Abstract
Understanding the effectiveness of premating reproductive barriers in contact zones of closely related lineages is essential to assess risks to their long-term persistence. Here, we document the first contact zone with interspecific copulations between the Macaronesian mountain endemic Eurydema lundbladi and the widespread Palearctic E. ornata , located in mid-elevation habitats on La Palma Island, Canary Islands. Four interspecific copulations were recorded during fieldwork in 2023 and 2024. We evaluated spatial (altitudinal and geographical distribution), morphological (male genitalia using geometric morphometrics), and ecological (climatic niche) prezygotic barriers. Geometric morphometric analyses performed on three groups— E. lundbladi (La Palma), insular E. ornata (La Palma), and mainland E. ornata (Iberian Peninsula)—revealed moderate but non-restrictive shape differentiation in genitalia, particularly in the paramere, and no significant differences between insular and mainland E. ornata . Neither genital morphology nor body size differences appear to function as effective mating barriers. Although ecological niches are distinct, both species converge in certain altitudinal zones where climatic conditions—particularly winter temperatures—influence their distribution. Given the lack of spatial and mechanical isolation, and the greater abundance and ecological generalism of E. ornata , reproductive interference could reduce mating success in E. lundbladi , especially under ongoing climate-driven range shifts. Although interspecific copulations were observed, effective hybridization remains unconfirmed. Implications for insect conservation Asymmetric reproductive interference from E. ornata may threaten the persistence of the endemic E. lundbladi in the Canary Islands, especially with ongoing climate change. Continued monitoring and targeted management of contact zones is needed to safeguard insular endemic diversity.