Using seedling and pericarp tissues to determine maternal parentage of dispersed valley oak recruits

The spatial pattern of established seedlings yields valuable information about variation in fecundity, dispersal, and spatial structure of distributed recruits, but separating maternal and paternal contributions in monoecious species has been hampered by the "2 parent" problem. It is now possible to determine the maternal parentage of established recruits with genetic assay of maternally derived tissues of the seed or fruit, but the DNA of weathered maternal tissues often yields unreliable genotypes, reducing the practical range of such assay. We develop a mixed assay of seedling and seed (pericarp) tissues and illustrate it with distributed recruits of California valley oak (Quercus lobata Née). Detailed analysis indicates correct maternal assignment rates of canopy patch recruits of 56% (seedling assay only) versus 94% (mixed assay). For open patch recruits, maternal assignment rates were less than 50% (seedling assay only) versus 91% (mixed assay). The strategy of choice is to use seedling genotypes to identify a small set of credible parental candidates and then deploy 3-4 well-chosen pericarp/endocarp loci to reduce that list to a single obvious maternal candidate. The increase in the number of recruits available for subsequent analysis is pronounced, increasing precision and statistical power for subsequent inference.