Repeating thermal performance curve measurements 25 years later to assess responses to climate change among pierid populations

Pierid butterfly phenotypes serve as mechanistic links between environmental conditions and organismal performance. In Pieris rapae (Cabbage White Butterfly), larval growth and development are strongly temperature-dependent and can be quantified using thermal performance curves. To assess whether selection on these curves has shifted in response to recent climate trends, we repeated a historical study on P. rapae populations from the Seattle, WA, area. We collected wild females and reared their offspring to the fourth instar, assessing larval growth rates at a range of temperatures (11°C, 17°C, 23°C, 29°C, 35°C). Larvae were then transferred to an experimental collard garden and monitored daily until pupation. At pupation, we recorded pupal mass; after eclosion, we measured adult mass, development time, and sex. This approach allowed us to compare contemporary thermal performance with historical baselines and evaluate evolutionary responses to recent climate pressures. Over the past 25 years, we observed a shift in thermal performance curves: larvae now grow faster at intermediate temperatures but more slowly at high temperatures. This shift reflects directional selection observed in 1999, favoring faster growth up to ~23°C but reduced performance at higher temperatures. Our findings demonstrate the potential for rapid evolutionary change in thermal sensitivity in response to climate change.