Functional variation in butterfly egg pore traits: The potential role of climate

Abstract Immobile eggs of terrestrial animals are exposed to variable environmental conditions. Insect egg pores, critical for gas exchange (aeropyles) and fertilisation (micropyles), are ecologically important yet understudied. While aeropyles likely adapt to climatic respiratory demands, and micropyles may respond to environmental pressures, their inter‐ and intraspecific variation remains poorly studied. Here, we compared egg pore morphology of three closely related Pieris butterflies sampled in the Netherlands. In addition, we compared egg traits of different P. napi populations sampled along a 4000‐km latitudinal gradient from northern to southern Europe and linked these traits with available climatic data. After several generations under identical greenhouse conditions, egg pore traits remained highly variable within and between species and groups. Remarkably, P. napi populations from divergent climates differed more in pore number and size than did co‐occurring Pieris species. Aeropyle number and width were strongly associated with climatic variables such as summer temperature and precipitation, independent of egg size. Additionally, we observed the micropyles of older eggs to be covered by a substance more often than fresh eggs. Our findings indicate that insect egg pores are highly dynamic traits, which may be shaped by ecological, behavioural and climatic factors and an under‐recognised role of egg adaptation. Read the free Plain Language Summary for this article on the Journal blog.