The pattern of inbreeding in Washoe pine and survival of inbred progeny under optimal environmental conditions
1997
Mitton, J.B. | Latta, R.G. | Rehfeldt, G.E.
Four enzyme polymorphisms were used to estimate the proportion of inbred offspring among seedlings of Washoe pine (Pinus washoensis MASON and STOCKWELL) grown in a shadehouse. Seeds from 10 trees in each of 4 natural populations were collected in the field, germinated in a green house, and grown for 2 years in a shade house at Moscow, ID. Progeny arrays were analyzed from each population. Among all populations pooled, the multilocus outcrossing rate estimate was t(m) = 0.862. The multilocus outcrossing rate exceeded the average of the single locus outcrossing rate by about 0.07 in the pooled data, indicating some degree of mating between related individuals. In addition, the correlation of paternal parentage was r = 0.07, indicating approximately 14% of progeny pairs in an array were full sibs. Thus, the number of pollen parents in each array was limited. While the seedlings exhibited a significant degree of inbreeding, the genotypes inferred for the maternal seed trees had an inbreeding coefficient of F-is = -0.037, significantly lower than the inbreeding coefficient predicted from the mating system (F-is = 0.11). These results indicate that the inbred genotypes detected in the seedlings persist when trees are cultivated under optimal environmental conditions, but are eliminated in natural populations. Single-locus estimates of F in the pooled sample of seed trees were consistently negative, with a mean of F = -0.10, indicating that selection favored heterozygous trees in the pool of outcrossed genotypes.
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