Morphological and genetic evidence of hybridisation between Mauremys mutica (Cantor, 1842) and Mauremys leprosa (Schweigger, 1812) in northeast Spain

Invasive species are one of the leading causes of biodiversity loss. During demographic monitoring of native turtle species in northeast Spain, we captured several alien species of semi-aquatic turtles, including Mauremys mutica . Among them, four individuals of this latter species showed external characteristics that were not fully consistent with the diagnosis of this species. These individuals showed a smaller postocular stripe and 2-3 lateral cervical lines and the typical plastral pattern observed in Mauremys leprosa . The analysis of mitochondrial DNA indicated that the maternal lineage was unequivocally M. mutica (pure or hybrid), but nuclear DNA revealed a heterozygote position at the C-mos gene, matching sequences for this gene in GenBank from both M. leprosa and M. mutica . These results highlight the negative impact of alien turtles, which can genetically contaminate vulnerable native turtle populations.