Seasonal specialization drives divergent population dynamics in two closely related butterflies

Seasons impose different selection pressures on organisms through contrasting environmental conditions. How such seasonal evolutionary conflict is resolved in organisms whose lives span across seasons remains underexplored. Through field experiments, laboratory work, and citizen science data analyses, we investigate this question using two closely related butterflies (Pieris rapae and P. napi). Superficially, the two butterflies appear highly ecologically similar. Yet, the citizen science data reveal that their fitness is partitioned differently across seasons. Pieris rapae have higher population growth during the summer season but lower overwintering success than do P. napi. We show that these differences correspond to the physiology and behavior of the butterflies. Pieris rapae outperform P. napi at high temperatures in several growth season traits, reflected in microclimate choice by ovipositing wild females. Instead, P. rapae have higher winter mortality than do P. napi. We conclude that the difference in population dynamics between the two butterflies is driven by seasonal specialization, manifested as strategies that maximize gains during growth seasons and minimize harm during adverse seasons, respectively. Seasons may impose different selection pressures on organisms. Here, the authors propose that species may either maximize gains during the growth season or minimize losses during winter, and provide empirical support of such seasonal specialisation in two closely related butterfly species.

Automated summary

Seasons impose different selection pressures on organisms, leading to varying adaptive strategies. This study investigates the resolution of seasonal conflicts in two closely related butterfly species through field experiments, laboratory work, and citizen science data analyses. The results reveal differences in fitness and population dynamics between Pieris rapae and P. napi across seasons, driven by physiological and behavioral traits. P. rapae maximizes gains during growth seasons but suffers from higher winter mortality, while P. napi minimizes harm during adverse seasons.