From ship to shore: the genetic legacy of the invasive black rat in Atlantic Islands

Abstract Islands offer unique ecological and evolutionary insights, yet they are fragile ecosystems, particularly vulnerable to invasive species. The present study focused on the origin of an invasive species in Macaronesia and other Atlantic islands, specifically the black rat, Rattus rattus . The ability of this species to thrive is attributable to its ability to coexist with humans in a commensal relationship. The objective of this study was to ascertain the origins of these insular rat populations through the analysis of a molecular marker, examining their genetic diversity within the islands and providing information for their management aiming for the conservation of native species. The mitochondrial DNA D-loop region of 41 individuals was sequenced to compare with sequences from public databases in order to infer their most likely origin, using phylogenetic and network analyses. A total of 106 different haplotypes were obtained from combining sequences from GenBank and new sequences, distributed into two distinct haplogroups. The Indian Ocean group included samples from India and a number of other countries and islands in the Indian Ocean region, as well as Italy and Cabo Verde. Meanwhile, the Atlantic Ocean group included samples from Europe, Oceania, Central and South America, and Africa. For the first time, an Indian lineage was found in Cabo Verde. These introductions are strongly linked to European trade routes and human colonisations, Understanding the routes by which these populations arrived on the islands, as well as their origins, is therefore crucial to understanding the patterns of biological invasions.