How (not) to use genetic data to assess nativeness: the case of the Italian crayfish in the Iberian Peninsula

Abstract

Species’ nativeness status sometimes remains unclear, particularly when the putative introductions would have occurred in a distant past. Unravelling these cases should rely on integrating knowledge from multiple disciplines, certainly including DNA analyses. But genetic data should be properly interpreted to contribute solidly to nativeness assessments. Good practices would involve a thorough knowledge of the genetic pool in the native area, prioritizing the analyses of genetic structure over genetic diversity and exclusiveness, and framing genetic results into the existing knowledge. Here, we show that misinterpreting genetic data may provide flawed nativeness assessments with important implications for biodiversity management, using the case of the Italian crayfish (Austropotamobius fulcisianus) in the Iberian Peninsula. In Spain, this species has been traditionally considered native and is currently managed as such. However, multiple lines of evidence solidly show that the species was introduced from Tuscany in the late-16^th century. Contradicting this narrative, different works in the last two decades have used mitochondrial DNA sequences to claim that the Italian crayfish is native to Spain, emphasizing the number and exclusiveness of haplotypes. We show that this interpretation is based on little-informative haplotype metrics and is loaded by the poor representation of Italian samples, which is particularly worsened in the most recent works. In fact, genetic patterns in Italian crayfish are very similar to those described for the American red swamp crayfish (Procambarus clarkii), and in both cases are only compatible with the non-native status of both species in the Iberian Peninsula.