Alien Amphibian Introductions Via the Plant Trade: a Breeding Population of the Catalonian Midwife Toad (alytes Almogavarii) in Central Spain

The plant-trade is among the main sources of accidental introduction of alien biodiversity. This includes amphibians, although effective colonization pathways have rarely been reported except from tropical areas. We document the discovery of an established breeding population of the Catalonian midwife toad, Alytes almogavarii almogavarii Arntzen and García-París, 1995, in a plant nursery in Madrid (Central Spain), 400 km away from its natural distribution. During surveys in 2023 we found adults, juveniles, and tadpoles, confirming reproduction. We used mtDNA sequences to genotype six individuals for taxonomic assignment and tracing their putative origin. Two haplotypes were found, one of them showing a broad distribution, precluding precise identification of the source of the introduction. We discuss conservation concerns, including the potential spread of pathogens. Our results suggest unintentional amphibian introductions via the plant-trade may be more frequent than perceived, and call for rigorous monitoring and education efforts.