| Component | Description | |-----------|-------------| | | Drosophila melanogaster (fruit fly) – a classic model for sperm competition, plus a secondary comparative set of three beetle species ( Carabus nemoralis , Gyrinus natator , Tenebrio molitor ) to test generality. | | Experimental Design | 1. Sperm phenotyping : high‑speed video microscopy + CASA (Computer‑Assisted Sperm Analysis) to measure velocity, curvature, and longevity. 2. Genetic manipulation : CRISPR‑Cas9 knock‑ins to create lines that over‑express either fast‑type or long‑survival‑type sperm proteins. 3. Female tract simulation : microfluidic chambers replicating viscosity gradients observed in vivo. 4. Paternity assays : fluorescently labeled sperm (GFP/RFP) and next‑generation sequencing of offspring to quantify fertilization success. | | Statistical Modeling | Bayesian hierarchical models (Stan) incorporating random effects for male genotype, female genotype, and interaction terms. Model comparison via WAIC and posterior predictive checks. | | Computational Simulations | Agent‑based model (ABM) written in NetLogo, calibrated with empirical parameters, to explore long‑term dynamics of sperm type frequencies under varying mating systems. |
| Result | Evidence | Interpretation | |--------|----------|----------------| | | Fast sperm (mean VCL = 150 µm s⁻¹) had median lifespan 30 min, whereas long‑survival sperm (VCL = 80 µm s⁻¹) persisted >2 h. | Confirms H1: intrinsic physiological trade‑off. | | Spatial Niche Effect | In microfluidic chambers mimicking the spermatheca (high viscosity), long‑survival sperm outperformed fast sperm (p < 0.001). In low‑viscosity chambers (proximal uterus), fast sperm dominated. | Supports H2: female tract heterogeneity selects for distinct phenotypes. | | Mixed Portfolio Advantage | Males producing a 1:1 mixture of both sperm types achieved ~23 % higher total paternity across varied female tract simulations than single‑type males (posterior mean Δ = 0.23, 95 % CI [0.18, 0.28]). | Validates H3: bet‑hedging increases fitness under environmental stochasticity. | | Evolutionary Simulations | ABM showed stable coexistence of both sperm strategies over 10⁴ generations when female tract variability (viscosity parameter σ) exceeded 0.15. Below this threshold, one strategy fixated. | Demonstrates frequency‑dependent selection maintains polymorphism. | | Cross‑Species Comparison | Beetle species with relatively uniform reproductive tracts exhibited a single dominant sperm phenotype, whereas D. melanogaster (highly modular tract) displayed polymorphism. | Extends findings beyond the primary model system. | saki kawanami spermmania