Low Nucleotide Diversity for the Expanded Organelle and Nuclear Genomes of Volvox carteri Supports the Mutational-Hazard Hypothesis
Bibliographic record
Abstract
The noncoding-DNA content of organelle and nuclear genomes can vary immensely. Both adaptive and nonadaptive explanations for this variation have been proposed. This study addresses a nonadaptive explanation called the mutational-hazard hypothesis and applies it to the mitochondrial, plastid, and nuclear genomes of the multicellular green alga Volvox carteri. Given the expanded architecture of the V. carteri organelle and nuclear genomes (60-85% noncoding DNA), the mutational-hazard hypothesis would predict them to have less silent-site nucleotide diversity (π(silent)) than their more compact counterparts from other eukaryotes-ultimately reflecting differences in 2N(g)μ (twice the effective number of genes per locus in the population times the mutation rate). The data presented here support this prediction: Analyses of mitochondrial, plastid, and nuclear DNAs from seven V. carteri forma nagariensis geographical isolates reveal low values of π(silent) (0.00038, 0.00065, and 0.00528, respectively), much lower values than those previously observed for the more compact organelle and nuclear DNAs of Chlamydomonas reinhardtii (a close relative of V. carteri). We conclude that the large noncoding-DNA content of the V. carteri genomes is best explained by the mutational-hazard hypothesis and speculate that the shift from unicellular to multicellular life in the ancestor that gave rise to V. carteri contributed to a low V. carteri population size and thus a reduced 2N(g)μ. Complete mitochondrial and plastid genome maps for V. carteri are also presented and compared with those of C. reinhardtii.
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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".