Life-History Evolution of Insects in Response to Climate Variation: Seasonal Timing Versus Thermal Physiology.

Climate adaptation in insects can proceed via responses in life-history traits and their thermal plasticity and through phenological shifts mediated by responses to photoperiodic cues (photoperiodism). While experimental studies demonstrate evolutionary potential for both modes of adaptation, it remains unclear how evolution will unfold in natural populations, limiting our ability to predict how insects will respond to climate change. Here, we review the literature and analyze published studies revealing that photoperiodism for diapause induction evolves predictably along latitude, with high-latitude populations entering diapause earlier. In contrast, although a few species showed clinal variation in life history and thermal plasticity, the direction of these clines was not consistent across taxa. These findings suggest that while insect life history and physiological adaptation to temperature can evolve, phenological shifts via evolution of photoperiodism are likely to be more common and predictable responses to future climate change.