The evolution of inbreeding in western redcedar (Thuja plicata : Cupressaceae)
Bibliographic record
Abstract
Long-lived woody plants usually show high levels of outcrossing, inbreeding depression and genetic diversity compared to other plants. A review of the literature showed a mean outcrossing rate of 83.5 in conifers, and a positive, but weak, correlation between outcrossing and genetic diversity. Among conifers, western redcedar (Thuja plicata, Cupressaceae) has one of the highest rates of self-fertilization and lowest amount of genetic diversity, and thus offers the opportunity to study the evolution of inbreeding in a predominantly outcrossing group of plants. This thesis links the evolution of inbreeding in redcedar with a loss in inbreeding depression and genetic diversity. Using one polymorphic isozyme marker, I obtained an average population outcrossing estimate of 71% over six natural populations of redcedar. I developed 13 highly polymorphic microsatellite markers to conduct a finer-scale study of the mating system and genetic structure of redcedar. A new method of bulking seedlings to estimate outcrossing rates was used to identify ecological correlates of outcrossing. Selfing rates increased significantly with tree height in four different populations. Pollen from larger trees probably made up a larger proportion of the surrounding pollen cloud, increasing self-pollination. There was no variation, however, in the amount of inbreeding among crown positions within trees. In a seed orchard, a combination of controlled crosses and isozyme markers showed evidence that post-pollination competition between embryos within an ovule decreased selfing. I used eight microsatellite loci to study patterns of range-wide genetic structure in redcedar. A phylogeographic analysis suggests that redcedar probably survived in three separate refugia during the last glaciation. These results also suggest that if a species-wide bottleneck is at the root of reduced genetic diversity in redcedar, it probably predates the last glaciation. The combination of an inbreeding mode of reproduction and a bottleneck probably contributed to the decrease in genetic diversity presently observed in redcedar. Finally, after screening 80 trees at eight microsatellite loci, a single stepwise mutation was observed, yielding a somatic mutation rate of 6.3 x 10-4 (95% CI: 3.0 x 10-5 - 4.0 x 10-3) mutations per locus per generation in western redcedar.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".