Human impacts on the distribution and genetic diversity of Eurasian minnows (Phoxinus: Leuciscidae) in the Rhenish Massif

Abstract

Introductions of non-native species, a key driver of biodiversity loss, may be underestimated due to cryptic species. In the Rhenish Massif (western Germany), anthropogenic introductions of Eurasian minnows (Phoxinus) caused discrepancies in genetic origin between historical samples from the Ahr and present-day specimens from the adjacent Sieg basin. This study assesses the autochthony of current Phoxinus populations in Ahr and Sieg and reconstructs introduction pathways using cytochrome c oxidase I (COI) barcoding and stakeholder surveys. We find that Ahr populations, free from intentional stocking, are almost exclusively inhabited by Phoxinus clade 5b (P. csikii). In the Sieg, Phoxinus populations exhibit a zonation pattern: clade 5b dominates mountainous regions, while clade 10 (P. phoxinus) is prevalent in foothill regions. Stakeholder surveys revealed substantial historical introductions from the Main/Neckar basin (clades 5b and 10) and Lower Rhine (clade 10), with rarer instances of Rhône (clade 12, P. septimaniae) and Weser (clade 11, P. cf. morella) minnows introduced as contaminants in brown trout (Salmo trutta) stocking. Combined findings indicate clade 5b's autochthony in the Ahr and mountainous Sieg, while clade 10 is suggested to be native to the Sieg's foothill regions, establishing the Sieg basin as a natural contact zone for these clades.

Keywords

• anthropogenic introductions
• coi barcoding
• haplotype network
• stakeholder surveys
• cryptic species complex