Fig. 6.

Rates at which inviability increases with genetic distance for three developmental stages. Measures of inviability at each developmental stage were regressed against phylogenetic distance (K_s between species and π_s within species). The three types of postzygotic isolation (i.e., death at a particular developmental stage) increase with genetic distance. (A) Embryonic lethality. (B) Larval lethality. (C) Pupal lethality. The thick lines represent fitted logistic regressions for each developmental stage. The thinner lines are the regressions for each of 10,000 bootstrap resamplings of the data. (D) Distributions of bootstrapped values of Threshold_Ks, a parameter that determines how quickly isolation approaches 1, are largely nonoverlapping. Regression coefficients (supplementary table S15, Supplementary Material online) show that early inviability (hybrid embryonic lethality) evolves faster than later inviability (hybrid pupal lethality).