Origins of the invasive red swamp crayfish (Procambarus clarkii) in the Santa Monica Mountains

Although native to the southeastern United States, the red swamp crayfish (Procambarus clarkii) has become established worldwide through accidental and intentional actions by humans. In the Santa Monica Mountains of southern California, the presence of the omnivorous crayfish is associated with the absence or reduced abundance of native amphibians. The original source of P. clarkii in southern California is unknown; however genetic analysis can be used to determine sources of invasion. We sequenced 16S rRNA subunit and cytochrome oxidase I (COI) mitochondrial genes to trace the origins of P. clarkii in the Santa Monica Mountains. The resulting haplotype network of the combined COI and 16S rRNA subunit genes showed 19 distinct haplotypes and suggested multiple introductions of crayfish to the Santa Monica Mountains from possible source locations in Texas, Florida and Louisiana. Identifying original sources and mechanisms of introduction can slow and prevent further expansion of P. clarkii.