Fig. 1.

Experimental design for measuring within-host selection and drift of Buchnera. A single female was injected with Buchnera from a donor line to establish a clonal aphid line heteroplasmic for two Buchnera haplotypes. After three to four generations, a founder female (G0) was used to initiate experiments in which successive female generations were allowed to reach adulthood and reproduce for 1 d and then harvested to estimate Buchnera haplotype frequencies. Three progeny were allowed to develop in each generation, and all aphids were sampled 1 d after beginning to reproduce. Experiments were performed under two thermal environments: constant 20 °C (“Cool”) and constant 20 °C interrupted daily by 4 h of exposure to 33 °C (“Heat”).