Florida man exonerated: an amphipod case study on the implications of cryptic species complexes and global invasions.

Abstract The crangonyctid amphipod Crangonyx floridanus is considered to have a natural distribution across much of the eastern United States and is thought to be invasive in parts of the western United States, Japan, and the British Isles. Recent investigations have revealed highly endemic cryptic species among populations of Crangonyx floridanus sensu lato occurring at approximately 30 oN latitude in the Panhandle of Florida, USA. To date, none of the published cryptic lineages of C. floridanus sensu lato phylogenetically align with the invasive populations. Despite years of collecting efforts, C. floridanus sensu stricto has not been identified from its type locality in Highlands Hammock State Park, in Highlands County, Florida, since its initial collection in 1962. To assess the status of C. floridanus sensu stricto, environmental DNA was used to analyze the V4/V5 hypervariable regions of the nuclear 18S rRNA gene from the type locality. These data revealed that the species has not been extirpated from the type locality, and that it is not the source of the invasive populations. In addition, populations of C. floridanus sensu lato collected for this study from Alabama, Ohio, and Pennsylvania, USA, displayed 100% identity to invasive populations in the western United States, Japan, and the British Isles, at both the 18S rRNA and mitochondrial cytochrome c oxidase subunit I genes. This study demonstrates that traditional diagnostic characteristics may lead to incorrect assumptions about the taxonomic status of invasive species.