Statistical Methods for Fitness Experiments
The effects of selection regime (Regime), pesticide exposure (PTx), Bt exposure (BtTx), and interactions between the three factors on beetle survival and development were investigated using population as a random factor in Cox mixed effects survival models with the package coxme (Therneau, 2015) in R. For both time to death and time to develop into adulthood, we evaluated the individual effects of pesticide exposure (PTx), selection regime (Regime), and Bt exposure (BtTx), and the interactions between selection regime and pesticide exposure (Reg:PTx), selection regime and Bt exposure (Reg:BtTx), and co-exposure to pesticides and Bt (PTx:BtTx). The full model for both time to death and adult development time is as follows: Surv(Day, Status) ~ (PTx + BtTx + Regime + Regime:PTx + Regime:BtTx + PTx:BtTx + (1|Population)). Hazard ratios were calculated from coxme survival models and were plotted using the sjPlot package in R (Lüdecke , 2021).