Evolutionary divergence in thermal sensitivity and diapause of field and laboratory populations of Manduca sexta

The tobacco hornworm Manduca sexta has been an important model system in insect biology for more than half a century. Here we report the evolutionary divergence in thermal sensitivity and diapause initiation between field and laboratory populations that were separated for more than 35 yr ( 1240 laboratory generations) and that are descendants from the same field populations in central North Carolina. At intermediate rearing temperatures (20 degrees-25 degrees C), mean body size was significantly larger and development time significantly faster in the laboratory than in the field populations. At higher temperatures (30 degrees-35 degrees C), these mean differences between populations were reduced or eliminated, and larval survival at 35 degrees C was significantly lower in the laboratory population than in the field population. F-1 crosses had survival and development time to wandering similar to the field population times at both 25 degrees and 35 degrees C; body mass at wandering for F-1 crosses was intermediate compared with that of the field and laboratory populations. Comparisons with earlier field and laboratory studies suggest evolutionary reductions in thermal tolerance and performance at high temperatures in the laboratory population. The critical photoperiod initiating diapause in field populations in North Carolina did not change detectably between the 1960s and 2005. In contrast, the laboratory population has evolved a reduced tendency to diapause under short- day conditions, relative to the field population.