Parental guarding behaviour affects the evolution of egg shapes

Abstract The understanding of the adaptive evolution of egg shapes has developed rapidly. In some insects, females adopt a straddling posture on substrates to guard clutches against predators. Eggs located in the peripheral area of such clutches experience high predation pressure. Thus, selection might favour compact clutches composed of longitudinally elongated eggs. Shield bugs (Heteroptera: Acanthosomatidae), in which maternal guarding of eggs has undergone repeated evolution, provide a good opportunity to test this hypothesis. Our phylogenetic comparative analyses revealed that eggs were more elongated in caring species than in non-caring ones, although this difference was obscured in species with large eggs. Reconstructed ancestral states of egg shape and maternal care suggested that the enhanced elongation of eggs occurred after the establishment of maternal care. These findings indicate that post-ovipositional parental care affects the evolution of egg shapes, depending on egg geometry.