Effects of maternal and offspring environmental conditions on growth, development and diapause in latitudinal yellow dung fly populations

Extensive phenotypic plasticity can allow populations to persist in changing environments. Maternal effects represent one important but often neglected source of phenotypic plasticity. Mothers and offspring of 2 high- (northern Norway and central Sweden) and 2 low- (northern and southern Spain) latitude yellow dung fly Scathophaga stercoraria (Diptera: Scathophagidae) populations were exposed to cold (12°C) and warm (18°C) temperatures and to short (8 h light:16 h dark) and long (16 h light:8 h dark) photoperiods in a fully blocked, split-brood common garden design of 8 treatment combinations. We also considered the role of energy content and size of the eggs in producing cross-generational maternal effects on offspring diapause, development time and growth rate. The incidence of diapause strongly declined towards the south, and the northernmost population grew and developed faster in response to perceived seasonal time constraints. There was strong population-specific phenotypic plasticity of all traits in response to offspring temperature and, more weakly, to offspring photoperiod, indicating a genetic basis of plasticity as well as genetic differentiation among populations. There were additional subtle cross-generational maternal effects exerted primarily by the lipid content of the eggs, largely independent of maternal treatment and population. Phenotypic plasticity of life-history traits in the yellow dung fly is predominantly influenced by the growing conditions during larval development, but populations can also respond to changing environments via trans-generational maternal effects.