High resolution analysis of mating systems:: inbreeding in natural populations of Pinus radiata

Pinus radiata has a history of population bottlenecks and is currently restricted to five relatively small populations, three in mainland California, and two on islands off the coast of Baja California. Using highly polymorphic microsatellite markers and a newly developed statistical approach, we were able to estimate individual inbreeding coefficients and can thus analyse the mating system with high resolution. We find a bimodal distribution of inbreeding coefficients: most individuals result from selfing whereas few (in the mainland populations) to a modest number (in the island populations) are likely selfed. In most other pine species and presumably in the ancestral P. radiata population, occurrence of mature selfed individuals would be impossible because of the high genetic load. We therefore conclude that inbreeding depression has been purged in P. radiata and that the mating system has changed as a consequence.