The relationship between the Pgi locus and the ability to fly at low temperatures in the monarch butterfly Danaus plexippus.

Differences in genetic structure of samples of monarch butterflies caught at different times of day have been reported previously. This paper compares differences in allele and heterozygote frequencies at the Pgi locus between animals flying early and those flying late in outdoor flight cages and between animals able and animals unable to fly at a constant low temperature. There were consistent effects across a number of tests and in comparisons with field data, especially in males. Animals with the M allele were more likely to be able to fly at low temperatures, to become active early in outdoor flight cages, and to be caught early in the field. Also, differences were observed between males and females in the effect of allele on flight activity.