Simulation of fig wasp inclusive fitness outcomes under differential hybrid embryo mortalities
We again used Python programming to model our ‘oviposition trade-off’ hypothesis (https://github.com/ctdarwell/wolPredictor/ciFitnessModel.py) and investigate how offspring fitness might benefit from preferential oviposition facilitated by reduced foundress egg load (or via selective oviposition) despite losses in fecundity resulting from the post-zygotic mechanism of CI. Our model allocates each foundress 1000 eggs whose fitness is determined by three variables: (i) the proportion of conspecifics in the population that the foundress can breed with; (ii) fitness of offspring of conspecific matings (between 0-1); and (iii) fitness of offspring of heterospecific matings (between 0-1). Further, we divide a syconium into five layers - at the centre, all eggs survive, while zero survive at the syconium edge (with 0.75, 0.5, 0.25 survival in the intermediate layers). We compare a ’CI ’ and a ‘no CI ’ model across variation in our three variables. See Fig. 4 for a schematic outline of the parameters.
For example, for the no CI model at 75% conspecifics mating opportunities: 75% of eggs get conspecific relative mating fitness (e.g., ω = 0.8) and 25% of eggs get heterospecific relative mating fitness (e.g., ω = 0.2). Each egg gets randomly assigned into a layer of the syconium and each egg’s relative mating fitness is multiplied by its oviposition site fitness (i.e., randomly assigned: 1.0, 0.75, 0.5, 0.25, 0). Finally, all 1000 eggs’ scores are summed to obtain inclusive fitness for the foundress. For the CI model (at 75% conspecifics mating opportunities) we lose 25% of the egg load but all eggs get the conspecific relative mating fitness (i.e., 0.8) - then they are randomly placed into the best remaining 750 oviposition site positions (mimicking that fig wasps preferentially lay in optimum sites). Scores are again multiplied and summed across 10 replicates. The key modeling assumption here is that unviable eggs are not oviposited and thus do not waste premium oviposition sites (this is also equitable to a scenario where egg oviposition order is prioritised). Results are obtained by subtracting realised CI versus no CI fitness across all combinations of conspecific-heterospecific relative mating fitness (i.e., 0-1 for both) surfaces. We display individual heat maps for outcomes at different percentages of conspecific mating opportunities.