Diapause induction and relaxed selection on alternative developmental pathways in a butterfly

Abstract

Summary1. Seasonal phenotypic plasticity entails differential trait expression depending on the time of season. The facultative induction of winter diapause in temperate insects is a developmental switch mechanism often leading to differential expression in life-history traits. However, when there is a latitudinal shift from a bivoltine to univoltine life cycle, selection for pathway-specific expression is disrupted, which may allow drift towards less optimal trait values within the non-selected pathway. 2. We use field-and experimental data from five Swedish populations of Pararge aegeria to investigate latitudinal variation in voltinism, local adaptation in the diapause switch and footprints of selection on pathway-specific regulation of life-history traits and sexual dimorphism in larval development. 3. Field data clearly illustrated how natural populations gradually shift from bivoltinism to univoltinism as latitude increases. This was supported experimentally as the decrease in direct development at higher latitudes was accompanied by increasing critical daylengths, suggesting local adaptation in the diapause switch. 4. The differential expression among developmental pathways in development time and growth rate was significantly less pronounced in univoltine populations. Univoltine populations showed no significant signs of protandry during larval development, suggesting that erosion of the direct development pathway under relaxed selection has led to the loss of its sex-specific modifications.

Genetic variation underlying local adaptation of diapause induction along a cline in a butterfly

“…The resulting adults (85 N and 61 S butterflies) were used to produce F1 offspring for the two populations SS and NN, as well as reciprocal F1 population hybrids NS and SN (female first). F1 offspring were assayed for the proportion of direct development in conditions where the SS population shows 100% direct development and the NN population shows 0%, that is, L:D 18:6 at 17°C (Aalberg Haugen & Gotthard, ). A second set of larvae were reared in conditions that produce 100% diapause development in both populations: L:D 13:11, 17°C.…”

Evolution of alternative insect life histories in stochastic seasonal environments

“…Many insects take advantage of long seasons by completing two or more generations within a single season (e.g., Blanckenhorn and Fairbairn 1995; Välimäki et al. 2008; Aalberg Haugen and Gotthard 2015). This variation in voltinism (the number of generations emerging within a season) is a consequence of alternative developmental pathways of diapause and direct development.…”

“…1991; Blanckenhorn 1994; Blanckenhorn and Fairbairn 1995; Kivelä et al. 2012; Aalberg Haugen and Gotthard 2015). Moreover, theory predicts direct development to be associated with a smaller (or equal) body size and a lower fecundity than diapause in deterministic environments (Kivelä et al.…”

“…Empirical data are largely consistent with these predictions too (Blanckenhorn 1994; Blanckenhorn and Fairbairn 1995; Teder et al. 2010; Aalberg Haugen and Gotthard 2015; but see Wiklund et al. 1991; Kivelä et al.…”

“…Shifts in voltinism are commonly associated with the emergence of partial generations in nature (e.g., Blanckenhorn and Fairbairn 1995; Välimäki et al. 2008; Aalberg Haugen and Gotthard 2015), so age‐structured life history models are needed to derive realistic predictions. Moreover, a gradual response to uncertainty is predicted for aphids in the form of stochastic polyphenism (“coin flipping”).…”