Abstracts (first author)
The evolution of alternative developmental pathways in a butterfly: local adaptation in developmental thresholds and footprints of relaxed selection on life history plasticity
The ability of many temperate insects to have more than one generation per year is due to the plastic induction of alternative developmental pathways - leading to either direct development during summer or diapause development during winter. Typically, the number of generations produced within a population decrease with increasing latitude and the developmental threshold determining which pathway to follow is predicted to show a latitudinal cline due to local adaptation to season length. Consequently, when moving north along a latitudinal cline, populations will ultimately become univoltine and only produce one generation per year, which always enter diapause development. In such locations where only the diapause developmental pathway is expressed, selection on developmental regulation of the direct pathway will be relaxed. I will present results showing how the photoperiodic threshold determining the pathway decision in the butterfly Pararge aegeria is locally adapted to season length. Moreover, I will explore footprints of relaxed selection on the developmental regulation of life history traits and sexual dimorphism when expressed in the direct development pathway. The results suggest that populations experiencing relaxed selection on the direct pathway show less pronounced differences between pathways in several life history phenotypes. In particular, relaxed selection on direct development was associated with a disruption of protandry (earlier emergence of adult males) expressed as sexual dimorphism in larval development time and growth rate. This suggests that relaxed selection on the direct pathway has allowed life history traits to drift towards trait values associated with lower fitness, and that ongoing selection is necessary for upholding this type of “fine tuning” of alternative developmental regulation.