Polyploidy and self-compatibility: is there an association?

Researchers have hypothesized that self-compatibility (SC) should be more common in polyploid taxa than their diploid counterparts because of selection for reproductive assurance and/or the expected decline in inbreeding depression associated with having 'extra' gene copies. Support for this view has come from an observed breakdown of self-incompatibility (SI) in some species with a gametophytic system (GSI). The purpose of this research was to assess the strength of this relationship across a wider array of SI systems. A large database, of diploid chromosome numbers, ploidy levels, and types of SI system, was assembled for angiosperm species and used to test for an association between ploidy and SC. No strong association was found between SC and polyploidy at the level of species or families, and there was no evidence that those having a functional SI system also had fewer polyploid taxa or that most polyploids experience a breakdown in SI. These results challenge the assumption that self-fertilization is strongly associated with polyploidy and suggest directions for further research on the evolution of polyploidy in relation to SI.