variation. Despite the apparent need for further investigation in this area, little work to date has examined multi-year estimates of inbreeding depression in perennial plants and no studies have examined the effects of inbreeding on clonal spread in herbaceous perennials
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