Authors: Taite, Morag; Waymouth, Thomas;George, Ruby;Wray, Ben;Clarke, Paul;Ironside, Joe;

The Chinese mitten crab, Eriocheir sinensis, is listed as one of the World’s 100 most invasive species and has been recorded in the River Dee, a special area of conservation, since 2006. Sequencing of the mitochondrial Cytochrome Oxidase 1 gene indicates that mitochondria originating from two different Eriocheir species are present in the Dee mitten crabs. We use morphometrics and single nucleotide polymorphism (SNP) genotyping to investigate whether the Dee mitten crabs comprise two separate, cryptic species or a single hybrid swarm. Mitten crabs were collected from Chester Weir in the River Dee at two time points in 2014-15 and 2020 and additional reference samples were collected from each of the putative parental species. Morphometrics were carried out following Clarke et al. (2000) and DNA samples were submitted for SNP genotyping. Understanding the taxonomy and potential to hybridise of the genus Eriocheir is important, given the biosecurity threat posed by mitten crabs and the potential for hybrids to exhibit greater invasiveness than their parent species.