Speciation in sympatric sticklebacks: hybridization, reproductive isolation and the maintenance of diversity
Bibliographic record
Abstract
This research examined genetic, morphological, ecological and behavioral mechanisms maintaining divergence between a pair of sympatric stickleback species (Gasterosteus aculeatus complex) from Paxton Lake, British Columbia, Canada. When raised in the lab, F₁ hybrids showed no evidence of inferiority relative to parental species for the following characters: fertilization success, hatch success, growth rate, fecundity, fluctuating asymmetry, and parental care. Although these are common postmating isolation mechanisms between many other species, if they operate in the wild in this system their effects are likely small and of little biological importance. When raised in the wild, in either of two main habitats, F₁ hybrids suffered a significant reduction in growth rate relative to parental species. Hybrid disadvantage resulted from morphological intermediacy which affected resource exploitation efficiency. Hybrid disadvantage is thus a function of the ecological environment, rather than developmental inviability or physiological inferiority. This ecological disadvantage provides the strongest postmating barrier known between these species. Though this is one of the first demonstrations that niche-based selection pressures are a dominant mechanism of postmating isolation, I argue that this may be common in the early stages of speciation. Since gene flow between species must occur through reproductively fit F₁ hybrids, I asked whether male F₁ hybrids are sexually selected against by females of the parental species. I provide experimental evidence that mate choice by females of the parental species must be coupled with habitat preference for there to be sexual selection against hybrids. I measured the degree of genetic divergence between the species in four morphological characters and one fitness component by rearing six lines (parentals and first and second generation hybrids; 109 families total) in the lab. Joint-scaling tests on phenotype means and variances suggest that epistasis contributes significantly to genetic divergence of parental lines for two of the characters, gill raker length and growth rate. Dominance effects contribute significantly to divergence in plate number and pelvic spine length. A simple additive model was sufficient for only gill raker number. A biometrical approach to gene number estimation suggested that character differences are coded for by 1 to 60 genes, depending on the trait. The tremendous discrepancy in these estimates may reflect real differences among characters in genetic divergence, but the estimates are likely unreliable due to the rejection of several important assumptions of the method. My findings are compared to other recent estimates of genetic divergence in natural populations, and discussed in the context of speciation in sticklebacks.
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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".