Reconstructing the spread of a global invader: a genetic study of red swamp crayfish, Procambarus clarkii

Abstract

Biological invasions are one of the biggest threats to global biodiversity. Understanding how introduced species succeed and become widely distributed within non-native areas is critical to reduce the threats posed by them. Propagule pressure (i.e. the size and number of introduction events) is thought to be one of the key elements driving invasion dynamics. Over the last 100 years, freshwater ecosystems have been widely invaded by the North American red swamp crayfish, Procambarus clarkii. In order to confirm the “official” history of the red swamp crayfish invasion process throughout globe, we aim to (1) determine whether there had been unrecorded introductions and (2) establish the genetic structure of native/invaded populations and (3) analyze the invasion dynamics. To do this, 1416 crayfish from 22 native and 100 invaded sites in the Northern Hemisphere were analyzed using mitochondrial gene sequences (COI) and 864 of them were analysed with 14 polymorphic microsatellites loci. A total of 65 haplotypes were found, 15 of which were shared between at least two populations. As expected, our results showed that the native area has the highest haplotype diversity (Hd: 0.902). However, diverse hotspots in some invaded areas, such as United States (Hd: 0.804) or South-western Spain (Hd: 0.663 and 0.716) were lower than native area, indicating possible bottlenecks due to the propagule pressure. Our results suggest a large and/or diverse population for initial introduction events and a spread involving several subsequent secondary introduction events thereafter with losses of genetic diversity, possibly due to the accumulation of population bottlenecks. However, the finding of new haplotypes also suggests that additional translocations of crayfish other than those initially introduced may have happened. Such additional introductions have so far not been well documented in the literature.