Seasonal time constraints reduce genetic variation in life history traits along a latitudinal gradient

1. Time constraints cause strong selection on life history traits, because populations need to complete their life cycles within a shorter time. We therefore expect lower genetic variation in these traits in high- than in low-latitude populations, since the former are more time constrained. 2. The aim was to estimate life history traits and their genetic variation in an obligately univoltine damselfly along a latitudinal gradient of 2,730 km. 3. Populations were grown in the laboratory at temperatures and photoperiods simulating those at their place of origin. In a complementary experiment individuals from the same families were grown in constant temperature and photoperiod that mimicked average conditions across the latitude. 4. Development time and size was faster and smaller, respectively, and growth rate was higher at northern latitudes. Additive genetic variance was very low for life history traits and estimates for egg development time and larval growth rate showed significant dec...