Alternative reproductive strategies in two cryptic species of the European earwig complex

Reproductive strategies often reflect species-specific adaptations to ecological pressures. However, identifying such strategies within cryptic species complexes remains challenging. We addressed this gap in two cryptic species of the European earwig complex (Forficula dentata and Forficula auricularia), both known for their agricultural importance, invasive potential, and maternal care. Using a common garden experiment with adults from seven populations, including sympatric ones, we quantified four forms of maternal egg care (egg gathering, egg defence, egg retrieval, and frequency of mother-egg contacts) and 20 additional life-history traits across the female life cycle. Species identity was then determined using COI analyses. Our results revealed that nine traits were species-specific, indicating distinct reproductive strategies. Both species produced a similar number of eggs. However, F. dentata females prioritized pre-ovipositional investment by delaying oviposition, a strategy that enhanced egg provisioning and offspring quality but shortened post-ovipositional egg development and reduced hatching success. Conversely, F. auricularia females invested more post-ovipositionally by laying earlier, which limited pre-ovipositional egg provisioning and resulted in lower-quality juveniles, but prolonged egg development, thereby increasing hatching success. These strategies did not alter three of the four maternal care behaviours, although F. dentata mothers showed stronger egg defence. Overall, these strategies may confer species-specific advantages in colonizing and competing for new environments, potentially contributing to the global invasive success of the European earwig complex.