GENETIC COORDINATION OF DEMOGRAPHY AND PHENOLOGY IN THE PITCHER-PLANTMOSQUITO, WYEOMYIA-SMITHII

Demographic and phenological traits compose the basic elements of an i nsect's life-history strategy in a seasonal environment. An insect's l ong-term fitness depends on its ability to exploit favorable condition s, to avoid unfavorable conditions, and to convert from one life style to the other. For the pitcher-plant mosquito, Wyeomyia smithii, we sh ow that genetic variation exists in both development time (a demograph ic trait) and critical photoperiod (a phenological trait) in six popul ations spanning much of the species' geographical range. During the no rthward range expansion of W. smithii in North America, these traits h ave evolved independently under strong directional and stabilizing sel ection. The correlated response in critical photoperiod to divergent s election on development time reveals significantly positive genetic co rrelations in five populations and a negative correlation in one popul ation. The positive correlations form a genetically coordinated phenot ype: faster developing individuals use a shorter photoperiodic switch point and are able to exploit the late favorable season; slower develo ping individuals use a longer photoperiodic switch point and are able to avoid extending development into the unfavorable season. This genet ic coordination of demography and phenology has not, however, prevente d their independent evolution. We propose that evolutionary flexibilit y in W. smithii may arise in part from the reorganization of their gen etic architecture following repeated founder events during their north ward invasion of North America.