Ecology of Sex Ratios in Mountain Pine Beetles, Dendroctonus ponderosae
Bibliographic record
Abstract
Biased sex ratios pose a fundamental question in evolutionary ecology. Populations are expected to have equal numbers of males and females when each offspring is produced from one mother and one father with equal genetic contributions. In mountain pine beetles (MPB), Dendroctonus ponderosae Hopkins, consistent reports of female-biased adult sex ratios (2:1 F:M) demand explanation. I investigated whether adult sex ratios of MPB reflected initial investment or became biased through adaptive or non-adaptive processes. Differential mortality is a potentially non-adaptive process that could bias sex ratios at later life stages, an idea often invoked to explain female-biased adult sex ratios in this system. However, Fisher noted that if mortality occurs during parental investment, selection will act to bias the primary sex ratio towards the sex with higher mortality, achieving an evolutionary stable state where expenditure to each sex is equal. Individual allocation strategies may differ depending on maternal condition. In insects, daughters were expected to benefit more from increased investment because of the strong relationship between body size and fecundity. Through genotyping of eggs from individual broods reared in the laboratory, I found that primary sex ratios of MPB were male-biased (~1:0.86). Male-biased primary sex ratios were counter to expectations if the sex-ratio distorter Wolbachia was acting in the system; Wolbachia was not detected in a screen of ten populations. Female-biased adult sex ratios arose from subsequent male-biased mortality, observed in both laboratory-reared broods and in experimentally manipulated overwintering field populations. Moreover, condition-dependent allocation occurred, but was counter to expectations, with larger females producing more males than did smaller females. Larger mothers produced larger eggs that experienced less male mortality. In this case, larger mothers gain more from investing in the rare sex than investing in daughters. Given male-biased developmental mortality, a male-biased primary sex ratio is consistent with Fisher’s theory of equal investment favouring the sex with greater mortality during parental investment. Further, differential mortality of the sexes is a strong selective force to which condition-dependent sex allocation may respond more strongly than increases in body size.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 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) | 0.001 | 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 source (direct Gemma or distilled Codex), 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".