Analysis of clines with variable selection and variable migration

We report a likelihood-based method that estimates both dispersal and natur al selection using the rate of change of the shape of a dine when selection and migration are not constant through time. We have investigated the case of local adaptation of the mosquito Culex pipiens to organophosphate insec ticides in the Montpellier area in France. We have analyzed the modificatio n of the clinal patterns at two resistance loci during the period from bree ding to overwintering. We show that mosquitoes migrate extensively from bre eding to overwintering sites at a rate that is markedly different from prev ious estimates made during the breeding season only. This migration is also strongly asymmetrical, which can be explained by different geographical di stributions of breeding and overwintering sites, by variation in mosquito d ensity along the transect, or by behavioral biases. We found that the start ing time of overwintering is likely to vary between northern and southern p opulations and that substantial fitness costs are associated with resistanc e alleles at the two loci during overwintering. These results illustrate ho w demography and adaptive microevolution can be studied using selected mark ers. The method provides a framework to use population genetics and statist ical models to reveal ecological and evolutionary processes.